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Leaf Sap Analysis: A Forward-Looking Alternative to Tissue Sampling

By
Sean Jacobs
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By quantifying the metabolically active and available nutrients in the sap and assessing their balance, growers are able to determine not just if nutrient deficiencies exist but also the future potential for nutrient deficiencies (photo by Cecilia Parsons.)

Leaf sampling in agricultural crops is a long-practiced sampling method where the analysis of the collected tissues is used to assess crop nutrient status. Sampling whole leaves, drying, grinding, digesting and then analyzing the sample for nutrient levels has aided farmers in managing their crop nutrition programs and optimizing crop yield.
This method, however, has some inherent limitations. Primarily, the results of the analysis are providing nutrient levels for ALL nutrients in the sample, including those that are structurally bound within cell walls, the leaf surfaces (cuticles) and organelles. While the analysis is accurate in quantifying the nutrient levels in the sample, these bound nutrients are largely immobile and unavailable to developing leaves and fruit.

Additionally, any nutrients found on the outside of the leaf or embedded in the leaf cuticle are included in the results. As an example, if a calcium carbonate material were applied foliarly to a crop and then tissue samples were pulled, the analysis would demonstrate that our tissue’s calcium levels increased. On the other hand, calcium carbonate materials have very poor foliar uptake and are commonly used as solar protectants or sunscreens. As a sunscreen, it is necessary that the material remains on the leaf surface to do its job, but a standard tissue sample analysis cannot differentiate between “in” or “on” the leaf. Further, tissues being prepped for analysis may be rinsed or washed in an attempt to alleviate leaf surface contaminants. What is commonly overlooked with this practice is the effect that rinsing can have on nutrients within the leaf. For instance, potassium, calcium, magnesium, manganese, nitrogen, phosphorus and zinc can all be leached to varying degrees from the leaf tissue with water.

Now, if the grower is analyzing the leaf tissue because it is the crop, then knowing the nutrient levels of the entire leaf structure and surface is appropriate. However, many growers are not selling leaves but are using the leaves as the machinery to develop the structure of the plant and produce the end crop. Whether that end crop is a tuber, fruit, nut, seed or simply a flower, knowing the number and quantity of nutrients available for assimilation within the plant as well as the balance among these nutrients may spell the difference between a mediocre crop and a stellar crop. Knowing and adjusting the nutrient balance is crucial to nutrient performance and preventing fruit nutrient disorders which can impact crop storability and shelf life. Other characteristics such as fruit sugar levels, size and color also can be positively impacted by proper nutrition.

Forward Looking Analysis
An alternative method to leaf tissue analysis is sap analysis. With sap analysis, leaves are sampled in sets with new leaves and old leaves collected separately without petioles. At the lab, a proprietary process under the NovaCrop brand then extracts the sap from the leaf. This process is done without rinsing, drying, grinding, cutting or crushing the leaves and the extracted sap is largely free from leaf structural components and surface contaminants. This results in the extracted sap being more similar to a blood sample than the biopsy approach akin to classical tissue sampling and analysis. In addition to analyzing the samples for 19 nutrients and five other nutrient and metabolic indicators, having the sap of both new and old leaves analyzed separately allows for the comparison of nutrient uptake, mobility and remobilization within the plant. This comparison is also valuable for assessing the movement of sugar in the plant, which is the plant’s initial building block and energy source.

Minerals, sugars and nitrogen-containing compounds, such as amino acids and proteins, found in the sap represent the majority of plant nutrients that are immediately available for use. By intentionally sampling and analyzing leaf sap, the results provide a forward-looking picture of the nutritional environment in which the plant is currently growing. With this information, deficiencies, toxicities and nutritional imbalances can be identified and corrected in a proactive manner, often before their physiological effects are visible. With traditional tissue analysis, the results are providing information largely about what has already happened nutritionally, leading to decisions being reactive in nature. As the demand for agricultural products continues to increase, farmers are often turning to more aggressive fertility programs, which frequently leads to over-applying nutrients or missing the best opportunity for the application.

Both over-applications and mistimed applications of nutrients can negatively affect crop yields and quality. The balance of nutrients within the plant can be upset by an over-applied nutrient. This can happen with foliar-applied nutrients as well as soil-applied nutrients. In some instances, as with nitrogen, it can alter the expression/regulation of genes and lead to a shift in growth toward vegetative and away from fruit development. In other cases, the over-applied nutrient can create nutrient imbalances that present as deficiency symptoms of other nutrients despite adequate concentration levels in the sap. This can be described as like-kind interactions where minerals of similar charge are competing with each other for space within the sap (cations affect cations and anions affect anions.) Physiological responses within the plant to an applied nutrient can modify the uptake or physiological activity associated with other nutrients, either positively or negatively.

Nutrient Availability
By removing unavailable nutrients from the analytical picture, the concentrations of available nutrients and their interactions are more easily seen in the analysis and accommodated for in the grower’s nutrition program. In the soil, colloidal and mineral properties influence how various nutrients, specifically cations, populate the cation exchange locations. A key takeaway is that these soil interactions occur primarily with available nutrients. The same is true within the plant with nutrient interactions primarily between available nutrients not unavailable and structurally bound nutrients. This is where sap analysis shines.

By quantifying the metabolically active and available nutrients in the sap and assessing their balance, growers are able to determine not just if nutrient deficiencies exist but also the future potential for nutrient deficiencies. With a NovaCrop sap analysis in hand, growers are able to evaluate the balance of nutrients in their crop and better understand how excessive levels of nutrients may impact the uptake and/or activity of others. Through this analytical report, a grower might determine that the most efficient way to increase the level of a certain nutrient is NOT by applying more of that nutrient, but rather is best achieved by decreasing the rate of other applied nutrients and restoring balance. Over-application of nutrients affect the safety of ground and surface water for human consumption and the wildlife dependent on those water sources. In an ever-increasingly regulated world, leaching and runoff of nutrients caused by over-application are not merely wasted money and crop potential, but could result in the grower being fined thousands of dollars, reclamation fees and civil judgements. Fertility management plan modifications, when based on NovaCrop sap analysis, and coupled with soil analysis, improves fertilizer use efficiencies and decreases over application of nutrients.

Review of Rhizoctonia Diseases of Row Crops

By
Steven Koike
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Rhizoctonia solani most often attacks the belowground parts of plants, such as these cauliflower crowns, resulting in loss of root attachment and decline of the plants (all photos by S. Koike.)

The soilborne fungus Rhizoctonia is an extremely important pathogen of plants worldwide. Hundreds of vegetable, field, fruit and nut, and ornamental crops are susceptible to this fungus. Rhizoctonia is common and severe on cereals and herbaceous row crops but can also cause disease on woody species. Found in soils throughout the world, this pathogen has evolved survival strategies that enable it to become established wherever it is introduced. Despite the implementation of integrated pest management tools, Rhizoctonia remains a challenging pathogen that is difficult to control.

Understanding Rhizoctonia solani
Rhizoctonia is the genus name that refers to a group or “complex” of fungi. Initially, fungal species were placed in this Rhizoctonia group because they shared certain features, such as the absence of asexual (anamorph) spores (remember that fungi can have two different phases or forms: asexual and sexual); a sexual (teleomorph) stage belonging to the Basidiomycetes; distinctive cell wall structures (septa) that divide the relatively thick hypha into sections, an existence that is primarily in the soil; and being mostly pathogenic to plants. For most row crops, the species Rhizoctonia solani is the most important pathogen.

Rhizoctonia is considered a “species complex” because of the many closely related species and subspecies that make up this group. Figure 1 outlines and breaks down this complicated, diverse group of organisms. The Rhizoctonia genus, first of all, can be divided into two major categories: (A) Those species that have two nuclei per mycelial cell (called binucleates) and (B) those species that have more than two nuclei per cell (multinucleates). R. solani and other species (e.g., R. oryzae and R. zeae) are in the multinucleate group. Note that each fungus listed in Figure 1 has two taxonomic names. The Rhizoctonia name refers to the anamorph or asexual stage and is the phase of the fungus that infects plants and causes disease. The second name is the teleomorph or sexual stage. This form is rarely found in the field and probably does not cause disease in plants; however, researchers employ the teleomorph names when studying the interrelationships between the various species. Our challenging fungal foe is therefore known mostly as Rhizoctonia solani (anamorph) but is also referred to as Thanatephorus cucumeris (teleomorph).

Rhizoctonia solani forms tiny, matted mycelial clumps (sclerotia) that enable the pathogen to survive in soil for prolonged periods.

The R. solani species is itself very diverse and can be separated into distinct groups. Different isolates of R. solani fall into one of many anastomosis groups, or AGs (Figure 1, see page 4). AGs are determined in the laboratory where two isolates are grown side-by-side in culture and the resulting reaction, whether the two hyphae fuse (compatible) or do not fuse (incompatible), is viewed under the microscope. Isolates that are deemed compatible are placed together into a numbered AG. Incompatible isolates cannot be in the same AG. There are currently 14 AGs: AG1 through AG13, and AGB-1. Seven of these AGs are further divided into subgroups. Molecular techniques are also available for AG classification; such techniques can be more accurate than searching for hyphal fusion under the microscope. Molecular methods, however, can be time-consuming to complete.
Categorizing R. solani isolates into these AGs is not an academic exercise but provides insights into how this pathogen functions in agriculture. Different AGs possess different traits; while some AG isolates have a broad host range, others are more restricted regarding the crops they can infect. For example, R. solani AG2-1 tends to be the main pathogen that causes wirestem on crucifers, while AG2-2/IIIB and AG2-2/IV cause brown patch in turfgrass and root disease on sugarbeet. R. solani AG3 is common on potato and causes stem and stolon lesions as well as black scurf on tubers. R. solani AG8 is primarily a pathogen of cereals but also infects potato roots. In contrast, AG4 has a broad host range and can infect many crops. So, identifying the AG status of an R. solani isolate can provide important information on the diseases caused by that isolate and the susceptibility of subsequent crops that might be placed in that field.

Figure 1. Complexity of the plant pathogenic Rhizoctonia group, and placement of R. solani.

Finally, isolates belonging to the same AG are not all identical to each other. While sharing the same AG designation, the isolates can differ physiologically in how carbon sources and other chemicals are metabolized, how fast they grow in culture, and other features. Isolates in the same AG can also differ genetically and have varying DNA sequences. This great diversity found within R. solani isolates accounts for the difficulty that researchers have in fully understanding this important plant pathogen complex.

Diverse Diseases Caused by Rhizoctonia solani
Rhizoctonia solani causes different types of crop diseases, all of which are related to the soilborne nature of this pathogen (Table 1). R. solani can be a seed pathogen. Once seed are placed in the ground, R. solani that is residing in the soil can invade the seed and kill it before it germinates. Even if the seed germinates, R. solani can cause a decay of the roots and shoots before the seedling emerges above the soil surface; this early seedling disease stage is called preemergent damping-off. Post-emergent damping-off occurs if the diseased seedling is strong enough to grow above the soil surface, only to succumb and collapse shortly afterwards (Table 1). Collectively, seed decay, preemergent damping-off and post-emergent damping-off can result in loss of plants very early in the production cycle, causing stand loss in the field. Healthy seedlings that escape death at the seed and newly germinated stages remain vulnerable to this pathogen; established seedlings can still be infected by R. solani and develop root rots and/or lesions on stems in contact with soil (Table 1).

Table 1. Categories of Rhizoctonia solani diseases of row crops

Plant leaves are not immune to R. solani. Field cultivation practices and splashing water can move bits of R. solani-infested soil up into the foliage of plants. Under favorable conditions, the introduced R. solani mycelium can colonize the leaf tissue and cause foliar blights in crops such as endive (Table 1). For head-forming vegetables such as lettuce and cabbage, the bottom leaves are unavoidably in direct contact with the soil. If R. solani is present in the underlying soil and if conditions (excess soil moisture) favor the pathogen, extensive rotting of the lower leaves and plant base can take place, resulting in bottom rot. If fruits (e.g., cucumber) and pods (e.g., beans) happen to be in contact with infested soil, these harvestable commodities can become diseased (Table 1). Finally, sweet potato roots, potato tubers and other similar plant structures under the ground can suffer from lesions, rots, and defects from R. solani in the soil surrounding these fleshy plant parts. Table 2 lists some row crops that are susceptible to R. solani.

Disease Development
Rhizoctonia solani has evolved to be a challenging, persistent soilborne pathogen. Tiny, tightly clustered clumps of mycelium grow together to form resilient structures (sclerotia) that can withstand unfavorable conditions and allow it to survive for years without a plant host. These sclerotia are the main mechanism for survival, since R. solani is not a particularly aggressive or successful saprophyte in the soil environment. When a host plant grows next to sclerotia and favorable soil conditions are present, the dormant mycelium germinates and can infect the plant.

For lettuce and other head forming row crops, Rhizoctonia solani can cause a rot where the basal leaves are in contact with soil.

Diagnostic Considerations

Diagnosing Rhizoctonia diseases based only on symptoms is risky because Rhizoctonia is not the only soilborne pathogen that causes seedling damping-off, root rots and stem lesions of row crops. On spinach, damping-off and root rot can be caused by R. solani, Fusarium and Pythium; visually, one cannot reliably distinguish between the symptoms caused by these three pathogens. Cilantro crops can develop similar-looking root diseases caused by R. solani and Fusarium. Cauliflower transplants are susceptible to both Rhizoctonia and Pythium, both of which cause the lower stem tissue to become discolored. Cauliflower disease diagnostics is further complicated because the root maggot insect feeds on lower stem tissue and causes symptoms identical to those created by R. solani. Precise and accurate diagnosis of Rhizoctonia diseases will therefore require lab-based examination and assays. Diagnosticians usually deploy culture tests in which surface sanitized bits of symptomatic tissues are placed in microbiological agar media. These scientists then use microscopes to examine the mycelium that grows out of the plated tissue. For most fungi, spores are important structures that diagnosticians rely on for fungal identification; since R. solani produces no spores, scientists must examine the hyphal structures or employ molecular assays to confirm this pathogen.

Rhizoctonia is one of the damping-off pathogens that can affect young seedlings, such as the Swiss chard plants pictured here: infected plants (left), healthy plants (right).

Managing R. solani
Rhizoctonia is a difficult pathogen to control. Attempts to manage this fungus will require the implementation of IPM practices.

Site Selection Plant in fields that do not have a history of Rhizoctonia problems and that have well-draining soils.

Crop Rotation Avoid planting a susceptible, sensitive crop in a field known to have significant problems with this pathogen. Rotate to crops that are either not susceptible or are less sensitive to damage caused by R. solani. Remember that some R. solani AG isolates have a very broad host range and can infect many row crops; however, other AG isolates show some level of host specificity and are pathogenic on only a few crops. It is therefore useful to know which AGs are present in the field.

Rhizoctonia solani-contaminated soil particles can be moved up onto the leaves, causing a foliar blight on crops such as endive.

Time of Planting In some cases, moving the planting date to a different time of year may help reduce losses from R. solani. Planting the crop in the warmer, drier part of the year allows the seedling to grow more rapidly and perhaps escape or minimize infection from R. solani.

Fungicides Plant seed treated with a fungicide.Note that the seed treatments used to protect against Pythium have little effect on Rhizoctonia. Fungicides applied to emergent plants have little benefit.

When testing plants, diagnostic labs use microscopes to look for the brown, relatively broad, distinctive branching mycelium that characterizes Rhizoctonia solani.

Resistant or Tolerant Cultivars There do not appear to be row crop cultivars that have genetic resistance to Rhizoctonia. However, if young seedlings escape infection early in development, the maturing stem tissue will later become resistant to infection by R. solani.
Sanitation Remember that as a soilborne pathogen, R. solani will be moved and spread via mud adhering to tractors and equipment. Prevent the introduction of R. solani into plant nursery and transplant facilities by using new or thoroughly sanitized containers and trays, disposing of used rooting media and other sanitation measures.

CCA of the Year Keith Backman Recognized at Crop Consultant Conference

By
Marni Katz
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Western Region CCA Past Chairman Jerome Pier, left, presented Backman with the CCA of the Year award at the Crop Consultant Conference in September.

This year’s Western Region CCA Crop Consultant of the Year, Keith Backman, has been advising farmers in the San Joaquin Valley since the mid-1970s on fertilizer and irrigation management and the wisdom of matching those nutrient and water applications to the needs of the crops. Today, in an environment of increased regulation and costs related to fertilizer inputs, that prudence has grown more and more important.

Backman went to work with Nat Dellavalle out of college in the 1970s and has been with Dellavalle Laboratory in one way or another ever since. Today, he splits his time in semi-retirement between traveling with his wife Gail and imparting his wisdom on plant nutrition and water analysis to a new generation of agronomists as part owner of Dellavalle Labs.
Jerome Pier, outgoing Chairman of the Western Region CCA announced Backman as the winner of the new CCA of the Year Award at this year’s Crop Consultant Conference in Visalia this past September. Pier said Backman sets the standard for the region’s 1,300 CCAs for his contributions to plant nutrition and soil science over his 40-year career and his contributions to the industry.

“He’s made a big impact on a lot of people in the Central Valley and on Central Valley ag for sure,” Pier said. “His understanding of nutrition in permanent crops is world class.”
Backman is known for having an advanced understanding about taking and interpreting soil tests, and making preplant and in-season recommendations for fertility and irrigation management that are well suited to crop needs and soil status while also being environmentally sound.

Career of Service
As a member of the Western Plant Health Association’s Soil Improvement Committee for more than 20 years, Backman helped write the chapters on irrigation management and nitrogen management for the revised editions of the Western Fertilizer Handbook. The latest edition was just released and has Backman’s expertise throughout.

He was also in on the ground floor of developing nitrogen management plans and was instrumental in drafting nitrogen budgeting and checkbook methods that have been adopted for nitrogen management plans by water quality coalitions.

“He basically authored these nitrogen management plans, and without those plans agriculture was going to get shut down by environmental activists,” Pier said. “This was the only way to show a good faith effort that we are doing something about it.”

Those principals are based on the relationship between nutrient and water management.
“Over the years I’ve come to realize that so many of our deficiencies are irrigation related,” Backman said. “Especially with nitrogen, you can’t have a good accurate nitrogen program unless you have an accurate irrigation program.”

Farmers and PCAs today have a much clearer understanding about the timing of fertilizer applications and rates at those particular times, he said.

Where growers might have done a single or split application of 150 pounds of N fertilizer a year, for instance, they now make multiple applications based on yield estimate, soil conditions, crop timing and soil and leaf analysis.

“This is where the CCA earns their money is helping a grower understand that,” Backman said. “Growers can’t guess anymore. They need proven solutions and so more and more they are relying on the diagnosis of a CCA.”

Humble Ag Roots
Raised on a small farm south of Yuba City, Backman was seventh out of eight children in an agricultural family. While getting a Master’s degree in pomology at UC Davis, Backman focused his studies on boron toxicity in orchard crops. This is a problem that became more of an issue as deep-rooted permanent crops went in up and down the Valley and water shortages made leaching out of those root zones more difficult.

He worked early on in his college career under Kay Uriu, a professor in the UC Davis pomology department in the 1970s, who did ground-breaking research on tree nutrition status and was known for being able to spot nutrition imbalances by looking into an orchard.

As a result, Backman said even today he “can’t help driving by an orchard and looking at it and thinking ‘what can I do to get it growing more efficiently?’”

In addition to his service for the industry, Backman has been a scout master in his community for more than 20 years and until recently was an active member of his church choir.

It is Backman’s dedication to his industry, community and exceptional dedication to training new agronomists that led to his nomination as CCA of the Year, Pier said.

“I was honored by the selection,” Backman said. “I appreciate the recognition; it’s nice to know what you have done for the past 45 years is valued and to be able to see the changes in the industry from some of the things I’ve introduced.”

Among the changes he has seen in recent decades: more accurate nitrogen and water applications; more accurate monitoring to take appropriate actions at the appropriate times; and the application of science in making those applications using plant science and physiology to guide those decisions.

This is the second year Western Region CCA presented an annual Crop Consultant of the Year award to recognize outstanding individuals who have advanced crop consulting throughout their careers. For information on nominating a CCA visit the Western Region CCA website at https://wrcca.org/cca-of-the-year.

Soil Microbes are Key Partners for Drought Management

By
Karl Wyant
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Management practices that improve soil health and soil quality have gained considerable attention over the past few years, and especially during the past year, as drought conditions have impacted large areas of North America. In this article, I focus on how the living, biological components of the soil (e.g., bacteria and fungi) can be key microbial partners in your future drought management strategy.

I detail how soil microbes impact soil physical properties, including the structure (e.g., aggregation and pore space) and the ability of the soil to move and store water. Additionally, I explain how soil microbes can help crops get through drought conditions using the substances they secrete. Finally, I close with a call to action to measure your soil biology so you can make management decisions now before the next season gets underway. If needed, a CCA can help you interpret data and make an actionable plan that can help tackle the continued drought conditions that are expected for the near future.

Figure 1. Here are two concepts to help organize the contribution of microbes to soil health and structure (Concept 1) and the substances that are released by the microbes themselves (Concept 2) that help crops get through a drought period (courtesy K. Wyant.)

Let us begin with a quick reminder of what soil health means to a grower and how it is connected to the living component underground and drought management. Soil health is directly related to the interaction, or lack thereof, between organisms and their environment in a soil ecosystem and the properties provided by such interactions. When you think of soil health, think of the biological integrity of your field (e.g., microbial population and diversity) and how the soil biology supports plant growth. There is a direct link between soil health and how a soil can be managed to meet the challenges of drought conditions.

Soil Microbes and Drought Management
Soil microbes impact your ability to manage drought via two major pathways, i.e., the “Two Concepts of Drought Management” (Figure 1).

Concept 1: Soil Microbes Help Increase Water Penetration and Infiltration
Soil microbes help restore soil structure which helps water move from the soil surface downwards. This is known as water penetration. Once the water has penetrated the soil, it moves down into the soil for storage. This is known as water infiltration. If you are not capturing and moving water into the soil, you will have a tough time storing water in your field. Simply put, healthy soils have good structure, which excel at receiving and storing moisture. But how exactly do microbes improve water penetration and infiltration?

Abundant and diverse soil microbial communities produce “free” services for your farm soil, including the ability to receive and store moisture. The key to this ability lies in the ability of microbes to contribute directly to improving soil structure by binding soil particles together, which, in turn, helps water move from the soil surface and into the root zone.

Soil bacteria produce a sticky, glue-like gel called extracellular polymeric substances (EPS) that form a protective slime layer around bacteria as they grow. The EPS acts as an adhesive to bind soil particles, thereby improving overall soil structure. Fungi, another important group of soil microbes, produce miles of microscopic threads in the soil called hyphae. The threads capture and “tie” soil particles together, like a net, which improves overall soil structure. Fungi also produce a sticky protein-like substance called glomalin which, like EPS, helps bind your soil structure together via adhesion of particles.

Key Message: Soils with healthy microbial populations can restructure and re-aggregate the soil, which leads to better soil structure overall. Good soil structure allows for water (e.g., snowmelt, rainfall and irrigation water) to move from the soil surface (penetration) to below the soil surface for storage around and on the soil particles themselves (infiltration). This results in a number of benefits, including reduced runoff losses.

Research and grower experience corroborate this connection as reports show that soils with good structure often can store more water relative to degraded control fields nearby. Good soil structure also reduces runoff losses as water quickly moves downwards instead of horizontally across the soil surface, which carries materials off the field. Thus, soil microbes can be crucial partners for capturing and storing soil moisture, which will certainly come in handy during forecasted drought periods.

Concept 2: Robust Microbial Communities Release Substances to the Soil Which Can Help Crops Get Through Periods of Drought

This next concept is not so easy to visualize like changes in soil structure and the ability to store water. Imagine the microbial community on the right side of Figure 2 for the next few sentences and contrast the microbial abundance and diversity when compared to the “business-as-usual” farm soil on the left side. Now that you have refreshed your snapshot of the microbial community, we can turn our attention to the benefits that improved microbial abundance and diversity bring to a drought affected soil. Recent work has shown that soil microbes help crops get through periods of drought stress via the substances they release into the soil around the roots. These molecules include osmoprotectants and antioxidants, to name just a few (see first reference for a deeper dive).

Figure 2. The soil on the left has poor soil health and soil structure while the soil on the right has excellent soil health and, as a result, the two fields have substantial differences in soil quality and their ability to mitigate drought stress (courtesy K. Wyant.)

Key Message: A hidden benefit of maintaining a thriving community of microbes during a drought are the substances they secrete. For example, osmoprotectants play a key role in managing challenges with plant water balance under drought conditions. In another example, antioxidants help mitigate oxidative stress and internal plant cell damage observed under drought stress. Studies show that when a robust microbial community releases certain substances belowground, a crop is better able to weather the stress of drought (e.g., low rainfall, higher temperatures) more successfully aboveground.

Managing Soil Biology
Now that we have examined how soil microbes can be crucial partners under drought conditions, we can now turn our attention to a crucial next step: managing the soil biology. I will walk through the basics on how to measure the biological activity of the soil and make the case to ask your trusted CCA for assistance if this management strategy is new to your operation or if you need help with interpretation of the results.

Tests are commonly used to measure chemical constituents of the soil (e.g., pH, nitrate, phosphate, etc.) or physical aspects of the soil (e.g., soil texture, cation exchange capacity). However, these tests do not determine how “alive” the soil is. You can accomplish this goal with a broad set of soil tests that target the living components of soil. Soil biology tests are diverse and include measurements of carbon dioxide respiration, extraction of DNA for microbial community analysis, and other key metrics (Table 1), depending on what parameter you are interested in measuring and your patience level to see a measurable change.

Table 1. There are several soil tests available to help you quantify the living components of your soil and their response to field management decisions. Please see the “Comprehensive Assessment of Soil Health” from Cornell University for an exhaustive list on what is available or call your local lab. Listed are a few common testing options in ag laboratories.

Testing the biological components of the soil is new to many growers and some have reported frustration about which test to choose, how to design a sampling program, and how to interpret and write an actionable plan based on the test results. This is where a Certified Crop Advisor can step in and help reduce the learning curve.

Final Thoughts
Soil microbes can help you mange drought in ways that are readily observable (e.g., changes in soil structure and water holding capacity) and in ways that are not (e.g., release of substances that help with drought stress). In any event, microbes are essential partners for dealing with drought conditions and their usefulness should be leveraged in any crop production program.

Dr. Karl Wyant currently serves as the Vice President of Ag Science at Heliae® Agriculture. To learn more about the future of soil health, you can follow his webinar and blog series at www.phycoterra.com.

Suggested Reading
Harnessing rhizosphere microbiomes for drought-resilient crop production – https://www.science.org/doi/10.1126/science.aaz5192
The Connection Between Your Soil Structure and Soil Moisture – https://phycoterra.com/connection-between-soil-structure-soil-moisture-crop/
Biological Management Practices to Maximize Soil Quality – https://progressivecrop.com/2021/05/managing-soil-structure-and-quality/
Comprehensive Assessment of Soil Health (The Cornell Framework) – https://soilhealth.cals.cornell.edu/training-manual/

UC Kearney Field Demo Sheds Light on Root Lesion Nematode Management in Walnut Orchards

By
Cecilia Parsons
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Significant findings in a California Walnut Board-funded trial show that post-plant applications of nematicides in walnut orchards frequently require multiple years before plant yields improve (photo by C. Parsons.)

When growers think about nematodes, they often only think about plant parasites. These are only about 10% of nematode species known. They pose a threat to walnut production, but among those that do cause loss of growth, vigor and production in trees, the walnut root lesion nematode is the most damaging. Other nematode species, so-called free-living species, are very important in nutrient cycling. They feed on soil bacteria and fungi. There are other species as well.

Research into management of plant-parasitic nematodes with rootstock selection and chemical control at the UC Kearney site was presented by UC Riverside Nematologist Andreas Westphal during a recent field demonstration.

Westphal said that about 85% of California walnut orchards have some parasitic nematode infestations. When planning and preparing a new planting, prior soil samples can show nematode species and infestation levels to help decide if soil fumigation is necessary. Westphal noted that post-plant application tools are needed when orchards become re-infested. Westphal and other UC and USDA-ARS researchers actively pursue rootstock selection for tolerance and resistance to nematodes, crown gall and Phytophthora rots.

Root lesion nematode is tightly associated with plant growth disruption, Westphal said. Rootstock trials and chemical trials are continuing at Kearney to develop management strategies.

Significant findings in a California Walnut Board-funded trial show that post-plant applications of nematicides frequently require multiple years before plant yields improve. Some reductions of nematode numbers by post-plant applications can already reap some benefits, but in pre-plant soil treatments, efficacy needs to be even higher to protect new plantings. New plantings have to cope with transplant shock, and any additional stress has a likelihood to damage them severely. Pre-plant treatments can be more challenging due to the scarcity of highly efficacious material and the need for optimal soil conditions. If nematode infestations are confirmed in a field, such treatments are highly desirable for successful establishment of walnut orchards.

When it comes to rootstock tolerance and resistance to nematode infections, Westphal said that tolerance alone will not ensure productive trees long-term. The level of nematode reproduction in orchard soils can have an effect on the productive life of a walnut tree.

The determination of a rootstock’s tolerance to nematode infestation is ongoing at Kearney. Westphal noted that environment and drought stress are also components in the health and function of a rootstock. The trials are using different treatment to see how the rootstocks and the scions respond to these stresses.

“We are still looking for answers to how different genotypes respond to stress and nematode pressure,” Westphal said.

Soil samples, root sampling and even use of drones have been used to detect patterns of tolerance or resistance to nematode pressure over time. Finding a balance between rootstock and the scion is important.

Trials used both pre-plant and post-plant fumigants as well as anaerobic soil disinfestation to manage nematode levels. However, Westphal noted that there is much adjustment work to do with chemical control. Root lesion nematode levels can build again over time, and researchers need to find the combination that will protect trees.

If nematodes are in a field, they are there to stay, growers need to manage them over time. Methods are being developed at Kearney to enrich growers’ tool cabinets to deal with these challenges.

Mechanical Pruning in Wine grapes May Improve Yields, Quality

By
Cecilia Parsons
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In winegrape vineyards, mechanical box pruning entails pruning the grapevine’s bearing spurs from the top, bottom and sides of the canopy (photo by G. Zhuang.)

Dormant pruning in winegrape vineyards is one of the most labor-intensive practices with an estimated 80% of labor costs accrued in pruning and harvest operations. Labor cost and availability have accelerated the planting of new vineyards to accommodate mechanical pruning, said Fresno County UCCE Viticulture Advisor George Zhuang.

“Almost all new vineyards in Fresno County are now designed for mechanical pruning,” Zhuang said.

He also noted that mechanical pruning operations in vineyards have had no negative effect on grape yield or quality. In some cases, he added, yields and berry quality have increased.

Mechanical pruning in table grape vineyards presents more of a challenge due to their trellising system. But Zhuang said progress is being made toward that goal. Raisin grape growers have also been moving toward mechanical pruning due to labor shortages. Delays in harvest have led to crop damage from early rain events.

In winegrape vineyards, mechanical box pruning entails pruning the grapevine’s bearing spurs from the top, bottom and sides of the canopy. Box pruning is not as selective as hand pruning, leaving all the nodes within the perimeter of the cuts, but box height and width can be manipulated by the machine operator. A pre-pruning pass may leave a 0.3-meter-wide by 0.4-meter-tall box and is recommended in frost-prone areas. A more precise pruning pass may leave a 0.10 to 0.15 box.

Types of mechanical pruning include minimal pruning to develop high numbers of clusters, pre-pruning and mechanical shoot thinning follow-up.

With minimal pruning, the high numbers of clusters would be balanced by early growth of numerous vegetative shoots. The result is high yields with smaller clusters and berries.

Pre-pruning leaves a 0.40-meater-tall by 0.10-meter-wide box retaining 120% to 200% of the desired number of buds. After bud break, the desired shoot density is achieved by manual pruning or shoot thinning.

With mechanical shoot thinning follow-up, dormant canes are mechanically pre-pruned to 0.1-meter-wide by 0.3- or 0.4-meter-tall, retaining 120% to 200% of the predicted bud load. After bud break, the desired shoot density is achieved by shoot thinning.

Hedger bar pruners are mostly used in minimal pruning applications in the dormant season, for summer pruning or as part of combination pruners. They have a single plane of cut and low penetration into the dormant canopy.

FRET Accuracy Evaluated for Irrigation Scheduling

By
Cecilia Parsons
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The CIMIS stations measure all the weather variables necessary for calculating the atmospheric water demand and calculate ETo values at hourly and daily time-steps, which are then made publicly available for agricultural and urban irrigation management (photo by D. Zaccaria.)

In a recent presentation at the 2021 UC Davis Winter Grape Day, Daniele Zaccaria, UCCE agriculture water management specialist, evaluated the accuracy of Forecast Reference EvapoTranspiration (FRET) for prospective irrigation scheduling.

FRET ETo is a National Weather Service product. It was developed in 2008 collaboratively by UC Davis, the California Department of Water Resources and the National Weather Service to improve high-frequency irrigation management and encourage the adoption of ET-based scheduling for irrigation of agricultural and urban landscapes in California. FRET ETo forecasts are now available for one-, three-, five- and seven-day leads.

Zaccaria said that FRET ETo is a valid alternative to using near-real-time ETo data from the California Irrigation Management Information System (CIMIS) network and provides clear advantages for irrigation scheduling of specialty crops.

While ETo data from CIMIS are considered near real-time, they are retrospective, i.e., they refer to the previous time period when it comes to scheduling water deliveries to growers (for irrigation districts) and on-farm irrigation (for farmers). As such, when information from CIMIS is used, ETo data from the period just passed (one-day, three-day, one-week, two-week) are used for scheduling water deliveries to growers and/or irrigation applications for the next period ahead.

Visible are the rapid changes of the three-day and one-week cumulative ETo values for Napa Valley.

If growers use retrospective ETo data (CIMIS), they may run the risk of over-irrigating or under-irrigating crops during times/stages that may be sensitive for fruit yield and quality. The graphs below show rapid changes of the three-day and one-week cumulative ETo values for Napa Valley. As such, using the ETo from one week to quantify irrigation applications for the following week may lead to scheduling mistakes.

FRET forecasts all the weather variables (using the Global Forecast System, GFS) needed for the ETo equation except solar radiation (Rs). Rs is calculated from forecast daily fraction cloud cover (using the ratio of actual to potential sunshine hours, n/N) and extraterrestrial radiation (Ra), which is a function of latitude and day of the year (DOY).
The CIMIS stations measure all the weather variables necessary for calculating the atmospheric water demand and calculate ETo values at hourly and daily time-steps, which are then made publicly available for agricultural and urban irrigation management.

Zaccaria said the comparisons between FRET forecast ETo and CIMIS ETo calculated from observed weather variable showed good agreement for all the 15 selected station locations across California, which spanned from low to moderate to high ETo demand for all the considered months (June, July, August and September). The results also show that the seven-day ETo forecasts are nearly as good as the one-day ETo forecasts, while the three-day and five-day ETo forecasts are slightly better.

With all data together, Zaccaria said the correlations between FRET ETo and CIMIS ETo showed a Coefficient of Determination (R2) ranging between 0.9 and 1.0 (1.0 meaning perfect match between the variables being regressed) while the Root Mean Square Error (RMSE) was in most cases less than 0.04 inches per day (RMSE being a measure of the differences between the predicted and measured values.) The poorest results were obtained from the Imperial Valley station at Meloland, Torrey Pines in north coastal San Diego County and the Camino forest area in El Dorado County. A slight overestimation of 10% to 20% of forecast ETo versus CIMIS ETo were noted for Bishop’s mountain range site and the Oakville station in Napa Valley.

Resurgence of INSV in Lettuce

By
Cecilia Parsons
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A lettuce field that tested positive for both INSV and Pythium in 2020. This is not a postharvest shot. The photo was taken at the time when the field should have been ready to harvest (photo by M. Zischke.)

Controlling host weeds and the disease vector are primary concerns for Salinas Valley lettuce growers as the reemergence of western flower thrips-vectored Impatiens Necrotic Spot Virus (INSV) has caused significant yield losses.

Mary Zischke, who leads an INSV task force created by Grower-Shipper Association of Central California, said the winter offseason for lettuce is a critical time to control host weeds.

INSV in lettuce causes necrotic patterns on the inner leaves of the plant as well as significant stunting. Zischke’s task force is identifying major research questions, examining treatment strategies and developing treatment efficacy levels. The task force is also building a grower education program specific to viral disease and is establishing a network for information sharing.

Lettuce is a key host for INSV during the lettuce production season, but during the winter when there are no lettuce fields, the virus survives in weedy host plants in a variety of habitats: roadsides, ditches, waste areas around equipment yards, and natural areas. Vineyards can also be habitat for INSV due to the presence of infected weed hosts.

Task force GAPS that are being recommended to growers and farm managers include disking harvested fields as soon as possible and aggressively managing weed hosts. That includes weeds in lettuce fields, other adjacent crops and border areas where possible.

Preferred weed hosts include hairy fleabane, annual sow thistle, common lambsquarter, purslane, field bindweed, malva, mare’s tail and nettleleaf goosefoot.

Little mallow, annual sow thistle and nettleleaf goosefoot are also common in vineyards and have relatively high levels of INSV, being good hosts for thrips, particularly when flowering.

Weed control is particularly important in the spring when thrips populations begin to increase. It is unclear how far thrips can move, but they rely heavily on the Salinas Valley winds for long-distance dispersal. Monitoring efforts showed that thrips are equally distributed in the wind column up to 10 feet high and have even been detected in moderate numbers at heights above 20 feet.

Zischke said a USDA Salinas monitoring program is in place to report thrips activity on a year-round basis.

Losses from INSV in 2020 exceeded $50 million. The INSV Task Force, composed of growers, PCA’s, the Grower-Shipper Association, the County Agricultural Commissioner and researchers, meets weekly to discuss ways of reducing the spread of INSV.

New, Three-Year Field Trial Results on the Efficacy of XylPhi-PD™ for Pierce’s Disease Prevention and Control

By
PCC
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Palo Alto, CA – December 9, 2021– A&P Inphatec, a specialist developer of bacteriophages, announces the release of important new three-year commercial field trial data on the efficacy of XylPhi-PD™, the biologically-based reduction of Pierce’s disease (PD) in grapevines.

XylPhi-PD™ (EPA Reg. No. 93909-1) is EPA-registered and is commercially available through Wilbur-Ellis Agribusiness locations. XylPhi-PD™ is OMRI-listed and approved for use in organic production.

An early-order discount is currently available for XylPhi-PD (Early Order Program)

A Virtual Field Day (see video link below) was held in October 2021 at a leading commercial vineyard in Sonoma, California with a history of high PD. Field Trial Specialists Amy Ritchardson and Sarah Atwood (from Wilbur-Ellis and A&P Inphatec) walk the vineyard, perform visual disease assessments, and review results. XylPhi-PD reduced detectable Xylella fastidiosa by 55 percent, increased fruit yield by 17 percent and prevented new infections by 80 to 100 percent.

Additional information on XylPhi-PD and A&P Inphatec is available on www.inphatec.com

State Considering New Pesticide Application Advance Notifications

By
Roger Isom
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CDPR is looking at several different areas to determine the bounds of this new program, including what types of pesticides and application methods will require notification, who gets notified, how they get notified and how far in advance the notification will be required (photo courtesy Western Agricultural Processors Association.)

The environmental justice movement has hit a new threshold as the state legislature has now approved, and the Governor signed, a budget that includes $10 million for a new statewide notification system for pesticide application. The California Department of Pesticide Regulation (CDPR) has wasted no time in moving on the effort and has already held a series of focus group meetings to discuss the issue and begin developing the framework of the new program. This new effort will focus on advance notification of potential pesticide applications. While admitting that California already has the most robust pesticide regulatory program in the country, CDPR indicated in a recent meeting that these new notification requirements are a priority for Governor Gavin Newsom and CalEPA Secretary Jared Blumenfeld.

Existing Notification Requirements

There are some existing requirements already in place for advance notifications. Two counties, Monterey and Kern, already offer some form of advance notification, albeit very limited. In Monterey County, the public can sign up for email notifications for fumigation applications made within a quarter mile of one of ten designated schools. In Kern County, the county provides email notification to other growers surrounding a farm where a restricted use pesticide will be used.

For certain soil fumigants, including chloropicrin, metam sodium/potassium, dazomet and methyl bromide, notice of emergency response information must be provided to occupied residences and businesses within a specified distance of a buffer zone unless the applicator provides onsite monitoring. Also, if a beekeeper requests notification, they must be notified if a pesticide toxic to bees is to be applied at a site within one mile of an apiary. Finally, schools must be notified in advance of any pesticide application that will occur within a quarter mile of the school.

Three other states (Florida, Michigan and Maine) have some form of notification requirements; however, they are limited in scope and application. Florida provides a registry for persons requiring notifications, but they must reside in contiguous or adjacent property within a half mile of the application site. Michigan requires notification to someone with a physician diagnosed condition if they reside in property immediately adjacent or contiguous to the property being treated. Maine has a notification registry for applications within 250 feet, which can apply to even residential lawn treatments, and notification must occur within 6 to 14 days prior to the application.

Potential Requirements
With these new notification requirements, CDPR is looking at going way beyond any of these previous requirements or those in other states. In a recent series of focus group meetings, CDPR asked several questions in attempting to determine the bounds of this new program. CDPR is looking at several different areas, including looking at what types of pesticides and application methods will require notification, who gets notified, how they get notified and how far in advance the notification will be required.

By far, the biggest question is who gets notified. Concerns from the agricultural industry abound on this specific piece due to fears over environmental activism. The environmental justice community has been vocal that they want a countywide or statewide notification system where anyone can sign up for an email notification. Why would someone who does not live next to a field or orchard being treated want or need to know about an application unless they have an ulterior motive? One such incident happened in Monterey County where activists tried to stop a planned field fumigation after learning of the fumigation through the notification system.

Another area of concern is how broad CDPR applies this requirement. In the focus group meetings, CDPR asked if this should be limited to only restricted use materials or any pesticide. They also asked if this should apply to all types of application methods or focus on ones they consider to be the greatest risk for pesticide exposure, such as fumigations or aerial applications. Risk is a key question here as what is true risk? Just because a chemical is applied via helicopter or airplane does not mean it imposes a greater risk.

CDPR also asked how far in advance the notice should be made as well as how the notification should be made. Typical notifications are made 24 hours in advance, but CDPR is seeking guidance on whether there should be a shorter or longer notification period. As for how the notification is being made, CDPR is asking if the notification should be made with mail, email, fax or door hangers.

In the end, CDPR is committed to doing something. For the agricultural industry, the fight against our industry continues, and we must be involved to protect what we have. As stated in the beginning of this article, CDPR has acknowledged they have the most robust regulatory scheme on pesticides in the country. This will only make it tougher for farmers and easier for the anti-pesticide groups to attack our industry. There is no doubt that farmers must be careful with pesticide applications and follow all label requirements to the letter. But notifying people that do not live anywhere near where the pesticide application occurs does nothing to protect those that do.

Whether it is water, air quality, labor or pesticides, the California agricultural industry is once again under attack. Consider this article a ‘notification’ that we must stand up against overbearing and unnecessary regulations. When the time comes, be sure to weigh in and comment against these burdensome requirements that go beyond any scientifically justified reason.

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