Texas A&M AgriLife research has led to the discovery of the first curative and preventive bacteriophage (bacterial virus) treatment against the pathogen Xylella fastidiosa, which causes the deadly Pierce’s Disease in grapevines. Bacteriophage therapy uses viruses that only infect and kill the bacterium. This precision treatment is injected with the use of a powered applicator directly into vines and targets the disease from within the plant’s vascular system, helping to cure the infected grapevine and stopping the spread to surrounding vines.

Pierce’s Disease is caused by the bacterium Xylella fastidiosa, which is spread by xylem-feeding leafhoppers known as sharpshooters. In California, the invasive glassy winged sharpshooter spread the disease beginning in the 1980s. Infection by this bacterium causes several important, often fatal plant diseases in California, including Pierce’s Disease in grapes, alfalfa dwarf and almond leaf scorch.

The bacterium works by blocking the xylem, which conducts the water around the plant. Symptoms include chlorosis and scorching of leaves, and entire vines will die after one to five years.

The work to develop a bacteriophage treatment for Pierce’s Disease was led by Carlos Gonzalez, plant pathology and microbiology professor at Texas A&M. He is a member of the AgriLife Center for Phage Technology and collaborated with Otsuka Pharmaceutical Co. in developing the treatment.

The treatment has been approved by the U.S. Environmental Protection Agency with the commercial name XylPhi-PDTM, and is registered with the California and Arizona Departments of Pesticide Regulation. It is also OMRI-listed and approved for use in organic production. Wilbur-Ellis is the distributor for this product and their advisors work with crop consultants.

“The development of this first-ever bacteriophage treatment for Pierce’s Disease is a significant step for the agricultural industry,” Gonzalez said. “We’ve proven that we’re able to develop a treatment, manufacture the product and put it into large-scale production, and develop it to a point where it’s been approved by the EPA as a treatment for Pierce’s Disease.”

At a virtual field day held in northern California at the end of the 2020 crops season, efficacy data from vineyard trials for XylPhi-PD were shared. After two seasons of use, it reduced Pierce’s Disease by nearly 60% in high-disease-pressure vineyards.

High yields in an alfalfa variety are positively correlated with weed, insect and disease resistance.

At a recent UC Alfalfa & Forage Virtual Field Day, Dan Putnam, statewide alfalfa & forage extension specialist, explained why alfalfa variety selection plays an important role in integrated pest management.

With high yields, Putnam explained, comes vigorous regrowth that suppresses weeds. Persistence in a variety means that plants can recover from insect pressure. Choosing an alfalfa variety for its resistance traits ensures a good stand for the life of an alfalfa field.

Taking into account the growing region where alfalfa is planted, Putnam stressed that yield performance should be the deciding factor in variety selection. Varieties may look similar in the field, but over the life span of an alfalfa stand, yield differences and return on investment can be significant. Yield differences can also overcome higher seed prices for high-yielding varieties.

“Always look at performance first, not the price of seed,” Putnam said.

Alfalfa varieties have been developed for different growing regions. Dormancy type should be matched with the specific growing region. A UC Davis website lists the regions and varieties developed for each.

Putnam said a high fall dormancy score for a variety equals higher yields. Alfalfa forage quality is higher in varieties with low dormancy scores.

When it comes to pest and disease resistance, Putnam explained that it is not always absolute as high numbers of pest or significant disease pressure can overwhelm even highly resistant varieties. Using highly resistant varieties does not negate other management, including monitoring, spray timing and beneficial insects.

A variety that is listed as highly resistant to a pest or disease means that at least 50% of the plants in a stand will survive. Since alfalfa plant numbers are so high, Putnam said 80% of seedlings can be lost and the stand will be viable.

In regions where aphid complex, stem nematode, fusarium wilt and Phytopthora are significant challenges to a healthy alfalfa stand, growers should choose highly resistant varieties.

Key points of alfalfa variety selection include performance, choosing a fall dormancy rating appropriate to the growing region and prioritizing pest resistance traits for specific sites. Growers should also consider biotech traits when making variety choices.

Where there is a yield/quality tradeoff in an alfalfa variety, Putnam said that in the current alfalfa market, yield is currently the most important consideration.

Hull split in almond signals that it is time to apply treatments to control navel orangeworm. This timing is critical. Split hulls release a scent that attracts female NOW moths who lay their eggs on the suture of the splitting hull. Fungal spores can also invade the almond hull at split and cause hull rot.

In an Almond Board of California Training Tuesday webinar, almond experts recommended tree inspections starting at the top of the canopy on the southwest corner to detect onset of hull split.

Almond hulls split as the fruit ripens. If the entire suture on the hull opens and exposes the shell when the nut is squeezed, hull split has occurred. Timing of hull split can vary depending on weather and variety. The almond industry’s leading variety, Nonpareil, typically splits in early to mid-July.

It is the stage prior to a visible hull split that growers want to catch. When the hull is at the deep “V” stage, susceptibility to NOW infestations and pathogens that cause hull rot increase. Monitoring the crop for this stage is important.

Nuts mature faster at the top of the tree canopy, and that is where monitoring must begin. Using a ladder, lopping off upper branches of smaller trees or even using a pruning tower will allow close inspection of nuts from the top of the canopy to determine their stage of maturity.

Noting any blank nuts, or those lacking a kernel, is important as those are the first to initiate hull split, often several days before sound nuts. Mel Machado, vice president of grower services for Blue Diamond, calls blanks ‘a warning shot’ that alerts growers and farm managers that the hull split is imminent.

Experts advise paying attention to trees on the edge of the orchard as their nuts ripen earlier.

When planning hull split applications, they note that it is better to be early than late. Hull split applications should be made no later than at 1% hull split. That is the most effective time to spray for NOW as the timing often matches initiation of the second flight of NOW.

Machado also advises that once hull split begins, the entire orchard should be sprayed in five days or less. Since nuts at the tops of the trees are most vulnerable, consideration of aerial applications should be made to achieve best coverage. The best time to spray is early morning or at dusk.

Citrus Research Board reports that in addition to visual inspections, regular treatments and scouting for Asian Citrus Psyllids, growers are conducting routine testing of leaf samples to positively identify Huanglongbing (HLB) infection in a tree. The testing involves direct detection of the bacteria that causes HLB.

CDFA has provided leaf collection and handling protocols. They include a visual assessment of each tree to be sampled and looking for known HLB symptoms. Searching for and collecting symptomatic leaves when possible is recommended. If yellow shoot symptoms are present, 12 leaves from that branch should be collected. The petiole must be attached to the selected leaves. If yellow shoot symptoms are not present, the entire tree should be inspected for other HLB symptoms, including leaf mottling, twisted leaf ACP damage and vein thickening.

Next, the tree should be divided into four quadrants (north, south, east and west), and four leaves should be collected from each quadrant for one sample. Leaves selected should be young and of medium size, one growth period old and as near to flush as possible.

If no symptoms are present in the tree, select 16 leaves, four from each quadrant, from fully expanded current season flush. Wipe or brush leaves to remove dust and debris and check each sample to ensure there are no thorns and all insects and their life stages are removed.

Next, fold each sample at the mid rib. Wrap the folded bundle of leaves in a dry paper towel and place the sample in a zip-lock plastic bag. The bag should be labeled with the unique sample identifier number, the date collected and the exact location of the host tree, including address, cross street, city and county. The labeled bag should be placed inside another zip-lock bag and placed in an ice chest with blue ice packs to keep the samples cool.

CDFA notes that it is essential to place protective material between the ice packs and samples to ensure they stay dry and do not get freezer burn.

The agency also emphasizes making sure no ACP are with the leaf samples or inside the package.

Growers or orchard managers must mark the trees from which the samples came from for retesting purposes. If any samples test positive for the bacteria, CDFA will be notified and will contact the grower to resample.

Currently, the Citrus Pest Detection Program (CPDP), operated by the Central California Tristeza Eradication Agency, is permitted to provide HLB testing services of plant samples from growers throughout the state, except in HLB quarantine areas, via mail. However, growers located in the San Joaquin Valley can request CPDP representatives take samples from their orchard for testing rather than mailing.

Samples can be sent to the Citrus Pest Detection Program at Attn: PCR Laboratory 22847 Road 140 Tulare, CA 93274. The Tulare laboratory director, Subhas Hajeri, would like to speak with growers or PCAs before they bring samples to the lab. The phone number is (559) 686-4973.

Scouting forage sorghum fields early in the growing season for sugarcane aphid infestations may save considerable crop damage.

UCCE Farm Advisor Nick Clark, in a presentation for the virtual UC Alfalfa and Forage Field Day, said this invasive crop pest reproduces rapidly, and infestations have the potential to cause severe crop damage if not recognized and controlled early.

Dairy producers and those who grow forage crops for dairy silage plant forage sorghum for its drought tolerance and high yields. In 2016, the sugarcane aphid, an invasive pest from Mexico, spread into California forage sorghum fields and caused crop losses.

Sugarcane aphids suck plant juices and excrete honeydew. Their feeding on forage sorghum causes stunting, delayed development, diminished grain production and early senescence. The honeydew causes sooty mold on plants, affecting photosynthesis.

Field trials have shown that early infestation by this pest causes higher yield loss. In 20% of infested fields with no treatment, crop loss of 80% to 100% can be sustained if infestation occurs in the pre-boot stage. Infestation in the boot stage can cause yield loss of 52% to 69%. At panicle emergence, yield loss can be 67%.

Sugarcane aphids can be light green to orange in color. They are distinguished by black antennae, black cornicles and black feet.

Sugarcane aphid infestations are easy to spot, Clark said. Honeydew makes the leaves appear shiny and aphids are easily visible on the leaves. He advised scouting field edges weekly until sugarcane aphid is identified in the field. When sampling, he said to take leaves from plants 50 feet in from the field edge. Pull top and bottom leaves from 15 to 20 plants. The treatment threshold is reached when 25% of the samples have 50 or more aphids per leaf. 50 aphids can cover a dime-size area on the leaf.

Preventative controls for sugarcane aphid include managing Johnsongrass, which can serve as an overwintering host to sugarcane aphid, planting the forage sorghum crop as early as possible, keeping plants healthy and vigorous and using neonicotinoid-treated seed.

If chemical control is necessary, an aphid-specific treatment recommendation is flupyradifurone (Sivanto) in a water volume high enough for good foliar coverage.

Clark noted that growing populations of natural enemies including parasitoid wasps have been observed to control sugarcane aphid, but not always prevent crop damage.

Crop S.A.F.E. is a new tool developed to help wine grape growers manage risk from smoke taint due to wild fires and help protect workers.

Wildfires are an annual threat to fruit, vegetable and other crops grown where wind, high temperatures and smoke are present.

Smoke And Fire Events (S.A.F.E.) platform provides remote intelligence to enable informed crop management decisions during wildfire season. UPL, in collaboration with 6th Grain Corporations, a digital agriculture technology company, is introducing Crop S.A.F.E. as an online application for growers and crop managers.

In grape production, wildfire smoke reduces the amount of sunlight reaching the vines, increasing the stress level and affecting fruit quality. Smoke taint can alter flavor of grapes.

Molly E. Brown, chief science officer with 6th Grain, explains that Crop S.A.F.E. provides growers and managers with more in-depth information about smoke than what they might obtain from weather reports. The information can allow them to determine management for vineyards and reduce concentration of smoke-related aromas, flavors and compounds in the final wine product.

Examples of management strategies to prevent smoke taint, Brown explained, include washing canopy leaves after a smoke event to remove ash. A grower or manager could also choose to hand-harvest a vineyard to minimize skin breakage or rupturing for as long as possible or to harvest earlier to reduce smoke exposure.

The system can also provide regional information about smoke impacts in other areas and states. Brown said knowing how many days a particular vineyard or area has been exposed to smoke throughout the year is a critical part of determining wine quality in the coming year.

In addition, this tool helps keep workers as well as managers in the field safe from smoke exposure and breathing difficulties.

Crop S.A.F.E. uses Aerosol Optical Depth from NOAA to estimate the intensity of smoke exposure accumulated over time. The satellite-sourced map shows regions with high accumulated risk of smoke taint for grapes and other produce as well as field activities. The online resource estimates the intensity of smoke and other atmospheric hazards such as ozone and particulate matter levels plus temperature history.

Brown reports that merging information on field management with satellite observations of weather, crop extent and crop health allows growers and managers to plan to avoid negative impacts of smoke taint.

“By knowing the level of exposure to smoke and avoiding working in high smoke areas, workers can reduce risk of breathing difficulties,” Brown said.

Trials conducted at the UC Desert Research and Extension Center and several commercial fields in Holtville are focused on best irrigation and nitrogen management in carrots. One of the major commodities grown in Imperial County, carrots are grown on an average of 16,000 acres.

Ali Montazar, UCCE irrigation and water management advisor in Imperial, Riverside and San Diego counties, said nitrogen and irrigation management in carrot production is critical for increasing efficiency in crop production and decreasing costs and nitrate leaching.

In desert carrot production, a common irrigation practice in stand establishment is to sprinkler irrigate the field every other day during the first two to three weeks after seeding. Many fields are furrow irrigated after germination. Montazar said a comparison of applied water and crop water consumption indicates that carrot fields could be over-irrigated during the stand establishment period.

There is a wide range in the length of carrot crop season anywhere from 125 days to 190 days. Montazar said the trials showed that carrot fields may also have variable water requirements due to soil types, early or late planting dates and length of crop season. A peak daily crop water use of 0.21 inches on March 23, 2020 151 days after planting was observed in a fresh market carrot field.

Use of sprinkler irrigation during the critical fruit set period allows for more frequent and lighter water applications than furrow irrigation and helps avoid wet and dry soil cycles which contribute to splitting of roots. Sprinklers also reduce salinity.

Montazar said that given an irrigation system efficiency of 70%, the approximate gross irrigation for carrots in that area is 1.9 to 2.1 acre feet, not including pre-irrigation.

Preliminary results of the trials show a notable amount of N uptake both in the roots and tops at harvest. Nearly 50% of the seasonal N accumulated in the tops and roots at 85 to 90 days after planting when the canopy is fully developed. An effective N application could be splitting N into 10% to 15% at planting, and the remainder through irrigation over the season, completed 15 to 20 days prior to harvest.

Montazar noted that 45% to 55% of total N accumulated in the carrot plants, mainly tops, are left in the field as residual soil N and can be a source of N for the next season.

This project was funded by the CDFA FREP and California Fresh Carrot Advisory Board.

Weed control in tree nut orchards can be a moving target. New species can be introduced, herbicide application timing varies depending on the weed type and weed species can become resistant.

Many management tools are available for growers and farm managers, but methods of use can vary from year to year and from orchard to orchard.

Weeds affect young orchard growth by competing for water and nutrients. Large weeds can provide habitat for vertebrate pests, insect pests and contribute to the presence of nematodes and disease.

Almond Board of California’s Senior Specialist in Pest Management Drew Wolter said changes in weed populations from year to year, plus new, invasive weed species, challenge tree nut growers every year.

Weather conditions can influence weed populations. Salt or drought tolerance in a weed species allows it to proliferate in those conditions.

Soil texture and organic matter also affect weed populations. Annuals, including Puncture vine and horseweed, and perennials, such as Johnson grass, nutsedge and Bermuda grass, can dominate in lighter textured soils. Heavier soils will host curly dock, field bindweed and dallisgrass.

The UC IPM guidelines report that higher rates of preemergent herbicides may be necessary in clay or clay loam soils to achieve the same level of weed control as a lower rate in lighter soils.

Soil texture and irrigation methods also play a role in weed germination and establishment.

Horseweed, Italian ryegrass and field bindweed are three major weed species that invade tree nut orchards. Palmer amaranth and another amaranth species, such as hempweed, are two newer weeds that can pose challenges to control due to herbicide resistance. This is particularly problematic since there are few products registered for managing weeds in young orchards.

Horseweed’s prolific seed production makes this weed difficult to control. Herbicide control is more effective when this weed is in the rosette stage.

Field bindweed is one of the most difficult weeds to control, Wolter said. Its persistence is due to a vigorous horizontal rhizomatous system that can give rise to new roots and shoots once aboveground vegetative matter is knocked down or when roots are disturbed.

Systemic herbicides, such as glyphosate, should be applied when the plant is in its full bloom stage. During this stage of growth, the roots’ carbohydrate reserves are at their lowest, and the sugars produced in the leaves are being moved downward to the root system.

Italian ryegrass’ genetic diversity makes it difficult to develop a specific management plan. A winter annual, its seeds can germinate year-round in some conditions.