Early detection of pocket gopher mounds in a vineyard can help with control decisions and prevent damage to grapevine roots.

These 6- to 8-inch rodents live underground and are rarely seen. They spend most of their time in a tunnel system 6 to 12 inches below the soil surface. The tunnels have lateral branches used for feeding or pushing excavated soil to the surface. These fan-shaped soil mounds over tunnel openings are signs of a pocket gopher infestation.

The UC Integrated Pest Management guidelines for pocket gophers in vineyards note that the tunnel openings are almost always closed with soil plugs unless active excavation is occurring. Gophers can be active throughout the year in vineyards and other irrigated crops. Populations are more likely to be present where there is extensive weed growth, including nutsedge. Cover crops, particularly perennial clovers and legumes, are also favored by pocket gophers. If food is available and no biological or other controls are implanted, populations can increase to 30 to 40 gophers per acre.

Gopher control can be problematic in vineyards adjacent to empty, weedy fields or crops where gophers are not controlled.

Trapping and baiting are listed as the most effective control methods. UCCE Kern County Farm Advisor Julie Finzel said when she receives calls about pocket gophers, she first asks growers what control has been tried and information on the infestation.

Recognition of pocket gopher mounds should be followed by some control methods. Mounding activity is highest through late winter, and the most common controls, trapping and baiting, are easier when vineyard soils are moist. Darker mounds indicate new activity. Nearby vines should be checked for girdling of roots or crowns at or below soil.

Biological and cultural controls include predators who may not keep numbers low enough, tilling which can disrupt tunnel systems and flood irrigation where possible.

According to UCCE Specialist Roger Baldwin, gopher populations don’t cycle like voles do. Over large geographical areas, their numbers are steady across years, although within a specific area, numbers can certainly increase or decrease given local conditions.

The UC Guidelines advise an integrated approach to gopher control. Baiting can be done with multiple dose anticoagulants, strychnine or zinc phosphide, which may require a permit from the county.

Baiting requires finding the main tunnel to place the bait. Start by finding the plug of the gopher mound and probe from 4 to 12 inches behind the plug. A tunnel is found when a drop in the probe is felt.

Trapping also requires some labor and skill for success. The Macabee Gopher Trap or the Gophinator are recommended. Traps need to be fastened in place and their location marked so they can be found.

Baiting with poison is another technique. Special probes that release bait are available. Strychnine and zinc oxide are legal in California for ag use, and they kill with one feeding. Anticoagulants may take multiple feedings. Poisons can have secondary effects. Tractor-drawn devices can create artificial burrows and deposit bait as they do, but soil conditions are critical for effectiveness.

Root knot nematodes are the most significant soil pest in California fresh carrot production.

In the 2022 Carrot Research Symposium, UC Riverside researcher Antoon Ploeg reported on 2021 trials of new non-fumigant nematicide products to prevent root knot nematode injury in carrots. The trials were conducted with UC Riverside researcher Ole Becker.

According to Becker’s report to the California Fresh Carrot Advisory Board, root-knot nematodes are widespread in central and southern California carrot production areas and are particularly damaging in lighter soil types. Becker noted that presentations at the carrot symposium narrowly focus on the previous year’s research with funding from the board. He said the trials do not capture the overall project that typically runs for several years.

Root-knot nematodes lower carrot quality due to forking and root galling and can significantly lower marketable yields. This plant parasite also affects other vegetable crops, including tomatoes and peppers, but does not have as large of an impact on marketable yield as in carrots.

The non-fumigant nematicides, Velum, Salibro and two unnamed products T1 and C, were tested. These nematicides were applied pre-seeding at different rates and with and without soil penetrant products. There is a short re-entry time, and no tarping is required after applications. There is no systemic activity or phytotoxicity when applied at recommended rates.

Traditional management for root knot nematode has consisted of the soil fumigants Telone II and metam sodium. Due to buffer zone requirements when using those products, portions of fields must be excluded from treatment. Restrictions on use to reduce emissions can also prevent applications.

The first trial at the South Coast Research Center in Irvine had 10 treatments with an untreated control. The products were sprinkled over the top of the bed and incorporated into the soil three days prior to hand seeding.

Ploeg said that nematode levels were overall fairly low. Some treatments appear to reduce nematodes at harvest, but no significant effects were found.

There were only minor differences in percentage of marketable carrots, results that did not agree with the previous year’s results. This was surprising, Ploeg said, because a previous trial showed that Salibro had a dramatic effect on percentage of marketable yields.

In a second trial, Salibro was both sprinkled and drenched at the regular rate and double rate and compared to the untreated control the double rate sprinkled did show an increase in marketable yield.

Ploeg said the 2022 trials would include some new biological products.

Weed control in California vineyards requires these ‘little hammers’: mechanical, cultural, physical, biological and chemical.

Continuous use of the same practice will select for weed species that become adapted to that practice. Multiple control tactics will prevent adaptation.

Fresno State University Professor of Weed Science Anil Shrestha, speaking at the 2021 virtual Lodi Grape Day, said resistance challenges in control of vineyard weed species may impact vine health, crop quality and cause economic loss for growers. Young vineyards are most susceptible to competition from weeds.

Integrated weed management is not a new concept, Shrestha said, but as effective herbicides were developed, fewer other tools were used. As weed resistance increased, the integrated approach is again being emphasized.

The International Survey of Herbicide Resistant Weeds (www.weedscience.org) showed that 263 weed species have developed resistance to herbicides. Only three modes of action in herbicides have no reported resistance, Shrestha said, and there are no new chemistries coming in the near future.

In addition to rotating modes of action in herbicide applications, there are steps to take in preemergent and post-emergent weed control that can maximize efficiency. For preemergent products, Shrestha advised removing debris from vineyard floors, using enough water to activate herbicide and to avoid frequent wetting and soil disturbance. Post-emergent weed control is best achieved with timing, meaning applications at early growth stages, using enough water volume and choosing effective nozzles for delivery.

Mechanical weed control in vineyards can be effective, but using the same tool over time can cause a shift in weed species. Shrestha’s example was use of a cultivator or French plow over time that cleaned up horseweed and fleabane in a vineyard, but nutsedge and grasses become an issue.

Palmer amaranth is an example of a more recent weed species to invade California vineyards. It is resistant to glyphosate even at eight times the label rate, Shrestha said. Mexican sprangletop and telegraph weed may also invade vineyards.

Shrestha said it is critical to maintain a weed-free environment around young vines for at least the first two years after planting. Studies showed that aboveground biomass could be reduced by 85% due to weed pressure. Cane length, leaf numbers and root biomass can also be impacted by weed growth.

Established vineyards may tolerate more weed pressure; however, vineyard weeds may also serve as disease or insect pest hosts. Loss depends on age of the vines, life cycle stage of the vines, weed species and density and duration of competition.

Advantages of using steam for soil disinfestation in strawberry production were presented at a February 2022 UCCE Strawberry Production meeting by Steve Fennimore, UC Cooperative Extension specialist in plant sciences.

Feasibility of using steam to kill soil pathogens and weed seeds in strawberry and other row crops has increased with new machinery development and field trials. As an alternative to fumigation, Fennimore said this sanitation treatment requires no buffer zones or plastic mulches used with chemical fumigation; however, current cost per acre for the propane and labor totals around $971.

An advantage of steam sanitation is that it lacks the negative environmental and worker health regulations associated with chemical fumigants.

Heat treatment for soil sterilization is not a new idea, but equipment availability and costs have been drawbacks to adoption. The machine in Fennimore’s presentation was built in South Korea.

The machine injects steam into the soil to raise the soil temperature to 158 degrees F for 20 minutes. The machine is moving while injecting steam, Fennimore said. The steam transfers heat from the heat source to target soil particles. When steam comes into contact with cold soil particles, the steam molecules condense, releasing heat to the soil particle. Steam kills the pathogen in and around the soil particle, and the steam also kills weed seeds and nutsedge tubers.

In a 2021 strawberry nursery trial, Fennimore said use of steam significantly reduced hand weeding costs for growers. Compared to untreated control ground, steam-treated soils yielded less than 272,000 weed plants while untreated control had 420,000 weed plants per acre. In strawberry nursery plant production, more daughter plants were produced under steam disinfestation.

In a production strawberry trial, steam treatment was as effective as PicChlor 60 in controlling soil pathogens and weeds. Fruit production from steam-treated soils equaled that of PicChlor 60 treated soils.

Band steam treatments in lettuce also proved effective for weed and pathogen control. In a Yuma, Ariz. trial, the steam machine operated at three quarters of a mile an hour and injected steam in a band where the lettuce crop was to be planted. The steam treatment reduced weed emergence and soil pathogens. It also increased lettuce size. A good fit for steam band technology, Fennimore said, may be organic production where there are few good disease and weed control options.

Fennimore reported increased interest in steam soil injection as a method of reducing weeds and soil pathogens. In addition to the South Korean machinery used in the trials, Fennimore said a Norwegian startup is also developing a soil steam injection machine and has expressed interest in bringing the machine to the U.S. for trials.

Orchard history, bud monitoring and the mathematical model Xanthocast are the three methods for attempting to predict or forecast walnut blight.

Sac Valley Orchard Source, a UCCE publication, notes that all three methods have advantages and disadvantages, and their use can be a guide to decision making when implementing a walnut blight preventative management program.

Walnut blight is caused by a bacterial pathogen that can overwinter in between scales of healthy buds. Rain can splash the bacterium onto developing flowers and leaves. Twig cankers are also an overwintering site that can supply inoculum for infection. Bud infections can result in bud death and fruit infections.

These infections can develop into twig cankers, which allow survival of the blight pathogen from one season to the next.

Orchard history involves surveying 10 trees for infected nuts the previous June. If fewer than 50 infected nuts are found, there is a low risk, and 50 to 150 infected nuts is a high risk. High disease levels can mean high bud populations and presence of twig cankers.

With bud monitoring, dormant buds are sampled for colony formation. Positive identification of bacterial species is needed. Orchard Source also notes that orchards can go quickly from low risk to high risk depending on weather conditions.

Xanthocast is a mathematical model that uses leaf wetness and temperature for forecasting emergence of the disease and timing of treatment intervals. Values should be combined with information from orchard history and bud monitoring.

The bactericide Kasugamycin, labeled as Kasumin, is used for managing walnut blight. According to Orchard Source, applications should be initiated when conditions favor disease development.

In orchards with a history of the disease and when high rainfall is forecast, applications should be initiated at 20% to 40% catkin expansion. Under moderate/low disease pressure, including low rainfall forecasts and minimal dews, applications should start at 20% prayer stage (leaflets unfolding, before expansion) and at 40% prayer stage when disease pressure is very low. These stages correspond to pistillate flower emergence.

In orchards with very low walnut blight infection rates or young orchards with no blight history, growers should consider a spray application at 40% prayer stage.

The newly launched Better Soils Alliance is offering an opportunity for almond growers and orchard managers to improve their efficiencies in water and nutrient use while demonstrating to buyers of almonds that they are intent on ensuring sustainability of the industry.

Announced at the 2021 Almond Conference, the Alliance uses the continual improvement concept and aims to verify improvement in resource use and reduction of greenhouse gas emissions by almond growers who participate.

Agricultural nutrient company Yara and food and agriculture technology company Heliae Agriculture initiated this alliance to determine management practices that will improve efficiencies in almond production and bring in growers who want to improve health of their soil.

Soil scientist Dr. Rob Mikkelsen, agronomic director for Yara North America, said the alliance is open to growers and others involved in the almond industry to incentivize improvements in water productivity and nitrogen use efficiency. The alliance will also be calculating greenhouse gas reductions that may provide alternative revenue streams for growers in the future. Validated and verified improvements would create opportunities for payments for carbon credits.

The Better Soil Alliance aims to provide greater support for growers and advisors by engaging all stakeholders to drive practical and profitable solutions in almond production.

Mikkelsen said precise and balanced use of nutrients in agriculture production could prevent soil degradation which happens over time as nutrients are mined from the soil.

Devin Clarke, permanent crop manager for Yara North America, indicated the need for a multi-tiered evaluation structure to reach more acres and conditions. This structure should dramatically decrease the time required to adapt to industry-wide challenges like water availability and consumer demands.

The Better Soil Alliance phase one efforts are focused on leveraging crop nutrition and soil biology to improve input use efficiency. The Better Soil Alliance will be conducting trials in the 2022 crop year to assess both improvements in plant-soil interactions but also yield, quality and grower profitability.

“Improving soil quality serves as the foundation to improving water use that helps optimize crop yield and quality”, said Norm Davy, Heliae Agriculture. “Between the increased consumer demand for almonds and tightening water supply in California, growers need solutions that increase yield and improve soil health and soil structure for future crops.”

UCCE Viticulture Specialist Kaan Kurtural’s study of cover crops under no-till systems in vineyards was done to determine if grape vineyard water use could be improved.

In a presentation for the virtual San Joaquin Valley Grape Symposium, Kurtural said the 2020 study was focused on finding the best management for vineyard floors using cover crop and tillage systems to preserve plant-available water in soils prior to the initiation of irrigation. He also evaluated cover cropping and no-till practices for their sustainability in regard to mitigation of greenhouse gas emissions and their combined effect on grapevine physiology.

Kurtural added that the study would provide growers recommendations regarding the use of novel low-stature permanent grasses in vineyard systems.

The study was done in Fresno with three cover crops, including a perennial grass (Poa bulbosa hybrid), annual grass, barley and resident vegetation under till versus no-till. The randomized study was done in a Ruby Cabernet on Freedom rootstock vineyard under drip irrigation.

Results noted were a 30% increase in mid-day leaf water potential in early spring and a 10% increase the following year with the perennial grass. When extrapolated to a hectare scale, the perennial grass cover crop demonstrated a decrease in soil respiration, one of the primary sources of carbon loss in agricultural soils.

Kurtural said the net carbon assimilation of the system grown with perennial grass under no-till management was enhanced compared to the system with annual grass or resident vegetation.

At harvest, there were no changes in berry mass, acidity or sugar content.

Kurtural also compared the Fresno study with a Napa County study.

In Napa, with a transition from tillage with resident vegetation or annual grasses as winter ground cover to perennial grass, he found no-till saves between 3% to 6% of annual cultural costs ($294 and $552 per acre, respectively.)

In Fresno, transitioning from tillage with resident vegetation or annual grasses as winter groundcover to perennial grass and no-till saves between 9% to 16% of annual cultural costs ($174 and $339 per acre, respectively.)

Kurtural said that cover crops under no-till systems may be implemented in the San Joaquin Valley irrigated vineyards with no effect on grape productivity and improvement in grapevine water use.

The remaining component of the research will include GHG flux calculation and characterization of bacterial and fungal communities.

Although Salinas Valley lettuce growers enjoyed a reprieve from virus pressure in 2021, the plentiful December rains have sparked intense weed growth, providing prime habitat for Western flower thrips, a vector for impatiens necrotic spot virus. The UCCE publication Salinas Valley Agriculture reports that this plant virus caused $100 million in lost gross revenue for Salinas Valley lettuce growers in 2020.

“It’s a blessing, yes, we need the water,” said Tony Alameda, managing partner of Topflavor Farms, which grows a variety of produce in Monterey and San Benito counties. “But, oh gosh, with that water, here come the weeds, here comes the habitat, here comes all the other problems that go along with it.”

The agricultural community called it “the biggest problem we’ve seen in a long, long time,” said Mary Zischke, facilitator of a task force convened by the Grower-Shipper Association to address INSV and a related affliction, Pythium wilt.

Even though 2021 was a “good” year, about one-third of all lettuce plantings in the Salinas Valley had at least a low level of infection, according to Zischke.

INSV on lettuce causes characteristic patterns of chlorosis and necrosis on the inner leaves of the plant as well as significant stunting. However, INSV can cause significant necrosis and lesions on and at the base of the ribs of lettuce plants. Lettuce plants infected with only INSV do not exhibit wilting of the outer leaves of the plant or show root rot or root discoloration.

Salinas Valley Agriculture reports that recent studies have identified several weeds as key reservoirs of thrips, including malva, marestail and hairy fleabane. Mustards, fortunately, appear to be poor hosts for thrips, although their pollen serves as potential food sources.

Aggressive weed management was an important factor in limiting the virus’ spread in 2021. Because weeds recognize no boundaries, managers of non-agricultural lands are being urged to keep their properties as clean as possible, including industrial sites, equipment yards and the edges of roadways, namely U.S. Route 101, which runs through the center of the valley. Some growers have been volunteering to weed their neighbors’ vineyards.

“We’re encouraging everybody, as best they can, to knock down known weed hosts; that’s really critical,” Zischke said.

Heat waves were a major driver of the INSV disaster of 2020. Researchers have established a link between warmer temperatures and population increases of thrips.

Alameda and Zischke point to the breeding of more resistant lettuce varieties as the ultimate solution to INSV.

With funding from CDFA’s Specialty Crop Block Grant Program, UCCE Irrigation and Water Management Advisor Ali Montazar will work on development of irrigation tools and strategies for avocado growers in Southern California.

Montazar, who works with growers in Imperial, Riverside and San Diego counties, said avocado growers in Southern California face uncertain water supplies and mandatory reductions in water use. Improved irrigation and water use efficiency are critical to sustainable avocado production. Efficient use of irrigation water is one of the highest conservation priorities, he added. Proper irrigation management is also crucial to managing tree nutrition as well as preventing Phytophthora cinnamomi or avocado root rot.

Avocado water demand may vary depending on canopy features, row orientation, weather, soil types and conditions, and irrigation practices. Different avocado varieties do not necessarily have different water demands while they might have different responses to water or salinity stress. The negative impact of stress can be different for different varieties.

Montazar said one of the main purposes of this study is to develop information on avocado water demands under different conditions. Deficit irrigation trials will be used to see responses in fruit quality and quantity.

New tools and resources developed in this project will help growers achieve water use efficiency goals, Montazar said.

The research team is collaboratively working with California Avocado Commission and several growers. In this project, a combination of field experiments, case studies and a robust outreach program are used to develop and disseminate information and tools to growers and stakeholders. These tools and information may have a significant impact on water quality and quantity issues, Montazar said, bolstering the economic sustainability of avocado production not only in the well-established production region of Southern California, but also in Kern and Tulare counties where new avocado plantings are growing.