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.

With 26 fungal species associated with canker disease, it is important for growers and farm managers to determine which pathogen is attacking their almond trees. Field diagnosis plus a laboratory test can reveal the responsible pathogen or point to an abiotic reason for canker formation.

Florent Trouillas, UCCE plant pathology specialist at the Kearney Agriculture Research and Education Center, noted during a presentation at The Almond Conference that in order to use the most effective control options, it is critical to understand which diseases can affect the trunks and scaffolds of almond trees. UCCE Plant Pathologist Themis Michailides and USDA researcher Greg Browne also provided information on control and prevention of canker diseases.

Most infections of fungal canker diseases occur at pruning wounds made for primary and secondary scaffold selection. Fungal pathogens that cause gumming and dieback in almond trees are the leading cause of death in young orchards, Trouillas noted. These pathogens include Botryosphaeria, Ceratocystis, Diaporthe, Eutypa and Phytophthora.

Botryosphaeria is associated with band cankers that infect cracks in the bark and pruning wounds. These cankers often present in a row around the trunk. Two- to five-year-old trees with vigorous cultivars are most affected by this disease.

Phytophthora and Ceratocystis infections also cause gumming on the tree trunk and scaffold branches. Ceratocystis cankers are more elongated and are common in prune and cherry trees. The pathogen is transmitted by insects and affects both young and old trees. Phytophthora infections are notable for their quick development as well as gumming of the trunk and scaffolds.

Eutypa infections begin in pruning wounds or in cracks near the tree crotch.

There are also abiotic reasons for trees to develop cankers. Those include herbicide injury, acid burn and boron toxicity. Foamy canker, marked by copious amounts of reddish gum that flows from the cankers, can be caused by a number of abiotic stressors.

Location on the tree and infection sites can help with a field diagnosis, but Trouillas said a molecular diagnosis is a tool that can now be made in 24 hours using a species-specific primer that targets all canker pathogens.

Michailides noted that band canker in almonds has been on the rise since 2005 and has the potential to kill trees. Bands of cankers develop in a circular pattern around the tree trunk. In severe cases, two to three bands may be present.

Preventative measures in young orchards involve obtaining clean trees from nurseries. Once planted, the fungicide Topsin-M should be applied to the trunks at label rates during the first-, second- and third-leaf years. Avoiding wetting tree trunks during irrigation and protecting pruning wounds with Topsin at label rates is advised.

When band canker is present in young orchards, it is recommended to keep tree trunks dry, apply Topsin-M to trunks and scaffolds and to also protect pruning wounds. Killed trees and stumps should be removed from the orchard and wood piles should not be located near orchard sites to lower inoculum levels.

Best management of perennial Phytophthora Canker (PCC) and Phytophthora crown and root rots (PCRR) involves integrated cultural, genetic and chemical control.

Phytophthora, a ‘water mold,’ is adapted to being spread by surface water and reaching plant roots, persisting in adverse conditions.

Browne said that PCC, which mostly results from scion infections, is most prevalent in mature orchards, while PCRR results mostly from rootstock infections and is most prevalent in young orchards.

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New information on the invasive fruit fly spotted wing drosophila (SWD) comes from Dr. Artyom Kopp at UC Davis. Published in the January 2022 ANR Blog Strawberries and Caneberries, the information sheds light on origins of SWD, how and why it attacks fruit and possible biological control tactics.

SWD was found in 2008 damaging fruit in many California counties. It infests ripening cherries throughout the state and ripening raspberry, blackberry, blueberry and strawberry crops, especially in coastal areas. It also has been observed occasionally attacking other soft-flesh fruit such as plums, plumcots, nectarines and figs when conditions are right.

SWD, Drosophila suzukii, is native to East Asia and has been established in Hawaii since the 80s, where it is found in large numbers on guava and other fruit. In California, the first SWD were collected in 2008, and by 2009-10, they were a major problem in California, Oregon, Washington and Florida.

Unlike most fruit fly species, SWD has a prominent saw-like ovipositor that enables it to lay eggs in undamaged fruit. The larvae are tiny, white cylindrical maggots a little longer than 1/8 inch when fully grown. One to several larvae can be found feeding within a single fruit. After maturing, the larvae partially or completely exit the fruit to pupate.

All Drosophila species use a mix of sensory cues to identify places suitable for egg-laying. They smell with their antennae, taste with their legs and mouthparts, and measure hardness with their ovipositors. SWD prefer the smell of intact fruit and do not mind hard surfaces.

Kopp noted that once SWD damages fruit by opening the skin, the fruit is accessible to Drosophila species such as D. melanogaster, D. simulans, and D. hydei. These species are more abundant, more prolific, faster-developing and more heat-tolerant than D. suzukii, so they tend to out-breed it once it provides them with access to the fruit. Kopp said most flies hatching are probably those other species, but it was likely D. suzukii that let them in.

Several generalist wasps native to North America and Europe can parasitize D. suzukii under laboratory and field conditions. Some Leptopilina and Ganaspis wasps, abundant in Asia, seem to be specialist parasitoids of D. suzukii, preferring it to other Drosophila species. They prefer to attack the larvae that are feeding on ripening fruit and cause high mortality in D. suzukii in its native range.

Kopp said use of transgenic tools to introduce artificial constructs can suppress population growth. Transgenic tools for D. suzukii have recently been developed, and several female-killing approaches have been tested in lab trials. 

Extending the profitable lifespan of a table grape vineyard includes management practices to prevent trunk diseases, weed and nematode control.

The UC Integrated Pest Management guidelines for table grape vineyards note that delaying vineyard pruning until late in the dormant period is effective in reducing fungal infections. The delay avoids the highest spore release time of December and January.

Preventative practices are most valuable in young vineyards, but they have also shown some efficacy in older vineyards with prior trunk disease infections. The guidelines report that post-infection practices, including sanitation and vine surgery, are more expensive than preventative practices adopted early in a vineyard’s life. Those include delayed pruning, double pruning and use of pruning wound protectants.

Dormant-season sanitation practices include destroying prunings of older, infested wood to reduce pest sources. Dried grape clusters should be removed from vines and weeds disced to remove overwintering sites for orange tortrix or omnivorous leafroller. Where branch and twig borers have been a problem, old pruning scars and dead parts of vines should be scouted for evidence of brown frass and wood dust. Where vine mealybug has been found in a vineyard, care should be taken to prevent spread of this pest to uninfested areas of a vineyard by sanitizing machinery.

Weed control is essential in young vineyards until canopies are large enough to shade out competition. Surveys can allow for identification of weeds that escaped control in the last growing season and to determine which perennial weeds are present. Finally, surveys help with choosing appropriate herbicides of cultivation.

Cultivation may be preferred to herbicide use in young vineyards to prevent injury to vines. In mature vineyards, herbicide application in the vine row should be used together with mowing or cultivation between the rows. In the absence of herbicide applications, mowing may be needed when weeds exceed six to eight in height. Cultivation in the rows may be necessary after irrigation causes weed seeds to germinate.

In the San Joaquin Valley, sampling soil for nematodes is done from November to February when X. index or dagger nematode populations are most likely to be detected. Root knot nematodes are found at any time of the year. Soil samples should be sent to a diagnostic laboratory for identification.

Xiphinema index can cause yield reduction in some varieties but is more important for its transmission of grapevine fan leaf virus, the cause of grapevine fan leaf degeneration disease.

An investigation into mid-canopy wood peeling in young almond trees by Cameron Zuber, a UCCE staff research associate in Merced County, found pole harvesting to be the likely culprit.

Zuber reported that fresh peeling of tree branches was typically seen in the fall and winter periods. Only a small portion of the branch was affected, and they were mid-canopy branches. The peeling exposed a large area of the inner wood and there was concern that it could be a site of infection.

In September 2021, fresh peeling was observed in a third leaf almond orchard in Fresno County with peeling ranging from the bark to sap wood layers. The peeling was found in about a quarter of the trees on the outer and inner canopy branches. Zuber said the outer branches seemed to have more damage.

He said the damage was new as the orchard was under observation to collect information for almond production research. The orchard observations included walking the entire orchard site and working within the tree canopy. The peeling was not present until it was observed in September.

The puzzle was that no orchard activity had occurred in the orchard that could explain the wood peeling. When it was learned that harvest at the orchard was done with a poling crew using metal poles and tarps to collect the nuts, Zuber began to examine the practice. It was done, he said, due to the young age of the trees and concern about shaker damage. The research being conducted at the site also required that nuts be collected from specific sets of trees.

Given the timing of the pole harvest and peeling damage, this was the most likely cause. The height of the peeling also lined up with the main area the poling crew was hitting trees the hardest at.

The reason for the peeling may be due to the energy from a hard-hitting pole causing fractures to form parallel to wood fibers. Tension from the undamaged fibers pulled this fracture and an opening formed, thus exposing the inner layers of wood. If the pole harvesting caused this peeling, it provides insight into the fresh peeling seen at other locations during the fall and winter since poling is also used to perform sanitation.

Zuber said that the wood peeling possibly caused by the pole harvest in the summer does not tell whether pole sanitation in the fall or winter would result in the same type or amount of damage. The high amount of peeling from pole harvesting a third-leaf orchard was probably due to the suppleness of the wood due to the trees’ age, irrigation making the wood swell or a combination of the two, increasing the chance of damage from a pole.

Prune bloom time will soon be here. UCCE orchard systems farm advisors have noted in Sac Valley Orchard Source that there are several management options that should be considered at this time of the year, though timing can vary depending on growing region.

If the forecast is for cold weather at bloom, tall weeds or a cover crop will cause colder orchard temperatures than a mowed floor. Newly disked soil provides the coldest conditions. On the other hand, if temperatures reach into the 80s during or soon after bloom, sprinklers can help reduce orchard temperatures one or two degrees.

Protecting this year’s crop from fungal disease begins at this time. To prevent brown rot, a single bloom spray is recommended at 25% to 40% bloom. Dew can provide enough moisture for brown rot infection and a second spray may be necessary. If rain is forecast during bloom, a spray at white bud and again at full bloom is advised. The full bloom spray is critical. A scab material can be included in the tank.

Significant rainfall during or right after bloom can trigger russet scab. Once the fruit is through the jacket, risk is minimal.

Monitoring for peach twig borer should be done during and after bloom. If this pest is present, chewing on buds is evident. Place pheromone traps at two per block no later than mid-March to determine biofix. If moths are caught on two consecutive trap checks, begin accumulating degree days.

For aphid control, two 440 oil sprays at four gallons per acre at bloom can be used to control mealy plum and leaf-curl plum aphids. Applications should be at slow ground speeds seven to ten days apart. For bee safety, alternative management timing avoiding bloom should be considered.

Weed control should also be part of an early spring management plan. Rotating or mixing herbicides with different modes of action will help with herbicide-resistant species.

Brad Hanson, UCCE weed specialist, has organized a chart to help, with herbicide name, a common trade name, the site of action group and the crops for which an herbicide has been labeled for use. Labels may have changed.