Egg Parasitism of the Virginia Creeper (Erythroneura ziczac), A Newly Invasive Leafhopper Pest in California

Organic grape growers in Mendocino and Lake County have been experiencing severe outbreaks of the Virginia creeper leafhopper (Erythroneura ziczac) for the past 3 years. Feeding by E. ziczac causes leaf stippling and reduced photosynthesis which can impact crop yield and quality. The primary natural enemies of E. ziczac are the small ‘mymarid’ egg parasitoids Anagrus daanei and Anagrus tretiakovae. A related pest, the Western grape leafhopper (Erythroneura elegantula) is also parasitized by A. daanei as well as Anagrus erythroneurae. Erythroneura ziczac and E. elegantula are commonly found together in North Coast vineyards. Anagrus daanei is the parasitoid species of most importance for E. ziczac control, whereas A. tretiakovae is rarely found in California.

Our approach to improving E. ziczac control involves a combination of short- and long-term strategies. Short-term work focuses on the evaluation of Organic Materials Review Institute (OMRI) approved pesticides. In 2014, we tested Stylet oil and DeBug® Turbo (applied twice) and Pyganic® (applied once) on the development of the first leafhopper brood. All of these products significantly reduced E. ziczac nymph populations relative to an untreated control.

Long-term strategies are focused on the identification and evaluation of Anagrus parasitoids to improve biological control. A survey in Mendocino, Lake, Napa (Pope Valley), Yolo and El Dorado County vineyards found that E. ziczac parasitism was consistently low (0-2%) with the exception of Yolo County, where rates reached 10-15%. Surprisingly, A. daanei was attacking E. elegantula in all of the surveyed vineyards, but only in Yolo County was it attacking both E. elegantula and E. ziczac. Therefore, we questioned whether or not the A. daanei in Yolo County are the same species as the A. daanei that don’t attack E. ziczac in other regions. Molecular comparison of the A. daanei from different Californai regions is still in progress, but to date morphological evaluations have not shown any differences among the A. daanei populations tested. We conducted a trial in which we forced A. daanei from Mendocino County onto E. ziczac eggs in order to see whether or not, in the absence of their preferred E. elegantula host, they would attack the E. ziczac eggs. Findings from this study indicated they would not.

In another trial, we separately inoculated potted grape vines with E. ziczac eggs from Mendocino, Lake and Yolo County and then exposed sets of these vines to the A. daanei in each of these regions. Results showed fairly consistent parasitism of all three E. ziczac populations by the A. daanei in Yolo County. Having verified that the A. daanei in Yolo County will readily attack the E. ziczac population in Mendocino and Lake County, we now feel that there is adequate evidence to support a collection and re-release program in which A. daanei from Yolo County are introduced into Mendocino and Lake County vineyards. This redistribution of California parasitoid material would be carried out in conjunction with an area-wide IPM program to promote additional best management practices to further reduce E. ziczac outbreaks.

Development of the Vineyard Advisor – A Mobile Application for Grape Disease and Pest Management Recommendations

The Vineyard Advisor mobile application was designed to provide up-to-date recommendations on disease and pest management for commercial grape production, including the most current federal pesticide labels. For a given grape disease, pest, or weed problem, the Vineyard Advisor delivers management recommendations following a standardized format with the following sections: Problem name; When to take action; Cultural management practices; Organic materials; Registered pesticides; and References. Recommendations are derived from published resources including viticulture books and Extension pest management guides from several states. Current federal pesticide labels are retrieved from the U.S. Environmental Protection Agency (EPA) using a modification of the system employed by the Mobile Access to Pesticides and Labels tool produced by the National Pesticide Information Center.

The Vineyard Advisor can be used by a vineyard manager who has observed a disease problem, for example, to look up the recommended cultural practices to manage the disease as well as a list of pesticide products labeled for control of that specific disease on grapes. The pesticide product is linked to PDF files of the most current national product labels approved by EPA. Alternatively, the vineyard manager could use the app to search directly for a specific pesticide product labelled for grapes. This feature is particularly valuable as changes occur in pesticide product availability or directions-for-use. The Vineyard Advisor pesticide label database is updated in concert with EPA updates to their database, which typically occur on a weekly schedule.

The Vineyard Advisor also seamlessly integrates with the Vineyard Doctor diagnostic system, through the Problem Profile pages of the Vineyard Doctor. An example of this use would be a vineyard manager using the Vineyard Doctor to identify an insect problem in the vineyard, and following the management recommendations link on the Problem Profile to the corresponding insect management recommendations page on the Vineyard Advisor. The scope of vineyard problems for which the Vineyard Advisor provides management recommendations fully coincides with the 150+ problems within the Vineyard Doctor system, and additionally provides weed management recommendations including links to herbicide labels. The Vineyard Advisor can be accessed by any computer with internet access as a web service at <> or via mobile applications downloadable from the Apple Store (iOS) or Google Play (Android operating system).

Development of Tools for Growers to Evaluate and Optimize Ecosystem Services of Birds in Vineyards

Establishment of songbird nestboxes in vineyards increases insectivorous bluebird populations. Our study investigated the diets of vineyard-nesting Western Bluebirds (Sialia mexicana) to document whether bluebirds consume insect pest species and offer growers ecosystem services in the form of pest control. To evaluate the impact of avian predation on arthropods in vineyards, we sampled both birds and arthropods across three vineyards and adjacent native forest patches. Over 4500 arthropods were collected, sorted, and identified. For bird sampling, we used non-invasive methods by gathering fecal samples from adult and nestling bluebirds to evaluate what prey were consumed. We tested several DNA extraction kits before developing a novel methodology that provided better quality and quantities of DNA from bird fecal samples. We applied next-generation sequencing to obtain a list of diet contents in the form of DNA sequences. We compared these sequences to a reference database that we constructed from DNA sequences of our collected arthropods. We found a rich and diverse abundance of arthropods in both the vineyard and adjacent woodland habitats. This signifies that insectivorous birds nesting in vineyards had access to plenty of food resources. Bluebirds were consuming a diverse diet comprised of many different arthropod orders, from millipedes to butterflies. We found that adult bluebirds regularly feed their nestlings isopods (also called roly-polys or pill bugs). These were abundant in the vineyards and are known to offer one of the few sources of calcium available to insectivorous animals. Calcium can be a limiting nutrient, and it is likely that high densities of isopods in vineyards offer nesting bluebirds high-quality prey items for their growing young.

No significant vineyard pests (including blue-green sharpshooters) were found in vineyard and woodland traps. This meant that avian populations did not have access to these pest insects, so it is not surprising that we did not find evidence of bluebirds consuming vineyard pests in this study. We did find evidence of bluebirds consuming treehoppers and caterpillars, so in vineyards where these pests are present, bluebird boxes may invite predators that successfully lower pest populations. We did not find evidence that bluebirds were consuming parasitic wasps (beneficial insects that lower pests populations). Consequently the presence of bluebirds did not harm growers. Nestboxes can bolster declining bird populations, and increasing vineyard nest box presence can be an important sustainability practice for growers. Consequently we connected with growers and presented our findings in numerous venues, distributing informational pamphlets and 100 nest boxes to eager growers. Our goal is to provide growers with the resources they need to maintain healthy populations of birds in their vineyard for year.

Maintaining UC IPM Pest Management Guidelines for Grape – 2012

UC IPM Pest Management Guidelines: Grape, the University of California’s official guidelines for managing pests in grapes, is being revised. The version being revised includes two year-round IPM programs (table grapes and wine and raisin grapes), 11 general information sections, 11 diseases, 7 weed sections; 24 insect and mites, and 1 nematode section. Revisions to be made include adding new pesticides and removing unregistered ones; improved management information such as discussions about herbicide drift reduction and the use of mating disruption for vine mealybug; and new pests: Virginia creeper leafhopper, spotted wing drosophila, and vertebrates (birds, deer, ground squirrel, meadow vole, pocket gopher, and rabbits)

Sustainable mite management: Effects of regulated deficit irrigation and the overwintering biology of mites in vineyards

We evaluated the effects of regulated deficit irrigation on spider mite (Acari: Tetranychidae) and leafhopper (Homoptera: Cicadellidae) outbreaks in a commercial vineyard in Madera, CA. We established three irrigation treatments corresponding to 50, 70 and 100%of crop evapotranspiration (ETc) and monitored leaf water potential, leaf temperature and spider mite (Acari: Tetranychidae) and leafhopper (Homoptera: Cicadellidae) densities through the growing season. Leaf water potential of vines in the three irrigation treatments was significantly different on one sampling date in September only, when vines in the 50%ETc treatment were significantly more water stressed than vines in the 70 and 100%ETc treatments. Similarly, on the same sampling date leaf temperature was significantly higher on vines in the 50%ETc treatment than vines in the 70 and 100%ETc treatments. The lack of differences in leaf water potential between the different deficit irrigation treatments in this vineyard suggest a problem with the calculation of the ETc requirements of vines and/or the amount of irrigation water needed to cover ETc. Densities of Pacific spider mite, Tetranychus pacificus, and Willamette spider mite, Eotetranychus willamettei, begun to increase towards the end of June. A miticide application in mid August due to concerns of potential mite damage reduced mite densities to zero within three weeks. Spider mite densities did not differ significantly among the three irrigation treatments. Leafhopper densities remained at very low levels. A glasshouse study was carried out to complement the field study and provide information on the effects of regulated deficit irrigation and temperature on T. pacificus outbreaks. Vines were assigned into two glasshouse rooms representing cool (22.4°C) and hot (27.4°C) environmental conditions and were kept under five irrigation treatments corresponding to 100, 80, 60, 40 and 20%of ETc. Vines under hot environmental conditions were significantly more water stressed than vines under cool conditions. In addition, vines in the 20%Etc treatment were significantly more water stressed than vines in the other four irrigation treatments. However, we detected no significant differences in T. pacificus densities among irrigation treatments or between vines kept under cool or hot environmental conditions. Our results suggest that different irrigation amounts may not result in differences in plant-based measures of water stress. Grape growers need to estimate crop evapotranspirational needs and corresponding irrigation amounts precisely in order to successfully apply regulated deficit irrigation. Further studies are required to understand the effects of regulated deficit irrigation on spider mite outbreaks in California vineyards.

Biology and Management of Argentine Ants in California Vineyards

Argentine ants exacerbate mealybug populations in coastal California vineyards by protecting them from natural enemies and in return collecting a carbohydrate-rich food source. Conventional ant controls were only moderately effective at controlling ants and included toxic,broad-spectrum pesticide sprays, which disrupt natural enemies, and dry, protein-based baits,which are unattractive to sugar-feeding ants. Over the last 5 years, we have worked to develop a sustainable ant control program, dispensing reduced-risk insecticides as liquid, sugar-based baits.These baits do not disrupt non-target species, nor do they contaminate groundwater (a concern with barrier insecticide sprays). Originally our system, although effective for grape and obscure mealybug control, was labor and material intensive, both of which were prohibitive to its adoption on a large scale by growers. We have fine-tuned various aspects of the bait program, and now report that our work in this area is near completion. As of 2006, several bait stations, including one designed as part of this project, can be legally deployed in vineyards and orchards (US EPA-ChemSAC), two baits on which we have collected efficacy data have cleared the US EPA registration process and should be available in 2007-08, and we have 2 years of data addressing optimal density and timing of bait deployment. In 2006, we continued testing commercially available ant products, in order to provide growers with information on their efficacy, and initiated tests on new bait matrices containing amino acid additives and designed to be more attractive to ants than a simple sucrose solution. We also concluded multi-year studies on bait density and temporal deployment, designed to optimize bait delivery to the ants. Bait delivery should coincide with optimal foraging times and nest-induced demand for resources, as delineated by our previous bait trials and studies of Argentine ant nest biology and dispersal pattern. Since our studies on the bait program are nearing completion, this year we began to focus on aspects of the ant-homopteran-natural enemy complex which remain unanswered. These include the mechanism by which ants interfere with parasitism and the effect of ants on predatory insects. Additionally, with an ant baiting program in place in a Central Coast vineyard, we were able to resume distribution studies of the encyrtid parasitoids that were released in 1999-2000. We surveyed vineyards to quantify establishment rates and used potted plants and mealybugs collected during surveys to recover adult parasitoids. With these studies, we have collected the background information necessary to provide growers a complete understanding of the ant bait program, including aspects of bait placement, initiation and duration of baiting, and density of bait stations per acre. This information continues to be extended to growers in the form of invited talks, informal interactions, a UC-ANR fact sheet, and articles in trade and peer-reviewed journals. We have also collected initial data on the interactions between Argentine ants and natural enemies, which will give us a better understanding of their interactions and provide impetus for future studies on the biology and behavior of these insects.

Filling in some Information Gaps on Willamette Mite: Water, Sulfer and the Economic Injury Level

We undertook studies in three commercial vineyards to answer questions about Willamette mite (Eotetranychus willametti) on grapes, including how cultural practices such as sulfur and water management affect mite population density, as well as the economic injury level (EIL) of the mite. At the field site which we used for the irrigation studies (Steinbeck-Paso Robles), Willamette mite density was too low to make any evaluations. The sulfur and economic injury level studies took place at the Shandon site (San Juan Ranch, Fillipponi and Thompson).

For the EIL study, we worked in a block of Chardonnay and attempted to regulate mite density in four categories, control, 10 mites/leaf, 30 mites/leaf and >40 mites/leaf, representing low, mid-low, mid-high and high densities through selective use of a miticide (Nexter® [pyridaben]). These levels ultimately corresponded to <1000 mite days (MD)/leaf, ca. 2000 MD/leaf, ca. 4000 MD/leaf and ca. 8000 MD/leaf (a mite-day is equivalent to one mite/leaf for one day). Treatment vines were allowed to reach the threshold and were subsequently sprayed with Nexter®.

For the sulfur study, we worked in a block of Chardonnay which was treated in early spring twice with wettable sulfur, and subsequently with DMI fungicides (Rally®), but not with sulfur dust. Our treatments were sulfur dust and attapulgite clay applied weekly, compared to an untreated control.

In the EIL study, end of the season mite densities were 725 MD, 1607 MD, 3478 MD and 7760 MD for categories 1-4, respectively. Mite density peaked at 65 mites/leaf, 75 mites/leaf, 105 mites/leaf and 192 mites/leaf in categories 1-4, respectively. Overall average mites/leaf were 4.8, 10.2, 26.9 and 91.8 for categories 1-4, respectively. The only measured vine parameters that were different among treatments was berry weight.

Field Evaluation of Potential Methyl Bromide Replacements for Grape Growers

Methyl bromide has provided an almost fool-proof procedure for avoidance of the replant problem including long-term relief from soil pests. Our suggested alternatives to methyl bromide can provide equivalent protection in some settings but not others. In vineyards the shortcomings will occur in finer-textured soils, settings having oak root fungus, settings having grape fan leaf virus and Xiphinema index, settings having aggressive root knot populations where previous rootstocks have failed, settings where root lesion is a problem including varietals such as Zinfandel. There is also no assurance that Telone or Vapam will be available as needed. Rootstocks provide some of the answer when properly started out and when broad soil pest protection is available. Some growers will lose the ability to quickly pull and replant their vineyards so fallow periods will be lengthened. Post-plant nematicides will become more popular. We have identified combination soil treatments with potential to replace methyl bromide but we need these studies to verify their performance and identify their limitations. Meanwhile, some of these soil pests including Xiphinema index and aggressive root knot nematode populations are now more prevalent in vineyard settings. Unfortunately, fumigants kill old grape roots and we have found no other treatment that does.

Field Evaluation of Potential Methyl Bromide Replacements for Grape Growers

As outlined in a text about to be released “The Replant Problem and its Management” there are only a few choices for grape growers once methyl bromide is no longer available. The best alternative is Telone applied deep followed by a one to two inch drenching of water containing Vapam. This treatment is performing well in a Gilroy site and we are making demonstration equipment that will facilitate such treatments. In a Caruthers site a Vapam drench via existing dripper system followed by planting of rootstocks having rather broad nematode protection is now in its second year without problems. We have not yet had the opportunity to treat with emulsified Telone (with or without chloropicrin) except at the field station in nursery settings. There it has performed very well. In a site originated by Michael Costello the differences in five rootstocks are dramatic but so is the value of MB relative to the return rate of ring and root knot nematodes. A similar separation between fumigated and non fumigated is occurring at the Gilroy site.

Spiders in Vineyard Agro-Ecosystems

Two workgroup sessions on “Spiders in Vineyards” were held during 1994 (CSU Fresno-March, UC Kearney Ag Center-October), providing outstanding opportunities for information exchange and research coordination. Round-the-clock spider sampling studies (6A, 12N, 6P, 12M) conducted near Madera indicated that overall, spiders as a group were collected (canopy shake technique) equally well at any time of day. Spiders were sampled during the unorthodox fall / winter season of 1993-94 at Ripperdan (Madera County) using pitfall traps and cardboard banding (to our knowledge, no other researchers in California have sampled spiders using this field protocol during the winter). Studies focusing on direct observation of Trachelas and Cheiracanthium behavioral ecology in vineyards provided 31 hours of nocturnal field viewing time, only 20%of which resulted in successful spider sightings. Of this total spider viewing time, over 92% involved Cheiracanthiunr, Trachelas comprised only 8%. Daytime leaf sampling data revealed that the small theridiid spider Theridion constituted over 2/3 of all spiders observed during 1994. Field researchers were mildly surprised to find the well-known clubionid spider Cheiracanthium frequenting malaise traps placed on vineyard trellis crossbars which were designed primarily to sample populations of parasitic insects. A total of 10 Cheiracanthium spiders (7 females and 3 juveniles) were found in the malaise traps; no other spider species were found in the malaise traps at any time during 1994.