Enhancing the integration of mite biological control in western United States vineyard managment programs

Enhancing the integration of mite biological control in western United States vineyard managment programs

Summary

Vineyards throughout Oregon have recently developed Short Shoot Syndrome, which is correlated to the pest mite, Calepitrimerus vitis. This vineyard-specific pest feeds on developing buds resulting in stunted shoots and crop (cluster) loss. Typhlodromus pyri is the dominant predatory mite in western Oregon vineyards and is believed to play an integral role in managing C. vitis populations. Intense fungicide programs are maintained in vineyards throughout the growing season and are believed to be detrimental to predatory mite populations causing increased pest mite outbreaks. Predatory mite preservation and enhancement are integral to successful biological control programs in western vineyards.

Objectives/Performance Targets

1. Conduct field and laboratory bioassays to determine the effects (direct mortality, fecundity, oviposition rate and longevity) of multiple vineyard fungicides on the predatory mite T. pyri
2. Determine the biology and foraging behaviors of T. pyri on C. vitis, particularly predation preferences and rate of predation.
3. Test the ability of methyl salicylate to attract and establish T. pyri populations in vineyard systems, field and laboratory experiments will be conducted to determine attraction rates.

Accomplishments/Milestones

Objective 1
To determine the effects of fungicide spray regimes in the field, experiments were conducted during the 2008 and 2009 seasons at two commercial vineyards (Dundee and Salem vineyards) located in Oregon’s Willamette Valley. Six different fungicide spray regimes were applied every 10-14 days depending on mildew pressure. Treatments were as follows: 1) Non-sulfur control (synthetics only), 2) Organic grower standard (sulfur only), 3) Sulfur early to fruit set and synthetics late, 4) Sulfur-synthetic rotation (rotated sulfur), 5) Rotation of Whey and Sulfur, 6) Sulfur late with synthetics early.
Leaf samples (basal and terminal) were collected every other week (n=16) until September and brought to the laboratory to count both predator and pest mite density.

Fungicide field trials have been completed and all data collected and recorded from leaf samples. Data from both years have been entered into Excel spreadsheets and are currently undergoing analysis. Initial results for the 2008 season show a trend of higher pest mite numbers in plots that only received synthetic fungicides in both locations. In the Dundee vineyard, mean seasonal pest mite numbers per leaf was 1.07 in plots that only received synthetic fungicides compared to 0.2 in plots that received a mix of synthetic fungicides and sulfur. The mean number of predatory mites ranged from 0.18 and 0.15 mites per leaf in each of the treatments. In the Salem vineyard, mean seasonal pest mite numbers per leaf were 8.1 in plots that only received synthetic fungicides compared to 3.44 in plots that received a mix of synthetic fungicides and sulfur. Mean seasonal predatory mites per leaf in synthetic fungicide plots were 0.48 mites per leaf compared to 0.21 mites per leaf in plots that received both synthetic fungicides and sulfur. Conclusions will be stated once statistical analysis is complete.

Laboratory bioassays were conducted using a precision Potter Spray tower to test the direct toxicity and sub-lethal effects of six vineyard fungicides on T. pyri adult females and juveniles (0-4d old). Fungicide treatments were micronized sulfur (92%), whey powder (milk bi-product), manganese ethylenebisdithiocarbamate (75%, mancozeb), boscalid (plus pyraclostrobin, 38%), myclobutanil (40%) and paraffinic oil (97.1%) at three different rates (recommended label rate (1X), 2X increase and 4X increase), a water spray and check (no spray) were also included.

Results indicate that five of the six fungicides tested can be classified as non-toxic to both adult female and juvenile T. pyri as levels of mortality were less than 50% for all rates at 7 DAT. Paraffinic oil was the single fungicide which showed direct mortality greater than 50% at 1 DAT for all three rates, and were significantly different from the check (Table 1 & 2). Fungicide effects on adult female reproductive potential appeared to be minimal as there were no significant differences detected for all tested fungicides compared to the check (Table 3). However, sub-lethal effects were more pronounced among the fungicides tested in the juvenile bioassays. Significant decreases were seen in the sulfur (2X rate) and mancozeb (2X, 4Xrate) treatments compared to the check (Figures 1-5). The percent fecundity reduction relative to the check was highest in the sulfur (28%, 51.2%), myclobutanil (24.7%, 45.7%) and mancozeb (21.8%, 83.2%, 70%) treatments at label rate, 1.0x rate and 2.0x rate, respectively (Figure 6). Whey powder and boscalid showed no significant differences, at all three rates, from the check and a low percent reduction in fecundity relative to the check. Fecundity comparisons between fungicides of similar rates, did show treatment differences at the 2X rate (P ≤ 0.001) and 4X rate (P ≤ 0.05).

Objective 2
The focus of this objective has been adjusted due to difficulties (resource and time limitations) in rearing C. vitis to adequate population numbers required for olfactometer preference and feeding rate experiments. Our current objective will also achieve the targeted goal to increase knowledge of T. pyri biology and development in relation to C. vitis.
Our new focus is to conduct life table experiments to determine longevity, developmental times, oviposition lengths and population rate of increase for T. pyri. The experiments will be conducted at seven different temperatures (12.5, 15, 17.5, 20, 25, 30, and 35ºC) under a mixed feeding diet which includes C. vitis. The mixed diet consists of 50% spider mites (reared in laboratory), 30% C. vitis (collected from commercial vineyard infested leaves) and 20% pollen (collected from Willamette Valley). Eggs (0-12 hours old) are placed in one of sixteen cells on a divided tray. Cells are checked twice daily (approx. every 12 hours) and developmental hours from egg to adult stage will be recorded. Adult females will each have one male added to ensure copulation. Pre-oviposition length, oviposition length and oviposition rate will be assessed and recorded. Trials are currently in progress and expected to be completed by spring 2010.

Objective 3
Y-tube olfactometer assays were conducted to test the behavioral response of Typhlodromus pyri toward methyl salicylate (MeSA) under controlled laboratory conditions. Six MeSA doses were tested (0.002µg, 0.02µg, 0.2µg, 2.0µg, 20µg, 200µg) on 18 individual predator mites and replicated 5 times over different days with different adult females. Each female mite choice (MeSA, control) was recorded upon reaching a decision, and if no decision was made after a five minute interval then a no choice was recorded. Experiments have been completed and data have been entered into an Excel spreadsheet. Preliminary graphs indicate a positive behavioral attraction to MeSA, particularly to the mid-range doses 0.02µg, 0.2µg and 20µg (Figure 2). Complete statistical analysis is required for additional conclusions.

Methyl salicylate field trials were carried out in two commercial vineyards located in the Northern Willamette Valley starting in 2009 season. Lures were placed in the center of each baited block (four/block or eight/block) and no lures were placed in the control block. Leaf samples (30/block) were collected to determine predatory mite and pest mite density in each block at a distance of 0, 5 and 10 meters from block center every two weeks until mid-October. Leaf samples were brushed and counted in the laboratory; to date all samples have been processed. Data for the 2009 season have been entered into Excel spreadsheets. Initial results and statistical analysis are anticipated for the spring 2010. A second field season will be in April 2010 at the same vineyard sites and blocks employed in the 2009 trials. The 2010 growing season trials are anticipated to finish by October 2010, with data entry and analysis completed by December 2010.

Impacts and Contributions/Outcomes

This research provides benefits to Oregon wine grape growers through promotion of sustainable management practices based on increased education regarding fungicide spray regimes, predatory mite biology and novel tools that may attract predatory mites toward areas of pest infestation. Producers are gaining the knowledge to develop spray regimes that are beneficial to predatory mite populations through compound choice and application timing. Producers will also gain an understanding of the efficacy and optimal employment of the commercially available MeSA lures (Predalure®™) as potential management tools in an IPM program for control of grape rust mite, C. vitis.

Outreach and educational presentations to date include:
• April 2009, Pacific Branch Entomology Society of America annual meeting (San Diego, CA), Impacts of six fungicides on the lethal and sub-lethal effects on Typhlodromus pyri, poster presentation.
• July 2009, OSU Extension Vineyard Workshop (Vineyard, Willamette Valley, OR), oral presentation on initial results of fungicide bioassays on T. pyri and the implications of this information for vineyard spray programs.

Planned outreach/education for 2010 will include:
• January 2010, 69th Annual Pacific Northwest Insect Management Conference (Portland, OR), Effects of six vineyard fungicides on the juvenile predatory mite Typhlodromus pyri, presentation and printed abstract.
• February 2010, Graduate Student Symposium, Oregon State University, poster and oral presentation, titles TBA.
• April 2010, Pacific Branch Entomology Society of America annual meeting (Boise, ID), paper presentation and poster, titles TBA.
• Summer 2010, OSU Extension Vineyard Workshop, location and presentation titles TBA.

Collaborators: