Management of Vine Mealybugs in California's San Joaquin Valley Through the Integration of Chemical and Biological Controls

Management of Vine Mealybugs in California's San Joaquin Valley Through the Integration of Chemical and Biological Controls

Summary

The vine mealybug is a severe, new vineyard pest in California. Typical treatment for infested vineyards relies on application(s) of an organophosphate (chlorpyrifos, dimethoate, or methomyl). We investigated the use of the less-toxic insecticide, Admire (imidacloprid), combined with releases of natural enemies. Results show Admire and parasite releases, used either in combination or separately, significantly reduced crop damage, as compared with controls. To reduce economic costs, we are currently investigating using these control tools separately or combined with newly developed mating disruption tools. These controls provide sustainable methods that work as effectively as organophosphates, although control costs are currently 50-80% greater.

Objectives/Performance Targets

Objectives for the 2003 season: developing sustainable vine mealybug controls

(1) Improve timing, dosage, and delivery methods for “least-disruptive” insecticides (e.g., Admire) that target early-season VMB populations.

(2) Test inoculative release(s) of Anagyrus pseudococci in vineyards using “least-disruptive” insecticides and compare parasitoid effectiveness in vineyards with “least-disruptive” and “standard” organophosphate insecticide applications.

(3) Involve collaborating growers, farm managers, and Cooperative Extension personnel in on-farm experiments and parasitoid rearing operations; conduct field days to extend information to a larger audience; and produce research- and grower-oriented publications to improve extension.

Accomplishments/Milestones

Research and extension activities began in spring 2002, ahead of schedule, because of the rapid spread of the vine mealybug throughout California, the great need for improved vine mealybug control tools, and grower interest in education forums (see the list of presentations). Research initially targeted WR SARE objectives 1 and 2, as outlined. Results from 2002 suggested that three additional control tools needed further investigation: monitoring vine mealybug with sex pheromones, mating disruption, and least-toxic ant controls. Research for these additional topics has been coordinated with the WR SARE research, with additional funding provided by commodity boards (California Table Grape Commission, American Vineyard Foundation, California Raisin Marketing Board) and federal or state programs (California Competitive Program for Enology and Viticulture, Viticulture Consortium, UC/USDA Exotic Pests and Diseases Program). We provide a brief description of research conducted in the 2002-03 season.

Insecticide Applications (Objective 1).

Procedures.

The vine mealybug is difficult to control with insecticides because there is always a portion of the population located in hidden locations near- or underground on the roots or trunk, where the mealybug finds protection from most foliar insecticide applications. To improve control options with less-toxic insecticides, we conducted a series of experiments that compared materials, delivery systems, and application timing. Our goal was to develop methods that used a systemic application of the neonicotinoid imidacloprid (Admire, Bayer Corporation), which is less toxic than the organophosphates used for mealybug control. Research blocks were located in commercial vineyards in Fresno and Tulare Counties (California). Earlier studies suggested that Admire provided excellent control and could be used with disrupting biological controls.

In 2002, we tested the timing of Admire applications. Treatments were a single application of 32 oz Admire per acre applied in (1) April, (2) May, or (3) June; (4) two applications of 16 oz Admire per acre applied in April and May; and (5) no insecticide control. The experiment was conducted simultaneously in vineyard blocks with either drip or furrow irrigation systems. Admire is a systemic insecticide that is applied near the roots, so a drip irrigation system is an ideal delivery mechanism. However, in furrow- or flood- irrigated vineyards there was some concern that the insecticide could not be effectively applied. Admire was applied in the furrow-irrigated blocks by French plowing the berm and furrow area to expose surface roots, pre-irrigating and then spraying Admire directly into the standing water via an herbicide spray rig positioned over the furrow on a boom. In the 2 drip-irrigated blocks Admire was applied using the existing drip irrigation system. Both furrow- and drip-irrigated blocks were irrigated before and after each Admire application. Treatments were arranged in a randomized block design, which was unique for each of the 4 vineyard blocks. There were five treatment replications per block, and each plot was 0.4-0.6 acres.

In 2003, we used the same vineyard blocks (as used in 2002) to determine if Admire applications applied in 2003 had a carry-over effect in 2003, as implicated in some trials for leafhopper pests. Treatments were a single application of 32 oz Admire per acre applied in (1) May 2003 or (2) May 2002, which were compared with a (3) delayed dormant (March) application of chlorpyrifos (Lorsban), (4) a June application of Applaud, and (5) no insecticide control.

Studies in 2002 showed that the insect growth regulator buprofezin (Applaud, Nichino America, Inc.) provided mealybug control. Because Applaud has lower mammalian toxicity than the organophosphates and a shorter residual period, we decided to test Applaud as an alternative to Lorsban. Treatments were: Applaud applied in (1) March, (2) December, (3) March and December, and Lorsban applied in (4) March, (5) December, (6) March and December, and (7) a no-insecticide control. The plot design was similar to the Admire trials.

In all experiments, VMB sampling and damage ratings were based on methodologies developed for the grape mealybug (Geiger et al. 2001). VMB density was determined using timed counts: 3-5 minutes per vine, depending on the study. The mealybug numbers were recorded by developmental stage, location on the vine, and condition (live, dead, or parasitized). Samples were taken on 20-25 randomly selected vines in each treatment replicate, depending on the study.
In all experiments, the effect of resident and augmented parasitoids was measured during from the 5-minute counts. We also collected 100 mealybugs from each treatment replicate each month. Collected mealybugs were isolated and held for parasitoid emergence. Percentage parasitism and parasitoid species composition was determined. At harvest-time, damage ratings were made on 25 randomly selected vines per treatment replicate. To rate damage, 9 bunches near the cordon wood were randomly selected per vine (3 from either side and 3 directly above the trunk). The grape bunches were scored using a 0-3 rating system: 0 indicates no sign of mealybug damage, 1 indicates some honeydew present but the bunch is marketable, 2 indicates a few mealybugs are present, a partial loss, and 3 indicates mealybugs and honeydew are present and the bunch is unsalvageable.

Results.

Under the right conditions, application(s) of Admire provided excellent vine mealybug suppression. What are the right conditions? First, drip irrigation to deliver the material is critical. In 2002 trials, Admire delivered through drip systems provided excellent control (Fig. 1A), with the May delivery period the most effective. Admire delivered in irrigation furrows was provided less than 50% control (Fig. 1B). In both irrigation systems, the May-timed application was better than the April, June or April/June timed applications (Fig. 1A, B). In 2003, we compared the May-timed Admire application to the standard delayed dormant application of Lorsban or to a summer application of Applaud. Results show the May-timed Admire application, delivered through the drip system, provided similar control as both foliar applications (Fig. 1C). There was no “carry-over” impact of Admire applied in the previous season and still remaining in the root-zone (Fig. 1C). In the furrow system, Applaud provided the greatest reduction of vine mealybug damage. We were surprised that, in this trial, Applaud provided better control than Lorsban, which typically provides the best control of the foliar applied materials (see Fig. 2).

To better determine the potential for Applaud as an alternative foliar insecticide, we compared the in-season effectiveness of spring treatment with a soil fumigant (Enzone, Helena Chemical Co.), and foliar treatments with imidacloprid (Provado, Bayer Corporation), and the organophosphates methomyl (Lannate, Dupont), and dimethoate (Cygon, American Chemical). All of the foliar-applied compounds had some level of “knock down” compared to untreated controls; however, only Applaud was comparable to the organophosphates (Bentley and Daane, data not shown). For this reason, we continued direct comparison of Applaud and Lorsban, using winter and spring application timings. Results show that the most effective “foliar” program to date is a “delayed dormant,” or before budbreak, application of Lorsban. The effectiveness of Lorsban may be dependent on the development stages and level of exposure of the vine mealybug population when Lorsban is applied, both of which may be dependent on uncontrollable factors such as spring temperatures and the cultivar or age of the vine (e.g., older vines have thicker bark and more protected places for the vine mealybug). We note here that this study was conducted in the San Joaquin Valley on sandy or sandy-loam soils. Growers have observed that Admire applications do not have as great an impact in some coastal vineyards. We suspect these results are associated with soil conditions (such as heavier clay soils) and/or root distribution outside of the drip irrigation emitter zones that prevented proper uptake of Admire.

Augmentation (Objective 2).

Prior to developing an augmentation program, a classical biological control program searched for vine mealybug natural enemies in Spain, Italy, France, Argentina, Chile, and Israel (Ball et al. 2003). Five parasitoid species were imported: Anagyrus pseudococci, Leptomastidea abnormis, Leptomastix flavus, Leptomastix dactylopii, and Coccidoxenoides peregrinus. Most of these species were already present in California, but the imported material came from regions with climate more similar to the Coachella and San Joaquin Valley areas and, hopefully, represented “biotypes” of these parasitoids species that were better adapted to California’s grape growing regions. As mentioned, the imported and resident natural enemies help to suppress but do not provide economically effective biological control because their patterns of parasites are too late in the season to lower the pest density before harvest. To increase the level of parasitism early in the season, we investigated the augmentative release of insectary-reared Anagyrus pseudococci, used singly and in combinations with Admire applications.

Procedures

To determine the potential for combining chemical and biological controls, we released A. pseudococci into sections of the drip- and furrow-irrigated treatment plots, described previously in the 2002 “Admire” study in the June treatment of Admire applied at 32 oz. per acre. In each plot, A. pseudococci were released on May 23 (before Admire was applied) and on June 14 (after Admire was applied). VMB were sampled, as described previously, with the portion of the treatment rows receiving A. pseudococci compared with the no-release portion (each receiving Admire) and the no Admire control. Four replicates were used in both the drip- and flood-irrigated blocks. We compared VMB density and damage in the Admire plus A. pseudococci treatment with the Admire only treatment.

In 2003, we tested release of A. pseudococci without a combined application of Admire. Five raisin vineyards with histories of vine mealybug infestations were each divided into 1 acre release, buffer, and control treatment plots. The buffer, situated between the release and control plots, served to minimize the impact of released A. pseudococci moving to the release plot. Adult Anagyrus pseudococci were provided by FAR Insectary and released at approximately 20,000 per acre on each of three release dates (June 12th, July 3rd, and July 30th). The release dates were timed to place adult parasitoids in the field as soon as vine mealybugs emerged from protected location under the bark (where the parasitoids are less effective). Vine mealybugs were sampled using a 5 minute visual count on 10 vines per treatment plot. When mealybugs were found, their development stage and vine location was noted. Additionally, 100 vine mealybugs were collected from each plot every two months. The mealybug development stage and position on the vine was recorded and the samples were held for adult parasitoid emergence.

Results

In the 2002 season, we combined applications of Admire with release of A. pseudococci. What is the impact of Admire on parasitoid densities? Results show that in the treatment receiving both Admire and augmentative releases of A. pseudococci, there was a significantly lower vine mealybug density, as compared with control plot. However, there was no significant difference in the mealybug damage rating (average score) between the section receiving the combined treatment (Admire and parasitoids) and the section receiving only Admire (F = 0.23; df = 1, 8; P = 0.644), although there was more total fruit loss on the Admire only section (Fig. 3).

These data suggest that Anagyrus release can be used in combination with Admire applications. These results are corroborated by laboratory data of A. pseudococci survival on grape leaves treated with Admire, which showed no mortality, compared with A. pseudococci survival on leaves treated with Lorsban, which had >80% mortality. The combined impact of both controls was not significantly lower than the application of Admire alone. Costs for Admire application (at label rate) range from $70-120 per acre, and we released A. pseudococci at rates between 50,000 adults per acre, which we estimate to cost near $100 per acre as well. For this reason, it is unlikely that vineyard managers would use both control programs concurrently as costs for Applaud or Lorsban are less than $70 per acre. More likely, Admire applications would be used to vine mealybug densities that were high enough to cause immediate crop damage, and this practice might be followed by parasitoid release. For this reason, in 2003, we investigated the release of (finish sentence, editor)

In the 2003 release, the number of mealybug crawlers and adults was lower in the release than the no-release plots, especially toward the end of the season (Fig. 4). In the no-release controls, most of the mealybug population (75%) was in hidden locations of the vine at the end of March, and unavailable to adult parasitoids. This dropped to 17% by the middle of July, which was more or less one month before harvest. Afterward, the proportion of hidden mealybugs again increased (90%) by August. This implies that there is a small window of time that the released parasitoids have to find exposed mealybugs for parasitism, in both release and control plots. In the release plots, the exposed proportion of the mealybug population on the vines decreased more sharply toward the end of the season and harvest (finish sentence? editor)

We did not find a season-long difference in percentage parasitism between the release and no-release plots. This may have been a result of the lower density of mealybugs in the release plots, which resulted in a higher percentage of the live mealybug found in hidden locations. There were three species of parasitoids recovered: A. pseudococci was dominant, followed by Allotropa sp. (2.8%), and Leptomastidea abnormis (0.7%).

Overall crop loss was lower in release than control sub-plots. A significant number more vines had no mealybug damage in the release sub-plots compared to the control sub-plots, and fewer vines were subject to partial or total crop loss. These observations may indicate that mass releases of A. pseudococci resulted in lower crop losses in the release sub-plots compared to the control sub-plots. However, we are still analyzing mealybug density and crop damage data from these plots. One problem encountered is that there was greater than anticipated differences in mealybug density among the vineyards, making comparisons difficult.

An example of the impact of A. pseudococci and its use in combination with Admire, is (unintentionally) seen in the research on Admire timing and application methods (Fig. 1). In 2002, the grower collaborators stopped applications of Lorsban and Lannate for vine mealybug control in the research plots. Into sections (one-third of each June treatment) of the research blocks we released A. pseudococci in 2002. At this time, percentage parasitism was low and damage was high in the no-insecticide control treatments (Fig. 1 A, B). In 2003, we did not release A. pseudococci in these plots because the impact of Admire resulted in such low mealybug population levels that it was difficult to compare parasitism levels. Nevertheless, A. pseudococci became well-established in this area and the control plots dropped from about 45-60% cluster infestation levels in 2002, to about 10-15% cluster infestation levels in 2003.

Extension and Impact Assessment (Objective 3)

The results of this vine mealybug research have been made available as they are developed. Furthermore, grower collaborators will maintain records of chemical use and labor costs for the different treatments imposed. These two measurements (damage and dollars) will provide a “bottom-line” assessment of the program for growers. Since research began in 2002, Daane and Bentley have made about 50 presentations on the vine mealybug. Both popular and refereed publications from this work have been completed or are in preparation. Presentations and articles are attached in the hard copy of this report.

We have also developed a mealybug website

Future Plans

New tests with systemic and foliar insecticides that will well in combination with parasitoid releases are underway. Research will focus not only on the immediate kill, but on season-long control of pests, residual impact on beneficial insects, application timing, and movement of material throughout the vine. We have also opened two new research avenues to work in conjunction with parasitoid releases: ant controls and mating disruption.

Ant Control

A key factor in successful biological is the reduction of the ant populations in the vineyard. Ants disrupt mealybug biological control by closing tending Homoptera for their honeydew and, in return, interfering with parasitoid activity. We have tested a 25% sugar-water and small amounts (0.0001%) of neoticotinoid insecticides placed in bait dispensers throughout the vineyard blocks. Their results were very promising, with a significant season-long reduction of ant activity in baited plots. There was also a late-season response of mealybugs, with significantly fewer mealybugs and less crop damage in baited plots.

Mating Disruption

Initial field tests with the synthetic sex pheromone for monitoring vine mealybugs suggested the synthetic pheromone was quite powerful – perhaps more effective than the real female at calling males. Because it is also relatively inexpensive to produce (compared with other synthetic pheromones), the possibility of developing a mating disruption program is being investigated. There are other reasons we are cautiously optimistic about the potential product development. The VMB pheromone is, relative to other insect pheromones, cheap to produce. Because grape vines extend only a few feet off the ground, the air volume that needs to be saturated with pheromone is relatively low in comparison to orchards, and grapevines have lots of foliage to help retain the pheromone. The males are very fragile and short-lived, and will die within a matter of hours when exposed to the pheromone, especially when burning up energy flying around in a pheromone-induced sexual frenzy. In particular, the adult males do not feed, so once they have burned up their energy reserves, they die. Male vine mealybugs are most commonly wind directed to a general location and then orient locally to the pheromone – which may imply that male populations can be easily misdirected, and females cannot fly, and consequently, immigration of mated females into pheromone-treated plots is not an issue. We believe that mating disruption will eventually replace insecticides as the combined tool for use with parasitoid releases.

References

Geiger, C. A., Daane, K. M., and Bentley, W. J. 2001. Development of a sampling program for improved management of the grape mealybug. California Agriculture. 55(3):19-27.

Geiger, C. A., and Daane, K. M. 2001. Seasonal movement and sampling of the grape mealybug, Pseudococcus maritimus (Ehrhorn) (Homoptera: Pseudococcidae) in San Joaquin Valley vineyards. Journal of Economic Entomology 94: 291-301.

González, D. 1998. Biological control of the vine mealybug in the Coachella Valley. Calif. Table Grape Comm. Ann. Rep. Vol.. Vol. 26: 4 pages

Figures are available in the hard copy of this report.

Captions.

Fig. 1. Percentage cluster infestation with mealybugs in the (A) drip and (B) furrow irrigation blocks in 2002, and the (C) drip and (D) furrow irrigation systems in 2003. Results show a significant reduction in cluster damage when Admire was applied through the drip system in both years, while Admire effectiveness was not as great when applied via the furrow irrigation system. In 2002, the April and May applications of Admire provided the best control. In 2003, Admire applied through the drip system provided similar control as foliar applications of an organophosphate (Lorsban) or insect growth regulator (Applaud). There was no “carry-over impact of the 2002 application of Admire in 2003.

Fig. 2. Percentage cluster infestation with mealybugs using winter or spring foliar applications an organophosphate (Lorsban) or insect growth regulator (Applaud) show that spring applications of the organophosphate had the greatest reduction in mealybug damage. Applaud may work best in spring and summer, when the mealybugs are more active.

Fig. 3. Damage ratings in plots treated with Admire in June with and without A. pseudococci releases. There was no significant difference between the Admire treatment with or without Anagyrus on the fruit damage (F = 0.23; df = 1, 8; p = 0.644) although there was more total loss of fruit on the Admire only (control) treatment.

Fig. 4. Average numbers of crawlers per vine in A. pseudococci release and no-release control plots show lowered mealybug densities in release plots.

Impacts and Contributions/Outcomes

Methodologies developed for sustainable vine mealybug control in vineyards are being rapidly adopted.

Daane and Bentley have given over 50 presentations at grower-oriented and scientific symposia. These presentations are listed in the hard copy of the report.

A commerical insectary has been working with the project leaders to produce Anagyrus pseudococci bring the augmentation program into more popular commercial use.

Bentley and Daane have helped popularize Admire and Applaud use for systemic and foliar insecticide control of vine mealybug, as a replacement for use of organophosphates. THe project leaders continue to investigate new soft products.

The use of sex pheromones for both monitoring new vine mealybug outbreaks and controlling infestations (mating disruption) is currently being tested. Work has progressed rapidly and there are now (in just 1 year) three companies marketing the vine mealybug pheromone. In 2004, we will investigate the combined use of mating disruption with augmentation of Anagyrus pseudococci.