Keith S. Mason

Relative Toxicity and Residual Activity of Insecticides Used in Blueberry Pest Management: Mortality of Natural Enemies

ABSTRACT A series of bioassays were conducted to determine the relative toxicities and residual activities of insecticides labeled for use in blueberry (Vaccinium corymbosum L.) on natural enemies, to identify products with low toxicity or short duration effects on biological control agents. In total, 14 insecticides were evaluated using treated petri dishes and four commercially available natural enemies (Aphidius colemani Viereck, Orius insidiosus [Say], Chrysoperla rufilabris [Burmeister], and Hippodamia convergens [Guérin-Menéville]). Dishes were aged under greenhouse conditions for 0, 3, 7, or 14 d before introducing insects to test residual activity. Acute effects (combined mortality and knockdown) varied by insecticide, residue age, and natural enemy species. Broad-spectrum insecticides caused high mortality to all biocontrol agents, whereas products approved for use in organic agriculture had little effect. The reduced-risk insecticide acetamiprid consistently caused significant acute effects, even after aging for 14 d. Methoxyfenozide, novaluron, and chlorantraniliprole, which also are classified as reduced-risk insecticides, had low toxicity, and along with the organic products could be compatible with biological control. This study provides information to guide blueberry growers in their selection of insecticides. Further research will be needed to determine whether adoption of a pest management program based on the use of more selective insecticides will result in higher levels of biological control in blueberry.

Seasonal Abundance of Ground Beetles in Highbush Blueberry (Vaccinium corymbosum) Fields and Response to a Reduced-Risk Insecticide Program

Abstract Seasonal patterns of ground beetle activity were examined at six highbush blueberry (Vaccinium corymbosum L.) farms in southwestern Michigan. On each farm, pitfall traps were used to monitor ground beetle activity in two adjacent fields: one managed under a conventional insecticide program (grower standard) and the other with reduced-risk insecticides. Overall, more active ingredient was applied in grower standard than reduced-risk fields, with the greatest amount used in June and July. During the 6-mo sampling period, we collected 11,322 ground beetles comprised of 34 species, with Harpalus pensylvanicus DeGeer representing 70.7% of the total beetles collected. The greatest amount of ground beetle activity occurred in August and September, mostly because of increased captures of the autumn breeding species H. pensylvanicus and H. erraticus Say. Only H. erraticus responded to the different insecticide programs, with eight-fold greater captures in reduced-risk compared with grower standard fields. Because H. erraticus are in the soil as larvae or pupae during June and July, we suggest that greater insecticide use in the grower standard fields resulted in increased mortality of immature H. erraticus. At one farm, where ground cover was absent between blueberry rows, H. erraticus activity did not respond to the difference in insecticide program. This suggests that enhancement of ground beetle activity may require suitable habitat in addition to a reduction in broad-spectrum insecticide use.

Control of Grape Berry Moth (Lepidoptera: Tortricidae) in Relation to Oviposition Phenology

ABSTRACT We monitored the phenology of oviposition by grape berry moth, Paralobesia viteana (Clemens) (Lepidoptera: Tortricidae), in grape (Vitis spp.) vineyards, to determine the optimal timing for control of this pest. Egg deposition was monitored throughout the growing season by visually inspecting grape clusters twice weekly and counting the number of eggs. Male moths were captured on pheromone-baited traps during the same period. Two main periods of egg deposition were detected in all farms and years: the first period in June-July and the second period during August. These episodes of concentrated oviposition were separated by a brief period of low intensity but continuous oviposition. The proportion of eggs laid during the first peak ranged from 9 to 35% of all eggs laid throughout the monitoring period at each site, whereas eggs laid during the second peak ranged from 43 to 78% of all eggs laid. From 49 to 99% of male moths were captured before or during the first peak in oviposition. In field trials with varying application timing of methoxyfenozide targeting the postbloom oviposition, a single application of this selective insecticide at ≈700 degree-days, or ≈12% of cumulative season-long oviposition, provided significant control of grape berry moth comparable with two applications of methoxyfenozide or a three-spray program with broad-spectrum insecticides. Use of predicted oviposition phenology and selective insecticides with long residual activity can improve protection of grapes against infestation by P. viteana.

Yield-Based Economic Thresholds for Grape Berry Moth (Lepidoptera: Tortricidae) in Juice Grapes

ABSTRACT A 3-yr field study was conducted at commercial juice grape (Vitis labrusca L.) vineyards to develop an economic injury level (EIL) for grape berry moth, Paralobesia viteana (Clemens) (Lepidoptera: Tortricidae) and to determine patterns of cluster injury. Infestation of grape clusters by P. viteana was measured biweekly from bloom until harvest, and fruit was sampled immediately before harvest to determine the yield and level of fruit injury by this pest. Comparison of fruit infestation at each sampling date to that found just before harvest revealed stronger relationships over time, and by early August at least 50% of the variation in preharvest infestation was accounted for by previous infestation. Grape yield declined with increasing infestation by P. viteana, allowing calculation of the EIL at which the value of yield lost to infestation equaled the cost of insecticide applications to prevent the infestation. Using two scenarios of pest control programs based on pyrethroid or diamide insecticides, the EILs were calculated to be 9.9 and 17.7% of clusters damaged, respectively. For use in juice grape vineyard integrated pest management programs, we propose using 5 and 10% damaged clusters at harvest as action thresholds for further testing in field trials to evaluate sampling plans and the use of thresholds to guide vineyard pest management decision-making under different insecticide scenarios.

Comparison of Three Dispenser Distribution Patterns for Pheromone Mating Disruption of Paralobesia viteana (Lepidoptera: Tortricidae) in Vineyards

ABSTRACT Over two growing seasons, Isomate GBM-Plus tube-type dispensers releasing the major pheromone component of grape berry moth, Paralobesia viteana (Clemens) (Lepidoptera: Tortricidae), were evaluated in vineyards (Vitis spp.) in Michigan, New York, and Pennsylvania. Dispensers were deployed in three different density-arrangement treatments: 124 dispensers per ha, 494 dispensers per ha, and a combined treatment with 124 dispensers per ha in the vineyard interior and 988 dispensers per ha at the vineyard border, equivalent to an overall density of 494 dispensers per ha. Moth captures and cluster infestation levels were compared at the perimeter and interior of vineyards receiving these different pheromone treatments and in vineyards receiving no pheromone. Orientation of male moths to pheromone-baited traps positioned at the perimeter and interior of vineyards was reduced as a result of mating disruption treatments compared with the nontreated control. These findings were consistent over both years of the study. Disruption of male moth captures in traps varied from 93 to 100% in treated vineyards, with the 494 dispensers per ha application rates providing significantly higher level of disruption than the 124 dispensers per ha rate, but only in 2007. Measurements of percentage of cluster infestation indicated much higher infestation at perimeters than in the interior of the vineyards in all three regions, but in both sample positions there was no significant effect of dispenser density on cluster infestation levels in either year. The contrasting results of high disruption of moth orientation to traps in vineyards that also had low levels of crop protection from this pheromone treatment are discussed in the context of strategies to improve mating disruption of this tortricid pest.

Spatially Targeted Applications of Reduced-Risk Insecticides for Economical Control of Grape Berry Moth, Paralobesia viteana (Lepidoptera: Tortricidae)

Abstract The grape berry moth, Paralobesia viteana Clemens (Lepidoptera: Tortricidae), is a key economic pest of vineyards in eastern North America, and prevention of fruit infestation is particularly challenging along vineyard borders that are adjacent to wooded areas containing wild grape (Vitis spp.). For three years, infestation and damage in vineyards where reduced-risk insecticides were applied to borders at timings based on a degree day model (Integrated Pest Management program) were compared to that in vineyards where broad-spectrum insecticides were applied across the whole vineyard (Standard program). Infestation at vineyard borders immediately prior to harvest was consistently lower in IPM vineyards than in Standard program vineyards, and in two of the years this was also true at veraison (fruit coloring). Grape berry moth infestation was similar between treatments at vineyard interiors throughout the study, despite no insecticide applications to the interiors of the IPM program vineyards. Populations of two other key vineyard pests, the eastern grape leafhopper, Erythroneura comes (Say) (Hemiptera: Cicadellidae), and Japanese beetle, Popillia japonica Newman (Coleoptera: Scarabaeidae), were not significantly different between programs, and natural enemy captures on yellow sticky traps were also similar. The per hectare cost of insecticides applied in the IPM program was consistently lower than for the Standard program, with a significant difference in the third year of this study. We demonstrate how spatially selective applications of reduced-risk insecticides can provide improved control of grape berry moth at lower cost than standard broad-spectrum insecticide-based programs.

Seasonal pattern of oviposition by the North American grape berry moth (Lepidoptera: Tortricidae)

The seasonal patterns of oviposition by the North American grape berry moth, Paralobesia viteana (Clemens) (Lepidoptera: Tortricidae) were monitored in juice grape (Vitis labrusca) vineyards in southwest Michigan. Egg deposition was recorded throughout the growing season at two vineyards in 2006, and at four vineyards from 2007 to 2009. In each vineyard, a random sample of 100 grape clusters was visually inspected twice‐weekly and the number of newly laid eggs was counted. We found that oviposition was continuous but variable throughout the season. Egg deposition started in early June coinciding with early grape bloom, continued at low level until mid‐ to late July, intensified in August close to veraison, and ended in September often before harvest. There were no consistent periods without oviposition that would indicate distinct generations. To determine the contribution of moth immigration into the vineyard to the pattern of oviposition, six grape plants located at the edge of a vineyard next to woods were covered with field cages and stocked with infested fruit. Oviposition and berry infestation were followed weekly on covered and exposed plants. Although higher numbers of eggs and infested berries were found on fruit of exposed vines than enclosed vines, egg deposition and berry infestation followed the same pattern in both treatments. This result indicates that the seasonal pattern of egg deposition is not dependent on immigration of grape berry moth of wild grape origin. The pattern of oviposition by grape berry moth described here contributes to the difficulty of controlling this pest using conventional insecticides with short residual activity.

Juice Grape Canopy Structure and Cluster Availability Do Not Reduce Middle- and Late-Season Captures of Male Paralobesia viteana (Lepidoptera: Totricidae) in Sex Pheromone Traps

Abstract Paralobesia viteana (Clemens) (Lepidoptera:Tortricidae), the grape berry moth, is a major economic pest of cultivated grapes in eastern North America. Although pheromone lures and traps are available for monitoring this pest, male moth captures in these traps decline as the infestation risk increases through the multiple generations that occur during a season. This makes it difficult to use traps to monitor this pests population dynamics and complicates the timing of pest management activities. To test whether seasonal changes in the plant canopy affect captures of male grape berry moth, we manipulated grapevine fruit density or canopy structure in multiple growing seasons, and measured male captures under these conditions. Removal of either 50 or 100% of the fruit clusters from vineyard plots did not consistently affect captures in pheromone traps. In 2013, significantly more males were captured in traps in plots where clusters were not removed compared to captures in traps in plots where 50 or 100% of clusters were removed, but this effect was not seen in 2014 or 2015. In the first year of a separate experiment, there were no differences in male captures between unaltered canopies and those held open artificially. In subsequent years we detected significant differences in male captures for some sample periods, and there was a prevailing trend of arithmetically more male captures in unaltered than in open canopies. We conclude that fruit presence, fruit density and canopy fullness do not reduce male P. viteana captures late in the season, and that other factors are driving this pattern.