Organic Aminoethoxyvinylglycine Is an Effective Alternative for Reducing Apple Preharvest Drop

Organic apple (Malus ×domestica Borkh.) growers lack effective strategies to manage preharvest drop. For susceptible cultivars, yield losses caused by preharvest drop can exceed 30% at the beginning of harvest. To address this issue, a formulation of aminoethoxyvinylglyine (AVG) designed for organic use was developed and compared with a commercially available AVG formulation. We evaluated the effects and interactions of the AVG formulation and application number on preharvest drop and fruit maturity in 2017 and 2018. We selected 30 pairs of mature ‘Oregon Spur II Red Delicious’/‘M. 111’ trees planted at the Mountain Horticultural Crops Research and Extension Center in Mills River, NC, USA. Trees were planted with spacing of 2.7 × 6.1 m, trained to a central leader, and received plant protectant sprays that adhered to local recommendations throughout the growing season. Both AVG formulations were applied at 132 mg⋅L−1 at 3 or 3 + 1 weeks before the anticipated harvest. An untreated control was also included for comparison. The experiment had six replicates and a randomized complete block design with a 2 × 2 augmented factorial treatment structure. A one-way analysis of variance was performed and single degree of freedom contrasts were used to compare treatment groups of interest. During both years, organic and conventional AVG were equally effective for reducing preharvest drop and delaying fruit softening and starch hydrolysis at harvest. During one year, increasing the number of applications of AVG reduced cumulative fruit drop, delayed fruit softening at harvest, and reduced internal ethylene concentrations. Inconsistencies in responses across years may be explained, in part, by abnormally warm temperatures observed in 2018. AVG approved for organic use appears to be a promising preharvest drop management technology with efficacy similar to that of conventional AVG

Beauveria bassiana and ELISA determination of neonicotinoids to improve management of Listronotus maculicollis

Bioassays were designed to evaluate Beauveria bassiana (Balsamo) Vuillemin strain GHA against Listronotus maculicollis (Kirby) adults. B. bassiana and its “inert” carrier oil in the product BotaniGard and the “inert” carrier oil alone provided 99 and 96% mortality respectively in Petri dish assays 1 d after treatment when applied in 1 ml water. When the same treatments were applied in 0.5 ml of carrier water mortality was only 1.4 and 0.7% respectively 1 d after treatment. After 10 d in Petri dishes, B. bassiana and its “inert” carrier oil and the “inert” carrier oil alone applied in 0.5 ml water showed 77 and 9% mortality respectively. When one-tenth the label dosage of B. bassiana and “inert” carrier oil was combined with neonicotinoids clothianidin, imidacloprid, and dinotefuran applied in 1 ml water, there were significant increases (34, 30, and 68% respectively) in weevil mortality over the neonicotinoids alone 1 d after treatment. When one-tenth the label dosage of “inert” carrier oil alone was combined with neonicotinoids clothianidin, imidacloprid, and dinotefuran applied in 1 ml water, there were also significant increases with clothianidin and dinotefuran (38 and 24% respectively) in weevil mortality over the neonicotinoids alone 1 d after treatment. B. bassiana and its “inert” carrier oil provided 28, 50, and 78% mortality at the highest label dosage and 47, 76, and 89% mortality at 4× the highest label dosage in turf plug assays at 7, 10, and 14 d after treatment. Addition of 5 or 20% MycoMax (a nutrient source for B. bassiana) did not significantly increase mortality in turfgrass plug assays. ELISA plates were used to determine the amounts of clothianidin and imidacloprid in Poa annua clippings from treated golf course fairways. Amounts of clothianidin ranged from 71.8 to 1238.1 ng/g tissue in 2011 and 68.8 to 2045.0 ng/g tissue in 2012. Amounts of imidacloprid ranged from 40.8 to 1679.2 ng/g tissue in 2011 and 116.8 to 3722.0 ng/g tissue in 2012. Listronotus maculicollis adults were caged on neonicotinoid and neonicotinoid/pyrethroid treated P. annua plugs. Substantial feeding on P. annua was observed; however, mortality of L. maculicollis adults was not significantly different from control plugs. We were not able to determine concentrations of either clothianidin or imidacloprid that were effective in controlling larvae. Our data help to explain the lack of control of this insecticide resistant pest