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The effect of adjuvants on apple disease management.
C. P. ABBOTT (1), J. L. Beckerman (1). (1) Purdue University, West Lafayette, IN, U.S.A.

Apple growers rely on the fungicide captan to manage apple scab (<i>Venturia inaequalis</i>) and bitter rot (<i>Colletotrichum </i>spp.). There is a low risk of either fungus developing resistance to captan, increasing the importance of this fungicide in disease management. Label restrictions limit growers to 40lbs of captan per season, which may not provide sufficient control of both apple scab and bitter rot in wet years. Adjuvants are tank additives that may reduce the rate of captan needed per season by improving disease management. One method is to use adjuvants to increase the coverage and retention of captan treatments. Another is to use adjuvants to improve urea-driven-leaf litter decomposition. In 2013 and 2014, we examined the role of adjuvants combined with a low rate of captan in field applications. In 2013, adjuvants did not improve captan performance due to low disease pressure. In 2014, Li700, Bond, and LatronB enhanced control of apple scab on Golden Delicious. In 2013, a preliminary study found adjuvants had the potential to improve urea-driven decomposition and inoculum reduction of scab infected leaves. A larger study is underway to further evaluate this. Overall, the addition of adjuvants can improve disease management by increasing fungicide efficacy and decreasing overwintering inoculum, which may reduce overall fungicide input during the growing season.

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