Sprayer type and pruning affect the incidence of blueberry fruit rots

Abstract

Highbush blueberries (Vaccinium corymbosum L.) in Michigan are treated annually with fungicides to control fruit rots caused by Colletotrichum acutatum J.H. Simmonds, Alternaria sp., and Botrytis cinerea Pers.:Fr. Control with recommended fungicide programs is often inadequate. The goal of this study was to compare the effects of two spray treatments and three levels of pruning severity on fruit rot levels in mature 'Jersey' bushes. Two spray treatments were tested for 3 years: 1) recommended fungicide rates applied with a conventional airblast sprayer; 2) 67% of recommended fungicide rates applied with a multifan/nozzle, above-row sprayer. Pruning treatments included light and heavy pruning (compared for 1 year), and light, moderate, and heavy pruning (compared for 3 years). Fruit rot incidence was determined after incubating individual fruit at 100% relative humidity and 21 °C for 7 to 11 days, and after exposing 0.24-L plastic clamshell containers of fruit to simulated commercial handling. The above-row sprayer provided fruit rot control at least equivalent to the airblast sprayer even though less chemical was applied. Anthracnose rot in berries from the top of the bush canopy were reduced by pruning, but those in the bottom of the bush, and levels of other diseases were not consistently affected. Pruning also reduced yields, although the study was too short in duration to determine the long-term impact on production.