Bronzing of strawberry fruit as affected by production practices, environmental factors, and thrips

Abstract

Strawberry fruit are subject to three different types of bronzing damage that cause discoloration of the fruit surface and loss of market quality. Type I and Type II bronzing both occur in localized areas of the fruit and are caused by arthropod feeding and chemical phytotoxicity, respectively. In contrast, Type III bronzing (T3B) covers the entire fruit and is associated with environmental and plant stress factors, although many growers and crop advisers believe that T3B is caused by thrips feeding. The purpose of our 3-year study was to investigate incidence of T3B as affected by crop management practices and thrips populations. Replicated field trials demonstrated that overhead cooling with sprinklers resulted in a significant reduction in T3B incidence. In addition, a series of foliar pesticide spray applications also resulted in reduced T3B damage to strawberry fruit. Foliar applications of Thiolux sulfur, other registered pesticides, and lignin products all resulted in reduced incidence of T3B in field trials. In contrast, T3B incidence was not associated with thrips populations; insecticide-treated plots had reduced thrips populations and comparable T3B incidence to nontreated plots that had greater thrips populations. Our study provides evidence that T3B occurrence is associated with exposure to elevated temperatures and solar radiation rather than thrips feeding and that growers can reduce T3B incidence by implementing production practices that reduce plant stress and protect fruit from radiation damage.