Fungicide responses of maize hybrids to grey leaf spot

Abstract

Grey leaf spot disease of maize (Cercospora zeaemaydis) has seriously decreased grain yields in the province of KwaZulu-Natal, South Africa, and has spread to infect maize in neighbouring provinces. No commercial hybrids, resistant to the disease have so far been identified, and fungicides have been shown to reduce disease severity. The response of sixty-four commercial hybrids to grey leaf spot under fungicide treatment were studied over two seasons. Overall, fungicides reduced disease severity and linear regression of gain in yield against disease severity enables the identification of hybrids with optimum responses to fungicides. Under low disease levels hybrids responded less to fungicides than under high disease levels. The most susceptible hybrids had the highest responses in control of leaf-blighting and gain in yield. Hybrids with lower-than-predicted leaf-blighting also had lower-than-predicted yield responses, indicating these to be less susceptible to grey leaf spot. These less susceptible hybrids are likely to require fewer fungicide treatments than more susceptible hybrids and are at lesser risk of serious yield losses.