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The Problem - Brown Rot

Brown rot (Monilinia fruiticola) is the most economically devastating disease for stonefruit growers. Infections can result in yield losses through fruit rots at harvest. Latent infections not visible at harvest develop into rots in storage and reduce shelf life in the post-harvest food chain.

Luna Sensation Bayer Brown Rot

Powdery mildew infections can arise in the spring from two sources. The most important in New Zealand is from diseased shoots called “flag shoots” (see photos below). These appear from overwintering diseased buds that were infected the previous season. These flag shoots are distorted and are stunted and produce spores which then infect nearby healthy foliage. An epidemic the previous season will result in higher levels of “flag shoots” infected and should prepare vineyard managers for increased vigilance regarding powdery mildew management for the next season.

A second source of infections can be through overwintering fruiting bodies (sexual stage) called cleistothecia. Cleistothecia are tiny yellow to black specks that are more clearly seen under magnification with a hand lens. In the spring with moisture, cleistothecia produce and release ascospores which can infect leaves. Until recently this sexual stage has not been present in New Zealand vineyards and its importance as an inoculum source in New Zealand conditions is not yet understood. The presence of the sexual stage will increase the genetic diversity of the powdery mildew fungus in New Zealand. This increases the risks of possible resistance developing to fungicides and emphasizes the importance of fungicide resistance management strategies in grapes.

Once infections develop a new generation of spores can be produced every 5-10 days. Its spread is favoured by mild-cloudy weather (optimum 22-28°C) with relative humidity greater than 40%. If uncontrolled, powdery mildew can steadily and then more rapidly spread. 90 days post infection the severity of leaf and bunch infections develops rapidly.