Botrytis cinerea causes plants to decay, rapidly. The fungus thrives in high humidity and cool to moderate temperatures. A grey-brown mass of fungal spores covers affected leaves and flowers. Flowers may also develop numerous small red or brown spots. Flower infestations begin within buds, so initial symptoms are not visible. Fan leaflets turn yellow and wilt, then pistils begin to brown. Stalk rot begins as a chlorotic discolouration of infected tissue, turning into cankers. Small, black sclerotia may form within stalks. Grey mould spores are always present in the air and infect plants through wounds and dead or dying tissue. Infections can also occur by contact between diseased and healthy tissues.
Prevent grey mould through good hygiene and by removing dead leaves and flowers promptly. The key to control though is ventilate carefully to reduce humidity (below50%), and water early in the morning. Avoid excess N and P. Brown wilted pistils are prime B.cinerea fodder, so harvest early. Do not crowd plants, avoid wounding, keep temperature and light levels high.
Foliage and flowers (and soil drenches) can be sprayed with Gliocladium roseum and related Trichoderma species. These fungi aggresively colonise plant surfaces, grow within senescent tissue and out compete pathogens for space and nutrients. They also produce metabolites that inhibit pathogens, induces resistance in hosts and it also parasitises other fungi and some nematodes.
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