Stem rot of Peanut
First symptoms are water soaked brown to dark-brown lesions on the stem just below soil level. Later on, the stem tissues become slimy and show signs of rot. Coarse cottony fungal growth and small, brown, seed-like structures spread on the collar, on leaf litter, or the soil, infecting other plants. Infected leaves turn necrotic and dry but remain attached to the plant. Affected branches turn yellow, wither and the whole plant might die. Affected pods start to rot, appearing as clear and watery spots in young pods and brownish patches with white mycelia in mature ones. Roots also show signs of rot.
Stem rot is caused by the soil-borne fungus Athelia rolfsii. It overwinters in infected tissues or plant debris for up to three years. It spreads from soil litter to the base of the stem and the roots. Groundnut plants can be infected at all growth stages, but younger plants are more susceptible and can damp off. The favorite conditions in the soil for an infection are high humidity and soil moisture, elevated temperatures (25-35°C) and pH below 7.0. High soil organic content also promote the disease, explaining why seedling mortality in sandy soil was significantly reduced. Stem rot is frequently the major limiting factor in attaining maximal yields in peanut production.
Bacterial biocontrol agents based on Trichoderma viridae, Trichoderma harzianum, Pseudomonas fluorescence and Pseudomonas cf. monteilii 9 are good alternatives to fungicide treatment of seeds. Soil application of Trichoderma viridae together with farmyard manure or in conjunction with organic amendments such as castor cake, neem cake or mustard cake also work fine.
Always consider an integrated approach with preventive measures together with biological treatment if available. Seed treatment with thiram, captan or carbendazim can be considered to avoid infection with stem rot. Other compounds that have been used as alternative soil treatment include azoxystrobin, pyraclostrobin and tebuconazole. Treet seeds whit mancozeb @ 3 grams per kg of seed or tebuconazole @ 1 gm per kg of seed.
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