Studies on the trunk rot of Japanese chestnut trees caused by Phytophthora castaneae

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Abstract:

Since its discovery in 1962 this disease of Castanea crenata has spread throughout the chestnut growing area and causes particularly severe damage in young orchards with bare ground between the trees. The fungus attacks trunks, branches, shoots and exposed roots, producing symptoms of black sap exudation from bark lesions which enlarge to girdle the trunk. A P. sp. isolated from lesion margins and described as P. castaneae [RPP 57, 2024] was shown to be pathogenic to chestnut and oak, and to rot inoculated apple and Japanese pear fruits. The opt. temp. for mycelial growth was 27 deg and for oospore production 20-30 deg C. The pathogen survives as oospores in infested soil and was isolated using young chestnut shoots as bait. The population density of P. castaneae in orchard soils was not correlated with disease severity. Every cv. of C. crenata tested was susceptible and also the European chestnut (C. sativa), but Chinese chestnut (C. mollissima) and American chestnut (C. dentata) were resistant. The disease was controlled by grassing infested orchards and damage was reduced by grass mulches. Sprays of Difolatan [captafol] or Bordeaux on the trunks from early May to early June were effective, especially when combined with insecticide sprays. Fungicide applications to the soil or to the trunks after early June were ineffective.

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