Rhizoctonia leaf web blight and collar rot, two new diseases of Cinnamomum camphora

Abstract

Two new diseases of Cinnamomum camphora namely leaf web blight and collar rot both caused by Rhizoctonia solani were recorded from Central Silviculture Nursery at New Forest, Dehra Dun and described. Two biotypes of the pathogen were associated with leaf web blight, one of which produced typical greyish brown to brown, hard, spherical to oval sclerotia in culture whereas the other biotype produced sclerotial bodies which were not so compact and hard and moreover, they did not have any definite shape and size. It is the latter biotype which occurred predominantly and was highly damaging to young seedlings. It caused defoliation to the extent of 60-100% at the peak of the growing season.Control of the disease included 1) reduction in the quantity of farm yard manure in the potting mixture to half, 2) sowing of seeds in late March or early April instead of June, and 3) application of Dithane M-45 (0.3%) @ 15 ml per tube as soil drench prior to seed sowing. Bayleton (0.1%) may be applied as foliar spray if the disease appears despite the above measures.Collar rot of C. camphora caused by R. solani was a serious disease problem as it wiped out 95-100% seedlings when they were attempted to be pricked in root trainers in July - August. Wrong timing of pricking of seedlings and large quantity of farm yard manure in the potting mixture are attributed to be the cause of the malady. Reduction in the quantity of farm yard manure in the potting mixture to half, pricking of seedlings in May instead of pricking them in July - August by timely sowing of seeds in late March or early April and application of Dithane M-45 (0.3%) @ 15 ml per tube before or at the time of pricking of seedlings are recommended to control collar rot.