In vitro evaluation of fungicides against rubber isolate of Thanatephorus cucumeris and management of Thanatephorus foot rot of Hevea seedlings

Abstract

Thanatephorus cucumeris, the causal agent of target leaf spot disease of Hevea also attacks the hypocotyls of germinated seeds and cause damping off and foot rot of seedling in Hevea nurseries in Sri Lanka. Sixteen fungicides were screened for their abilities to reduce the saprophytic growth of T.cucumeris on agar and in soil while five fungicides were tested to control foot rot of Hevea seedlings in pots. Five fungicides (benomy 1,Metalaxyl 8% + mancozeb 64%, tebuconazole, thiram and tridemorph) were found to be effective in inhibiting fungal growth 100% (EC 100 %) on agar at a very low concentration of 50 ug/ml. Three fungicides,viz.captan,mancozed,oxadixyl 10% + propineb 56%, pencycuron,propineb and triadimenol) showed EC 100 between 200-800 ug/ml.However,only four fungicides (benomyl,pencycuron,propineb and tebuconazole)reached the EC 100 within the tested range when assessed in the presence of soil indicating that these are the potential fungicides in management of rubber isolate of T.cucumeris. In pot culture trials two fungicides,pencycuron and benomy1 were found to be effective in controlling the disease.However,the disease was completely checked by traditional burning of soil.