Control of Rhizoctonia stem and stolon canker of potato by harvest methods and enhancing mycophagous soil mesofauna

Rhizoctonia solani (AG-3) is a soil-borne plant pathogen that causes canker on potato stems an, stolons, resulting in a reduced quantity and quality of the tuber yield. Two approaches for non. chemical control of stem and stolon canker in potato, caused by soil-borne inoculum, were investigated.

Two field experiments were conducted to investigate whether harvest methods of potato affect soil infestation with R. solani. Soil infestation was estimated on the basis of stem infections of potato in the subsequent year. Immature-crop-harvesting lowered the disease severity in the next crop compared with haulm pulling and chemical haulm killing. However, this harvest method was only successfull in controlling the disease when the formation of sclerotia did not start before harvest and the crop debris was incorporated into the soil with a rotary hoe.

Control of Rhizoctonia stem and stolon infections by mycophagous soil animals was investigated in experiments under controlled conditions (growth chambers) and in field experiments. The mycophagous soil mesofauna was equally effective in reducing of stem infections at 10 and 15 °C, and they were effective over a broad range of soil moistures. Under controlled conditions, adding dried fresh rape material to the soil enhanced the populations of the springtail Folsomia fimetaria and the nematode Aphelenchus avenae. F. fimetaria reduced stem canker under a broad range of conditions, but when rape was added to the soil at pH-KCl 6.2, its suppressive effect disappeared completely, probably due to the presence of alternative food sources.

In field experiments, oats grown as green manure crop or farmyard manure plus white mustard as green manure crop enhanced the populations of the mycophagous soil fauna and reduced the severity of Rhizoctonia stem and stolon canker. Oats especially increased the populations of mycophagous nematodes, whereas farmyard manure plus white mustard mainly enhanced the populations of mycophagous springtails.