Sclerotium oryzae, the cause of stem rot, over-winters either in rice residue or free in the soil. Previous research, verified again this year, shows that burning of crop residue is effective in minimizing stem rot disease. Other studies are seeking a better understanding of how the disease organism behaves in the soil and whether control features other than field burning can be effective.

A study to compare the effect of removal of straw with that of burning indicates that harvesting of rice straw near ground level, followed by straw removal, is as effective as either spring or fall burning in reducing stem rot disease. Total straw removal, however, is not yet economically feasible.

Another experiment was conducted to determine the infection potential of stem rot disease organisms remaining in the soil. Field soil was artificially infested with sclerotia to determine their longevity. Treatments included sclerotia which were rototilled into the soil to a depth of 18 centimeters (8 inches) either with or without an amendment of dried, noninfected rice residue and sclerotia killed prior to introduction. The rate of decrease in numbers of sclerotia was the same for all treatments. A calculated half-life of 1.9 years was obtained.

There was an initial rapid decline in the inoculum potential of freshly produced sclerotia incorporated into field soil due to the rapid loss in the ability of sclerotia to germinate, but the numbers of sclerotia decreased only slightly during this period. After the rapid decline, inoculum potential stabilized and, thereafter, is expected to be influenced mainly by a decline in actual numbers of sclerotia. Since the decline in numbers of sclerotia was relatively slow, alternate year cropping of rice is not expected to control stem rot.