|Stem Rot Disease - 72
Project Leader and Principal UC Investigators
R.K. Webster,Cause and Control of Rice Diseases
Stem rot of rice is caused by Sclerotium oryzae. This fungus is widespread
in California but heaviest in the rice-producing areas of the northern
Disease severity and consequent yield losses vary with the amount of fungus carried over, plant stage when infected, fertilization, and influences on plant vigor (damage by wind or herbicides, etc.). Losses in the field have been measured at 18%, and under commercial conditions they may be considerably higher.
All California varieties are susceptible, with Earlirose the most susceptible and Colusa the least. Earlier assumptions that Colusa's low susceptibility was based on earlier maturity were unfounded, for both varieties mature within similar periods. That finding may be important to continued breeding for resistance.
FERTILIZATION VS STEM ROT
In field and greenhouse, stem rot was more severe on plants with high nitrogen and very low phosphorus content. Potassium level did not affect it.
Different nutritional levels were achieved at various stages of growth of Calrose in field trials. When total nitrogen (100 lb/A) was applied 1/a before planting and 3/4 at early boot stage (84 days after seeding), stem rot was delayed and yields greater than when nitrogen top dressings were applied at earlier stages of rice development.
MANAGING RESIDUE TO CONTROL STEM ROT
A 5-year study (beginning in the fall of 1969 near Richvale, Butte Co.) compared burning vs nonburning, spring and fall incorporation by moldboard plow, stubble-disc plowing, and rotovating. Numbers of dormant fungus and disease severity continue to increase where residue has been incorporated. but remain about the same where it is burned in the fall. Yields were lower with incorporation, though the cause was not inadequate nitrogen, phosphorus, or potassium in the plant.
Predisposition to infection and stem-rot losses will be minimized by sticking closely to recommended uses of fertilizer and herbicides. Recommended where stem rot has a history is the variety Colusa (1600).
Stem rot inoculum levels are minimized as well by open burning as by total destruction of the residue.
Where stem rot is a problem, burn the residue as soon after harvest as possible, and then till the field (either stubble-disced or plowed).
With open burning, stem rot inoculum is minimized more effectively by spreading the straw behind the harvester. (RP2)