Diseases 71

Diseases - 71
	NEW TECHNIQUES VS STEM ROT New knowledge is being developed on the stem rot fungus, its life cycle, and factors affecting disease severity. Chemicals and cultural practices for control are being sought. New techniques have been devised toward speedier evaluation of 5,000 rice varieties for resistance. In short: Advances are being made on three fronts against this increasing problem. No surefire solution yet, but things are looking up. If you have a stem rot problem, completely cover all old rice crop residue. Colusa is the most tolerant of stem rot of all the California commercial rice varieties. Also of importance: Plants resist stem rot (Sclerotium oryzae) when not injured by improper use of fertilizers and herbicides. For example, nitrogen absorption from early top-dressing of ammonium sulfate resulted in nitrogen levels in leaves that were temporarily above normal. In such cases, disease incidence was higher. þ RESIDUE MANAGEMENT VS STEM ROT Latest findings on stem rot call for residue management as follows: Field burning is the most economical way yet for minimizing inoculum levels. Where stem rot is a problem, burn the residue as soon after harvest as possible; then till, either stubble-disked or plowed. Spreading the straw behind the harvester improves burning control of stem rot inoculum. Where stem rot is sufficient for economic damage, burning residue minimizes loss. Stem rot and residue incorporation are both at a critical point today, calling for increased study to be sure of the general long-range effects of incorporation on the over-all environment in rice production. Studies elsewhere in this report show no yield reduction from incorporating crop residue, but all of those tests have been where stem rot has not yet been a problem. SEED COATINGS FIGHT FUNGI Fungicidal seed coatings improved yields, with the highest yield (70.71 cwt per acre) from a seed coated with a blend of bentonite and talc in a lignosulfonate dispersant-adhesive containing flowable thiram. The other high-yielding batches used a similar dispersant, indicating that the important thing is spreading the fungicide's zone of action around the germinating seed.

Diseases - 71

NEW TECHNIQUES VS STEM ROT

New knowledge is being developed on the stem rot fungus, its life cycle, and factors affecting disease severity. Chemicals and cultural practices for control are being sought. New techniques have been devised toward speedier evaluation of 5,000 rice varieties for resistance.

In short: Advances are being made on three fronts against this increasing problem. No surefire solution yet, but things are looking up.

If you have a stem rot problem, completely cover all old rice crop residue. Colusa is the most tolerant of stem rot of all the California commercial rice varieties.

Also of importance: Plants resist stem rot (Sclerotium oryzae) when not injured by improper use of fertilizers and herbicides. For example, nitrogen absorption from early top-dressing of ammonium sulfate resulted in nitrogen levels in leaves that were temporarily above normal. In such cases, disease incidence was higher.

þ RESIDUE MANAGEMENT VS STEM ROT

Latest findings on stem rot call for residue management as follows: Field burning is the most economical way yet for minimizing inoculum levels. Where stem rot is a problem, burn the residue as soon after harvest as possible; then till, either stubble-disked or plowed. Spreading the straw behind the harvester improves burning control of stem rot inoculum. Where stem rot is sufficient for economic damage, burning residue minimizes loss.

Stem rot and residue incorporation are both at a critical point today, calling for increased study to be sure of the general long-range effects of incorporation on the over-all environment in rice production. Studies elsewhere in this report show no yield reduction from incorporating crop residue, but all of those tests have been where stem rot has not yet been a problem.

SEED COATINGS FIGHT FUNGI

Fungicidal seed coatings improved yields, with the highest yield (70.71 cwt per acre) from a seed coated with a blend of bentonite and talc in a lignosulfonate dispersant-adhesive containing flowable thiram. The other high-yielding batches used a similar dispersant, indicating that the important thing is spreading the fungicide's zone of action around the germinating seed.