Disease Control-74
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Project Leader and Principal UC Investigators R.K. Webster C.M. Wick R. Keim J. Bolstad S. Ferreira R. Jones
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Seed Rot and Seedling Disease: Rice seedling diseases caused by
Achlya Klebsiana and Pythium species play an important role in
the establishment of uniform optimum stands of water-sown rice in
California. These diseases, although prevalent throughout the rice producing
areas of California, are generally more severe when temperatures during the
planting season are cool and unfavorable for the growth and establishment of
seedlings.
þ Seed treatment with fungicides has
been shown to be an effective control for rice seedling disease. Seed
processors throughout the state have become equipped to provide this service
for California growers. The benefits from fungicide seed treatment in
water-sown rice are most obvious during the early planting season when
environmental conditions are often unfavorable fur germination and seedling
growth. Primary benefits include: (1) cost savings from reduced seeding
rates and planting far exceeding the cost of treatment per acre, (2) more
uniform stands and subsequent higher yields, and (3) elimi Stem Rot: Stem rot of rice, caused by Sclerotium oryzae, is endemic over a large portion of the California rice-producing area. The causal organism overwinters in the form of sclerotia either in the soil or in association with crop residue. At planting time, sclerotia float to the water surface when fields are flooded and infect plants as they emerge through the water. Initial infections appear as small dark lesions on the leaf sheaths at the water level. These enlarge and penetrate the stem as the season progresses. Infections that occur early in the season often kill tillers or result in smaller panicles with unfilled grains of poorer quality. Infections occurring later usually do not kill the tiller but result in smaller panicles and enhance lodging, resulting in additional yield losses due to decreased harvester efficiency. The average loss due to stem rot in California is estimated to be between 5-8% annually, with much higher losses occurring in certain areas and individual fields where the disease is more severe. Here in capsule form are the research findings about this very costly disease:
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