Production Practices-76



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Project Leader and Principal UC Investigators

Glenn Nader, livestock farm advisor, UC Cooperative Extension Butte/Sutter/Yuba Counties


Combining various cultural practices to reduce costs and improve pest control is a continuing research aim. Four distinct objectives have been established:

  1. To determine how new herbicides, algacides, and other agricultural chemicals can be used most efficiently in agronomic systems for rice.
  2. To investigate interactions of biological and ecological factors that affect the responses of different rice varieties to weed competition and to different methods of weed control.
  3. To investigate the reproductive biology and ecology of the important varieties of watergrass that affect California rice, determine the nature of their apparent resistance to herbicides, and improve cultural and chemical control methods.
  4. To develop improved multipurpose rice seed coatings containing various crop-protection and nutrient chemicals.

Progress toward all objectives has been considerable. Knowledge developed regarding rice seed coatings (no. 4 above) is likely to have commercial application in 1977 or 1978.

New herbicides prove highly promising in field trials.

In a trial involving 12 different granular herbicide combinations, several - variously treated gave as good weed control and rice grain yield as did sequential applications of molinate (Ordram 10G), postflood at 4 lb ai/A, followed by MCPA at 1 lb ai/A. Among the 19 new herbicides evaluated in small-plot field trials, six were most promising for control of watergrasses in watersown coated rice. The outstanding performance of these new herbicides is noteworthy, because they were evaluated in fields heavily infested with the late-heading form of watergrass.

Hydrothol 191 granular applied to a rice field did not harm mosquitofish placed in the field a day before. The chemical gave excellent control of a severe infestation of sago pondweed and scattered patches of American pondweed.

Surveys show that early watergrass, not barnyardgrass, is the major grass problem throughout the rice-growing areas of California.

Barnyardgrass (Echinochloa crus-galli) is widespread but is a problem mainly on levees and in shallow-water areas, or where poor water management has enabled it to start growing in flooded fields. The most serious of our weeds is a close relative, watergrass (E. oryzicola). Late watergrass (the "rice mimic") is a serious problem in a few fields, where control has been extremely difficult either by herbicide or by deep water.

Germination experiments revealed that seed of early and late watergrass has very little innate dormancy, whereas barnyardgrass has strong postharvest dormancy. Seeds of the three forms also were found capable of germination at temperatures as low as 50F, though subsequent seedling growth was greatly retarded at temperatures below 70F. In tank and field experiments, seedlings of both watergrass forms that were germinated on the soil surface emerged through 12 inches of water, whereas very few seedlings of bamyardgrass emerged through 3 inches of water. However, seeds of all 3 forms failed to emerge when buried under 1-2 inches of flooded soil. Subsequent soil drainage, or bringing the seeds to the soil surface, enabled this enforced dormancy to be broken, and the seedlings emerged from 2 inches of drained soil. Other experiments on the competition of these grass varieties with rice indicate that the early-heading form of watergrass was the strongest competitor.

In a field infested with the early and late forms of watergrass, split applications of molinate gave nearly perfect control of the early form but only about 80% control of the late form.

By adding weight to dry seed rice in the form of a coating, the costly and bothersome seed-soaking operation can be eliminated, since the weighted, dry, coated seed can be applied by air directly onto flooded paddies.

In the past three years, research has progressed well in developing methods of coating rice seed to include fungicides, zinc nutrients, and possibly herbicides. Resulting technology has attracted the attention of two commercial organizations which are now making preparations to supply coated rice seed to their customers.

Durakoat, a new polymeric emulsion material, was found to be a more versatile and economical adhesive than sodium silicate for making weighted rice seed coatings. It was compatible with most of the other ingredients used for multipurpose coatings, and polymerizes to bind coating materials to the seed without becoming sticky. It should be useful in developing continuous processes for rapid and economical coating of large amounts of rice seed.

Drepamon, a herbicide used in seed coatings, performed well in field trials. Durakoat as the coating adhesive did not improve the performance of Drepamon significantly, but a wettable powder formulation of Drepamon (used in place of an emulsifiable liquid formulation) gave less phytotoxicity, higher grain yields, and slightly improved watergrass control.

Formulations of 23 new herbicides were evaluated as seed-coating additives. Four of these showed the greatest promise, and all gave less injury to M5 rice and better control of watergrass than did Drepamon in a small-scale trial. Since Drepamon may not be available for future development in California, these new herbicides offer encouragement for continued work with rice seed as granular herbicide carriers for combined planting and weed control.

Figure 2. Midge larva damage to seedling rice. UCD entomologists are increasing research efforts to provide protection to rice fields during stand establishment. (A. A. Grigarick, UCD photo)


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