|Crop Protection and Growth Regulation-69
A. WEED CONTROL
There are two major screening trials, one pre-emergence and one postemergence, at UC Davis and at the Biggs Rice Experiment Station, for grass and broadleaved weed control. In addition, the Agricultural Extension Service is conducting ten county weed-control trials, in Butte, Fresno, San Joaquin, and Sutter counties. These trials were developed to evaluate the most promising herbicides under grower conditions.
Field studies (with Agricultural Engineering and Environmental Toxicology) concerning propanil and 2,4-D were initiated after June 1, 1970, to coincide with the normal application period. The studies are aimed at further identifying particle movement and the influence of propanil on tree growth. Emphasis will be placed on drift control through promising application techniques. Drift will be measured biologically with potted French prune trees, as well as with air samplers and fallout sheets. The intent is to develop means to reduce and control drift while maintaining chemical efficacy. The field tests were preceded by considerable laboratory and wind tunnel studies on atomizers, conducted during the winter.
The extent of aerial transport of propanil was delineated last year by known application test runs and also by monitoring chemicals dispersed downwind from large applications of propanil applied to rice. There is now no doubt that propanil causes a yellow spotting of prunes and other susceptible plants and crops. Control of this drift appears to b e good, however. Tao atomizers have been investigated, and others are to be examined this season.
The movement of chemicals from application sites to nearby and more distant crop areas is related primarily to the particle size of the spray cloud generated by the application machine. The Microfoil boom (Amchem Products) can reduce the numbers of small drops normally occurring from regular aircraft, reducing propanil drift to less than with ground-operated equipment, but the drops are very coarse and there is considerable question whether they can give sufficient coverage of the weeds (watergrass) to do a good job. Thus, more efficacy tests are needed on this device.
The second device is a design of our own, which we call a low-turbulence nozzle (LTN). This is similar to Amchem's device but drop size is 1/3 to 1/4 the size of the Microfoil drops although fine drops (under 100 microns diameter) are still not formed.
It appears that some form of nozzle will be found which will make possible a significant reduction of drift of all types of pesticide sprays.
County tests of the Agricultural Extension Service include work on control of duck salad weed, preplant screening tests of 22 chemicals as replacements for the phenoxy herbicides, preplant weed trials, and postemergence tests involving 12 chemicals.
B. DISEASE CONTROL
The disease-control program contains two separate yet intricately related areas of investigation: the cause and control of rice diseases in California and the effect of various methods of residue management on the occurrence and severity of rice diseases.
1) Cause and Control of Rice Diseases in California
a) Seedling disease
The fungi involved in rice seedling disease have been identified, and the nature of the disease studied. Captan and thiram are recommended for use as seed treatments. With the advent of seed treatment, a continual program of evaluation of chemicals and the manner in which they are applied is necessary to ensure that the best control measures are being used. This year's trials have been directed mainly toward evaluating currently recommended chemicals, the effect of planting dates, location, the seeding rate required to obtain optimum yields and screening new candidate chemicals. Toward these ends the following trials were established this season:
(1) Effect of location and seeding date. Results obtained thus far indicate that seed treatment, properly used, helps the grower obtain a stand even when stand establishment conditions may be adverse.
(2) Seeding rate. To determine optimum seeding rates of chemically treated seed, four field trials were established. Seeding rates of 50, 100 and 150 lbs./acre were used. Yield data will be collected at the end of the season.
(3) Mode of application of fungicides and screening of new chemicals. A large trial was established in Merced County to determine the effect of incorporating fungicides into a seed coating. Results indicate that fungicides may be incorporated into the seed coating with a direct benefit from the seed treatment. Ten new candidate fungicides were screened for effectiveness against seedling disease at the Biggs Station. The results indicate that chemicals even more effective than captan or thiram may be available.
b) Stem rot of rice
Investigations on the stem rot of rice have determined the fungi involved, their life cycles, and factors that affect disease severity. We hope this study will provide information needed to formulate control methods.
Various seed-treatment tests in the counties conducted by the Agricultural Extension Service, are aimed at determining the effectiveness of several fungicides on seedling establishment and subsequent growth, decreasing seeding rates required, controlling rice seedling diseases, and determining optimum methods of commercial seed treatments.
2) Effect of residue management on occurrence and severity of rice diseases
Information on rice diseases in other parts of the world suggests that the burning practice may have substantially reduced the incidence of certain diseases of rice in California. Of prime interest to us is the stem rot of rice. With probable limitations on the burning of residue, trials have been established to determine the effect of various means of residue management on the populations of the fungi known to occur in rice fields. We have developed techniques for sampling and assaying soil and plant residue samples on a quantitative basis. These techniques are being used to determine the existing levels of the pathogens and also the changes in the populations which may result from different cultural practices.
The methods developed for testing pathogenicity and varietal susceptibility to the stem rot organism are being used at the rice station for screening a large number of introductions for resistance to stem rot.
C. CONTROL OF INSECTS AND OTHER INVERTEBRATES
Currently under way are programs dealing with the protection of rice from insects and other invertebrates, and the effect of rice crop residues on invertebrate fauna in rice fields.
Studies in progress include:
1) Overwintering habits of the rice water weevil in relation to levee and field vegetation--burned and unburned.
2) Role of rice residue incorporation on invertebrate fauna. Weekly aquatic light trap collections, substrate and soil samples.
3) Rice water weevil control as levee margin treatments vs. solid field treatments in commercial fields.
4) Rice water weevil control. Tests with carbofuran and Bux to determine relationship of dose, formulation, timing, and water management; and to obtain residue information for insecticide registration.
5) Effect on sunfish and mosquito fish of insecticides used for water weevil control.
6) Screening tests in the greenhouse for new compounds for rice water weevil control.
7) Rice water weevil life history--trapping studies
8) Rice plant resistance to rice water weevil damage.
9) The effect of nematode attacks on rice water weevil larvae.
10) Tadpole shrimp control in relation to water weevil control.
11) Tadpole shrimp life history studies.
The overwintering habits of rice water weevil adults indicates that many more adults can be found overwintering in vegetation on the levees than in the field proper; and apparently the fall burning of the levees does not cause an appreciable reduction in the adults. They are usually found deep at the base of various bunch type grasses.
Preliminary observations were made on the effectiveness of preflood water weevil treatments with B me and carbofuran on the tadpole shrimp. Tests show that both materials at 0.5 lb. active ingredients per acre applied to the soil surface would, at best, only partially reduce the shrimp population as they hatch from eggs.
D. GROWTH REGULATORS
Field and greenhouse studies in 1969-70 on regulation of rice growth involved: 1) a study to determine cultural practices to improve the protein content of rice grain; and 2) investigations to locate chemicals which could be applied either to the seed or to growing plants so as to: a) stimulate seedling vigor, thereby speeding stand establishment; and b) restrict plant height and improve straw strength while improving grain yield and quality.
Increased Rice Protein. Simazine, applied to flooded rice in the heading stage, significantly increased the protein content of the mature grain, although with an accompanying decrease in grain yield at the rates of simazine used. When rice seed from the treated plants was germinated and grown under laboratory and greenhouse conditions, the high-protein rice seed germinated and grew more uniformly than the low-protein control seed, and the resulting seedling plants grew faster.
Coated Seed. Calrose rice seed was coated with 11 different fungicides and growth-stimulating chemicals at various rates to determine whether: a) the present commercial rice-seed soaking procedure could be eliminated while b) using a substance in the seed coatings which would protect and stimulate seedling growth. Of the different materials and methods tested, none performed more satisfactorily than did the application of fungicidally-treated dry seed to a dry seedbed followed by field flooding.
Plant Dwarfing Tests. Cycocel and RH531 were applied as a foliar spray to rice in the jointing stage. The RH531 compound at some of the rates used eliminated lodging but yield was adversely affected. Cycocel at most rates did not affect yield but was totally ineffective in reducing lodging or in reducing plant height.