Weeds - 71



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Research in the last three years has made rapid progress against weeds-one of the most costly items in growing rice. Many new compounds are being screened to develop more economical and safer ways of controlling all types of weeds of California rice fields. Accent is on locating compounds that in a single application will kill all weeds and not injure rice. Chemical companies are providing materials and some financial support.

Since propanil is not generally allowed north of Interstate 80 in California, growers in '72 will fight rice weeds primarily with molinate (Ordram) and MCPA. Be sure to follow manufacturer's directions and local regulations exactly!

TOK (nitrofen) is offered to growers on an experimental basis. It appears effective in tests at both Biggs and Davis. WARNING: Follow manufacturer's treatment time and seeding-delay time precisely.

Studies have confirmed that MCPA for control of broadleafs should not go on until jointing or stem elongation (50 to 62 days after planting) are well under way. Then the rice is most resistant to it.

Two new herbicides, OCC 188-50 and AC 87528, show extreme promise for broad-spectrum weed control in rice. Extensive further study in '72 will consider safety of herbicides sprayed near major crops associated with rice areas.

Of 18 herbicides evaluated in a new planting-systems test, involving rice, best weed control came from Butachlor and RP-17623 (respectively at 3 and 1.5 lb active ingredients per acre) applied after planting and before initial flush irrigation.

Control of annual grasses, sedges, and broadleaf weeds was excellent (without serious rice injury) from experimental formulations of molinate + MCPA-isopropyl ester (IPE) and molinate + 2,4-D-IPE. At all application times (18, 21, or 24 days after seeding), the safer and more effective combination was molinate + MCPA-IPE.

Granular Hydrothol 191 gave good control of American pondweed. Control was nearly 100% in a 15-acre Glenn County field uniformly infested, converting expected zero yield to 45 cwt per acre. The application was 2 lb active ingredient per acre.

Preflood applications of IMC-3950 were slightly less effective than molinate in controlling grass in continuously flooded fields, but were about half as effective when the field was drained during early cool weather to increase rice stands. The more important drawback of early draining is stimulated weed growth and retarded rice growth consequent to nitrogen losses. IMC-39SO may be a useful alternative to molinate for postflood applications, since it controlled sprangletop and ducksalad as well as watergrass. Expected in '72 is experimental registration of IMC-39SO under the new trade name Bolero (formerly Saturn).


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