WEED CONTROL IN AGRONOMIC CROPS

Jack Orr, Farm Advisor UC Cooperative Extension Service Sacramento County - Sacramento, California

ALFALFA

Alfalfa is a crop where integrated pest management is very important. In the early Spring when grasses are germinating, and alfalfa weevil populations are starting to increase, it is essential to achieve excellent insect control, if you want good weed control. Work by Dr. Norris has shown a sharp decrease in yield and a sharp increase in Setaria lutescens (yellow foxtail) unless you achieve good weevil and long term grass control.

For winter weed control hexazinone (Velpar) gives excellent broadleaf control and excellent ryegrass control. Diuron (Karmex) gives better winter grass control, overall, than Velpar. Velpar, a soil activer and contact herbicide, performed well under 30 inches of rainfall last winter.

New postemergence grass herbicides to consider for the future when registered for seedling alfalfa would be sethoxydin (Poast) and fluazifop-butyl (Fusilade). Additional postemergence broadleaf control could be obtained with a combination of the grass herbicides and 2,4-DB or bromoxynil (Brominal). None of these treatments are registered.

Promising herbicides for summer weed control in established alfalfa are Poast, asulam (Asulox) and Fusilade applied in June postemergence after the third cutting for Setaria control, and Brominal for broadleaf control.

A pre-emergence application of oxyzalin (Surflan) prior to first cutting gave good long term control of yellow foxtail with no injury to the alfalfa.

In the northern counties on heavier soils, Poa Annua and Downy Brome are two problem weeds. Sinazine will give good control of the Poa Annua and Fusilade looks promising on the Downy Brome.

BEANS

In beans the worst weed problems are nightshade, yellow nutsedge and bindweed. Preplant herbicides for control of nightshade include EPTC (Eptam), alachlor (Lasso), metolachlor (Dual) and ethalfuluralin (Sonalan). Bean tolerance is good with Lasso, except for blackeyes. Nightshade control is generally good, but can be erratic due to moisture conditions.

111 Dual gives good control of nightshade and excellent control of yellow nutsedge. Full registration is expected in the Spring of 1983.

Eptam gives fair to good control of nightshade with poor crop tolerance in blackeyes and lima beans. Yellow nutsedge control is fair to good with Eptan, having a short soil residual.

Sonalan gives fair to good nightshade control with good bean tolerance and no control of yellow nutsedge. Soil residual is long.

In terms of postemergence applications, acifluorfen (Tackle or Blazer) shows fair results in controlling black nightshade with fair bean tolerance. Basagran + pace (1%) postemergence is giving good suppression of yellow nutsedge and good control of nightshade with fair kidney bean tolerance.

The postemergence grass herbicides, Poast, Fusilade and Hoelon, give good watergrass control with good bean tolerance. The combination of Basagran + the grass herbicides postemergence showed fair yellow nutsedge suppression, and excellent watergrass and broadleaf control with good crop tolerance.

Excellent field bindweed control has been obtained by applying four quarts/acre of glyphosate (Roundup) postemergence on actively growing field bindweed the previous fall to planting beans. A 22 to 40% increase in bean yields resulted from this treatment. The bindweed must not be under stress or covered with dust or poor control results.

CEREAL

The biggest breakthrough this year in controlling wild oats and ryegrass in wheat and barley was the recent registration of diclofopmethyl (Hoelon). This is an excellent herbicide, but cannot be combined with 2,4D for broadleaf control because of antagonism. The grass control will be diminished considerably. At least seven days must lapse before the 2,4D application can be made.

A good combination for ryegrass and broadleaf control would be Hoelon + Brominal, where no antagonism exists.

American Cyanamid has a promising new wild oat herbicide, AC-222,293. However, there has been some variety yield reduction interactions with this herbicide. Wheat varieties affected are Yolo, Yecora Rojo and W-444. Varieties not affected are Anza, Probred, Probrand 771, Oslo and Westbred 911. This wild oat control would more than compensate for any affect on the variety. As few as five wild oat plants/ft2 can result in a 3,000 lb/ac yield decrease out of a 6,000 lb/ac yield potential with no wild oats.

112 FIELD CORN

A promising new postemergence grass herbicide for use in field corn is Dowco 356 (Tandem). This herbicide has shown good herbicidal activity and good crop tolerance.

Recent field corn weed competition studies show corn to be a very good competitor with general annual broadleaves and grasses. Yield studi~s the last two years showed the herbicide treatments did not pay for themselves by significant yield increases. Preplant herbicides EPTC + Safener (Eradicane), butylate (Sutan) and alachlor (Lasso) compared to a postemergence treatment of atrazine + oil and cultivation. Weeds consisted of light to moderate populations of redroot pigweed and watergrass.

In another, Herbicide-Miticide Interaction Study, cultivation + comite resulted in the highest corn yield when compared to herbicides + comite, cultivation + control and herbicides + control. There was only a 0.24 ton/acre difference from highest to lowest yield between treatments.

COTTON

Harold Kempens Research:

Research in 1982 emphasized application and timing techniques for five new selective grass herbicides on Johnsongrass, bermudagrass and barnyard grass. Sethoxydin (Post) and fluazifop-butyl (Fusilade) are expected to be registered by EPA in February or March, 1983 on cotton and soybeans.

Results show excellent control of annual grasses at 0.1 to 0.3 lb/A and perennials at 0.2 to 0.5 lb/A, but with two applications usually necessary on perennials, Drought stress reduces effectiveness markedly. Cotton safety appears to be superb, though leaf strippling sometimes occurs.

Other areas of study show glyphosate (Roundup) and oxyfluorfen (Goal) to be a successful herbicide for weeds on fallow beds before cotton planting but research shows prometryn (Caparol), linuron (Lorox), diuron (Karmex), cyanazine (Bladex), fluometuron (Cotoran) and chlorpropham (Furloe) also could be useful on fallow beds, if registered.

No new nutsedge herbicides are on the horizon. Oxyf luorfen (Goal) is now registered at layby, but offers little utility not offered by Bladex, Coparol, Cotoran or Karmex. However, it does not persist beyond harvest after tillage.

Roundup is registered for a defoliation "perennial weed cleanup" treatment by EPA and will be registered by ground application only. Banvel is being evaluated for a similar "cleanup" treatment of field bindweed.

113 RICE

Three major changes in California rice production have contributed to increased weed problems. The changes are crop stature, water management and nitrogen use. The new short-statured varieties are less competitive. Shallow water depth enhances barnyardgrass populations. At higher nitrogen rates and higher barnyardgrass densities, the barnyardgrass out competes the rice for nitrogen resulting in severe yield reductions.

Dr. Don Seaman's Research at Biggs Experiment Station:

Increasing the seeding rate from 150 to 175 lb/A enabled the short-stature variety S-201 to compete with watergrass, sedges and broadleaf weeds more successfully and increased its yield about 12 cwt/A where weeds were not controlled. The yield of tall variety S6 was increased slightly by the higher seeding rate where watergrasses were controlled, but it was decreased where they were not controlled. At 150 lb/A, broadleaf weeds and sedges caused similar yield reductions in each variety, but watergrass caused twice as much loss in S-201 as in S6. At the higher seeding rate yield reduction by watergrass has halved in S-201 which exceeded the yield of the taller variety at both seeding rates with not weed control at all.

Very shallow water management was more harmful than beneficial to the short-stature variety S-201 by enchancement of watergrass growth and reduction of herbicide efficacy. Increasing water depth from means of 3 to 7 inches with continuous flooding increased densities of California arrowhead, monochoria and roughseed bulrush slightly, but it reduced those of blunt spikerush, smallflower umbrellaplant, redstem and watergrass greatly without affecting rice stand establishment. Watergrass control by molinate or thiobencarb was incomplete at the lower depth and nearly perfect where the water was deeper. MCPA gave effective postemergence control of sedges and broadleaf weeds at both water depths. Consequently, rice grain yield was nearly 30% higher where the water was kept deeper.

Linear regressions of surviving watergrass densities measured at midseason and rice grain yields among treated and untreated plots of five weed control experiments indicated that early watergrass may compete more severly with rice than late watergrass. Calculations based on this mehod of weed competition assessment showed that a 10 cwt/A loss of rice could be caused by average densities of 0.8 early watergrass plants/square foot, 1.2 late watergrass plants/square foot or 1.7 plants/square foot of combined early and late watergrasses.

Dr. Dave Bayer's Research in Sacramento County:

114 Studies on the Demeter Corporation test site focused on methods and timing of application with respect to broadleaf and grass weed control and on the interaction of cultural practices and weed control. Significant findings for the second consecutive year show that MCPA applications at early stages of growth (35 days after flooding) provided the better weed control and higher yields than later treatments. Both MCPA and Basagran provided less control of smallflower umbrellaplant in 1982 than in 1981 due to a cool 1982 spring resulting in delayed germination of this weed.

Michele LaStrange's Research:

Competition studies with barnyardgrass indicated a highly significant effect of increasing nitrogen fertilizer on increasing competition of this weed. Competition curves developed from this project have been used to demonstrate the benefit of herbicides to the rice industry.

Nitrogen assimilation may be negatively affected by MCPA as compared to Basagran. Leaf tissue nitrogen levels were depressed by MCPA although the depression appears to be temporary and the effects on yield may not be significant.

Dr. Don Seaman's Research:

Among the 15 new herbicides evaluated initially, three from Mitsubishi Petrochemical Company, one from Rohm & Haas Company and two from Sandoz, Inc. performed outst~ndingly. The most promising of all was a granular combination of two herbicides (MY-93E) from Mitsubishi, which gave excellent control of most common weedy grasses, sedges and broadleaf weeds without rice injury. Reevaluation confirmed that RH-1903 (Rohm & Haas), DPX-5384 and DPX-6632 (DuPont), and Ordram R-33865 (Stauffer Chemical Company) still were viable candidates, but bifenox (Rhone-Poulenc's Modown 10-G), PPG-884 (PPG Industries) and SAN-369 (Sandoz) were found unworthy of further development for rice in California. Slow release granular formulations of bifenox, dicamba and molinate prepared by Sierra Chemical Company were found disadvantageous, but hat company's "fast" and "slow" release granular butachlor (Monsanto's Machete) and a slow release MCPA all performed with promising safety and efficacy in water-seeded rice.

SUGAR BEETS

New promising grass herbicides for use in sugar beets include sethoxydin (Post), fluazifop-butyl (Fusilade), DPX-Y62-2 (NCI-96683), CGA 82725, and Hoe 00581.

There is a tank mix incompatability between these grass herbicides and Betamix. The herbicidal activity of the grass herbicide will be reduced considerably. Therefore, split,

115 delayed applications must be made. Best grass control is obtained when good soil moisture is present. Where Johnsongrass is a problem, applications should be made at an early growth stage. One winter annual grass that escapes Poast and Hoelon, is annual bluegrass (Poa Annua).

Two other excellent new pre-emergence herbicides to be registered last year are ethofumesate (Nortron) and dienthatyl ethyl (Antor). Nortron fits best as a Fall/Winter treatment in combination with pyrazon (Pyramin). Its soil residual is about 10-12 weeks. Good control of volunteer cereals can be expected. It's weak on ryegrass.

Antor fits best in sugarbeet production as a late Winter or Spring treatment. Applications in combination with Pyramin where incorporation is from Winter rainfall or sprinklers look excellent. The weed spectrum is increased with the addition of Pyramin.

Competition studies by Dr. Norris at University of California, Davis, indicates sugarbeets are poor competitors with watergrass. As few as five watergrass plants/ten meter can result in a 35% decrease in yield.

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