Weed Control 73

Weed Control - 73
Project Leader and Principal UC Investigators D.E. Bayer, Weed Control in Rice (RP1) R.S. Baskett B.B. Fischer C.M. Wick J.F. Williams J. Goss W. Tsai D.E. Seaman, D.S. Mikkelsen, Integration and Improvement of Alternative Cultural and Crop Protection Practices for Rice Production (RM1)	þ NEW HERBICIDES Significant progress is indicated by new herbicides available to growers this year - Plus others in the immediate future. MCPA (now available) appears to increase stem rot, correlated with severe leaf and tiller burn. So, in areas of high stem rot, use MCPA only where needed for weed control. Bolero® (not yet approved) controlled sprangletop and barnyardgrass at 4 lb. per acre 10-12 days after seeding (best control and least rice injury when weeds are in the 1 to 2 leaf stage and the rice in the 2 to 3 leaf stage; rice injury is found when postseeding applications are made before rice is well rooted). Bolero applied about 18 days after flooding was generally too late for good control. (RP1) þ ALARMING PONDWEED SPREAD American pondweed infestations are expanding at an alarming rate in Butte, Colusa, Glenn, Sutter, and San Joaquin counties. Irrigation districts are equally concerned about this threat. Granular Hydrothol 191 in recent aerial applications practically eradicated American pondweed with single applications of 2 lb. active ingredient per acre. Equal success with more severe infestations required treatment in two successive years. Since American pondweed regrows each year almost entirely from winter buds, applications made in time to prevent their formation have reduced regrowth the next year roughly in proportion to the initial kill. The manufacturers' request for 1974 experimental label clearance to permit grower applications of Hydrothol 191 has just been rejected by EPA, pending field-scale tests. (RM1) þ POSTFLOOD WEED CONTROL Unnecessary deflooding of fields after herbicides have been applied can result in loss of herbicide effectiveness, leading to costly losses from weed competition. (RM1) HERBICIDES IN SEED COATINGS Weed control appears promising from seed coatings that combine selected herbicides with algacides for water seeding. Clay-coated seeds containing herbicides M3432 and NTN4725 have given excellent control of barnyardgrass and 2 1/2 and 3 1/3 lb. of active ingredient per acre. (No rice injury was found at double those rates!) Advantages of the seed-coating approach would be elimination of separate application of herbicides or algacides and avoidance of presoaking. Because of the favorable results, this will be vigorously pursued as a new system of combined planting and crop protection. The new system promises savings in both fuel and application costs besides improved weed control. Several preemergence herbicides were selective enough to be used in rice seed coatings. The new thiocarbamate herbicide M3432 gave outstanding control of annual grass, whether applied separately to the soil before flooding of applied with clay as a seed coating. AC87528 gave fair weed control but was highly toxic to rice in seed coatings. As seed coatings, NTN4725, chloroxuron, DPC6774, and simetryn performed as well as M3432 of better, whereas benthiocarb, EMD70610H, MC4379, and MTN6867 were quite toxic to the rice.. The thiocarbamates M3432 and NTN4725 controlled only grasses, whereas the substituted ureas chloroxuron and DPX6774, and the riazine simetryn, controlled a broader spectrum of weeds - and algae also. (RM1)

Weed Control - 73

Project Leader and Principal UC Investigators

D.E. Bayer, Weed Control in Rice (RP1)

R.S. Baskett

B.B. Fischer

C.M. Wick

J.F. Williams

J. Goss

W. Tsai

D.E. Seaman, D.S. Mikkelsen, Integration and Improvement of Alternative Cultural and Crop Protection Practices for Rice Production (RM1)

þ NEW HERBICIDES

Significant progress is indicated by new herbicides available to growers this year - Plus others in the immediate future.

MCPA (now available) appears to increase stem rot, correlated with severe leaf and tiller burn. So, in areas of high stem rot, use MCPA only where needed for weed control.

Bolero® (not yet approved) controlled sprangletop and barnyardgrass at 4 lb. per acre 10-12 days after seeding (best control and least rice injury when weeds are in the 1 to 2 leaf stage and the rice in the 2 to 3 leaf stage; rice injury is found when postseeding applications are made before rice is well rooted). Bolero applied about 18 days after flooding was generally too late for good control. (RP1)

þ ALARMING PONDWEED SPREAD

American pondweed infestations are expanding at an alarming rate in Butte, Colusa, Glenn, Sutter, and San Joaquin counties. Irrigation districts are equally concerned about this threat.

Granular Hydrothol 191 in recent aerial applications practically eradicated American pondweed with single applications of 2 lb. active ingredient per acre. Equal success with more severe infestations required treatment in two successive years.

Since American pondweed regrows each year almost entirely from winter buds, applications made in time to prevent their formation have reduced regrowth the next year roughly in proportion to the initial kill.

The manufacturers' request for 1974 experimental label clearance to permit grower applications of Hydrothol 191 has just been rejected by EPA, pending field-scale tests. (RM1)

þ POSTFLOOD WEED CONTROL

Unnecessary deflooding of fields after herbicides have been applied can result in loss of herbicide effectiveness, leading to costly losses from weed competition. (RM1)

HERBICIDES IN SEED COATINGS

Weed control appears promising from seed coatings that combine selected herbicides with algacides for water seeding. Clay-coated seeds containing herbicides M3432 and NTN4725 have given excellent control of barnyardgrass and 2 1/2 and 3 1/3 lb. of active ingredient per acre. (No rice injury was found at double those rates!)

Advantages of the seed-coating approach would be elimination of separate application of herbicides or algacides and avoidance of presoaking. Because of the favorable results, this will be vigorously pursued as a new system of combined planting and crop protection. The new system promises savings in both fuel and application costs besides improved weed control.

Several preemergence herbicides were selective enough to be used in rice seed coatings.

The new thiocarbamate herbicide M3432 gave outstanding control of annual grass, whether applied separately to the soil before flooding of applied with clay as a seed coating.

AC87528 gave fair weed control but was highly toxic to rice in seed coatings.

As seed coatings, NTN4725, chloroxuron, DPC6774, and simetryn performed as well as M3432 of better, whereas benthiocarb, EMD70610H, MC4379, and MTN6867 were quite toxic to the rice..

The thiocarbamates M3432 and NTN4725 controlled only grasses, whereas the substituted ureas chloroxuron and DPX6774, and the riazine simetryn, controlled a broader spectrum of weeds - and algae also. (RM1)