COMPARISON OF MICRO HERBICIDE RATES FOR WEED CONTROL IN SUGAR BEET.

Don W. Morishita and Michael J. Wille
University of Idaho
Twin Falls R&E Center

INTRODUCTION

Sugar beet growers in southern Idaho and eastern Oregon began using micro herbicide rates for the first time during the 2000 growing season.  Studies conducted by the University of Idaho at Twin Falls and Oregon State University at Ontario have shown that weeds can successfully be controlled in or drier climate.  However, after two years of field studies, some problems still remain.  Among those problems is kochia control.  This has been a difficult weed to control in our micro rate studies.  Thus, in 2000 several micro herbicide rate combinations were compared for weed control in sugar beet (variety 'HM PM-21').  The objectives of this experiment were to: 1)compare the standard early postemergence combination of Progress^® + UpBeet^® + Stinger^® to micro rate broadcast and band applications of the same or similar herbicide combinations; 2) evaluate increasing micro rates with sequential applications, and 3) compare methylated seed oil to Hasten^®, an ethylated vegetable oil and nonionic surfactant blend and Placement^®, a petroleum-based drift control agent.

MATERIALS AND METHODS

This study was conducted at the University of Idaho Research and Extension Center near Kimberly, Idaho.  The crop was planted April 18, 2000, on 22-inch rows at a seeding rate of 57024 seed/A.  Experimental design was a randomized compleete block with four replications and individual plots were 4 rows by 30 ft.  All herbicides were applied with a CO₂-pressurized bicycle-wheel sprayer calibrated to deliver the equivalent of 20 gpa broadcast in an 11-inch band using 8001 even fan nozzles or 10 gpa broadcast using 11001 flat fan nozzles.  Additional application information is shown in Table 1.  Crop injury and weed control was evaluated vusually June 15 and July 14, which was 8 and 44 days after the last treatment (DALT) was applied.  The two center rows of each plot were harvested mechanically September 21.

Table 1.  Herbicide application information and weed species densities.

RESULTS AND DISCUSSION

Crop injury in the form of cholorotic leaves was ovserved 8 DALT among several of the treatments.  The injury was attrubuted to air temperatures exceeding 80 F on the afternoon of May 27, which was the third appplication date.  At 44 DALT, no injury was observed in any of the berbicide treatments.  Overall, weed control with the standard 7-inch band rate of Progress + UpBeet + Stinger at 6 +1/6 +1 1/3 oz/A controlled common lambquarters, kochia, redroot pigweed, hairy nightshade, and green foxtail 91 to 100% across both evaluation dates.  Between the two micro rate 11-inch band applications, increasing the Progress rate form 3 fl oz/A on the first and second applications to 4.5 fl oz/A on the third and fourth applications controlled the six weed species better than using the same Progress rate on all four applications. Comparing band and broadcast applications at equivalent rates showed that weed control with an 11-inch band application was about equal to the broadcast applications.  Adding Nortron^® to the Progress + UpBeet + Stinger tank mix improved kochia control from 56 to 80% 44 DALT compared to using Hasten or Placement alone, which controlled kochia 81 and 78%, respectively.  Redroot pigweed control 44 DALT and hairy nightshade control 8 DALT ranged from 91 to 100% for all herbicide treatments.  All herbicide treatments had higher sugar beet yields than the untreated check.  The standard 7-band rate treatment consisting of Progress + UpBeet + Stinger at 6 + 1/6 + 1.33 oz/A applied four times had the highest numerical yield at 27 ton/A, but was statistically equal to all but two of the micro rate treatments.  This study shows that kochia is difficult to control with micro rateds applied at the same rate at each application.  However, kochia can be satisfactorily controlled with the micro rates if the Progress rate increases with the last two applications, or if Nortron is added to the tank mixture.

Table 2.  Crop injury, weed control, and sugar beet yield with micro rates near Kimberly, Idaho.