FUNGICIDES FOR CONROL OF SUGARBEET POWDERY MILDEW

PARMA, IDAHO, 2004

  John J. Gallian and Dixie Vargas, Sugarbeet Specialist and Plant Pathologist, and Scientific Aide, University of Idaho, Twin Falls Research and Extension Center, P.O. Box 1827, Twin Falls, Idaho 83303-1827.

  Powdery mildew of sugarbeets, caused by Erysiphe polygoni, occurred earlier this year in much of the sugarbeet growing area of Idaho, eastern Oregon, and Washington.  Fungicide treatment is necessary to prevent economic loss when average disease exceeds 10% mature leaf area diseased for the season.  Most areas of the Treasure Valley of Idaho and eastern Oregon usually require two fungicide treatments to prevent economic loss. 

  METHODS   

  Studies were conducted at the Southwest Idaho Research and Extension Center at Parma, Idaho to test the efficacy of eight fungicides for the control of sugarbeet powdery mildew.  The fungicides are listed below in Table 1.

  Table 1. Fungicides, companies and chemistry class for 2004 powdery mildew test.

The field was fertilized in late October, 2003 and bedded into 22-inch rows. Variety Beta 4773 R was planted on April 1, 2004 with a 3.6-inch seed drop. Nitrogen was applied again on May 14 and June 24, 2004.  The field was furrow irrigated and the first irrigation was applied on April 7.  Insecticide applications were Temik 20 lbs/A on April 1 and 13 lbs/A on April 26 and Asana XL 7 oz/A on April 23 for root maggot.  For weed control, Progress 10 oz/A, Upbeet .25 oz/A, and Hasten COC 40 oz/A were tank mixed and applied on April 13.  Hasten COC 40 oz/A, Nortron 4 oz/A, and Progress 12 oz/A were applied on April 23 and again on May 17.  Dual II  32oz/A was applied on May 25, 2004.

  Experimental design was a randomized complete block with 11 treatments and 5 replications.  Individual plots were 6 rows (11 ft.) wide by 22 feet long.  Fungicide applications were made to the four center rows of each plot on July 14 and August 2 using a CO₂ backpack sprayer.  Applications were applied at 30 psi using XR 1102 nozzles.  All applications were applied at 25 GPA.  Weather conditions were clear, wind 0-5 mph and 82^oF for the July application and clear, wind 3-5 mph and 88^oF for the August application.

  Disease ratings were taken by plot on July 13 and August 2, with a final disease rating on September 8.  Both sides of recently matured leaves in each plot were rated for percent leaf area infected with powdery mildew using a 0-5 rating scale with the following values: 0 = no disease; 1 = 1-10%; 2 = 11-35%; 3 = 36-65%; 4 = 66-90%; 5 = 91-100%.  Percent mature leaf area diseased (%MLAD) was calculated from the average disease rating for each treatment.  The experiment was harvested on October 11. Roots were topped and the two center rows of each plot were dug and weighed using a tractor mounted two-row lifter. Two sugar samples of approximately 8 roots were taken for each plot and analyzed for sugar content and conductivity at Amalgamated Sugar Company’s tare laboratory at Nyssa, Oregon.

  RESULTS

  Disease onset was early and rapid. The average disease was 4% of the mature leaf area at the first fungicide application.

  The average disease ratings and % MLAD are given in Table 2.  Disease was uniform throughout the test, and there were no significant differences (LSD 0.05) in disease among treatments immediately prior to the first application.  All treatments except the Rubigan and Sulfur had significantly lower disease ratings than the untreated check on August 2.  However, on September 8, all of the treatments had significantly lower disease ratings than the untreated control. 

  Most treatments had significantly higher (LSD 0.05) gross yield, percent sugar, gross sugar, and recoverable sugar in lb/T and lb/A than the untreated check (Table 3). There were no differences, however, among treatments in conductivity and percent extraction. The increased gross return due to treatment, without deducting the cost of fungicide and its application, ranged from $47/A to $329/A based on the Amalgamated Sugar Company contract at $20.00 net return/100 lb sugar. 

  ACKNOWLEGMENT:  Appreciation is extended to Dennis Searle, Terry Cane, Robert Huffaker, George Schroeder, and Howard Binford of the Amalgamated Sugar Company LLC, for assistance in taking disease ratings.