Imazethapyr imazapyr, dicamba San 1269H, dicamba atrazine, mesotrione and atrazine applied postemergence for woolly cupgrass control in corn, Lewis, IA, 2002

摘要

The purpose of this study was to evaluate various preemergence and postemergence herbicide combinations for crop phytotoxicity and woolly cupgrass control in corn. The soil was a Marshall, Exira clay loam with a pH 6.0 and 5.0 percent organic matter. The experimental design was a randomized complete block with three replications and plots were 10 by 25 ft. The 2001 crop was soybean. Tillage included a spring field cultivation. Fertilization included 140 lb/Aactual N applied as anhydrous ammonia. Crop residue on the soil surface was 11 percent at planting. "Garst hybrid 8464 IT" corn was planted 2 inches deep on May 15, at 30,000 seeds/A in 30-inch rows. Preemergence (PRE), early postemergence (EPOST), and mid-postemergence (MPOST) treatments were applied on May 16, June 13, and 18, respectively, at 20 gpa and 30 psi using flat fan nozzles. Conditions on May 16 were: air temperature 16 C, soil temperature at the 4-inch depth 16 C, 12 mph wind, 100 percent cloud cover, 73 percent relative humidity. Conditions on June 13 were: air temperature 24 C, soil temperature at the 4-inch depth 21 C, 15 mph wind, 60 percent cloud cover, 40 percent relative humidity. Corn growth was V4 and 9.5 inches tall. Weed species, size and number per ft~2 in the untreated control included: woolly cupgrass two to four leaves, 3 to 5 inches tall, zero to thirty plants; velvetleaf three to five leaves, 1 to 4 inches tall, zero to ten plants; common waterhemp and common lambsquarters with numerous leaves, 0.5 to 6 inches tall, zero to fifteen plants. On June 18 conditions were: air temperature 27 C, soil temperature at the 4-inch depth 22 C, 15 mph wind, 45 percent cloud cover, 71 percent relative humidity. Corn growth was V4 to V5and 10 inches tall. Weed species, size and number per ft~2 in the untreated control included: woolly cupgrass three to four leaves, 3 to 7 inches tall, zero to seventy-five plants; velvetleaf three to five leaves, 1 to 4 inches tall, zero to one plant;common waterhemp and common lambsquarters with numerous leaves, 2 to 8 inches tall, zero to forty plants. May rainfall included: 0.14, 0.03, 0.11, 0.02, 2.51, 0.01, 0.23, 0.07, 0.32, 0.04, 0.03, and 0.23 inches on May 1, 5, 6, 10, 11, 17, 22, 23, 24, 25,28, and 29, respectively. Total rainfall for May was 3.74 inches. June rainfall included: 0.43, 0.88, and 0.02 inches on June 10, 11, 12, respectively. Total rainfall for June was 1.33 inches. July rainfall included: 0.87 inches and 1.16 inches from July 1 through 15 and 16 through 31, respectively. Total rainfall for July was 2.03 inches. Rainfall total for August was 3.23 inches.