PREEMERGENCE AND POSTEMERGENCE HERBICIDES FOR WEED CONTROL IN FIELD CORN

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1 PREEMERGENCE AND POSTEMERGENCE HERBICIDES FOR WEED CONTROL IN FIELD CORN Corey V. Ransom and Joey Ishida Malheur Experiment Station Oregon State University Ontario, OR 1998 Introduction These studies evaluated preemergence and postemergence herbicides for weed control and crop tolerance in furrow-irrigated field corn. Procedures Three trials comparing registered and experimental herbicides were evaluated for weed control and crop safety in field corn. The soil was Nyssa silt loam with ph 7.5 and 1.6 percent organic matter. Pioneer 5731 field corn was planted with a John Deere, model 71 Flexi Planter on May 19, 1998, at 26,800 seeds per acre in 30-in rows. The field was fertilized with 190 lb N/acre preplant, sidedressed on May 1. On July 1, 100 lb P/acre, 21 lb N/acre, and 10 lb Zn/acre were hand-broadcast to the entire trial. Plots were 10-ft wide by 30-ft long and replicated three times in a randomized complete block design. Herbicide treatments were applied with a CO 2-pressurized backpack sprayer delivering 20 gpa at 30 psi. Within the two weeks following application of the preemergence treatments, there was approximately 3 in rain providing excellent moisture for herbicide activation. For each trial, corn injury and weed control were evaluated throughout the growing season. Corn yield was determined October 23 by harvesting corn ears from the two center rows of each plot, threshing the ears, and recording the dry weight of the grain. Grain yields were adjusted to 12 percent moisture. On July 4, corn plants were partially defoliated by a severe hail storm. Balance for Weed Control in Field Corn Balance was evaluated alone and in combination with registered corn herbicides. Registered herbicides applied in combination with Balance were applied at 3/4 of the typical use rate. Herbicide treatments were applied May 19. Crop injury was rated as a percentage of injured plants on June 10, June 24, July 21, and August 13. Weed-population counts were made on June 10 and recorded as plants per square foot. Weed control ratings were made on June 24, July 21, and August 13. Preemergence Herbicides for Weed Control in Field Corn Experimental herbicides including Balance, Axiom, and Epic were compared to registered herbicides including Dual, Frontier, Prowl, Topnotch, and several herbicide combinations for weed control and corn tolerance. Herbicide treatments were applied May

2 Efficacy of Basis and Accent on Weed Control in Field Corn Basis, Basis Gold, Accent, and Accent Gold were applied at several postemergence timings. Basis plus Atrazine was applied as corn was just starting to emerge May 30. An early postemergence treatment of Basis was made June 8 when the corn was 3-in tall. Mid postemergence treatments were made on June 20 when the corn was 7-in tall. Accent was applied at a late-postemergence timing on June 24 at a crop height of 12 in. Results Because rainfall was above average during the spring, preemergence herbicide activity was high, and weeds were controlled extremely well. Balance for Weed Control in Field Corn All plots treated with Balance exhibited corn injury June 10 with the exception of Balance plus Dual II Magnum (Table 1). Injury consisted of stunting and some bleaching of the leaves. Balance applied in tank mixture with Dual II Magnum had less injury than Balance tank mixtures with Lasso, Frontier, and Axiom. By July 21, no significant injury was apparent for any treatment. Balance alone at lb ai/acre provided slightly less redroot pigweed control (92 percent) compared to the other treatments (98 percent). All treatments provided at least 97 percent control of common lambsquarters. Balance (0.059 lb ai/acre) alone was less effective in controlling barnyardgrass than when applied in combinations with other herbicides. Barnyardgrass control with all treatments ranged from 88 to 98 percent. Because of variability, differences in corn grain-yields were not significant among treatments. Preemergence Herbicides for Weed Control in Field Corn On June 6, treatments with Axiom or Balance alone and in combinations caused corn injury (Table 2). The highest rate of Epic (premix of Axiom and Balance) and the combination of Axiom (0.64 lb ai/acre) plus Balance (0.058 lb ai/acre) had among the highest injury. On July 21 Epic (0.544 lb ai/acre) still had significant injury (25 percent) which was mainly crop stunting. All treatments provided 90 to 98 percent control of redroot pigweed except for Dual Magnum, Dual II Magnum, and Dual II which provided 67, 47, and 45 percent control, respectively. Common lambsquarters control was also less than all other treatments with the Dual treatments as well as Topnotch and Frontier applied alone. All treatments provided greater than 89 percent control of barnyardgrass. All herbicide treatments increased corn grain-yield in comparison to the untreated check but, yields were not different among treatments. Efficacy of Basis and Accent on Weed Control in Field Corn For Basis and Accent treatments, no significant corn injury was observed throughout the duration of the trial (Table 3). Redroot pigweed control was not different among herbicide treatments (93 to 98 percent) while common lambsquarters control was greatest with Basis plus Atrazine applied to spike corn. Basis Gold applied at the mid-postemergence timing was less effective than Basis plus Atrazine but more 30

3 effective than the other herbicide treatments. Accent alone did not control common lambsquarters. Accent and Accent Gold provided greater barnyardgrass control (90 to 95 percent) than Basis plus Atrazine (63 percent) but was not significantly different from Basis and Basis Gold (75 to 79 percent). Corn grain yields were not statistically different among treatments, including the untreated check. Table 1 Weed control and corn yield with preemergence Balance combinations, Malheur Experiment Station, Oregon State University, Ontario, OR, Corn injury Weed controlt Corn Redroot Lambs- Barnyard- Treatment Rate pigweed quarters grass yield lb ai/acre % bu/acre Balance Balance Balance Dual II Magnum 0.83 Balance + Surpass Balance Harness Extra 1.5 Balance + Lasso Balance + Frontier Balance + Axiom Balance + Atrazine Lasso + Atrazine Untreated LSD (0.05) 14 NS NS t weed control evaluated July 21, tcorn yield taken October 23, 1998, then adjusted to 12 percent moisture. 31

4 Table 2. Weed control and corn yield with registered and experimental preemergence herbicides, Malheur Experiment Station, Oregon State University, Ontario, OR, Treatment Corn injury Weed controls Lambsquartergrass yields Barnyard- Corn Rate Pigweed lb ai/acre %- bu/acre Prowl Prowl + Atrazine Prowl + Dual II Prowl + Lasso Prowl + Frontier Dual Magnum Dual II Magnum Dual ll Atrazine + Dual II Axiom + Atrazine Axiom + Atrazine Balance Axiom + Atrazine Epic Epic Epic + Atrazine Axiom + Balance Axiom + Balance Balance Topnotch Frontier Axiom Untreated LSD (0.05) tweed control evaluated July 21, 1998 tcorn yield taken October 23, 1998, then adjusted to 12 percent moisture. Experimental premix of balance and atrazine with unknown percentage 32

5 Table 3. Weed control and corn yield with postemergence applications of Basis and Accent, Malheur Experiment Station, Oregon State University, Ontario, OR, Weed control* Corn Lambs- barnyard- Corn TreatmenttRate Timing injury* Pi weed quarters grass yield lb ai/acre % bu/acre Basis + Atrazine EMERG Basis + COC EPOST Basis Gold + COC MPOST Accent Gold+ COC MPOST Accent + COC LPOST Untreated LSD ( 0.5%) NS NS tcoc applied at 1% VN; applied at 2 qt/acre. *Corn injury and weed control were evaluated July 21. Corn yields were taken October 23, 1998, then adjusted to 12% moisture. 33