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ARS Home » Research » Publications at this Location » Publication #70281
Title: DICAMBA ANTAGONIZES GRASS WEED CONTROL WITH IMAZETHAPYR BY REDUCING FOLIAR ABSORPTION

Author
item HART, STEPHEN - UNIV OF ILLINOIS
item Wax, Loyd
item Stoller, Edward

Submitted to: Weed Technology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Development of corn hybrids that tolerate imazethapyr allows the use of imazethapyr for weed control in corn. When weeds are present that are tolerant or resistant to imazethapyr, inclusion of a growth regulator herbicide such as dicamba may be desired. In our field work, adding dicamba to a tank mix with imazethapyr reduced grass control normally achieved with imazethapyr. Thus we conducted experiments in the greenhouse and lab to confirm if this antagonism of grass control occurs, to determine why it happens, and to provide means of overcoming this problem. Three grass species were evaluated: shattercane, giant foxtail, and large crabgrass. We found that sodium dicamba did reduce the effectiveness of imazethapyr for grass control, when the two were used in combination in a tank-mixture. The reason for this reduction in control was due to dicamba reducing the amount of imazethapyr that was absorbed by the plants. Reduction in absorption and retention appeared to be due to the sodium salt of dicamba, rather than the parent acid of the dicamba itself. MSO (methylated seed oil) as an adjuvant was much more effective than NIS (non-ionic surfactant) in promoting absorption of imazethapy and reducing the level of antagonism toward grass control. The addition of AMS (ammonium sulfate) to the spray mixture maintained imazethapyr at normal absorption and retention rates, and thus prevented any antagonism of grass control. These results have identified a potential problem, explained why it occurs, and provided a solution to the problem. These findings should be beneficial to those in the weed science community who are involved in planning weed management programs in corn.

Technical Abstract: Greenhouse and laboratory studies were conducted to determine the effects of tank-mixing the sodium salt of dicamba (Na-dicamba) with imazethapyr on the efficacy and foliar absorption of imazethapyr, applied with non-ionic surfactant (NIS) or methylated seed oil (MSO), by shattercane, giant foxtail, and large crabgrass. The effects of various salt formulations of dicamba and the addition of ammonium sulfate on efficacy, 14C-absorption and on foliar spray retention by the same species were also evaluated. Na-dicamba antagonized imazethapyr efficacy by reducing 14C-absorption. Using MSO instead of NIS prevented antagonism when Na-dicamba was applied at 70 and 140 g/ha and reduced the severity of the antagonism at greater application rates by greatly increasing 14C-absorption compared to NIS. Reductions in 14C-absorption and spray retention were due to the salt formulations of dicamba rather than the parent acid. The addition of ammonium sulfate prevented dicamba antagonism of imazethapyr toxicity to grassy weeds by maintaining 14C foliar absorption and spray retention at normal levels.