Abstract
AbstractAcetochlor (WSSA Group 15) is a very-long-chain fatty acid–inhibiting herbicide used to control grass weed species in row crops and could potentially be effective when used in a rice herbicide program. A field study was conducted in 2016 and 2017 at four locations to determine the effects of acetochlor formulation and rate on rice tolerance. Overall, rice was more tolerant to the microencapsulated (ME) formulation of acetochlor than to the emulsifiable concentrate (EC) formulation, likely because of the potential for immediate absorption of acetochlor from the EC formulation following rainfall. Differences in rainfall among experimental sites and years caused variation in acetochlor activation and influenced crop injury. In all environments, PRE applications of either formulation resulted in the greatest injury at 2 WAT (61%), while injury following delayed PRE (DPRE) or early POST (EPOST) applications averaged 30% and 16%, respectively. When ME acetochlor was applied EPOST, rough rice yield was 97% of nontreated rice or 9,020 kg ha−1, indicating that applications should be delayed until this stage to minimize crop damage and maximize yield.
Highlights
Barnyardgrass [Echinochloa crus-galli (L.) Beauv.] has become resistant to a number of herbicides that were once effective in U.S rice production systems, including several acetolactate synthase–inhibiting herbicides, clomazone, and quinclorac (Heap 2018)
In 2016, rice was planted into relatively dry soil and received 1.4 and 0.9 cm of rainfall within 7 d after planting at the Pine Tree Research Station (PTRS) and University of Arkansas Pine Bluff (UAPB) sites, respectively (Figure 1)
Rice was planted into adequate moisture in 2017 and received an additional 2.5 and 4.0 cm of rainfall within 7 d after planting at PTRS and Research and Extension Center (RREC), respectively (Figure 2)
Summary
Barnyardgrass [Echinochloa crus-galli (L.) Beauv.] has become resistant to a number of herbicides that were once effective in U.S rice production systems, including several acetolactate synthase–inhibiting herbicides, clomazone, and quinclorac (Heap 2018). Very-long-chain fatty acid (VLCFA)-inhibiting herbicides (WSSA Group 15) are not currently labeled for use in U.S rice but have been used successfully in Asian rice production (Chauhan 2012; Rao et al 2007). This herbicide site of action includes the chloroacetamide, oxyacetamide, and pyrazole chemical families, which contain several herbicides used in U.S row crops, including S-metolachlor, pyroxasulfone, acetochlor, and flufenacet. The Group 15 herbicides inhibit cell division in developing shoots and roots of annual grasses and smallseeded broadleaves but do not affect emerged species (Babczinski et al 2011) They should be applied after rice germination but before weed germination. Because there is limited research available on rice tolerance to acetochlor formulations, and none on the EC formulation, experiments were conducted to determine the influence of acetochlor formulation and rate on rice tolerance to PRE, DPRE, and 1- to 2-leaf (early POST [EPOST]) rice timings
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