Abstract
Echinochloa crus-galli is the main weed in direct dry-seeded rice systems worldwide and is the target of most herbicide applications. Numerous cases of E. crus-galli biotypes with resistance to herbicides have been reported in different regions of the world; however, to date, no cases have been reported in Uruguay. The purpose of this research is to assess the presence of herbicide-resistant E. crus-galli in the rice fields of Uruguay. More than 40 E. crus-galli biotypes were sampled from eastern to northern regions in different years and assessed following the Herbicide Resistance Action Committee (HRAC) protocols of confirmation, using the herbicides propanil, quinclorac, clomazone, bispyribac–sodium, penoxsulam, imazapyr + imazapic, profoxidim and cyhalofop. Herbicides rates included 0, 0.125, 0.25, 0.50, 1, 2, 4 and 8 times the label rate. Most E. crus-galli biotypes (35) resulted as resistant to quinclorac. Furthermore, resistance was confirmed to propanil in at least seven biotypes, 12 to imazapyr + imazapic, and three to penoxsulam. Five biotypes showed multiple resistance to propanil and quinclorac, and one biotype was resistant to quinclorac, penoxsulam and imazapyr + imazapic. No biotype showed confirmed resistance to clomazone, bispyribac-sodium, cyhalofop or profoxidim—herbicides that ensure satisfactory control. The presence of E. crus-galli herbicide resistant-biotypes reduces herbicide options, threatening rice production in Uruguay. In this context, a redesign of the productive systems would represent an opportunity to complement the chemical control, integrating larger-scale cultural and management practices.
Highlights
Rice is one of the most important crops in Uruguay, with more than 90% of its production exported to many markets worldwide, where uniformity and quality standards are appreciated [1]
LCh01 susceptibility attracted our attention because it came from a field in which a rice–soybean-alternating rotation was in place from 1979 to 1988, followed by five years of continuous rice (R5Y). During this 10-year period, trifluralin alone or triflurain and imazaquin tank-mixes were used as preemergence in a non-glyphosate-resistant soybean crop. This management contributed to lessening the selection pressure on the E. crus-galli biotype, due to the fact that these herbicides present different modes of action than those used in rice
This paper contributes to establishing the presence of herbicide-resistance E. crus-galli biotypes in rice production systems in Uruguay
Summary
Rice is one of the most important crops in Uruguay, with more than 90% of its production exported to many markets worldwide, where uniformity and quality standards are appreciated [1]. With a rice area of 165 thousand ha and average yields of about 8.5 t ha−1, rice systems include an important proportion of the acreage in rotation with sown pastures and other crops [2]. This characteristic is well known, attracting the attention of rice specialists worldwide, and is thought to be responsible for the low input level associated with this high yield [3]. Beauv (barnyard grass) is the main weed in direct dry-seeded rice systems worldwide and, in Uruguay, is the target of most herbicide applications
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