First report of severe tolpyralate sensitivity in corn (Zea mays) discovers a novel genetic factor conferring crop response to a herbicide.

BACKGROUND: Tolpyralate, a relatively new inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPPD), is registered for postemergence use in all types of corn (Zea mays L.) and has a record of excellent crop tolerance. A report of severe crop injury to sweet corn inbred (XSEN187) led to the following objectives: (i) determine whether sensitivity to tolpyralate in XSEN187 exists, and if confirmed, (ii) determine the genetic basis of tolpyralate sensitivity, and (iii) screen other corn germplasm for sensitivity to tolpyralate. RESULTS: Inbred XSEN187 was confirmed sensitive to tolpyralate. Inclusion of methylated seed oil or nonionic surfactant in the spray volume was necessary for severe crop injury. Tolpyralate sensitivity in XSEN187 is not conferred by alleles at Nsf1, a cytochrome P450-encoding gene (CYP81A9) conferring tolerance to many corn herbicides. Evidence suggests that tolpyralate sensitivity in XSEN187 is conferred by a single gene mapped to the Chr05: 283 240-1 222 909 bp interval. Moreover, tolpyralate sensitivity was observed in 48 other sweet corn and field corn inbreds. CONCLUSIONS: Severe sensitivity to tolpyralate exists in sweet corn and field corn germplasm when the herbicide is applied according to label directions. Whereas the corn response to several other herbicides, including HPPD-inhibitors, is conferred by the Nsf1 locus, corn sensitivity to tolpyralate is the result of a different locus. The use of tolpyralate should consider herbicide tolerance in inbred lines from which corn hybrids were derived, whereas alleles that render corn germplasm sensitive to tolpyralate should be eliminated from breeding populations, inbreds, and commercial cultivars. © 2023 Illinois Foundation Seeds, Inc and The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Deteriorating weed control and variable weather portends greater soybean yield losses in the future.

Since the 1950's much of the US soybean growing region has experienced rising temperatures, more variable rainfall, and increased carbon emissions. These trends are predicted to continue throughout the 21st century. Variable weather and weed interference influence crop performance; however, their combined effects on soybean yield are poorly understood. Using machine learning techniques on a database of herbicide trials spanning 28 years and 106 weather environments we modeled the most important relationships among weed control, weather variability, and crop management on soybean yield loss. When late-season weeds were poorly controlled, average soybean yield losses of 48% were observed. Additionally, when weeds were not completely controlled, low rainfall and high temperatures during seed fill exacerbated soybean yield loss due to weeds. Since much of the US soybean growing region is heading towards drier, warmer conditions, coupled with growing herbicide resistance, future soybean yield loss will increase without significant improvements in weed management systems.

Diminishing weed control exacerbates maize yield loss to adverse weather.

Both weed interference and adverse weather can cause significant maize yield losses. However, most climate change projections on maize yields ignore the fact that weeds are widespread in maize production. Herein, we examine the effects of weed control and weather variability on maize yield loss due to weeds by using machine learning techniques on an expansive database of herbicide efficacy trials spanning 205 weather environments and 27 years. Late-season control of all weed species was the most important driver of maize yield loss due to weeds according to multiple analyses. Average yield losses of 50% were observed with little to no weed control. Furthermore, when the highest levels of weed control were not achieved, drier, hotter conditions just before and during silking exacerbated maize yield losses due to weeds. Current climate predictions suggest much of the US maize-growing regions will experience warmer, drier summers. This, coupled with the growing prevalence of herbicide resistance, increases the risk of maize yield loss due to weeds in the future without transformational change in weed management systems.

Future efficacy of pre-emergence herbicides in corn (Zea mays) is threatened by more variable weather.

BACKGROUND: By 2050, weather is expected to become more variable with a shift towards higher temperatures and more erratic rainfall throughout the U.S. Corn Belt. The effects of this predicted weather change on pre-emergence (PRE) herbicide efficacy have been inadequately explored. Using an extensive database, spanning 252 unique weather environments, the efficacy of atrazine, acetochlor, S-metolachlor, and mesotrione, applied PRE alone and in combinations, was modeled on common weed species in corn (Zea mays L.). RESULTS: Adequate rainfall to dissolve the herbicide into soil water solution so that it could be absorbed by developing weed seedlings within the first 15 days after PRE application was essential for effective weed control. Across three annual weed species, the probability of effective control increased as rainfall increased and was maximized when rainfall was 10 cm or more. When rainfall was less than 10 cm, increasing soil temperatures had either a positive or negative effect on the probability of effective control, depending on the herbicide(s) and weed species. Herbicide combinations required less rainfall to maximize the probability of effective control and had higher odds of successfully controlling weeds compared with the herbicides applied individually. CONCLUSIONS: Results of this study highlight the importance of rainfall following PRE herbicide application. As rainfall becomes more variable in future, the efficacy of common PRE herbicides will likely decline. However, utilizing combinations of PRE herbicides along with additional cultural, mechanical, biological, and chemical weed control methods will create a more sustainable integrated weed management system and help U.S. corn production adapt to more extreme weather. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.