CHAMPAIGN, Ill. — Research findings focusing on the interactions of weather variability, weed control and crop management were revealed during University of Illinois’ virtual Agronomy Day.
Christopher Landau, U of I doctoral student, with Martin Williams, U.S. Department of Agriculture Agricultural Research Service scientist, and Aaron Hager, U of I Extension weed specialist, presented the findings.
“The overall goal of this research project was to determine the most important factors that can affect corn yield loss due to weeds,” Landau said.
“Over the next 30 years, rainfall and temperature patterns are expected to change and become more variable throughout the entire U.S., specifically in the Corn Belt where we’re expecting a shift toward wetter springs and warmer, drier summers.
“Most of the increased spring rainfall that we’re expecting is predicted to come more in the form of some more extreme rainfall events similar to what we’ve seen in the last couple of years.”
Rainfall and temperature have major impacts on corn yields. Too little or too much rain, or too hot or too cold during the wrong time of the season can severely reduced our corn yields.
However, little is known about exactly how the predicted variable weather will impact weed control and corn yield loss due to weeds in the future.
“So, to look at the interactions of weather, weed control and crop management, we used a rather large database of individual herbicide evaluation trials conducted between 1992 and 2019 by the Herbicide Evaluation Program at U of I. The Herbicide Evaluation Program conducts trials on both corn and soybeans,” Landau continued.
“Each trial in this current research contained only corn yield and weed control data for a variety chemical and non-chemical control treatments.
“By pulling all of these trials together and analyzing them together we were able to compared weed control and weed management practices across more than 200 unique weather environments.”
Competition
The first finding from the trials is surprise. Higher levels of weed control reduce yield losses. However, weeds that are completely uncontrolled can reduce yields by 50%.
The trials also found that poor control of waterhemp and foxtail species, specifically giant foxtail, is especially damaging to corn yields.
“Both of these species are of growing concern as they have and continue to develop more and more herbicide resistant populations and herbicide resistance severely limits the number of viable options we have to control these weeds and as such there’s a need for more integrated weed management strategies which utilize different mechanical, different cultural and our chemical control options all together to control these and some of the other problematic weed species that we have,” Landau said.
Most Susceptible
The second major finding from the research was that corn is most susceptible to drought stress at silking, or R1, and a couple of weeks leading up to the silking stage.
Moreover, it was determined that damage from drought was especially high in conditions of poor or no weed control. Poor water availability during these periods can reduce pollination and reduce kernel development.
“Poor or no weed control makes the situation much worse by taking a lot of the already low amounts of water away from the corn and further stressing it,” Landau noted.
“While we can’t control the weather, we can help reduce some of the yield losses by providing season-long weed control to prevent a lot of that competition for the water. We can choose more drought-tolerant hybrids and if possible utilize irrigation to subsidize the predicted lower summer rainfalls in the future.”
Planting Date
The third majoring finding from the research was that planting corn later in the season may help reduce some of the yield losses caused by uncontrolled weeds.
“We found that if the corn planting date was delayed until after May 4 they had roughly 23% lower yield losses compared to when the corn was planted before May 4. Delayed planting may help expose the corn to fewer weed species and lower densities of those weed species,” Landau continued.
“There’s been a recent trend toward earlier planting dates over the last 25 years which has been shown to provide several benefits to the corn such as more available days for crop development and earlier maturity and dry-down compared to some of the later planting dates. However, if weeds are not controlled adequately during the growing season, corn planted early is susceptible to high weed densities and some of the highest yield losses due to weeds.
“In the future with more variable weather an integrated weed management strategy which combines some of the different cultural and chemical control methods with the selection of a more drought tolerant hybrid and possibly delayed planting dates can be useful for reducing corn yield loss due to weeds under a changing climate.”