By JORDAN STRICKLER

Kentucky Correspondent

BRISTOL — A plant's biological clock could make certain times for spraying herbicides more beneficial than others. A new report out of the University of Bristol states that the timing of application can make a crucial contribution to crops' growth and their responses to fluctuating environments.

The researchers found that the death of plant tissue in weeds and slowdown in growth resulting from glyphosate depends upon the time that the herbicide is applied, due to the biological clock of the plant. Crucially, that clock led to a daily change in the minimum amount of herbicide needed to affect the plant, so less herbicide was needed at certain times of day.

This provides an opportunity to reduce the quantity of chemicals used, saving growers time and money and reducing environmental impacts.

While glyphosate was the primary herbicide used in the study, Dr. Antony Dodd, senior lecturer in Bristol’s School of Biological Sciences and senior author of the paper, said the same conceit could apply for multiple herbicides.

"We tested in the study a second herbicide active ingredient, diflufenzopyr, which also gave us a rhythmic response," he said. "More broadly, about 30 percent of genes in plants – at least in arabidopsis – have circadian rhythms, and many aspects of plant metabolism have daily or circadian rhythms.

“Herbicides tend to target metabolism or photosynthesis, and because so many aspects of plant metabolism have rhythms, it seems quite likely that the principle we identified might apply to certain other herbicides and/or other chemicals that are used for agricultural purposes."

The same practice is used in the medical industry explained Dodd, who compared herbicide application to the chronotherapy, or the rhythmic cycles of a condition's symptoms, for taking antibiotics. Human medications consider the body clock when deciding the best time to give a medicine or treatment.

This new research suggests a similar approach could be adopted for future agricultural practice, with crop treatments being applied at times that are most appropriate for certain species of weed or crop. By employing a form of ag chronotherapy, there might be a future role in the sustainable intensification of agriculture required to feed the growing population.

"In medicine, a really large proportion of drug targets have rhythms, which is why giving drugs at certain times of day can have a bigger effect," Dodd explained. "We have no reason to think that plants are any different, because herbicides are basically drugs that affect plant cells just like medical drugs affect animal cells."

Dr. Bill Johnson, professor of weed science at Purdue University, was involved in similar tests in the 1990s and said timing might be more physically related.

“It's fairly well accepted that there are a few weeds that do show some time-of-day effect with glyphosate. You can definitely see this with weeds like velvet leaf, morning glory, and even giant ragweed,” he noted. “With a lot of weeds dropping their leaves at night, it just stands to reason that you aren't getting as much herbicide on the plant.

“Also, if you have a lot of dew on the weed in the morning, like right after sunrise, you can have a delusion of the herbicide and have less-than-optimal activity.”