Weeds often emerge at the same time as vulnerable crop seedlings and sneak between plants as crops grow, so how do farmers kill them without harming the crops?
Seed and chemical companies have developed two major technologies to avoid crop injury from soil- and foliar-applied herbicides: genetically modified herbicide-tolerant crops and safeners, chemicals that selectively -- and mysteriously -- protect certain crops from damage.
In a recent University of Illinois study, researchers identified genes and metabolic pathways responsible for safener efficacy in grain sorghum, and the discovery goes a long way in explaining how safeners work.
After nearly 50 years of commercial use in corn, rice, wheat and grain sorghum, safeners remain a mystery, but figuring out how the protective mechanism switches on in cereal crops could one day help scientists induce protection in broadleaf crops like soybeans and cotton.
The first step is understanding what happens inside cells of cereal crops when exposed to safeners. The team used an approach known as a genome-wide association study. They grew 761 grain sorghum inbred lines in a greenhouse and compared plants treated with safener only, herbicide only or both. Scouring the genome for differences, they found specific genes and gene regions that were switched on in the safener-treated plants. In addition to finding a key gene for detoxification, the research also revealed a plant defense pathway pulling double duty.
The link to one of sorghum's allelochemicals, or chemical defenses, "was kind of a clue. Maybe the safener is tapping into a chemical defense pathway the plant is already using to protect itself," study co-author Dean Riechers said.
The ability to turn on defenses and protective pathways with safeners could have all sorts of applications, Riechers said.
"It doesn't seem logical there would be a pathway that's only specific for synthetic herbicides," he said. "Maybe safeners could be deployed to protect crops against insect herbivores, chemical pollutants or environmental stresses. The possibilities and applications are very promising."
In a year of uneven crop emergence, University of Missouri Extension agronomists say not to count out runts that emerge late.
"A late-emerging corn plant is better than no corn plant," MU Extension agronomist Bill Wiebold said.
Yield loss can happen when smaller plants compete for nutrients and sunlight with larger, earlier-emerging plants. Smaller plants likely produce barren or small ears.
MU Extension corn specialist Greg Luce said uneven emergence happens for several reasons including soil crusting, compaction, inconsistent and especially shallow seeding depth and differences in soil temperature. Seed-to-soil contact also matters. This year, cool weather provided fewer growing degree units, which are needed for corn to develop strong root systems and emerge uniformly.
But most uneven stands do not warrant replanting. "A ragged stand is better than no stand," Wiebold said.
"Although uniformity is the goal, the most important factor is the total plant population," Luce said. "Too many skips and a low plant count is what calls for replanting."