Ubaldo Torres noticed something strange when he visited his cotton herbicide drift research plots in summer 2022. Every row of young cotton plants sprayed with auxin herbicides, such as dicamba and 2,4-D, was covered in thousands of tiny crawling yellow and black specks.
Aphids had infested the injured plants, the then-Texas A&M University graduate student realized. And that infestation was spreading to neighboring rows. But the aphids seemed to completely avoid rows sprayed with certain other herbicides -- atrazine, paraquat, nicosulfuron and isoxaflutole -- and they avoided older cotton plants, as well.
The strange findings prompted Torres to alert his advisor, Muthukumar Bagavathiannan, fellow graduate student Purushottam Gyawali, and Texas A&M University entomologist Greg Sword. From there, Gyawali created his own strand of research investigating how aphids respond to cotton plants injured by different herbicides.
The research ultimately emphasizes just how intertwined weed and insect management are. Extension specialists, farm advisors and farmers need to consider how their weed management plans could influence other agronomic problems in the field.
Understand aphids
Aphids, or ‘plant lice,’ are small insects that suck sap from plants, which causes the affected plants to wither and even die. Aphids then produce honeydew from that plant sap, which covers the plant and eventually molds. Those insects also jump from plant to plant during their one-month lifespan, making them a vector for transmitting disease between plants.
Aphid infestation, understandably, stresses cotton plants and reduces yields. And the honeydew can coat cotton lint and create a sticky problem for cotton harvesters. The University of California reports that having as few as five aphids per cotton leaf late in the season can create harvest-disrupting honeydew accumulation.
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