Warm weather is lasting well into the fall in parts of the northeastern U.S. All the more reason producers there should check timothy and other grass hayfields, as well as small-grain fields, for signs of grain aphids, says John Tooker, Penn State University Extension entomologist.

“Small populations of aphids, no matter the time of year, are usually not a problem, because these small, sedentary, soft-bodied insects are sitting ducks for many common predators like lady beetles and damsel bugs,” he says. “But this late in fall, natural-enemy populations have been reduced by a few frosts, while aphid populations are more resilient and able to withstand the cold temperature longer, providing them a window of predator-free time.”

Under the right conditions, he says, economically damaging populations can develop.  “In some cases, these large populations can induce a color change in the crop, causing small grains to turn yellow, brown or even purple at the tips of leaves.

“And then this color will slowly spread down the plant. This color change is often the clue that aphids are in the field, revealing populations that should have been detected earlier with scouting,” he says.

Beyond the threat of small aphid populations becoming large, aphids can also increase the risk that barley yellow dwarf virus (BYDV) will spread. “This pathogen may not be evident until spring, but may be acquired by small aphid populations feeding in fall.”

If populations exceed 25 aphids/foot of row, Tooker recommends treating that portion of the field with an insecticide.