Don’t spray wheat crop just yet, says Arkansas entomologist

From Delta Farm Press

Yes, those are stink bugs in your wheat field. No, you probably shouldn’t start spraying just yet.

That’s the assessment of Gus Lorenz, Extension entomologist for the University of Arkansas.

After weeks of significant rain and mud, “I guess it got dry enough to walk some fields today,” Lorenz said. “My phone was ringing off the wall with calls, mostly about stink bugs in wheat.”

It’s good that farmers are paying attention to those pests, but Lorenz cautions that it’s not yet time to break out the pyrethroids. That’s because the stink bugs – and, he notes, the true armyworm – are not yet being found in numbers that justify the expense and effort of spraying.

“There’s an occasional brown stink bug or sometimes a rare green stink bug, but mostly they are rice stink bugs,” he said of the insects being brought in from the field. “We are seeing fairly noticeable numbers of these stink bugs, but I haven’t seen or heard from anyone of the levels that I consider worth spraying.”

Stinkbug threshold

How many Stink bugs is that? The generally accepted threshold is one stinkbug per five to 10 heads while the wheat is in the milk to soft dough stage, which is where most of the Arkansas crop seems to be right now. That’s when they can do the most damage, said Lorenz.

Once you get into the hard dough stage, the stink bug can’t damage the kernel anymore. Still, said Lorenz, one bug per five to 10 heads isn’t really a lot, “so don’t get too excited.”

If you are seeing stink bugs, Lorenz advised farmers to pay careful attention to exactly where they are cropping up. The highest concentrations, he believes, are currently being found at the edges of fields — particularly in proximity to levees, tree lines and pastures. Move farther into the field and the stink bug count should drop off precipitously.

If a grower does decide to spray, though, Lorenz suggests that only spraying the field borders could be the best approach, with two passes sufficient to do the job. As always, follow the instructions on the label.

True armyworms

The other pest that’s starting to be found is the true armyworm, not unusual in the wheat crop at this time of year.

“The difference this year is they are still small and haven’t moved up the plant at all,” said Lorenz, “one of the few advantages of a cold spring, I guess.”

The worms that are being spotted range from about one-eighth to one-quarter of an inch in length and are remaining low in the canopy. Numbers seem to range from a low of one or two, to a high of four or five, per square foot. Most importantly, there hasn’t been any real evidence of cutting heads, which means there’s not any point at spraying yet.

“You are making money by not spraying,” said Lorenz. “We worked hard on that threshold, and I have every confidence that the yields are maintained once the wheat reaches the soft dough, even if they eat the flag leaf.”

If the populations had hit earlier, for instance at bloom or during the milk stage, that could have caused yield loss. But at the soft dough stage, “we should be fine.” All bets are off if the armyworms start cutting heads, though, at which point pyrethroids are again the product of choice. However, growers need to be sure there is a legitimate need before they start paying for spraying.

“I guess the gist of all this is scout closely and don’t get caught up in thinking you need to spray because there are a few pests out there,” Lorenz said.

For more information about pest management, visit, or contact your county Extension agent.

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