Weeds, insects come and go in Illinois crops

2017-07-12T16:30:00Z Weeds, insects come and go in Illinois cropsBy Nat Williams, Illinois Farmer Today Illinois Farmer Today

Goodbye, sudden death syndrome and cocklebur. Hello, frogeye leaf spot and Palmer amaranth.

While Illinois farmers today face many of the same pests they did decades ago, there are also some crop challenges that vary over time. SDS and cocklebur haven’t actually disappeared, but they don’t carry the same threat as other pests that have entered the scene more recently.

University of Illinois weed scientist Aaron Hager is quick to point out that despite the efforts of farmers and those serving them, man cannot claim victory over Mother Nature.

“It’s pretty safe to say that we’ve not eliminated any plant species we call weeds, at least not since the 23 years I’ve been at Illinois,” Hager said. “Eradication is generally unlikely. That’s because your seed bank is such that you’ve got a tremendous buffer. Rather, we refer to population shifts. Species become more common, and species become less common.”

Levels of weed infestation fluctuate due to management factors such as crop rotation or herbicide applications. Palmer amaranth is one weed that has made an impact in recent years.

“Palmer has been in Illinois for decades. It’s not something that just popped up here recently,” Hager said.

Use of large machinery in modern farming operations have led to instances of Palmer amaranth spreading relatively quickly across Illinois.

“It’s partly because of the method of seed introduction,” he said. “It’s something we’ve not experienced before. Forty to 50 years ago, you didn’t buy machinery that traveled long distances.”

Today’s farms typically are spread across counties and even states.

“When I was a kid, we farmed 1,500 acres that was probably within a 6- or 7-mile radius,” Hager said. “Now you’re talking people who are farming six or seven states, and moving this equipment. So the scale has changed.”

Latest challenges

One disease that has infiltrated soybean fields in recent years is frogeye leaf spot. It is among foliar diseases that have been on the uptick since the drought year of 2012.

“Last year we had reports even in Iowa,” said Jason Bond, a plant pathologist at Southern Illinois University. “It’s all over the Midwest. Even in southern Illinois, where we’ve dealt with it for several years, it’s becoming more and more challenging.”

Farmers have also seen insect threats come and go. Among the latter are corn borer and corn rootworm. That is largely due to plant genetic engineering.

“As we’ve gone from conventional corn into this transgenic era, those populations have been drastically reduced,” said Kelly Estes, survey coordinator with the Illinois Cooperative Agriculture Pest Survey Program.

“With refuges, we still have pockets around Illinois of people growing conventional corn, and you still hear of corn borer. But they are much lower numbers than what we’ve seen in the past.”

Other insects are emerging as a force to be reckoned with, however. They include Japanese beetles and brown marmorated stinkbugs.

“In terms of soybeans, Japanese beetles are everywhere this year,” Estes said. “They’re hitting hard and heavy through several areas of the state. When I started in Extension in 2003 I remember first report of Japanese beetles in Quincy. It was a huge deal. Now western Illinois has very high populations and lots of Japanese beetles.”

Causes include mild winters, which favor insect survivability.

Brown marmorated stinkbugs, which are moving into the state from the East, have been reported in 34 counties in Illinois, mostly in urban areas, where they are little more than minor pests for homeowners. But there is potential for crop damage.

“They’re pretty well established out East,” Estes said. “When populations got really high, three to five years after that, they started seeing injury in corn, soybeans, apples and other crops.”

Sudden death syndrome, a soybean disease so named because it can rapidly kill soybean plants after infestation, has for years been on the cusp of being a major problem in Illinois. But weather patterns have curbed its spread, for the most part.

“We haven’t seen that in at least seven or eight years,” Bond said. “But that’s one that people still need to be conscious of.”

Major shifts

Hager has witnessed some major shifts in weed infestations in his more than two decades at the university. Some once-troublesome species have virtually disappeared, though they are not gone.

“I haven’t been asked a question about how to control cocklebur in 20 years. Nightshade, also probably that long also,” he said. “We’ve effectively controlled these populations.

“Johnsongrass was the bane of the southern portion of Illinois for decades. Farmers struggled to control it. Finally, Accent and Beacon came on the marketplace; they were the first effective herbicides. It was the same with shattercane and dogbane. I can remember seeing patches encompassing acres. Rarely do you see patches of dogbane anymore.”

Foxtail is another weed species that has been effectively controlled.

“It’s still there, but not on your list of troublesome weeds,” Hager said.

Now, waterhemp tops that list.

“Many people, if you’d asked 30 years ago what waterhemp is, they wouldn’t know,” Hager said. “But now it’s your No. 1 broadleaf species across much of the acreage in the state. How fast this thing has become established in the state is absolutely remarkable.

“Our strategy so far is, we’ll throw something at it. If it quits working, we’ll throw something else at it.”

Will farmers someday be hard-pressed to remember waterhemp? Not likely, at least in the near future.

“It’s hard to imagine there will be anything we’ll be dealing with that will give those species a run for their money,” Hager said. “There will be eventually, but I’ll be retired.”

Copyright 2017 Illinois Farmer Today. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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