MO crop late summer

Crops have faced challenges from weeds, bugs and diseases, but overall it has been a good year for pest management. 

For farmers, each year brings its own challenges in the battle to protect crop yields from weeds, bugs and diseases. The top pest management threats can vary from year to year, although some remain as obstacles.

One of those familiar foes is waterhemp. Kevin Bradley, University of Missouri Extension weed scientist, says it has been an effective year for weed control.

“It was pretty good overall,” he says. “We had timely rains. We didn’t have too much trouble getting things sprayed when we needed to get things sprayed. … Any failures we saw can’t be blamed on environment.”

Bradley says there were still fields where weed problems persisted, but it was mostly due to other factors, like increasing weed resistance.

“Most of our waterhemp now is glyphosate-resistant,” he says.

MU researchers are working to document which waterhemp populations are resistant to which herbicide controls, Bradley says, as well as looking at other management control options to complement herbicide use.

Another issue this year was wet weather during planting, which can allow weeds to get a jumpstart against crops.

“The problems in wet years are just can we get on the land,” Bradley says.

Palmer amaranth remains a growing concern in the state. Bradley says waterhemp and palmer amaranth are regularly the top two weed concerns for farmers in Missouri.

“It’s pretty consistent,” he says.

As for insect pest concerns, MU Extension state entomologist Kevin Rice says weather is a key factor. This year, some fields saw spider mites popping up as a concern, especially as conditions turned hotter and drier in August.

“They’re pretty patchy,” he says. “But they’re very associated with weather conditions, the dry droughty weather.”

Rice says the spider mites can double in population about every five days in dry conditions, and untreated fields can see rapid population growth. It is important to scout fields.

“Scouting is key for all our insect pests,” Rice says.

Spider mites can be tough to see since they are only about 1/60th of an inch, although they usually show up along field borders or waterways and cause injury that looks like yellow speckling or spots on soybean leaves. The injury can spread across fields as populations increase and can even cause leaves to turn brown and drop.

“They can be extremely damaging to yields,” Rice says. “If they are left untreated in soybeans, you can see up to 60% losses.”

Japanese beetles have been a concern in recent years in Missouri fields, although the previous year’s weather often determines to what extent, Rice says.

“Last year we expected reduced population levels because of the drought we had in 2018,” he says. “This year, we did hit threshold peak in July, for 30 to 40 days. We are seeing a rapid decline in our traps right now.”

Another ongoing pest development is the arrival of the soybean gall midge in Missouri, Rice says. MU Extension personnel confirmed the invasive pest was in Atchison County last year, in northwest Missouri, and it has spread to a neighboring county this year.

“Unfortunately it is starting to spread,” Rice says. “We did detect it in Holt County this season.”

Researchers are working to learn more about the midge and the best ways to control it.

“They are coming from our neighboring states,” Rice says. “We had been expecting this to happen.”

There have been a few disease concerns this year, including bacterial leaf streak and tar spot in corn, and sudden death syndrome (SDS) in soybeans.

Kaitlyn Bissonnette, MU Extension plant pathologist, said in a release that bacterial leaf streak and tar spot first appeared in Missouri corn in 2019, and they have been an issue for surrounding states.

“Missouri is late to the game,” she says. “Kansas, Nebraska, Iowa and Illinois have reported the presence of BLS for several years.”

Bissonnette says SDS begins in soybeans in years with a wet spring, like this year, when the soil-borne pathogen that causes the disease infects soybean roots. Too much rain during reproductive growth stages can allow the toxins to move from the roots to the leaves, showing up as yellow blotches between leaf veins that turn brown in the center. Yield losses can be as high as 80%, although the most common yield losses from SDS are 5-15%, according to MU.

Farmers in different areas of the state have seen issues with SDS, although it has not been too extreme so far.

Danny Kuenzel, who farms in Washington and Franklin counties in east central Missouri, says the hot, dry weather in August may have limited the impacts of SDS in his area.

“Sudden death in soybeans has appeared in many fields,” he says. “However, with the hot, dry weather it doesn’t look to be any worse than other years when it shows up this late, in my opinion.”

Ben Herrold is Missouri field editor, writing for Missouri Farmer Today, Iowa Farmer Today and Illinois Farmer Today.