COLUMBIA, Mo. — After a late and wet start, 2019 crops have been trying to catch up while farmers deal with the annual challenges of pests, weeds and diseases.
In some cases, such as weed control, the planting delays have changed the usual timetable. However, when it comes to invasive Japanese beetles, this year is bringing more of the same.
Kevin Rice, University of Missouri Extension entomologist, says Japanese beetles are providing a challenge to crops again this year.
“We’re seeing similar trends that we’ve seen the last few years,” he says.
Speaking on July 2, Rice says the invasive insects should be hitting their peak around mid-July in Missouri.
“Two weeks ago they started, and we should be hitting our peak emergence in about two weeks,” he says. “We should see pretty high populations in July.”
Rice says the Japanese beetles have reached Missouri after a slow migration from the east.
“They’re actually a very slow-moving species,” he says. “They were introduced unintentionally in 1916 in New Jersey. It took them a long time to get to Missouri.”
Invasive species are especially a problem because their populations can grow rapidly in new areas where they have no natural predators, Rice says. But one remedy has been “classical biological control,” he says, meaning introducing natural predators. Wasps released in New Jersey in the 1920s as a control to Japanese beetles have started to show up in Missouri, Rice says.
MU researchers are also working on using nets to control Japanese beetles. They install the nets — treated to attract the bugs — next to fields. The beetles die after landing on the treated nets.
Rice says he recommends spraying for the bugs if plants reach 30% defoliation.
“Soybeans can withstand a lot of defoliation,” he says. “It mostly comes down to the cost of spraying. In corn, they mostly only damage the silks. When they feed on the silks during pollination (it can cause yield loss).”
On the upside, Rice says the wet weather has helped provide control for lepidopteran caterpillars.
“Because of the wet weather, a lot of the lepidopteran caterpillars have a fungus, so that’s providing some control for us,” he says.
Weed control timetable
Kevin Bradley, MU Extension weed scientist, says weeds sprouted aggressively after flooded fields dried out.
“Once the rains stopped and the floodwaters receded, I would say this year the biggest thing that happened was a pretty quick and sudden explosion of weeds,” he says. “Usually we have a slow process and people are able to stay on top of things better.”
Bradley says significant spraying is being done in July to try to keep weeds under control.
“A lot of them got too big, particularly marestail or horseweed,” he says.
For many crops, it’s been a race to get a canopy formed.
“Early season competition is the most damaging to yield,” Bradley says. “Get to canopy as early as possible.”
As for weather impacts during spraying, Bradley says the delayed planting and spraying schedule mean more spraying during hot and humid conditions this year.
“For Liberty Link, the humidity and the high temperatures are good,” he says.
However, Bradley says the warmer conditions can mean more risk for volatilization and movement of herbicides. He says there have been fewer dicamba drift concerns as of early July, but that is likely due to the timetable being pushed back. Bradley’s colleagues to the south have been seeing dicamba drift issues.
“As of last week the Missouri Department of Agriculture only had four or five cases,” Bradley says. “This season is so different. I’ve gotten a fair number of calls, but certainly less than the last two years. We haven’t done much dicamba spraying in the state, but we’re probably going to see some over the next two weeks. Everything is just so far behind.”
Bradley says another concern is resistance to group 15 inhibitor herbicides in neighboring states.
“We’re on the lookout for group 15 resistance,” he says.
Kaitlyn Bissonnette, plant pathologist for MU Extension, says the schedule is behind, but otherwise it’s a fairly regular year for diseases.
“We’re a little bit behind, but I’m not anticipating any extra disease problems,” she says.
One concern is where later-planted corn or replanted corn is next to older corn, a common sight this year.
“When you put younger plants next to older plants, the younger plants are more susceptible to disease,” she says.
Like most years, Bissonnette says the main disease concerns are stripe rust, gray leaf spot and northern corn leaf blight.
She says producers should also be on the lookout for soybean cyst nematode.
“Soybean cyst nematode is pretty well established in Missouri,” Bissonnette says. “Probably 75% of Missouri soybean fields have SCN.”
She says the flooding this year may have transported some of the nematodes as well.
Bissonnette says the main way to control SCN is crop rotation with non-hosts like corn, cover crops and grasses. Producers can also use resistant varieties.
“Most populations are building up resistance to the resistance,” she says. “Rotate resistant sources.”
However, she says 95% of SCN-resistant varieties use the same source of resistance, so this can be a challenge.
Overall, Bissonnette says this year’s crop still has a lot of potential, although it remains to be seen how it will fare.
“The season will tell us,” she says.