Be aware of these threats to beans going into 2023

MOORHEAD, Minn. — Anthony Hanson talks about “who’s knocking on the door,” of farmers fields.

He’s referring to pests like the soybean gall midge and a leaf-mining insect that have established a foothold in Minnesota. Soybean growers also need to be aware of sudden death syndrome and other fungal diseases that have been spreading north.

Hanson, who works as a University of Minnesota Extension educator out of Morris, was letting farmers know what to look for in the 2023 growing season during the Best of the Best in Wheat and Soybean Research session on Thursday, Feb. 9, in Moorhead.

Hanson was showing growers examples of soybean leaves with white veins that will grow and eventually become puffy, like a tent. That’s a sign of a new pest, the tentiform leafminer. But the pest is so new that the name isn’t even official yet.

It so far is mostly known to be in southern Minnesota and mostly found along edges of fields where there are trees.

“When we haven’t been looking for it, we don’t know what the range is yet,” Hanson said. “That’s why we put the word out, ‘hey, we have a new pest species out there, be on the lookout for it.”

A pest that might be more familiar is the soybean gall midge . It mostly has been a problem in southwest Minnesota but it has the potential for 100% yield loss on field edges where it strikes.

“This is another one where it is feeding on the stem of the plant. It is basically a orange maggot you’ll find if you peel back the outer layer of the plant a little bit,” Hanson said. “Push the plants a little bit, if they’re heavily infested, the plants will literally just fall over.”

Scouting for it can be a challenge because the evidence of the midge will show up at the base of the plant and the adults are tiny.

“The adults are the ones out there laying the eggs; they're so small, they’re the size of a gnat. You’re not going to be able to see them easily, you’re not going to be able to identify them,” Hanson said.

There’s also a look-alike species, the white mold gall midge, that is slightly less orange and feeds on white mold. If there are no signs of white mold, the pest is likely the soybean gall midge.

A soybean disease that became more prevalent in 2022 is sudden death syndrome, but it can hit edible beans, too.

“The fusarium fungus that causes sudden death syndrome also can cause root rot in dry edible bean, so it’s not exclusively a soybean pathogen, although that’s where most of the research has been,” said Dean Malvick, plant pathologist with the University of Minnesota.

And the name isn’t very accurate. Sudden death syndrome could really be “slowly dying but not noticeable until it’s too late,” syndrome. Wet soil at planting helps it get started.

“The fungus infects the roots, probably within a month or so after the seed is planted, although we usually don’t see the main damage and disease until August,” Malvick said.

“What we look for typically in August is interveinal chlorosis, patches of yellow, between the veins on the leaves.”

Those leaves will turn brown, curl and ultimately fall off.

“What is really unique about SDS is how the fungus attacks the roots but it also produces a toxin that affects the leaves. So that’s where a lot of the damage occurs, a combination of the leaf damage and the root damage,” Malvick said.

Unfortunately, there isn’t much to be done about sudden death syndrome after it is found.

“Either we plant a resistant variety, if we can find one resistant against SDS, or we can use a few seed treatments that work against SDS, but obviously all that has to be done before planting or at the time of planting,” Malvick said.

Reports of sudden death syndrome have been creeping north in Minnesota and in North Dakota, it has been confirmed in Richland County in the southeast and Cavalier County near the Canadian border. Malvick said it is likely in other counties, too, but may be confused with a similar fungal disease.

“There are other diseases out there that can cause similar symptoms, such as brown stem rot, so it’s important to distinguish them and know which one is which because we want to manage them differently,” Malvick said.

Malvick encouraged growers to submit potential samples of sudden death syndrome to plant pathology labs at the University of Minnesota or North Dakota State University.

Hanson said if growers find evidence of a pest they are not familiar with, to take pictures and submit them to Extension.