Crop Invaders - 4

Trio of New Threats

Pamela Smith
By  Pamela Smith , Crops Technology Editor
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Clockwise from upper left: Cotton leafroll dwarf virus (photo by Tom Allen, MSU); random oversized cotton plants that whip above the canopy are one symptom plants may be infected with CLRDV (photo by Tom Allen, MSU); spotted lanternfly (Pennsylvania Department of Agriculture photo); and gall midge larvae begin as white maggots and turn orange as they mature and devour the inside of soybean stems (photo by Justin McMechan, University of Nebraska).

Just when you thought you'd battled every crop pest under the sun, an all-new problem pops up. How problematic the threat becomes is sometimes a question, but early awareness is key.

Here are three new invaders scientists are currently working hard to figure out:

SOYBEAN GALL MIDGE

Wayne Martin may not plant many soybeans this year. The Shelby, Iowa, farmer isn't sure he can stomach another round with soybean gall midge, a pest that showed up in his fields in 2018.

The maggotlike critter eats away inside soybean stems until the plant dies. It's now in parts of Iowa, Minnesota, Missouri, Nebraska and South Dakota.

Giant leaps have been made in understanding gall midge habits, said Justin McMechan, a University of Nebraska entomologist. "The challenge is there is still no practical way to manage the pest without limiting the yield potential of the crop," he noted.

Scientists have identified the adult -- an entirely new species of midge. In 2019, McMechan found adult flies emerging and laying eggs continuously in June and July -- the long emergence period means that insecticides can't be the only means of control. Also, the orange larvae overwinter in the soil.

Early planted soybeans sometimes suffer more because adults prefer laying eggs in the cracks that open naturally in the soybean stem around V3. McMechan said alfalfa and sweet clover were identified as alternative hosts, but soybean fields planted near soybeans that were infested last year are likely most at risk.

"We are sharing information as fast as we get it, but farmers need to understand that many of our findings aren't replicated and to expect changes in what we know," McMechan said.

COTTON LEAFROLL DWARF VIRUS

Those strange-looking cotton plants that whip above the late-season plant canopy may actually be infected with cotton leafroll dwarf virus (CLRDV). Transmitted by aphids, the virus causes cotton leafroll dwarf disease (CLRDD) in cotton.

CLRDV is difficult to diagnose, as symptoms vary and can mimic other production issues. Compact internodes in the terminal, leaf discoloration, tissue reddening, leaf rugosity (puckering), reduced boll set and late-season vegetative growth are common clues.

However, Tom Allen, Mississippi State University plant pathologist, said plants that appear to be symptomatic don't always test positive for the virus, and infected plants don't always have symptoms.

Documented in Alabama in 2017, the virus and disease have now been confirmed in numerous states across the Cotton Belt.

"We're working hard to unlock its secrets and advising growers not to panic," Allen said. "So far, CLRDV isn't presenting huge yield losses, but we want to keep it that way."

SPOTTED LANTERNFLY

The spotted lanternfly's bold coloring and spotted wings combine with a large body to make it a visible invader. Still, its proclivity to lay eggs on nearly any flat surface like car bumpers and railroad cars also turns it into a moving threat.

While currently causing havoc in the mid-Atlantic states, University of Missouri entomologist Kevin Rice urged Midwest farmers to watch for the pest. "Most insects are really good moms and like to put their eggs where they can survive by eating that host," Rice said. "This pest is an indiscriminate egg layer, and the transportation element threatens a potentially explosive spread."

The lanternfly is partial to the tree of heaven (Ailanthus altissima) but feeds on 70 different U.S. crops and plants. Last year, USDA made $17.5 million in emergency funding available to stop the pest's spread in Pennsylvania, where it has caused damage to stone fruits, grapes and residential properties.

If you find one of these bawdy invaders, contact your local Extension office or department of agriculture.

Pamela Smith can be reached at pamela.smith@dtn.com

Follow her on Twitter @PamSmithDTN

(ES/AG)

Pamela Smith

Pamela Smith
Connect with Pamela: