7 days ago
Kansas ash trees under attack from returning pest
MANHATTAN, Kan. (KSNW) — A pest that last made a major appearance in Kansas nearly a decade ago is back — and it's feasting on ash trees across the state.
Kansas State University entomologist Raymond Cloyd said the brownheaded ash sawfly is once again active, and residents are starting to take notice.
'We've had a number of inquiries regarding these caterpillar-looking insects,' said Cloyd, a professor in K-State's Department of Entomology. 'And they're not caterpillars — they're sawflies. It's important to make the distinction because certain insecticides will work on caterpillars but not sawflies.'
The insect's larvae — yellow-green with white and green stripes and a brown head — feed on the leaves of green ash trees, leaving behind shot holes before consuming entire leaves, often sparing only the veins. 'They feed with chewing mouthparts,' Cloyd said, 'and can compromise the aesthetic quality of the plant.'
This year marks the first widespread return of the brownheaded ash sawfly since 2016. The insect is specific to green ash trees and typically only produces one generation per year in Kansas.
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Cloyd noted that while the sawfly is not as destructive as the emerald ash borer, it can still leave trees severely defoliated. 'If they continue to feed, your tree won't have any leaves on it, and that's the issue,' he said.
Fortunately, there are a few simple ways to manage the problem. 'Heavy rainfall will wash them off,' Cloyd explained. 'You can use a high-pressure water spray to dislodge them, handpick them if feasible, or just let them go and know it will eventually stop.'
If the insects have already moved to the base of the tree, Cloyd suggests collecting them in a bag for disposal. 'At this point, it's almost getting too late to apply some type of insecticide,' he said. 'It's either live with it, handpick, or remove the ones that have migrated to the base of the trees.'
He also emphasized the importance of correct identification: 'Sawflies have prolegs—appendages on every section of the abdomen—while caterpillars typically don't. The feet of a caterpillar also have hairs or crochets, which sawflies lack.'
In most cases, Cloyd recommends avoiding insecticides unless the damage is extensive. 'If populations are causing significant aesthetic damage, contact insecticides can be applied, but thorough coverage of the canopy, especially the leaf undersides, is important,' he said.
For more details on identifying and managing the pest, K-State offers a free publication, Brownheaded Ash Sawfly.
Residents can also reach out to their local Extension office with questions.
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