It happens every year at about this time. Every single black locust tree on our road turns brown. This occurs gradually over about a 2-3 week period.
I first notice it when the leaves begin to turn a dull green. Slowly a light brown cast spreads over the trees and by late July, the foliage is completely brown. The damaged trees really stand out against the dark green oaks, cedars, and pines that make up the majority of the tree species along the road. It is especially obvious because the black locusts are among the tallest of the trees.
You can also see quite a few of these crispy black locust trees as you drive along many of the highways in Virginia. It looks like the trees have all died, but not so. The damage is caused by a small beetle called the locust leafminer (Odontota dorsalis).
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Most of the noticeable browning is caused by the larvae of these beetles which tunnel through the leaves feeding on the tissue between the upper and lower leaf surfaces. It is the “mines” left by their feeding that causes the leaves to dry out and turn the rusty brown color. The larvae pupate in the mines and when the adult beetles emerge in midsummer, they feed on the underside of the leaves leaving them skeletonized. It’s a double whammy! Quite often the trees eventually lose all their leaves.
Despite this seemingly major damage and defoliation, these trees are normally not adversely affected and are able to recover often putting out a second set of leaves (which are sometimes attacked by a second generation of the leafminers). However, if a tree is stressed for any reason, including stress from drought or lack of adequate nutrition, repeated defoliation due to these pests may further weaken the tree and result in its death.
In our area, locust leafminer infestations have been occurring year after year with little or no long-term effects on the trees. For the most part, they seem to be able to withstand the damage from these pests.
I sort of wish the leafminers would kill off a few of our black locusts, though! I’m not at all a big fan of these trees. We consider them a weed tree that pops up all over the place – mostly where we don’t want them. This is because new shoots (which eventually grow into new trees) develop along the extensive root system. Through these root sprouts, a single locust tree can give rise to an entire grove of trees. We find them popping up everywhere – in our vegetable garden, in our flower beds, in our orchard … They’re very annoying. If you cut them down, it just seems to encourage the development of new sprouts. Hmmm, pretty good survival tactic!
Normally, black locust is not grown as an ornamental tree so control of the locust leafminer is rarely necessary. However, if these trees are in your landscape, the browning of the foliage can be quite unattractive! If desired, you can protect your trees from leafminer damage by applying Bayer Advanced 12 Month Tree & Shrub Protect & Feed II at the base of the tree according to the label directions. This will give systemic protection against these destructive pests. Always read and follow the label directions. This product may not be available in all states.
Until next time – Happy Gardening
The farmers in PA used to use them for fence posts because they didn’t rot.
Bill Bruce
Yes, that’s true and my husband, Eric, reminded me last night that locust honey is very delicious. We have also used the young saplings for bean poles. I guess the tree does have a few more redeeming qualities than just pretty flowers. But it’s still annoying when they pop up from a root sprout in the middle of my vegetable garden when the closest tree is at least 50 feet away!
Hi, I’ve been enjoying reading your blog. You wrote about Voles back on 4/20/12. My plants started disappearing in 2010. So I started trapping them. I trapped 61 voles last year. My yard is so much better this year. The count so far is 13. I’m glad to see the number of voles has declined. A mouse trap, peanut butter and a pot covering the the trap and hole is all you need. I have a trap set up in the vegetable garden now. One is attacking a tomato plant. I need to get him quick.
Cheers,
Louise
14 and counting. I hope that will be then end of the voles. I’m picking cukes, tomatoes, swiss chard and peppers every day now. My residence is in zone 7, Stafford, Va. Since we have had such a drought this year, I’m planting fall crops in a furrow. I have small raised beds but will try anything to keep the water on what needs to grow. What zone are you in? It helps to relate.
Cheers,
Louise
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