Every spring and fall I find these skinny beetles with heads like grasshoppers that chew on my dogwood and redbuds. They seem to cut around the branches making a cut which goes deeper and deeper. Sometimes the branch is cut off and then I find them doing this to another branch! Why are they cutting down my tree? I don’t see them eating any of the leaves or the bark. It’s like they’re just gnawing on the limbs and branches.
TWIG GIRDLER BIOLOGY
These are either twig girdlers or twig pruners. They typically target trees like basswood, bradford pear, cherry, dogwoods, elm, hickory, honeylocust, hackberry, oak, pecan, persimmon, poplar, redbud, wisteria and various other hardwood or fruit trees. Twig pruners are more active in the spring and twig girdlers are mostly active in the fall. Both are cutting branches so they can lay eggs because their young eats wood when they hatch.
TWIG GIRDLER DAMAGE
So after she cuts (or girdles) the branch, females will lay eggs in the fresh pulp down toward the center of the branch. Many times the branch will fall off the tree as it dies and rots. When the egg hatches, the larvae will feed on the dead branch (cellulose). They need the wood to be dead which is why the female cuts or girdles the limbs. This insures the twig will die and be good food.
Here is what twig girdler damage looks like. Notice the limb targeted is less than 1 inch wide.
The larvae of both species will feed for a month or two and then go into a stage known as the pupae. The pupae typically hatch out adults which want to continue the cycle. Trees which experience activity will tend to have more and more activity. This happens because females leave a scent that other girdlers and pruners can smell. Twig girdlers can detect these scents from great distances and will come from far and wide to take advantage of a good tree to girdle.
TWIG GIRDLER TREATMENT
To stop the damage, you’ll need to spray the targeted trees. Treatments usually only need to be done once in the spring just before the activity starts and then again in late summer before they start their fall egg laying. There are two products that work well for this; one is a natural insect repellent and the other is a true pesticide that will last a lot longer and provide the best protection.
ORGANIC TWIG GIRDLER REPELLENT
The organic option is to apply some NBS INSECT REPELLENT to the limbs they want to girdle. It’s made from plant oils and insects will stay off treated surfaces. This spray won’t kill anything and is perfectly safe to spray on trees. Treatments will last 3-6 weeks. Expect to treat 1-2 in the spring and then 1-2 in the fall.
BEST TWIG GIRDLER SPRAY
The second option is a concentrate known as BIFEN. This product will provide a longer lasting residual and will keep both twig girdlers and twig pruners off treated surfaces for 4-8 weeks.
Be sure to spray the limbs they’ll target when treating. These are usually the smaller sized limbs toward the outside edges of the tree and not so much the sections close to the middle trunk of the tree. Any kind of sprayer will do but a HOSE END is usually most effective since you’ll have to reach up high in some instances to reach all the branches they might target.
So if you want to stop them from chewing and damaging, give the trees you want to protect a good spraying with one of the products listed above and this should do the job.
Hose End Sprayer: http://www.bugspraycart.com/equipment/sprayers/gilmour-20g-390
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