A reader from California contacted us about some cottonwood trees he planted outside of his apartment building. He planted these trees several years ago, but is just now beginning to notice some damage to the trees. After doing some research on the problem he believes the issue might be cottonwood borers. Although he has never seen any of these creatures, he has seen some evidence of their molting. For those who are curious, molting is shedding old skin, hair, or feathers to make room for new growth. Finally, he found a living organism while breaking up some branches. He sent us a photo of the creature he discovered and requested any information we can provide.
The creature is round, small, has a white body with small legs, and a brown head. This is definitely a grub, or the larvae of a beetle. As our reader suspected, we believe this is the larva of a cottonwood borer. Cottonwood borers are part of the long horned beetle family. They depend on cottonwood trees for their livelihood.
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Small trees that are planted in stressful environments attract more of these borers than healthier trees. Our reader planted his trees in a small patch of dirt between the sidewalks and street in Los Angeles. This “stressful environment” could be why his trees are struggling. Cottonwood borers can also cause malformation of new branches because they feed on sensitive new growth areas.
It can be very difficult to eliminate these creatures from cottonwood trees. Since the larvae live within the trees and don’t leave emergence holes, it can be hard to find them or even know if they are there. There are some chemical options that our reader can explore at a local gardening store if he is interested.
Overall, we think it might be best that he attempt to plant something that will survive better in an urban environment.
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To conclude, a reader found a grub in the branch of his cottonwood tree. We believe it is the larva of a cottonwood borer.