We have a cherry tree that gives us a lot of delicious cherries, but unfortunately we have found little worms in the fruit without any telltale signs on the outside of the fruit. What is this?

I'd like to have some cherries this year without these little invaders!

— Geri

What you have is called the western cherry fruit fly.

This is a small fly that overwinters in the soil as a pupa beneath your cherry tree. It emerges in the spring and the female lays eggs in the developing fruit of cherry trees. The larva hatch and feed on the ripening fruit.

You don't see much evidence of their presence superficially since the "sting" the female made laying the egg is very small. It's just when you open a cherry and see this small, disgusting maggot that you realize what's going on.

This little monster is pretty much everywhere in western Colorado. If you have a cherry tree, chances are you have some of these in the fruit of the tree.

Most people don't realize they're getting a little extra protein with each cherry. The bugs won't hurt you, it just grosses most of us out.

The most important aspect in controlling this guy is the timing of your insecticide sprays. Sprays should start about May 20, and you should spray every week or 10 days until harvest. The best sprays to use are Sevin, Permethrin and Spinosad.

I think it's a good idea to rotate the sprays. It does a better job of controlling the flies and avoiding unintended problems like insecticide resistance or outbreaks of other destructive pests such as spider mites.

Be sure to do a thorough job of spraying. You want to coat the developing cherries completely so when the female lands to lay her eggs the insecticide is there to zap her before she can lay them.

A common recommendation for control of other related fruit flies is to mix the insecticide with an attractant bait. It helps the insecticide last longer and will greatly enhance your control efforts.

There are baits available in the marketplace, but they are usually only available in large quantities for the commercial grower. Your best bet is to mix 4–6 tablespoons of molasses per gallon of spray. I haven't seen this specifically for cherry fruit fly, but I'd think it would work.

I have a tree that looks similar to an aspen. The tree appears to be struggling to come back, any suggestions for resurrecting the tree?

— Kevin

I don't have anything for sure to tell you, but assuming what you have is an aspen or other poplar, I'd worry a bit about a fungal disease called cytospora canker.

This can occur on a wide range of different host plants, but we see it overwhelmingly on aspen trees. It's a stress- related disease, attacking trees that are weakened for one reason or another.

We see it most often on newly planted trees, since they can often be under some stress in the digging and transplanting that goes on, and on older trees (15–20 years old) since that seems to be about the lifespan of an aspen in the valley. We also see it on trees that have been neglected.

Since I don't know any details about your tree, I'm not sure what's going on in your case.

The disease travels through the vascular tissues of the plant, killing them and choking the plant to death. Branches with small, sparse, pale green or yellow leaves or small twigs that fail to leaf out are usually the first symptom. That's followed by death of larger branches.

If your tree does have cytospora, I'm afraid you're eventually going to lose the tree and there's really nothing you can do about it. We don't have any fungicides that will do the job for you.

About all you can do is to cut the infected tissue out by completely removing the branch that's involved. That is usually not an option because by the time we figure out what's going on, the disease is in the trunk of the tree and you end up cutting the tree down anyway.

You might bring in a branch that is dying and one that's dead for us to look at to confirm this is what's really going on with your tree.

If you do have cytospora, you should remove the tree as soon as it's practical before the disease has a chance to spread to any other aspens.

Dennis Hill is the nursery manager at Bookcliff Gardens, bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506, or email info@bookcliffgardens.com.

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