Bing cherry most likely besieged by fruit flies

Feb. 19—Q: My Bing cherry tree is over 30 years old. The cherries had been beautiful and delicious. The last two years, inside the cherries at harvest, there have been white worms. What do we need to do to avoid the worms again this summer so we can enjoy a worm-free cherry harvest? — M.M., Albuquerque

A: I've done a lot of reading about this because finding small, white worms in your beloved cherry fruit, well, that's just gross.

I think the pest the fruit is hosting is called a Western cherry fruit fly but aiming to trap one for true identification would be difficult, so let me discuss prevention, OK?

The first step I believe you need to take will be getting the cherry tree sprayed with a dormant oil ASAP. The weather is going to turn soon, and dormant oil spraying can disrupt the blooming and leaf unfurling, so as long as the temperature is within label requirements, go for it.

The dormant oil concentrate needs to be applied at the recommended dilution through a hose end sprayer. You want to spray the whole tree top to bottom, inside and out. Aim for the most complete, soaked to dripping wet spraying you can humanly apply, and be sure to drench the trunk too.

Also, I recommend spraying the soil underneath the tree. It's a good way to begin a growing season by eliminating a few other pests that might be hanging around. Since you've been living with this tree for 30 odd years, I suggest you tend to it as usual, fertilizing and watering like you have been.

The next step will be after the fruit set and the small green cherries are forming. Nothing I read suggests spraying the tree while it's in bloom. You certainly don't want to harm any bees or other pollinators the tree will attract.

Now, as soon as the small cherries start to barely change color you'll want to spray with a pesticide containing either pyrethrin or spinosad, again through the hose end sprayer. Once the fruit has set, the adult female fruit fly will have finished pupation, exit the soil as an adult and be hunting a place to lay her eggs.

The green fruit is too hard for the newly hatched fruit fly to bore through, so that's why you need to start spraying just as the fruit barely starts to change color. Everything I've read suggests spraying once every ten days until you harvest.

The next lesson I learned is to consider laying weed fabric under the tree. You do this so if any of the worms have made it to their next stage in life they don't fall to the ground, bury themselves and pupate over next winter to start their cycle all over again next year. Also, don't allow any fruit that you don't harvest to fall and stay on the ground. You need to keep the area under the tree as tidy and clean as possible.

Another trick is to hang pieces of yellow poster board in the tree that you have smeared with Vaseline or a product called Tanglefoot. The yellow color attracts bugs and the gooey stuff traps them. Make new yellow hanging traps often to keep the gooey stuff gooey. You'll be amazed not much sand gets caught too.

One more thing, go out and poke around the soil looking for any copper-rust-brown colored things that look sort of like a plump piece of wheat seed. If you find any, collect and drown them in a glass jar. Those are the fruit flies that are in the process of pupating, so if you can prevent them from continuing their lifecycle to adulthood, you'll be ahead of the game.

I have no explanation as to why your tree started hosting what I believe from your description is the Western fruit fly, but if you are diligent and keep your tree as healthy as you can, you could just enjoy a worm-free cherry harvest again.

Good luck and Happy Diggin' In!

Tracey Fitzgibbon is a certified nurseryman. Send garden-related questions to Digging In, Albuquerque Journal, 7777 Jefferson St. NE, Albuquerque, N.M. 87109, or to features@abqjournal.com.