Larvae/small white worms in tart cherries

Question: I have two Northstar dwarf cherry trees i my yard that were planted nine years ago.  I’ve had no disease or pest problems with them until this summer.  When I started pitting a batch of them recently, I discovered the many of them have small (

responder: The Question Asker Replied July 05, 2023, 4:17 PM EDT
response: The question I submitted a few minutes ago seems to have been cut off.  Here’s the complete version: "I have two Northstar dwarf cherry trees i my yard that were planted nine years ago. I’ve had no disease or pest problems with them until this summer. When I started pitting a batch of them recently, I discovered the many of them have small (<1/4”) white worms or larvae inside near the pit. From searching online it seems that these might be a type of fruit fly larvae. Is there anything I can do to control them going forward, without resorting to spraying chemicals. I have many flowers nearby so don’t want to hurt the pollinators. I’d read a suggestion online that one should pick and dispose of all the cherries to lesson the number that overwinter, but I’m not sure I can get all of them even with a ladder. Any suggestions? Thank you!"

responder: Terri   Replied July 05, 2023, 6:06 PM EDT
response: If they are 1/4" they are likely the cherry fruit flies. If they are smaller, they could be spotted wing drosophila. This gives some more info on the western cherry fruit fly. We are more likely to have eastern cherry fruit flies here than the western described, but they are very similar. : https://treefruit.wsu.edu/crop-protection/opm/western-cherry-fruit-fly/   See also  https://extension.umn.edu/fruit/growing-stone-fruits-home-garden#insects-2836760.   It is really important to clean up all dropped fruit so they don't overwinter. That and spraying are really the only options, but are not always totally effective or possible.  See https://hortnews.extension.iastate.edu/faq/i-occasionally-find-small-white-worms-my-cherries-what-best-way-control-them#:~:text=Answer%3A,one%2Dquarter%20of%20an%20inch.  Both the fruit flies and drosophila are serious problems. Some of the berry farms up here near Duluth have closed because they were unable to control the drosophila worms.   The cherries with worms are still safe to eat if that is any consolation.   Sorry!

responder: The Question Asker Replied July 06, 2023, 2:11 PM EDT
response: A few more questions: 1) How would these cherry fruit flies (or SWD) have gotten to my trees? Do they just travel from cherry tree to cherry tree through a neighborhood? Have had these trees for nine years with no problems until now. 2) A couple of neighbors w/in less than 1/2 block have tart cherry trees in their yards — varieties are different from mine.  Is it likely that there trees are also infested with the same pest that I have (cherry fruit flies or spotted wing drosophila)? 3) Is there a downside if I decide to keep the trees for aesthetic reasons, but give up on and not pick the cherries in future years? Would this make the infestation in my neighborhood worse? Thank you!

responder: Terri   Replied July 06, 2023, 8:09 PM EDT
response: The adult flies flew in from another property. They lay their many eggs in soft fruits like berries. The eggs hatch into the pupae (worms), which then burrow a few inches into the ground. They stay there all winter and emerge in the spring and start the cycle again. That is why it can be so hard to control the insects. If you are dealing with SWD on a raspberry, you can reduce infection by covering with a exclusion cloth. Cherry trees are usually too big to cover. The good thing is that the flies (both cherry fruit flies and SWD) have particular temperatures that they need for each life cycle, so if you chose to spray for the fruit flies, it is not something that needs to be done all season. But even if you wanted to spray and did it perfectly, the flies don't respect property lines and one or a hundred could come over from another yard.   Sometimes a cold winter can kill a lot of the larvae.   I wouldn't cut down the trees to protect the neighbor. They are likely to be dealing with the same issue or will be soon. If their cherries ripen later than yours, they may not see the worms because the pupae have dropped to the ground before they harvest, but they may see the damaged fruit.   Cleaning up the dropped fruit should do a lot to keep the population down. You never know when a bad winter or the emergence of a new predator will reduce the number of pupae to a level that you will be able to harvest the fruit again. And want to eat it.

responder: The Question Asker Replied July 07, 2023, 11:40 AM EDT
response: Thank you for all of the helpful info.  I think they are most likely the eastern cherry fruit flies since the largest ones are 1/4” or slightly larger (probably about 8mm).  There are smaller ones but I assume those are still growing. I will most likely try sanitation — keeping the cherries picked and off the ground — and hope for a cold winter.  I will probably not try spraying but curious if you have any thoughts on using need oil for this pest. A neighbor mentioned it as a possibility, but I’m guessing it may not be very effective if stronger pesticides have only limited success.

responder: The Question Asker Replied July 07, 2023, 11:43 AM EDT
response: I meant “neem”  oil.  Spell checker gets a little aggressive sometimes.

responder: Terri   Replied July 07, 2023, 2:27 PM EDT
response: Neem is a contact insecticide, meaning it has to hit the pest. It smothers them. That won’t work with these. it is tough when insects can’t easily be picked or washed off or something similar. Sorry!