Question from Barbara:
My daughter called me last night, upset because she discovered that many of the cherries she and her son had been eating (from their own tree) contained little white worms.
They live in Pleasant Hill, CA (Contra Costa County) and have never had this problem before. The tree is several years old, located in her front yard which faces south.
We’ve searched IPM info, but can’t find any suggestions that would eliminate the problem for next year – except really serious pesticide spraying.
Is it possible to grow organic cherries? Do you have any suggestions?
Answer from Pat:
Tiny white worms are an increasing problem with home-grown cherries of both sweet and tart varieties. These worms are the larvae of the Western cherry fruit fly (Rhagoletis indifferens Curran), first discovered in Colorado in the late 1990′s. The first thing to do is to report this infestation to your local agricultural department or UC Farm Advisor. It’s important that these agenciest monitor this pest since it threatens commercial groves.
The larvae of Western cherry fruit fly don’t harm human beings who have accidentally ingested them since they are not adapted to living in human intestines, and they are mainly, after all, made up of cherry meat, but it is certainly a disgusting thought to know you have been eating worms. Western cherry fruit flies emerge in spring from pupa that have wintered over in the ground under the trees. As soon as they emerge they fly up into the tree. These black flies are tiny with striped wings are sluggish flyers. People seldom notice them, but yellow sticky traps can catch them and tell you of their presence. Most stay in the same tree but some are blown by wind to other trees. Their lifespan is about 15 to 35 days. They can lay eggs seven to ten days after first emerging when the temperatures are about 75 degrees Fahrenheit to 85 degrees in daytime. They eat aphids and honeydew. Once they mature, they mate and females pierce holes into fruit, laying one egg inside each cherry. The eggs hatch inside the cherry and tiny larvae commence munching. After the larvae mature and get fat inside the cherries they drop to the ground and bury themselves in the soil under the tree where they pupate and remain in dormant state until emerging as flies in spring. Then, once again the process repeats itself. Unless checked they will become worse every year and will spread to all other cherry trees in your area.
Unfortunately, the solutions given by experts are often to spray fruit repeatedly to kill the flies before they can lay eggs. Also with a pest that occurs in various stages experts may recommend attacking it with various specific products to kill the pest at different times of year. Otherwise you couldn’t possibly get them all.
The safe way to get rid of this pest would be to interrupt its life cycle in an organic or natural way without using pesticides, but I don’t have a cherry tree and cannot try out these controls. What I recommend is cleaning up fallen twigs and leaves under the tree, then spreading a layer of dry bagged earthworm castings now under the tree to kill the worms as they fall to the ground. Cover the ground from the trunk to the drip line and a foot or two beyond. Earthworm castings contain chitinase which destroys chitin, the exoskeleton of insects. Insects are killed when trying to burrow through a layer of earthworm castings. Renew the castings in late winter to kill any remaining flies as they emerge and keep it up from year to year. A few fruit flies will migrate into your garden but the castings will get them so they won’t be able to proliferate. This system works for giant whitefly on begonias which have a similar life cycle in the ground under the plants and then emerging to attack the foliage. If you try it please report back with your results.
The Colorado State Cooperative Agricultural Extension recommends putting yellow traps into trees to make sure when flies are first present, and then repeatedly spraying the trees with Spinosad every seven days to get the various generations of flies while they are present. Spinosad is an organic spray but harms bees if used where bees are found. Also, I fear that using it in great quantities will eventually destroy its efficacy.
No related articles.