Stopping Wormy Fruit in Cherries and Apples

Stopping Wormy Fruit in Cherries and Apples

Marianne C. Ophardt
Washington State University Cooperative Extension
Area Extension Agent  

There seems to be a great deal of confusion about the need for spraying fruit trees to control insects and diseases.  There are a number of pest problems on fruit trees that require frequent and regular chemical applications to keep the trees healthy and producing quality fruit.  When fruit trees are large, this becomes a difficult, costly, and time-consuming responsibility for their owners.  Smaller, dwarf trees are easier to handle, but still require regular attention.  Owning and caring for fruit trees is not a low maintenance endeavor.

One of the major pest problems faced by backyard fruit growers... the cherry fruit fly.  It’s first and foremost on the list because it’s the pest that causes worms in cherry fruit.  The adult of this pest is the cherry fruit fly.  The adult is a fly that begins to emerge from the ground in late may or early June.  The adult fly takes about seven to ten days to fly around and mate.  After mating, the female lays eggs underneath the developing cherry’s skin.  (No hole is visible in the cherry after she lays the egg.) 

The eggs hatch into small larvae, actually maggots, and begin feeding close to the pit. After about five to eleven days, the maggots each make one or two breathing holes in the skin. (These holes are small but visible.)  Several days after making their breathing holes the maggots are fully mature.  They exit the fruit and drop to the ground where they go into their resting pupae stage.  They spend the rest of the year as pupae in the soil until next spring.

While eating one of these maggots (yuk!) won’t hurt you, it’s certainly not appetizing.  An entire load of commercially grown cherries can be rejected if even one larva is found.  Control of the cherry fruit fly is aimed at killing the adult fly before she lays her eggs under the cherry’s skin.  Once they’re under the skin, pesticide sprays are useless in killing the developing maggot.  That’s why it’s so important to spray regularly and get rid of the flies before they have a chance of laying eggs.

To control cherry fruit fly, backyard cherry growers should recommended sprays regularly, every seven to ten days starting about Mother’s Day weekend..  (Remember, you can’t tell by looking at them whether cherries contain maggots or not.) 

If you’re doing a good job of controlling the cherry fruit fly in your yard but you have a neighbor who isn’t, you may still get maggots in your fruit.  That’s because the flies from your neighbors’ trees are capable of coming over to your tree and laying eggs after you spray.  That’s why it’s important for all backyard orchardists to control this pesky fly... as they cause problems to others growing cherries including the many commercial cherry growers in this area.

Let’s move on to worms in apples.  This is a very different insect pest... the adult is a moth.  Worms in apples are the result of codling moths.  The adult moths emerge sometime in May... about 14 to 21 days after the tree was in full bloom and start laying their eggs on leaves and the surface of developing apples and pears. (They also may attack quince, crab apple, hawthorne, and English walnut.)  It takes anywhere from six to twenty days for the eggs hatch into little larvae.

Once they hatch, the codling moth larvae chew their way into the fruit and proceed to eat their way to the center and eat on the seeds.  As they start to mature, they eat their way out of the fruit, usually exiting at the base.  They then find their way to the branches and trunks to spin a cocoon under loose bark or other little hiding places.  They pupate or go into their resting stage in the cocoon.  There are usually two generations of codling moth a year, but there can be three during longer, warmer seasons.

Control of codling moth is aimed at killing the baby larva before it enters the fruit.  Since it chews on the skin of the fruit before entering, pesticides applied to the fruit will kill the larva both through direct contact and through ingestion.  Because there are at least two generations a year, pesticide applications must be made regularly starting soon after adults start laying eggs and continuing through the summer.  Spray apples and pears on a regular basis with the recommended material starting when codling moths are present and laying eggs.  That’s usually two to three weeks after full bloom... usually around Mother’s Day weekend.

Things you should know about controlling cherry fruit flies and codling moths:

  1. Dormant oil and dormant fungicide sprays do not control either pest.  They control overwintering insects, such as aphids and scale.
  2. Good coverage of the tree with pesticide spray is important. Start at the top of the tree and thoroughly cover the tree just to the point of runoff. Spray the leaves, fruit, limbs, and trunk.
  3. Don’t spray when it’s windy.
  4. Don’t spray when it’s hot... over 85 degrees Fahrenheit.
  5. Avoid wetting the leaves with irrigation sprinklers right after applying the material.