Deb Babcock: Special alert on cherry trees
August 16, 2010
Steamboat Springs — Just as home gardeners are bringing in cherry harvests, we're finding a problem with some cherry produce in Routt County. In certain areas, ripe cherries are found to be infested with white, maggot-like larvae from the western cherry fruit fly. This has been particularly noticeable in cherries from home gardens in Old Town Steamboat. Once a cherry has been infected, the fruit is no good.
The western cherry fruit fly (Rhagoletis indifferens Curran) first was found in cherries in the western part of Colorado in the late 1990s. As of 2004, it was found in Mesa, Delta and La Plata counties but has been expected to migrate to other areas of the state. Apparently, it has found its way to Routt County this year, probably on trees brought in to meet demand for this popular plant. This pest attacks only cherries and is a problem with all varieties.
The western cherry fruit fly produces one generation of offspring per year. The pest spends the winter in the soil as a pupa and then comes out as an adult fly throughout a two-month period in the springtime when the weather warms up. It lays its eggs (50 to 200 per fly) in the cherry fruit — one egg per cherry, when temperatures reach 75 to 85 degrees Fahrenheit. The eggs hatch within a week, and the larvae spend the next two weeks inside the fruit, ruining it, before burrowing out and falling to the ground to push themselves into the soil to overwinter as pupae.
Smaller than a housefly, the western cherry fruit fly has a black body with thin white stripes across its stomach. Once it reaches adult stage, it can be identified by a pattern of distinctive black markings on its wings.
Home gardeners are requested to hang yellow sticky traps from tree branches in early spring when cherries are green. Check it daily until you spot the first fruit fly and then begin a spray program within the week.
Four primary controls are recommended for eliminating this pest. Spinosad is the least toxic to mammals and will last about a week and should be repeatedly sprayed up until a week before harvest.
Carbaryl products such as Sevin also are effective but can cause spider mite problems if used repeatedly. Therefore, you should alternate this product with other ones.
There are several products containing malathion that can be used to control cherry fruit flies, but they have just a two- to three-day residual value so need to be repeated often.
And two pyrethroid insecticides called permethrin and esfenvalerate can be used for cherry fly control. These insecticides give a week or more of residual value.
Keep in mind with any of these controls that as your cherries grow larger, the fruit will outgrow the insecticide. As a result, you need to stay on top of spraying as the fruit expands in size.
If you have any questions about your cherry trees, please contact the Routt County Extension Office. Or to learn more, Google "Western cherry fruit fly control."
Deb Babcock is a Master Gardener through the CSU Extension Routt County. If you have questions, call 879-0825.