The Western cherry fruit fly has destroyed the romantic notion of plucking and eating cherries directly off our backyard trees. For those who may have been with Rip Van Winkle for the past 10 years and have never heard of this pest, rest assured it is here to stay. The most often asked horticulture question at the USU Extension Office has been, "What do I do about the worms in my cherries?"
This pest did not exist in Utah until some 10 or 11 years ago, when it was first discovered in the Holladay area. It has now spread to all areas in the northern part of the state and into many southern counties. The small worms or maggots in the cherries are the larvae of a picture wing fly. This fly is slightly smaller than a common housefly and is dark brown or black with transparent, banded wings.Of the pests that affect our fruit, picture wing flies are some of the most difficult to control. In addition to a couple of species of cherry fruit flies, apple maggots, Mediterranean fruit fly, currant fruit fly and many others fall in this category. Adult flies lay their eggs through the skin of the fruit, so pesticides applied after egg laying are not effective. The eggs hatch into maggots that feed on the interior of the fruit. As the maggots mature they burrow through the skin and drop to the ground. Those fruits with holes in them are probably better to eat than those without the holes. Holes mean the maggot is not inside the fruit!
Cherry fruit fly control programs are directed at the adult flies. I don't know how you control adult flies at your house, but I generally depend on a fly swatter. Unfortunately, it's rather difficult to swat all the flies in a cherry tree. Those unwilling to spray should probably remove their cherry trees, since they serve as a point of infestation, spreading to the other cherry trees in the neighborhood.
Controlling the pest is not easy, even by spraying. Regular and thorough coverage of the trees is important to prevent the adults from laying their eggs. To prevent flies from migrating from tree to tree, encourage everyone in the neighborhood to spray at the same time. Spray timing is critical and based on trapping insects in selected locations. Call GOT-BUGS (468-2847) for the date to spray.
This year flies are two to three weeks later than last year. If you live in an area where traps are not placed, spray the cherries when they turn from a bright green to a straw yellow color. Pie cherries require a additional sprays because they are harvested later in the season.
Products registered for cherry fruit fly control include Diazinon, Methoxychlor and Malathion. It is important to follow the interval between the last application and the time of harvest. Diazinon requires a 10-day harvest interval, Methoxychlor seven days and Malathion three days. Since sprays are applied every seven days, gardeners need to switch to Malathion for the last sprays prior to harvest time.
As with most other fruit pests, organic controls are difficult and limited in their effectiveness. The tremendous reproductive capacity of the fly interferes with even carefully planned, integrated control programs.
If this pest is not controlled, 90-95 percent of the fruit is infested. As mentioned, only those cherries where the maggots have emerged will have holes in them. There is no practical way to determine which cherries are infected and which are not.
Peach tree borer and Oriental fruit moth often infest apricots and peaches. The twig borer causes two distinct kinds of damage. At blossom time the partially grown caterpillars burrow into new twigs of peaches, plums, prunes and apricots, causing the terminal ends to die. The damage later in the season affects only the fruit. This second generation should be controlled when Elberta peaches are about 1/2 to 3/4 of an inch in diameter. Imidan or Diazinon can be used to control the pest. A second spray two weeks later is generally required. Don't confuse these pests with peach tree borer that attacks the trunk of the trees. Control for that pest is not needed until the first of July.
Recent rains have generated many questions about mushrooms in lawns. There is no chemical control for the mushrooms. Sprays are not needed nor are they effective. If the mushrooms are a hazard because of young children or pets, rake them up and dispose of them. Normal precipitation will solve the problem very quickly.
- THE 1991 UTAH ROSE SHOW, sponsored by the Utah Rose Society, will be Sunday, June 16, 1-5 p.m. Garden Club Building, Sugarhouse Park, 1602 E. 2100 South, Salt Lake City. Open to the public, no charge.
- EACH THURSDAY THE STATE ARBORETUM sponsors a garden talk at the Red Butte Gardens from 11:30 a.m. to 1 p.m. For more information, call 581-5322.