Pests that attack fruit trees

Pests that attack fruit trees

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Pests that attack fruit trees can make up for their natural fragility by stripping the fruit of its delicious flesh, leaving the sour pit and damaging the tree. For professional tree growers, however, pests are a big challenge. Finding a solution for attacking insects that have chewed their way into fruit-producing tissues can be crucial in helping the business survive.

An explosion of biotechnology products and new pest control technologies in the past few years has delivered many welcome benefits to commercial fruit growers, but the problems they were supposed to solve are far from solved. Grown-tree products, in particular, can be of special value to tree growers because they are not destroyed by heat, so these pests are not killed if the weather turns warm or cold or if the trees are soaked with water for long periods of time. They also have the added advantage of giving the grower total control over the disease-fighting properties of the chemicals used to kill insects and pathogens.

Precision Fruit Technologies, a pest-control specialist in Taylor, Calif., has one of the industry's most successful on-site programs for adult flies, and it also offers a range of tools for managing the populations of larvae and flies and both white- and brown-vinegar flies in fruit and other trees.

Precision Fruit Technologies began using the larvicide calcium algicide in 1983 to control honeydew and white vinegar fly larvae on peach trees and took a two-year sabbatical from larviciding to make changes in the technology. Now it uses the same system to control three pests that feed on the fruit of many crops: the adult white vinegar fly, the spotted cucumber beetle and the screwworm fly.

The company developed a reliable and dependable system that works within the second generation of a vine after grafting and can be carried out in a single application. It starts with a controlled broadcast of the liquid calcium algicide at about 6 weeks after grafting. After it is broadcast, the vines are sprayed with a systemic pesticide at about 6 weeks later. The most commonly used systemic pesticide is the chlorantraniliprole, a contact pesticide that is volatile enough to be spread around the branches. After this application, control is sustained for two to three years. The price of the program is about $40 per acre.

The fly deterrents Precision Fruit uses on apples include Ethephon, a foliar fertilizer containing a compound called ethylene. The company's fruit fly program started in 1991 when it applied Ethephon as a mixed spray to a test orchard in Walnut Creek, Calif. It quickly became apparent that the bait killed not only adult flies but also larvae, because there was less for the larvae to eat. The bait did not leave behind any residues, so Precision Fruit expanded the use of Ethephon, and it was soon applied as a granular fertilizer (also at the time called Optio X for the fly protection it provided).

Numerous studies have shown the fly-control effectiveness of the granular Ethephon. It was patented in 1978 by K.S. Griffin and D.L. Wilson, and a University of California study showed that it is more effective for controlling adult flies in apples than other biocides. The company can specify the type of Ethephon and its concentration for use on orchards. The effective contact herbicide Optio X costs about $3 per acre, and the granular Ethephon costs $35 per acre for 6 months.

Precision Fruit's white vinegar fly program is another mature program. The company began using calcium algicide in 1981. It is broadcast into the canopies of apples in the early fall and, in the spring, it is applied in the roots of trees using a backpack sprayer.The company can control adult flies for one to two years with the program, but the program has much more impact on the flies' larvae because of the mass of larvae.

The company's strawberry fly program started about eight years ago. In early fall, it uses a foliar application of Ethephon. Later, when temperatures drop, the company also uses a soil application in which it spreads a weed-killer-like agent (named Superthach). The Superthach, which costs about $20 per acre, controls the flies for one to two years.

In the spring, the company sprays with calcium algicide. It also tests the efficacy of calcium algicide and Superthach in the orchards. The company uses a multispecies program that includes other strategies.

• Lime sulfur, which is made of a calcium compound and sulfur, is applied after the orchard is sprayed with calcium algicide and before any larvae are present.

• Sanitation can be a problem in orchards with a history of being underpopulated. Precision Fruit uses commercialized slug baits, which can be left in orchards from spring to late fall. In the spring and summer, Precision Fruit increases the amount of slugs in orchards and the areas surrounding them by 25 to 50 percent. The increase also occurs at the edges of the orchards. It will die of starvation in fall.

A targeted program can be a tool for bringing desirable insects back into an orchard, and it can work well in times of resource scarcity, such as the 1960s, when the government's fiscal policies left apple growers with less money to buy fruit-fly control products. These targeted programs are also very effective at managing the damage caused by pest populations when weather conditions are not favorable for the insects.

Growers may choose to use targeted programs that have been perfected through field trials and applied at high-tech orchards, but their risk is that some of the pests they want to repopulate the orchard with might show up at high levels because of this introduction.

Chris Ford, a grower in Twentynine Palms, Calif., for 25 years, says he realized this problem in 1989 when he was offered a targeted program to repopulate his orchard. At first, he tried to find the specific fly he wanted to bring back, but this proved difficult. He says