A new, highly effective pecan casebearer control is derived from a naturally occurring soil micro-organism that is safe for beneficial insects and the environment.
The product, "Green Light Lawn and Garden Spray with Spinosad," is good news for pecan lovers with only a few trees, said Dr.Allen Knutson, Texas Cooperative Extension entomologist. Other products containing spinosad have been labeled for commercial use for several years, he said.
"Spinosad is effective against pecan nut casebearer and other caterpillar pests, and it is also less toxic than conventional insecticides," Knutson said. "In fact, one formulation of spinosad, trade name, Entrust, is approved for organic production by the U.S. Department of Agriculture National Organic Standards Board."
Many Texans grow pecans for pleasure or profit. In 2003, Texas growers produced and marketed nearly 70 million pounds of pecans, approximately one-quarter of the total U.S. production, according to the USDA.
In 1906, shortly before his death, Texas governor James Hogg asked that a pecan tree be planted at his grave in place of a headstone. He also requested that nuts from the tree be planted throughout the state to make Texas "a land of trees." In 1919, the Texas Legislature named the pecan the state tree.
Most of the state's pecan production is in Central and West Texas, with scattered production elsewhere. But between spring and late fall, a multitude of insects can attack the clusters of pecans before harvest. One of the most damaging pests is the pecan nut casebearer.
"The casebearer is the most common and damaging insect pest of pecan trees," Knutson said. "The small, dark-colored caterpillar tunnels into the pecan fruit just after pollination in the spring, destroying the nutlet in the cluster. Tunneled nuts shrivel and fall from the tree. Because casebearer larvae feed directly on the pecan nut, their damage directly reduces the number of pecans at harvest."
Before the new spinosad product was available, backyard-pecan growers had three options for control: malathion, carbaryl formulations and another biological control, Bacillus thuringiensis, or Bt.
Malathion and carbaryl products are sold under many brand names for homeowner use. Both are toxic to fish and bees. Both can be hazardous to human health during application if not handled carefully, Knutson noted.
"Because they are broad-spectrum insecticides, they are toxic to beneficial insects like lady beetles and lacewings," Knutson said. "Over-using these insecticides can kill these beneficial insects and lead to outbreaks of aphids and spider mites."
Bt, on the other hand, is toxic only to caterpillars, but is less effective than malathion, carbaryl and spinosad products, Knutson said. For example, Bt requires two or more applications several days apart for effective control; only one application of the other products is usually required.
Like the Bt insecticides, spinosad (pronounced spin-OH-sid) is also derived from a naturally occurring bacterium.
"Spinosad provides the low-toxicity of Bt-based insecticides with the greater efficacy of conventional insecticides such as malathion and carbaryl," Knutson said.
Also, while many Bt products break down quickly in sunlight, spinosad persists and provides longer residual control, he said.
"Since spinosad kills only caterpillars and some thrips, lady beetles, lacewings and other beneficial insects remain unharmed," Knuston said.
Spinosad is toxic to bees exposed to direct spray and should not be applied when bees are actively foraging, he said. Spinosad will also control other pecan pests such as hickory shuck worms and web worms.
The optimum time for applying an insecticide for pecan nut casebearer is usually mid- to late-May in north Texas, but chemical control of insects, whether by natural or synthetic product, may not be for everyone, in every case, even with spinosad. For homeowners with very large trees, spraying for casebearers may be more trouble and cost than the savings in pecans "will justify," he said.
"Letting nature provide what pecans she will at harvest, and making up the difference by buying pecans in the fall, can often be a better solution," Knutson said. "In addition to the need for powerful sprayers and the extra expense, spraying large trees can risk the threat of drift of insecticide onto nearby gardens, landscapes and neighbor's property."
