Small, nondescript, horned larks inflict millions of dollars of damage by feeding on seeds and seedlings of lettuce, tomato, and other vegetables crops, and efforts by growers, such as firing off shotguns and propane cannons in the field, are largely ineffective.
But a recent project funded by the California Tomato Research Institute Inc. has encouraged development and registration of compounds for foliar sprays to repel the birds.
As principal investigator in the project, Terrell P. Salmon, wildlife specialist with Cooperative Extension at the University of California, Davis, first determined distribution of the larks and then overlaid it with tomato production.
Salmon reviewed literature on bird control, visited USDA's National Wildlife Research Center (NWRC) at Fort Collins, Colo., to review bird repellent research there, and contracted repellent manufacturers to discuss how materials might help solve the problems for tomatoes.
In the annual report for the institute, Salmon said the NWRC's trials with several compounds demonstrated anthranilate and methiocarb to be most promising.
His later trials in the San Joaquin Valley showed these two compounds and a third, anthraquinone, to be effective as foliar sprays on lettuce seedlings.
“Portable aviaries were placed over treated as well as untreated seedlings. Six horned larks were released into each aviary, which represented an equivalent population of about 6,000 horned larks per acre,” he said.
“Under this very intense pressure, 100 percent of the nontreated seedlings were consumed. The three repellents all had significantly less damage, with the best, methiocarb, having only 20 percent of the seedlings consumed.”
Salmon noted that neither methiocarb nor anthraquinone are registered as foliar sprays for lettuce seedlings. However, the Gowan Co. of Yuma, Ariz., is resuming product registrations for Mesurol 17, the trade name for the methiocarb formulation, and Environmental Biocontrol of Wilmington, Del., is supporting registration of Flight Control J, the anthraquinone product. Trials on lettuce in California were planned for this year.
He added that discussions with NWRC are exploring the possibility of adding similar tests trials for tomatoes.
“Data generated from these tests will be essential if the repellent registrations are to pursue these materials as bird repellents for seedling tomatoes.”
Even though the two products may provide some relief, Salmon cautioned that questions remain. The costs of the materials and the necessity for treating large areas where the birds might appear are unknown. “Hopefully, the repellents will be effective enough to encourage significant use which should help keep the costs of the chemicals affordable.”
Although a major pest of seedling crops, horned larks are small, brownish birds often found in loose flocks favoring open habitats with few trees or shrubs.
They keep low to the ground, and their damage is easily overlooked until bare spots are noticed in the middles of fields. Damage typically begins when the birds nip off parts of seedlings or pull them entirely out of the soil.
For slow growing plants, the damage may extend over a long period and end once plants are three to four inches tall. Damaged areas may expand rapidly until only a narrow band of undamaged plants remains along field borders.
Hazing only control
Horned larks were once controlled by strychnine treatments, but that practice was terminated by a court order in 1990. Growers were left with only hazing methods with shotguns and propane cannons, since no effective pesticides for the species are registered in California.
Salmon said an example of the costs of horned lark damage is the estimated loss in 1996 of $4.6 million to lettuce seedlings alone. That figure is based only on the amount invested in seedling emergence and does not include crop loss because of sparse stands or total crop failure.
The California Tomato Research Institute Inc., funded by voluntary contributions from growers, is dedicated to research in disease management, weed control, agronomy, breeding and other practices to keep the California processing tomato industry competitive.