May 10, 2018Professors describe a practical approach to biocontrols
The pest of a pest is the friend of growers.
But in order to recognize that ally, growers need to know the pests attacking their crops, and who the pest’s natural enemies are.
For 20 years, Cornell University entomology professor Anthony Shelton has maintained and updated a website cataloging natural-born enemies of common agricultural pests. Biological Control: A Guide to Natural Enemies in North America contains more than 100 individual pages of natural controls, including parasitoids, pathogens, predators and weed feeders.
“In any vegetable field, there’s already some biological control that’s going on,” Shelton said.
The number of companies offering biological products and services in recent years has exploded, but Shelton said the basic idea is “a very old science” with noted successes. As early as 1890, vedalia ladybird beetles were used to control cottony-cushion scale for California’s citrus industry.
“It can work very well in certain situations,” Shelton said. “It’s more of a knowledge-based tactic, so a grower’s really got to know what he’s doing.”
What Shelton calls “augmented” biological controls get especially good results in greenhouses or controlled environment agriculture (CEA). Biocontrols are used extensively in European countries such as the Netherlands where land is scarce and high-value crops such as tomatoes and peppers are often grown in CEA settings, he said.
As a graduate student in Boston, University of California entomologist Mark S. Hoddle successfully used natural predators such as Encarsia formosa to control whiteflies in a Boston greenhouse that specialized in growing Christmas Poinsettias.
The grower entrusted Hoddle with the task only after impressing upon him that a crop lost to pests would be a disaster for the business.
“That was a real good real-world experience for me,” Hoddle said. “This was the ground-zero of pest management.”
While Hoddle was successful in controlling the whiteflies with natural predators, he said the outcome would be much different in an open field.
Using biological controls in an open field presents many problems. There is often a certain lag time between distributing helpful insects and seeing them go to work on the pests, Shelton said. And when the helpful insects are released in an open field, they can easily be scattered by a thunderstorm or other inclement weather.
“You can really nurture them better in greenhouses,” Shelton said. “You’ve got them indoors and they’re protected from the environment.”
Hoddle said the cost of natural predators also is an issue for outdoor crops.
“The amount of area that you need to cover with these natural enemy releases pretty quickly makes it cost-prohibitive,” he said. Annual crops leave little time for growers to order natural predators, distribute them, and work before harvest. Contrast that to perennial-bearing plants like fruit trees, which can provide a long-term habitat supporting natural predators.
Shelton said there are many ways to help existing natural controls in the field. Growers should study and make an effort to identify the different insects and organisms among their crops. Some of the insects may be worth saving so they can control pests.
Integrated pest management and narrow-spectrum pesticides are less harmful to natural predators of pests. One example of a pesticide with a narrow focus, Shelton said, is the common lawn-and-garden B.t. sprays that kill caterpillars.
Shelton advocates avoiding broad-spectrum pesticides likely to kill most insects in the field. Many pests have evolved resistance to the “miracle pesticides” of earlier years and so new products are needed deal with the tougher pests, Shelton said.
“You get into this vicious cycle of just waiting for the next insecticide to come along,” Shelton said.
Top photo: University of California entomologist Mark S. Hoddle. Photo: University of California