Control Ants for Real Control
GrapeGrower Magazine (May 2003)
by Devin Carroll
Although ants are not a direct pest of grapes, they can be a major problem because they interfere with natural enemies of mealybugs and soft scale insects. Control the ants, and biological control becomes more dependable.
Unfortunately, companies developing ant baits have focused on other crops such as almonds, where the ants damage the nuts, and citrus, where ants can harm young trees.
Three ant species are important in grapes in the San Joaquin Valley.
The grey field ant, Formica aerata, is the largest and usually most common species. Nests can often be found at the base of almost every vine. These ants forage as individuals on the ground and in the cover crop. If many are found on the vine, you can bet they are tending mealybugs, scale insects, or aphids. Sometimes they will pile dirt on the crotch of the vine, burying the mealybugs. Like the other ants, field ants will move mealybugs from vine to vine. They scare away parasites, and sometimes kill both the adults and the larvae inside mummies. They occasionally bite people, but do not sting.
The western fire ant, Solenopsis xyloni, is typically limited to a few scattered vines. It often nests inside the vine in termite tunnels. Fire ants mass together, sting aggressively, and are even more viciously protective of mealybugs than field ants.
The argentine ant, Linepithema humile, a common kitchen pest, is typically rare in vineyards unless they border on residential areas. It requires a good source of water. The colonies are interconnected and cooperative, and they spread by “budding”, that is, the workers move with the queens to a new site. In most other ants, individual queens fly to new sights where they found colonies by themselves. Because they do not fly, Argentine ants spread slowly unless transported in dirt by humans. Argentine ants forage in long narrow lines. They do not bite or sting, but they are very effective at protecting mealybugs.
Agricultural ant baits such as Clinch and Esteem Ant Bait target mainly the fire ant. The attractant is either vegetable oil, or a protein source such as silkworm pupae, or both. Field ants will be more attracted if sugar or molasses is added. Argentine ant baits, designed mainly for household use, use sugar water with a toxicant such as boric acid. All baits have only a small amount of toxicant. Otherwise, the workers would die before they carried the poison back to the colony.
Worker ants do not eat solid food. They ingest the oil or sugar water. Workers sometimes feed solid foods to the developing larvae, which digest it and give it back. Colonies grow more slowly when the habitat lacks a liquid food such as mealybug honey dew.