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Extension Agent: Texas leafcutting ants a headache for homeowners

By By Peter J. McGuill
Feb. 5, 2013 at midnight
Updated Feb. 4, 2013 at 8:05 p.m.

Peter McGuill

The Texas leafcutting ant is rearing its ugly head again this winter and wreaking havoc on evergreen trees and landscape plants in the Victoria area. Cut ants, or night ants as they are often called, can be extremely destructive as a result of their habit of defoliating landscape plants, trees and gardens.

Living in colonies of up to two million, these pests collect leaf fragments and take them to their underground nest. Against popular belief, the ants don't feed on the plant material that they harvest but use it to cultivate a fungus that provides nourishment for the ants and their growing larvae. Because this fungus is their only known source of food, they don't respond well to most ant baits that are readily available.

Leafcutting ants are more noticeable during the winter months. This is, in part, because of the lack of abundant foliage with the exception of the green landscape and garden plants and evergreen trees and shrubs. They are, however, active throughout the year and turn to night feeding in mid-spring when daytime temperatures become summerlike.

Above ground, the colony is marked by numerous crater-shaped mounds, 5 to 14 inches high and 1 to 11/2feet in diameter. According to writings by Dr. Mike Merchant, extension entomologist, defoliation by leafcutting ants can resemble damage produced by several other leaf chewing insects, particularly sawflies and leafcutting bees. Trees defoliated by the leafcutting ant usually are within sight of an ant nest. and the ants themselves may be seen carrying leaves. Foraging trails will be littered with pieces of leaf tissue that can be traced to a feeder hole. Considerable damage to a plant can occur in a few hours.

Control of Texas leafcutting ants can be difficult. Although plants can be protected temporarily using dust or granular formulations of contact insecticides like acephate (Orthene), carbaryl (Sevin) or permethrin (Terro), such treatments must be reapplied frequently. Also, plant applications do little to eliminate the underground nest. The large size and complexity of leafcutter ant nests makes it difficult to obtain good control with dust, liquid or granular insecticides.

A special formulation of hydramethylnon, sold under the trade name Amdro Ant Block, is currently the only widely available bait product labeled for control of leafcutting ants. This product can be used on most sites such as lawns, landscaped areas, golf courses, ornamental gardens and other noncropland areas such as roadsides, commercial grounds, etc.

Apply bait according to label directions while ants are foraging. Ant activity in the treated colony will decline over a four- to six-week period. However, about half of the time, activity will return in four to six months, requiring a second treatment.

Peter J. McGuill is the Victoria County extension agent - ag and natural resources. Contact him at 361-575-4581 or pjmcguill@ag.tamu.edu.

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