How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

The most prevalent of the ant species in vineyards, the Argentine ant, is about 0.13 inch (3 mm) long, uniformly deep brown to light black and does not bite or sting. The Argentine ant has one petiole node (hump) between the thorax and the gastor (swollen part of abdomen right behind the petiole). Worker ants travel in characteristic trails on vines, trellis wires, the ground, and drip irrigation laterals. They forage during all daylight hours. Ant populations peak in midsummer and early fall. Their nests are very shallow, usually within 2 inches of the soil surface.

The pavement ant is 0.13 inch (2–3 mm) long and has a dull, blackish brown body that is covered with coarse hairs. The head and thorax have many parallel furrows. Pavement ants have two nodes between the thorax and the gastor. They move in slow deliberate motion. They prefer to nest in sandy or loam soils.

The southern fire ant, also called the California or native fire ant, is light reddish brown with a black abdomen. The entire body is covered with golden hairs and has two nodes between the thorax and the gastor. Workers range in size from 0.1 to 0.018 inch (2.5–4.5 mm ). They do not usually travel in conspicuous trails and will swarm over the ground when disturbed. This ant will sting when provoked. Southern fire ants build nests of loose mounds or craters near bases of vines around wetted areas and do not aggregate in colonies as large as those of the Argentine ant. They forage in the morning and early evening and are underground during hot periods.

Native gray ants, also called field ants, are larger than the other ants, measuring up to 0.3 inch (7.5 mm) and, like the Argentine ant, have one petiole node (hump). These gray ants nest in topsoil or under rocks and debris, move in an irregular jerky manner, and generally do not travel in trails or sting. Formica aerata is more common in the San Joaquin Valley whereas Formica perpilosa occurs primarily in the Coachella Valley. Native gray ants do not trail and appear solitary.

Thief ants are extremely small ants (1–1.5 mm) with yellowish, shiny bodies. They are pests of grapes primarily in the Coachella Valley.

An illustrated key that covers common ant species (except gray ants) may be of value when identifying ants in vineyards.

DAMAGE

Ants can be extremely disruptive to IPM programs, especially Argentine and native gray ants. These ants feed on honeydew excreted by the European fruit lecanium scale and mealybugs. As part of this relationship, they also protect these honeydew-producing insects from predators and parasites, thus disrupting biological control.

MANAGEMENT

Ants may be more of a problem in vineyards with cover crops; the exception appears to be a vetch cover crop, because it supplies ants with adequate amounts of nectar and keeps them from moving into vines. Manage ants when they are interfering with biological control of pests. Cultural practices and sprays can be used in an integrated program.

Cultural Control
Tilling the soil for weed control will also disturb the nesting sites of ants and help to reduce their populations. Use of a French plow in the vine row will disrupt ant colonies.

Planting a cover crop of common vetch (Vicia sativa) can help to keep gray field ants (Formica sp.) off the vines. Common vetch has an abundance of nectaries that attract the ants away from the honeydew-producing insects. In studies it was planted in a 80:20 mixture with 20% Merced rye so that it could establish in late fall and winter in order to attract the ants during spring and early summer. The addition of rye to the mixture helps to provide structure and support in the cover crop for the vetch. A heavy seeding rate (120 lb/acre) helps to ensure a good stand. The effect of other nectary-bearing cover crops on attracting ants has not been evaluated. (Research using cover crops to attract Argentine ants, Linepithema humile, has not been conducted.)

Organically Acceptable Methods
Organically acceptable management tools are the cultural controls.

Monitoring and Treatment Decisions
Monitor the vineyard in spring when honeydew-producing insects such as scale and mealybugs appear as outlined in DELAYED-DORMANT AND BUD BREAK MONITORING and record observations on a monitoring form. (100KB, PDF) Check the abdomen of ants descending the trunks to see if they are swollen and translucent; this helps identify them as honeydew-collecting species. Periodically inspect for ants on arms, cordons, and canes. For the most effective and economical ant control, treat when ants are active in early spring following winter rains and again in late August.

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PUBLICATION

UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
L. G. Varela, UC IPM Program, Sonoma County
F. G. Zalom, Entomology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma County
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
P. A. Phillips, UC IPM Program, Ventura County
D. R. Haviland, UC IPM Program, Kern County
K. M. Daane, Kearney Agricultural Research Center, Parlier
M. C. Battany, UC Cooperative Extension, San Luis Obispo County
Acknowledgment for contributions to the insects and mites section:
J. Granett, Entomology, UC Davis

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