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Ants on the March

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So you've done everything right so far: Dormant, spring and hull-split sprays were all perfectly timed, and you harvested early to beat the third flight of navel orange worm. You figure you've got the maximum premium sewed up this year. Possibly, but maybe not.

Take a closer look at those nuts lying on the ground out there. See any little critters moving in and out of those shells, each one carrying a mouthful of your perfect almonds? If so, your reject level may be headed straight up as it was for many growers last year, when rejects due to ant damage nearly set a record. According to Greg Savage, Blue Diamond® assistant manager for receiving and testing, ant damage has shown an upward trend statewide in recent years.

The above figures reveal only part of the damage done by ants. An unknown quantity of ant damage goes undetected because it is left unharvested in the field. That's because of the way ants feed on almonds. They enter a nut on the ground (or a nut on a limb that is touching the ground) through the open suture, chew a small hole in the brown skin of the nut, and take bites out of the kernel to carry back to the folks at home. Eventually, the kernel is gone and only the skin is left. The hollowed-out nut ,being much lighter than the others, is discarded by the harvester. Consequently, growers may not know how much damage ants are doing to their crop. The partially eaten nuts count as rejects.

Ants Love Almonds

Why are ants an increasing problem for almond growers? UC experts say it is largely because of shifts in cultural practices over the past decade or so, such as switching to nontillage, low-volume irrigation, and early harvest. Cover crops produce seed, which is a food source for ants. Microsprinklers and drip irrigation provide a ready source of moisture in just the right amount without disturbing the nest. And early harvest to minimize NOW damage generally means that the nuts will be on the ground longer to complete the drying process, which gives ants more time to do their dirty work.

"A modern-day almond orchard provides an ideal environment for ants," says Mark Freeman, U.C. Extension tree crop specialist in Fresno County, "so look for the ant problem to get worse, not better." He notes that long wet winters knock ant populations back somewhat, but that they bounce back quickly.

The ant problem seems to be greater in the San Joaquin Valley, where fire ants cause most of the damage, than it is in the Sacramento Valley, where pavement ants are the major culprit. But growers up and down the state need to keep an eye on ant populations in their orchards and do battle with the critters when populations approach the danger level.

When to Treat

First, determine whether or not you have problem ants in your orchard. Only two species of ant eat almonds _ fire ants and pavement ants. Most of the others are either benign or beneficial. The field ant, for example, eats other insects, including the pupae of the peach twig borer.

Refer to an ant identification chart, descriptions, and photos for help in identifying the ants that you find in your orchard.

James Brazzle, Kern County U.C. Extension entomologist, offers some additional hints for distinguishing between ant species. "The pyramid ant closely resembles the fire ant," he notes, "however the behavior of the two species is in no way similar. A good test is to pound on the ground near the colony opening. The fire ant will respond by swarming out of the nest and will sting if contacted. The pyramid ant will not swarm, and it does not have a stinger."

Ant damage potential, Brazzle explains, is related to density of ant colonies in the orchard, length of time the nuts are left on the ground to dry, and temperatures while the nuts are drying.

To determine the ant damage potential in your orchard, Brazzle recommends that you survey your orchard to estimate colony density in average number of colonies per thousand square feet. Survey several areas in each block. Choose a large area for each survey, such as the alleys on either side of ten trees, which will total roughly 5,000 sq. ft.

Colonies are easiest to detect two to three days after irrigation, because the soil on top of the mounds appears freshly turned. It may be difficult to determine where one colony begins and another ends, so count mounds that are at least two feet apart. Determine the number of colonies per 1,000 square feet in each sampling area and use the following chart to estimate potential damage.

Potential percent damage by fire ants

Number of Days Nuts are on the Ground 4 days 7 days 10 days 14 days 21 days
3 Colonies Per 1000 Sq. Ft 0.9% 1.6% 2.1% 3.1% 4.9%
9 Colonies Per 1000 Sq. Ft 1.4% 2.3% 3.2% 4.7% 7.0%
37 Colonies Per 1000 Sq. Ft 2.0% 3.6% 5.0% 7.0% 11.1%

Variety: Nonpareil. Damage to Carmel, Butte, and Mission is much less. Softer-shelled varieties are more susceptible to damage.

Brazzle recommends treatment when colonies reach a density of 3 to 5 per 1000 sq. ft. He also suggests taking into consideration past ant reject levels and the varieties in each block. Softer shelled varieties, such as Nonpareil and Merced, are more susceptible to ant damage, he notes.

Weather also plays an important role in the amount of damage that ants cause and the need for treatment, says Brazzle. When temperatures are above 95 degrees F. fire ants will not forage. "Examining the orchard floor and monitoring temperatures while the nuts are on the ground is useful in determining the urgency of collecting the nuts off the ground," he advises.

Treatment

If your survey indicates that treatment is necessary, apply Lorsban-4E. It is the only ant treatment currently approved for almonds. According to DowElanco, Lorsban kills ants three ways by contact, residual contact, and its unique foaming action.

The following label direction were applicable at the time this article was written, always follow the current label directions:

Sprinkler or drip irrigated orchards Apply Lorsban-4E as a broadcast spray to the entire orchard floor using ground spray equipment at 4 to 8 pints per acre in 25 or more gallons of water. Use the high rate for heavy infestations and the low rate for light infestations. In orchards where ant activity is concentrated around the irrigation emitters, apply the high rate to a 6 to 8 foot band along the drip irrigation line and the low rate to the rest of the orchard.

Flood irrigated orchards Apply Lorsban-4E at 4 to 8 pints per acre in 25 or more gallons of water to the entire orchard floor using ground spray equipment. Apply the high rate to heavily infested areas and the low rate to lightly infested areas. Where ant colonies are abundant only in the berm areas, apply Lorsban-4E at 8 pints per treated acre in 50 or more gallons of water to a 6 to 10 foot band along the tree line (berm).

Note: Do not apply Lorsban-4E where weed growth or other obstructions would impede uniform coverage of the orchard floor. Mow or chemically control weeds before the application of Lorsban-4E. Use when ant activity becomes evident with the orchard. The best results will be achieved with applications made at temperatures below 90 degrees F at time of application.

For best results

Brazzle offers these tips for maximizing the effect of your treatments:

  • Mow the ground cover
  • irrigate prior to application
  • treat in morning while ant activity is greatest
  • focus treatment on mounds where activity has been observed

Remember, Lorsban takes about two weeks to have maximum effect on an ant colony, so apply early enough to get control before harvest, and allow 4 to 5 days before irrigating.

Get a handle on your ant situation now and maybe that premium will be yours, after all.