Ants

The pavement ant is 0.13 inch long, dark brown and covered with coarse hairs. It has ridges on its head, which can be viewed with a hand lens. It prefers to nest in sandy or loam soils. The ant hills often appear as small mounds or patches of loose soil. It is found throughout the Central Valley but is more common in the northern San Joaquin and Sacramento valleys.

The southern fire ant is 0.07 to 0.25 inch long, has an amber head and thorax with a black abdomen. It has a painful sting that causes visible swelling. Fire ants vigorously swarm from the nest entrance when disturbed. Nests in orchards with low-volume irrigation tend to be located around the edges of the wetted areas. In flood-irrigated orchards with heavy soils, nests tend to be concentrated on the berms. Where lighter soils are present, nests are located both on the berms and in the middles. Frequently, southern fire ant nests are associated with clumps of weeds, such as nutsedge or spotted spurge. Activity of these ant pests peaks in the morning and again just before sunset. In the San Joaquin Valley, it is a more important pest than the pavement ant.

Do not confuse southern fire ant with the pyramid ant, which is a beneficial species that is similar in size but active during mid-day and found in sandy, weed-free areas. The pyramid ant does not swarm.

The southern fire ant generally causes more damage than the pavement ant. Ants are more prevalent in drip- or sprinkler-irrigated orchards than flood-irrigated orchards. Ants feed on other hosts and are principally a problem after almonds are on the ground; nut damage increases in relation to the length of time they are on the ground. The ants can completely hollow out nutmeats leaving only the pellicle. Damage potential of ants appears to be less in weed-free orchards and those without cover crops. Damage is also lower on varieties that have nuts with tight shell seal or with shell splits less than 0.03 inch wide. Shell seal can vary greatly from year to year depending on variety, crop size, and horticultural practices. Heavy crops that result in small nuts will likely have less open shells and thus less potential for ant damage.

Survey your orchard for ant colonies in April or May to determine need for treatment. Apply baits before harvest; this is the best way to manage potentially damaging populations. Remove nuts from the orchard floor as soon after shaking as possible to limit losses caused by ants. A harvest sample for damage will help assess the effectiveness of your management program.

Remove nuts from the orchard floor as rapidly as possible following shaking to prevent ants from infesting them. The table under MONITORING AND TREATMENT DECISIONS shows how increasing the days between shaking and pickup can increase damage done by ants.

Rapid removal of harvested nuts is the best way to reduce ant damage in organic orchards.

Survey the orchard floor for ant colonies 2 to 3 days after irrigation in April or May in the southern San Joaquin Valley or June in the northern San Joaquin and Sacramento valleys.

1. Choose five survey areas per block of the orchard, each about 1000 square feet, including the soil area from mid-alley to mid-alley beneath trees.
2. Count the number of active pest-ant colonies in each area, sampling five different areas of the orchard.
3. Total the ant colonies to get the number in a 5000 square foot area and compare it to the table below which gives an indication of the amount of damage you can expect at harvest.  
4. Record your results (example form— PDF).

Use baits if treatment is necessary. Foraging ants collect the bait and take it back to the colony. The bait eventually kills or sterilizes the queen and developing larvae fail to mature. Appy traditional bait products (e.g., Clinch, Esteem, Extinguish) 4 to 10 weeks prior to the intitiation of harvest to allow time for their full effects to be seen. A newer bait, Altrevin, works much quicker (within days) than traditional baits, but does not have as long of a residual effect. Apply Altrevin approximately 2 weeks before shaking begins.

Maintain bait quality and maximize bait pickup by ants:

• Do not use baits within 24 hours after an irrigation or 48 hours before an irrigation with sprinklers or microsprinklers. The soil surface should be dry so that moisture is not absorbed by the bait, or its attractiveness to the ants will be reduced.
• Use bait products soon after opening, and do not store bait for more than a few weeks. Bags of bait product that have been stored for a few weeks or more should be turned over so that the soybean oil attractant remains evenly dispersed throughout the corn meal carrier. Product in open bags must be used within a week or two so that the soybean oil does not turn rancid. Rancid oil is not attractive to ants.
• Purchase only as much bait as can be used in the current season.
• Use good weed management practices, which minimize weed seeds that may be a more attractive food source for ants than baits.

• Ant colony monitoring form (PDF)
• Harvest sample