How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

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 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. The ant hills often appear as small mounds or patches of loose soil. Fire ants vigorously swarm from the nest entrance when disturbed; nondamaging species do not. 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 ants 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. 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.

DAMAGE

The southern fire ant has a wider distribution and 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.

MANAGEMENT

Survey your orchard for ant colonies in April or May to determine need for treatment. Application of baits before harvest is the best way to manage potentially damaging populations. To limit losses caused by ants at the processing plant, be sure to remove nuts from the orchard floor soon after shaking. A harvest sample for damage will help assess the effectiveness of your management program.

Cultural Control

Remove nuts from the orchard floor as rapidly as possible following shaking to prevent ants from infesting them. The table below under Monitoring and Management Decisions shows how increasing the days between shaking and pickup can increase ant damage.

Organically Acceptable Methods

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

Monitoring and Treatment Decisions

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 Valley. Choose five survey areas per block of the orchard, each about 1000 sq. ft., including the soil area from mid-alley to mid-alley beneath trees. If your trees are spaced about 22 feet apart, this will include the area under about 10 trees. Count the number of active colonies in each of these areas and repeat the procedure in 4 other areas of the orchard. Total all 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. Damage increases the longer you leave nuts on the ground after shaking. See more details on monitoring and a record form (PDF* 17K).

If treatment is necessary, baits are the preferred method of ant control. When conventional sprays are used, only foraging workers are killed. Baits, however, are taken back to the nest and weaken and kill the whole colony. Bait products are slower acting than the spray because of the nature of the toxicant and must be applied several weeks before harvest. Ants switch preference for food during the season, so a particular type of bait might only be effective during certain periods. Follow label directions for timing of applications.

Do not use baits within 24 hours after an irrigation or 48 hours before an irrigation with sprinklers or micro-sprinklers. The soil surface should be dry so that moisture is not absorbed by the bait, or its attractiveness to the ants will be reduced. Bait products must be used within a few weeks of purchase. 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. Do not purchase more bait than can be used in the current season.

If you choose to use a conventional insect spray, the best timing is 2 weeks before harvest. Applications of sprays in May or June are generally not as effective.

*You need Adobe Acrobat Reader version 4 or later to view or print this PDF. If this software is not installed on your computer, you can download a free copy of Acrobat Reader.

PUBLICATION

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431
Insects and Mites
F. G. Zalom, Entomology, UC Davis
C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter/Yuba counties
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
R. L. Coviello, UC Cooperative Extension, Fresno Co
R. A. Van Steenwyk, Insect Biology, UC Berkeley
M. W. Freeman, UC Cooperative Extension, Fresno Co.
Acknowledgment for contributions to the insects and mites section:
R. E. Rice, Kearney Agricultural Center, Parlier
L. C. Hendricks, UC Cooperative Extension, Merced Co.

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