How to Manage Pests

UC Pest Management Guidelines

Almond

Ants

Scientific names:
Pavement ant: Tetramorium caespitum
Southern fire ant: Solenopsis xyloni, S. molesta

(Reviewed 3/09, updated 3/09)

In this Guideline:


DESCRIPTION OF THE PESTS   (household ant key)

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 Treatment 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. Count the number of active colonies in each area, sampling five different 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. Record your results (example form) (PDF).

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 sprays so they 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.

Percent Damage by Ants to Almonds on Ground in an Almond Orchard
No. of Colony Entrances per 5,000 sq. ft. in April-May Days Nuts Are On Ground
4 7 10 14 21
15 0.9% 1.6% 2.1% 3.1% 4.9%
45 1.4% 2.3% 3.2% 4.7% 7.0%
185 2.0% 3.6% 5.0% 7.0% 11.1%
Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
 
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
 
BAITS
 
A. PYRIPROXYFEN
  (Esteem) 2 lb 12 1
  MODE OF ACTION GROUP NUMBER1: 7C
  COMMENTS: An insect growth regulator that has little immediate effect on foraging worker ants. Foraging ants take the bait back to the nest and feed developing larvae and the queen. Developing larvae fail to mature and queens become sterilized. Therefore, existing foraging workers must die off naturally before visible impact on the population is evident. Apply 5–7 weeks before harvest to allow sufficient time for workers to die off and prevent nut damage. Baits may be less effective where weedy cover crops exist. Weed seeds, particularly spurge, may attract the ants away from the bait, reducing the amount of bait consumed.
 
B. ABAMECTIN
  (Clinch Ant Bait) 1 lb 12 0
  MODE OF ACTION GROUP NUMBER1: 6
  COMMENTS: Has insect growth regulator effects on the colony and some direct toxic effects on foraging worker ants. Foraging ants take the bait back to the nest and feed developing larvae and the queen. Developing larvae fail to mature and queens die or become sterilized. There are some direct lethal effects on foraging workers and they will begin to die off within 2–3 weeks after application. Apply 4 weeks before harvest to allow sufficient time for workers to die off and prevent nut damage. Baits may be less effective where weedy cover crops exist. Weed seeds, particularly spurge, may attract the ants away from the bait, reducing the amount of bait consumed. This is particularly important with Clinch since the active ingredient degrades rapidly after application and is no longer effective after 24–36 hours.
 
C. METHOPRENE
  (Extinguish) 1–1.5 lb 4 0
  MODE OF ACTION GROUP NUMBER1: 7A
  COMMENTS: Has insect growth regulator effects on the colony and some direct toxic effects on foraging worker ants. Foraging ants take the bait back to the nest and feed developing larvae and the queen. Developing larvae fail to mature and queens die or become sterilized. There are some direct lethal effects on foraging workers and they will begin to die off within 2–3 weeks after application. Apply 4 weeks before harvest to allow sufficient time for workers to die off and prevent nut damage. Baits may be less effective where weedy cover crops exist. Weed seeds, particularly spurge, may attract the ants away from the bait, reducing the amount of bait consumed.
 
CONVENTIONAL SPRAYS
 
A. CHLORPYRIFOS*
  (Lorsban 4E) 2 qt 24 14
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Apply to orchard floor in a minimum of 50 gal water; 50–100 gal have given longer control in trials. In orchards where nests are concentrated on the berms or around low-volume emitters, use 8 pt/treated acre in a 6- to 10-ft band along the berm or drip line. Orchards where ants are more widely distributed will require treatment over the entire orchard floor. Do not allow livestock to graze in treated orchards. Avoid drift or tailwater runoff into surface waters.
 
** For dilute applications, rate is per 100 gal water to be applied in 300–500 gal water/acre, depending on the label; for concentrate applications, use 80–100 gal water/acre, or lower if the label allows.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of these two intervals is the minimum time that must elapse before harvest may occur.
* Permit required from county agricultural commissioner for purchase or use.
1 Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

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
D. R. Haviland, UC IPM Program, UC Cooperative Extension, Kern County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
Acknowledgment for contributions to Insects and Mites:
R. E. Rice, Kearney Agricultural Center, Parlier
L. C. Hendricks, UC Cooperative Extension, Merced County
R. L. Coviello, UC Cooperative Extension, Fresno County
M. W. Freeman, UC Cooperative Extension, Fresno County

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