California is home to approximately 270 different ant species. With only a fraction of this population found in almond orchards, few types will prove to be an economic threat to almond growers.
Almond Board of California (ABC)–funded research by UC researchers has provided guidelines on the UC Statewide IPM program website on which ant species are of concern, how to identify them, treatment and monitoring guidelines and chemical options.
For almond growers, the primary concern is the direct damage caused by the southern fire ant, thief ant and pavement ant. In addition to the economically harmful ants found in almond orchards, there are ant species that do not feed on the nuts. These include the native gray ant, pyramid ant, and California harvester ant. The native gray and pyramid ant feed mostly on other small insects and arthropods, while the harvester ant feeds exclusively on small seeds.
Identifying Characteristics
Since both pest and non-pest ant species so commonly exist in the same orchard, monitoring plays an important role in efficient ant management. In agricultural cropping environments, coarse morphological differences, such as number of nodes on the petiole, presence of a sting, and color and size provide enough information to properly identify pest and non-pest ants. Learning about foraging activity and behavior, nest location and manner in which ants deposit tailings around the entrance hole is also helpful when distinguishing different ant species.
The UC IPM link above provides descriptions and a key for identification. In addition to what is on the website, other characteristics can help in identification. For instance, during hot daytime temperatures the foraging activity of southern fire ant diminishes considerably, while that of the native gray remains high. Also, during foraging, the native gray moves in a more herky-jerkey fashion than the southern fire ant. Both the southern fire ant and native gray ant construct flat disperse nests in shaded areas and with multiple entrances. However, tailings deposited around entrance holes of southern fire ant tend to be finer grain size and are generally hillier.
Examining ants using a 10x hand lens works well. An effective method of capturing ants consists of placing bait such as a whole Frito corn chip or a piece of Bologna in a small plastic vial and placing 10 vials of each bait type in various locations in the orchard for about four hours. Captured ants can be killed or immobilized and inspected by placing the vials in a freezer overnight.
Treatment Thresholds, Options and Timing
The UC guidelines recommend monitoring the mean number of ant nest openings in five orchard areas of about 1,000 square feet each. A table gives the expected percentage damage based on mean number of nest openings and days nuts are expected to be on the orchard floor at harvest.
Baits are the preferred treatment options and UC outlines four effective baits:
- Insect growth regulator (IGR) baits: Esteem (pyriproxyfen) and Extinguish (methoprene)
- Stomach poison baits: Clinch (abamectin) and Altrevin (metaflumizone).
The baits all use soybean oil as the attractant and toxicant carrier, and specifically attract protein-feeding ants. Note that when deciding on a management strategy, be sure to consider the lag time between bait application and population reduction. IGR baits work slower, taking up to eight weeks before showing significant results. In contrast, the stomach toxicants abamectin and metaflumizone work much faster, requiring just one to three weeks before significantly reducing foraging activity.
