We've all heard almond growers say those famous last words: “I don't have ants.” Well, don't be so sure, say experts who gathered recently at Manteca for talks about the profit-robbing insects and their habits.
Mel Machado, grower representative for Blue Diamond Growers, says part of the problem is almond growers typically tour their orchards with their heads up, watching the crop, of course, but missing what's crawling on the ground. And what's more difficult is ants can be there but unseen on the surface.
Rejects due to ant damage can have a dramatic effect on returns, Machado warned. “It's a double-whammy: you lose on both price per pound and the weight itself. With a 2,000-pound crop, for every 1 percent of damage, you lose 20 pounds, and more.”
Some growers say they simply cannot afford to treat for ants because they aren't that damaging, but Machado reasons differently.
Ant damage may be overlooked when the secretive insects gnaw out the meats leaving the whole skins, which blow out of pickup machines. Often, he says, growers find their true losses are twice that estimated and may range into the teens and above.
Against that caveat, Benny Fouche, San Joaquin County farm advisor, said he and several other Extension entomologists and cooperating growers have been evaluating ant control throughout the San Joaquin Valley in recent years.
Fire ant damage
Southern fire ant, notable for its stinging of humans and animals, is a major pest of almonds throughout the SJV, while pavement ant is most damaging in northern SJV and the Sacramento Valley.
Damage is mainly on nuts on the ground, but the ants can also feed in the trees, Fouche said during the field day sponsored by Valent USA Corp.
Other species, including carpenter, field, and harvester, feed on other plants or insects and may be considered only a minor threat, if not beneficial. Argentine ants are a pest of citrus and households.
One way to identify whether damaging ants are present is to leave four or five almonds or pieces of hotdog in a perforated PVC vial in the orchard. If the bait is consumed a day or so later, the orchard has a harmful population of ants. If the morsels last four or five days, the problem is less but should be monitored.
Among the few controls, Dow-Elanco's Lorsban is a contact, fuming, organophosphate product having the active ingredient, chlorpyrifos. Although effective, it has come under scrutiny for its environmental concerns, costs, and difficulty of application.
After trying several combinations over four seasons, the Extension researchers found that the more recently available ant baits, Novartis' Clinch (abamectin) and Valent's Esteem (pyriproxyfen), performed best. “The baits work, but you generally need to use them on a clean, mowed orchard floor,” Fouche said.
The baits should be applied four to seven weeks before harvest. Clinch kills ants after they ingest it. Esteem, carried back to the nest by workers, sterilizes queens and stops development of existing larvae. Existing worker ants then die off naturally.
Esteem, he added, was the most consistent in the multi-year trials and was successful in cleaning up an orchard near Oakdale with an advanced infestation in the trees.
“Unfortunately, we don't have a good threshold for ants. If you have damage at harvest, you know you have to treat next year. And you have to be careful with a light crop and a lot of ants,” Fouche added.
A few ants and a large crop are less of a hazard, as are ants in hard-shell varieties.
Fouche recommended growers collect a sample of 200 or so almond nuts across their orchards, freeze them and inspect them for ant damage later when they have an opportunity.
He had one positive note that once the populations are under a control program, they will probably diminish year by year. Sampling at the same time every year and record keeping will show how a program is performing.
Ants are quite prolific and as few as 25 workers can support a queen, according to Larry Allen, senior entomologist with the San Joaquin County Agricultural Commissioners Office.
“They are most active at night when you can find 10 times as many as during the daytime,” he said, adding that they are beneficial in “cleaning up” other insect pests but harmful in foraging on almonds just before harvest.
The quarantined red imported fire ant from South America, he said, has found its way across the U.S. to California in the counties of Orange, Los Angeles, Riverside, Merced, and Sacramento. Harmful to humans and livestock, it continues to be a concern for eradication by the California Department of Food and Agriculture.
Merced County is combating recent infestations of southern fire ant across 2,300 acres. One incident of severe stinging of humans was recently reported. It has been found in almonds, peaches, raspberries, grapes, and pasture.
Responding to a question, Allen noted that ants easily survive flood irrigation because they have the ability to capture oxygen bubbles on their bodies.
Tom DeWitt, senior research specialist with Valent, said Esteem, broadcast at 1.5 to 2 pounds per acre with a Herd spreader, is most effective when ants are actively foraging. Corncob bits and vegetable oil carry the active ingredient.
It can be applied on bearing almonds six to eight weeks prior to harvest and a second application can be made 12 to 16 weeks later if a reinfestation occurs. It is not to be applied within 24 hours of harvest, and another ant-control is not to be applied for seven to 10 days.
Pyriproxyfen is also registered in citrus, apple, pear, walnut and pistachio.