Combating Navel Orangeworm: Pyrethroid Considerations
April 8, 2015 Navel orangeworm (NOW) is one of the biggest pest concerns almond growers face.
David Haviland, entomology farm advisor with University of California Cooperative Extension in Kern County, says sanitation should always be growers’ first line of defense against the pest, which overwinters as larvae within nuts left on trees from the previous year.
“Growers are encouraged to go in after harvest, shake those nuts off, knock them off with poles — whatever needs to be done to get them out of the tree,” he says. Once on the ground, the nuts should be destroyed. “That way, a grower starts off with the lowest possible number of navel orangeworms at the beginning of the season.”
While broad-spectrum pesticides such as pyrethroids can be highly effective against NOW, it’s important for growers to consider the benefits and concerns related to pyrethroid use.
Major almond growers have been monitoring pyrethroid resistance over the last few years, and research has shown some decline in their efficacy. They do still work — just not quite as well as they used to, Haviland explains. “And because they are effective, it is in a grower’s best interest to use these products in a way that they’re going to keep working for a long period of time,” he says.
Haviland suggests growers follow these tips for applying pyrethroids to reduce the risk of further resistance:
- Never use two insecticides in a row that have the same mode of action. In other words, rotate chemistries.
- Never use more than one pyrethroid within the same field within the same season.
The other concern with pyrethroids is that they’re broad-spectrum pesticides, which, of course, can be both good and bad. “The good side of that is they can control a wide range of pests at the same time — navel orangeworm, as well as stink bugs and leaffooted bugs and several different things,” says Haviland. “The downside to a broad-spectrum insecticide is that it may kill something that you don’t want it to kill — for example, some of the beneficial insects that are present in almonds.”
Spider mites are of particular concern, because pyrethroids can kill beneficials that control mite populations. “Therefore, by improving your navel orangeworm control, your spider mite situation may be worse than it would’ve been otherwise,” Haviland says. “Growers should weigh both the benefits and concerns when making the decision that they’re going to use these products.”
Stay tuned for Part 2 for tips on IPM approaches to reduce pyrethroid resistance.
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