Efforts by almonds growers to keep ahead of insect threats are in a temporary lull. Populations from the spring hatch of navel orangeworm (NOW), for which some growers sprayed in May, are declining.
Treatment is generally required only if more than two mummies remain per tree after bud swell, says Walt Bentley, University of California IPM entomologist at the Kearney Agricultural Center. Even then, usually only one treatment is needed, either in the spring or at hull split. Dormant sprays do not control NOW.
Peach twig borer (PTB) numbers are declining now, too. Some growers who didn’t treat for this pest with a dormant or bloom spray, but were concerned about it, applied a May spray.
Bentley says NOW and PTB numbers are down this year.
Next up for growers who were unable to spray for navel organgeworm in May is the insect’s second hatch of the season, which coincides with hull split. Then, only Nonpareils, and possibly Carmels, are at risk, Bentley says. Larvae are unable to penetrate hard shell varieties, such as Butte, Mission and Padre.
He recommends making any NOW spray in July at the beginning of hull split, if eggs are being laid on egg traps. Otherwise, time the spray to the start of egg laying after hull split. Hull split begins when sound fruit in the tops of the trees begin to split.
The best time to spray is between 1 percent and 10 percent hull split, Bentley says. That can occur quickly. “An orchard can go from no hull split to 30 percent hull split in a week,” he says. “Last year, hull split on the West Side started July 24 — that’s the latest I’ve ever seen. We’re estimating hull split in Nonpareils will begin around July 15.”
One insecticide option is a pyrethroid. In addition to posing a contamination threat to surface water in the spring, it can encourage development of spider mites, he says. Reduced-risk chemicals are an alternative for treating NOW.
“They’re every bit as effective as pyrethroids for controlling NOW and peach twig borer, but won’t trigger spider mites,” he says. Because trees under water stress are more susceptible to spider mites, some growers still include a miticide when using a reduced risk material as an extra measure of protection.”
Soon, some orchards may require a spider mite spray if they haven’t already been treated. “So far this season, spider mite populations in almond orchards have been relatively low,” Bentley says. ‘They could be in an orchard now, but in most cases, they start showing up in July.
A spider mite treatment can be combined with a hull split spray for NOW and PTB. However, in cases where trees are under stress from mites, treatment before hull split may be warranted.
“Often, it’s a matter of balancing the cost of treatment with the amount of pressure from mites,” Bentley says. “In general, if you see mites on 50 percent of the leaves, it may pay to apply a miticide.”