If you’ve not been satisfied with the performance of hull split sprays that target navel orangeworm in your almond orchards in the egg stage, it may pay to start spraying a few days earlier.
Insecticide sprays are available in two categories: Those with ovicidal activity that penetrate the egg and kill the embryo while it is developing, and those that lack ovicidal activity but kill the worm as it chews through the treated egg to emerge.
Both are effective if they hit eggs that have already been laid on nuts, and are also toxic to worms as they crawl over treated surfaces, says Joel Siegel, USDA Agricultural Research Service entomologist at the Kearney Agricultural Center, Parlier, Calif.
Ovicidal insecticides include insect growth regulators and pyrethroid insecticides. Among non-ovicidal insecticides are neonictinoids.
“Ovicidal insecticides are even more effective when eggs are laid on a treated surface,” Siegel says. “For codling moth, an insect growth regulator was over five times more effective when eggs were laid on surfaces that had already been sprayed. That may mean spraying three or four days earlier than you’re used to doing, if possible. Improving your timing this way can be especially beneficial for minimizing applications that are too late when treating large acreages. Another advantage of this earlier spraying is that you’re preparing the tree in advance for NOW, rather than trying to catch up with the moth later.”
The increased selection of insecticide products, both ovicidal and non-ovicidal, has added to the challenge of timing applications for best results.
“It’s wonderful that growers have a number of choices,” Siegel says, “but it will take several years of tinkering with their use to find the way that best fits your own operation.”
Application timing is also being complicated by the expansion of almond and pistachio orchards, since both are hosts for NOW. This adds to the risk of a NOW invasion from a nearby orchard, he notes. Increased movement of NOW between the two different crops could change the most effective timing of applications from what it has been.
“To reduce NOW damage in the future, you may have to do more scouting and be more vigilant for the insect from year to year,” Siegel says. “That’s another reason to be ready to spray sooner than in the past. It’s better to have everything ready to go and then wait a few days, rather than suddenly having to scramble to get all your equipment together because NOW activity has picked up sooner than expected.”