The Achilles heel of damaging Navel orangeworm (NOW) in almonds is a well-timed spring pesticide application, according to veteran entomologist Walt Bentley.
However, growers and PCAs have gotten away from that because the cure can be very costly in the long run, according to Bentley, University of California IPM advisor based at the UC Kearney Ag Center, Parlier, Calif.
Bentley told growers at a field day in the Locke family’s young almond orchard near Mendota that there are a host of new non-disruptive, lepidopterous-specific insecticides on the market that can minimize the consequences of an early-spring NOW spray.
In the past when growers tried to control overwintering NOW in almonds, invariably it would flare spider mites, particularly when pyrethroids were used.
Growers often tank-mixed a miticide to minimize mite flare-ups or budgeted as many as three or four miticide sprays to follow early-season NOW sprays to keep mite populations in check.
“These new materials are not only non-disruptive, but are just as effective against lepidopterous (caterpillar) pests and in some cases better than older material,” he told growers and PCAs at the field demonstration sponsored by the Almond Pest Management Alliance, a collaborative project of almond industry stakeholders to demonstrate the latest research and production practices in almonds.
Although proven effective, the use of products like Delegate, Belt, Intrepid and soon to be registered Altacor is all about timing egg hatching of overwintering NOW.
NOW that have overwintered will begin egg laying during mid-April to mid-May. This is when traps are to be used to determine populations and timing of sprays.
Bentley says to place traps 6 to 7 feet above ground and 1 to 3 feet away from tree drip or micro sprinkler lines.
He recommends trapping where there has been high levels of damage the previous three years; where NOW may come in from nearby orchards, including pistachios, particularly at hull split.
These traps are to be baited with almond meal and crude almond oil. There are commercial traps available or growers can buy empty traps and mix the bait themselves.
“If you buy already baited traps, make sure they have oil in them. They will not work without oil,” Bentley warned.
Black traps function better than white traps, according to researchers. For one to 20-acre orchard blocks, one trap per five acres is sufficient, but never fewer than three traps per orchard. For tree blocks of 20 to 80 acres, one trap per 10 acres is sufficient and no fewer than three traps per orchard. For orchards larger than 80 acres, hang one trap for every 20 acres.
Monitor traps one to two times per week. Clean out and replace with fresh bait every two months or after a rain.
Bentley said overwintering NOW moths will lay eggs along the ridges of the trap and under the cap.
“They will be white initially and then turn red and look like a string of beads,” said the UC entomologist.
When 50 percent to 70 percent of the traps have eggs on them, growers need to be aware egg hatch is close at hand.
“These eggs can hatch quickly in about 150 degree days roughly in a week’s time” he says.
During this April-May period, growers and PCAs need to determine when egg laying occurs consistently on 75 percent of the traps over three to five consecutive days.
Treat the orchard when the first eggs hatch among those collected, according to UC researchers.
Bentley is encouraging growers with NOW problems to look at returning to May sprays since trees have fewer leaves then and therefore easier to penetrate with a pesticide application, and growers do not have to deal with hull split issues where hatching eggs are difficult to reach with pesticide sprays.
Bentley also says a well-timed spring spray along with equally precise hull split spray would make for more efficient use of spraying equipment.
“If you have only one sprayer for maybe 160 to 200 acres, by using the trapping and proper timing a grower could treat part of his orchard at the optimum time in May and then come back in July and treat the rest of the orchard at that optimum timing,” he explains.
This trapping method can also be used to time mid-season treatments ahead of hull split. In the heat of summer, UC researchers are recommending a minimum of three traps per orchard.
Treatment then is based on 1 percent to 5 percent hull split of Nonpareil. Wait until eggs are deposited on traps prior to initiating treatment.
Bentley added that in many seasons, timing of peach twig borer (PTB) sprays is also good timing for NOW treatments. “This year it is almost right on,” he added.
“What we are trying to do with this trapping system and May spray with non-disruptive insecticides is to get the biggest bang for a grower’s buck … to get optimum timing to limit NOW sprays to maybe only one treatment per season,” he says.
“Not everyone has NOW problems,” Bentley explains.
Those who don’t are generally practicing post harvest sanitation by winter shaking mummies off trees. Mummies are ideal locations for overwintering NOW moths to lay eggs.
And remember, Bentley said, even with the best shaking and shredding of mummy nuts, growers will have missed mummies. “Even if you have four or five mummies per tree, NOW moths will find them and lay eggs. You usually see eggs along the suture of the mummy just like you do at hull split,” he explains. “However, if the sutures are full — the moth will lay eggs elsewhere on the mummy nut.”
Bentley adds that overwintering NOW will not lay eggs on green almonds. If they do, it will result in suicidal emergence.
Control of Navel orangeworm has become critical as a food safety issue. In the past, 4 percent NOW damage was tolerated, but the kernel damage inflicted by NOW can lead to aflatoxin contamination.
The goal today is 2 percent or less NOW damage at the huller/sheller.