It looks to be a late and extended almond hull split this year, says PCA Rene Forbes, Forbes Consulting, Inc., Dos Palos, Calif.
Typically, he says, hull split is when farmers apply insecticides to reduce damage to the nuts from navel orangeworm (NOW) and peach twig borer (PTB) and to control late-season mite pressures. Nonpareil is the cultivar most susceptible to NOW and PTB.
A few growers in Madera County, Calif., began hull split sprays around July 5, she says, but the process didn’t really begin in her area until early in the second week. Forbes’ growers applied their first hull split spray from July 13-21.
Fortunately, orchards are in great shape, Forbes says. “The trees look beautiful. Because of all the rain, I thought we’d have more rust and anthracnose by now, but I haven’t seen much in my area.”
Trees have not been stressed for water, thanks to abundant rainfall and irrigation water, and that’s reflected in the number of nuts she’s seeing in orchards. “It seems we’ll have a very large almond crop this year,” she says.
Her assessment jibes with the July 15 forecast by USDA/NASS California almond crop projection for an unbelievable record 1.95 billion meat pounds this year. That’s up 11 percent from the May subjective forecast and 19 percent above last year's crop. Production for Nonpareil, which represents 38 percent of California’s total almond production, is predicted to be 750 million meat pounds, 35 percent more than last year’s deliveries.
Second generation NOW moths infect at hull split, laying eggs on the suture and surface of the nut and inside of a split hull. With the typical 100-degree temperatures and dry air of Madera County summers, almond hulls dry out faster, producing a more uniform hull split in a shorter time.
As a result, the hatching larvae of navel orangeworm (NOW), which feed on the nut, tend to emerge closer to the same time, which makes for better timing and increased effectiveness of insecticide applications to control the pests.
Not this year. The cooler weather has caused hull split to spread out longer than usual.
“This summer, we’ve had mornings with temperatures in the 50s and dew,” Forbes says. “Most daytime temperatures have been no higher than the 80s and 90s — in fact, during the second week of July we had the lowest high temperature for the date ever. ”This situation underscores the importance of timing sprays to make the most of the insecticides’ residual activity to control NOW throughout egg-laying by the second-generation of the insect.”
Forbes tracks degree-days and trap counts of eggs to follow flight patterns and calculate the date when the NOW larvae are likely to hatch. But, she times the spray to control eggs and larvae based on when hull split actually occurs.
“That’s when the nut is susceptible to the worms,” she says. “If the hull isn’t split, the worms can’t get inside. Timing the spry at hull split gets the chemical on the hull when it will do the most good. Those worms that hatch before the hull splits will starve to death since they can’t get into the nut meat. That’s why I’d rather spray at 1 percent to 2 percent hull split, instead of basing the application on the flight pattern of NOW if the pest is coming off before hull split.”
She has another reason for waiting to treat for NOW at hull split: “If you have successive generations of the pest in your orchard simultaneously, egg counts in a trap may not give you a conclusive picture of the threat,” Forbes says. “Waiting to spray until hull split gives you a better chance of controlling overlapping generations.”
If hull split is erratic or strung out, more and more surface area becomes available for NOW egg-laying at later times. Thus, it becomes increasingly difficult to cover all of the areas of the nuts when applying a pesticide that will last through a lengthy hull split.
So, to increase the odds of controlling NOW, as well as any peach twig borers that may have escaped a May spray, she brackets her hull split insecticide applications — making the first spray at early hull split and a second one at later hull split. This provides more control than a single spray of insect growth regulators, which Forbes says are less harmful to good bugs and less risk to employees.