Navel orangeworm is always a troublesome pest, but forecasts are predicting that damage in 2017 is likely double the average year, said Dr. Emily Symmes, UCCE Area Integrated Pest Management Advisor for Sacramento Valley.
Not only was the damage severe in 2017, but it could translate into contamination risk and further spread of navel orangeworm in 2018, if growers don’t take steps to sanitize their orchards, Symmes told an attentive crowd at the Tree & Vine Expo in Turlock.
First, the reasons Symmes gave why it was an especially bad year for navel orangeworm:
“2017, it rained a lot, and it didn’t let up. What did that mean? It meant if you didn’t have your rigs in and sanitized your orchards, earlier than most folks, it was darn near impossible to get the rigs in the field,” Symmes said.
That meant mummy nuts in the fields didn’t rot enough to be uninhabitable by navel orangeworm.
Another reason for the explosion in activity?
“2017, it got hot. We’re used to it being hot, but the heat hit earlier and really just did not let up,” Symmes said. “It got hot and stayed hot through September. Insects are exothermic…these hot temperatures drove more rapid development of insect populations, including navel orangeworms.”
The unusual heat pushed population development earlier, meaning that the fourth flight of moths for the season was out flying around for an additional two weeks with almonds on the trees.
Lastly, Symmes pointed to other damage to walnuts that in many cases let Navel Orangeworm in during the season. In one test plot of walnuts, she saw 30% damage. In some cases, 6 or 7 larvae shared a single nut.
It’s a big deal, Symmes said, point to a startling statistic:
For every 1% of nuts damaged by navel orangeworm, the industry around the state loses $67.5 million.
So what can growers do to prevent it from happening again?
The main point Symmes drove home was sanitation.
“Sanitization is not cheap to do, but it’s absolutely critical we go out and do it,” she said. “There’s a lot of damage out there—what does that mean? Contamination risk for next year.”
Even if your orchard is pretty clean, Symmes said, mummy nuts on the ground can lead to contamination, with navel orangeworm moths flying up to half a mile away.
“The more and more you can destroy the nuts, the better impact you’re going to get on your navel orangeworm populations,” she said.
Growers should gather as much information as possible about where navel orangeworm risk is highest. That can mean laying egg traps, pheromone traps, and kairomone traps.
Data to consider can also include proximity to infestation sources like navel orangeworm habitats and infested orchards, the damage level in the prior season, and carry over populations in mummy nuts.
Symmes recommended cracking open mummy nuts on trees in the orchard, either getting help from a Pest Control Advisor or a niece or nephew to see what ratio of mummy nuts are infested.
“You gather all the information you can, you put it in a witch’s brew and hope you get something out of it,” she said. “It becomes just as much art, honestly, as it is science.”
For more information on mummy nut cleaning standards, traps, and sprays, see the UC Agriculture & Natural Resources website on navel orangeworm.