How to the fight the battle against Navel orangewood (NOW) and coddling moth in walnuts was the take home message of Emily Symmes, UCCE Area IPM Advisor, Sacramento Valley, in her presentation at the West Coast Nut hosted Annual Walnut Trade Show at the Yuba-Sutter Fairgrounds on Jan. 6, 2017.
“Coddling moth hit pretty hard this last harvest, as did Navel orangeworm,” she said. “A lot of people were caught a little off guard by both.”
Of particular concern was damage seen in the later maturing varieties, which have historically been considered less vulnerable to worm damage.
“Earlier-than-typical, and spread out husk split and maturation led to many later varieties experiencing higher damage in 2016. The high NOW damage at harvest may have been the result of large overwintering populations, the mild, dry winters over the past few years and earlier springs,” Symmes added.
The earlier springs and high temperatures during the growing season is a recipe for additional generations being able to complete development, at times allowing a partial or full fourth generation in late summer through fall.
Symmes stressed the importance of considering all varieties of walnuts in managing these pests and proposed management program options in planning for 2017, with an emphasis on Navel orangeworm (NOW) as its damage is becoming more common over the past few years.
“A key component in the battle is identifying NOW and codling moth, and the differences in their appearance and behavior,” Symmes stated.
The tip of each codling moth forewing has a coppery-tinged, dark brown band that distinguishes it from other moths found in walnut orchards.
NOW is silver-gray with irregular black patches on the forewings. The snoutlike palps in front of the head help distinguish this moth from the codling moth, as does the presence of a dark, cresent-shaped mark behind the head of Navel orangeworms, absent in codling moth worms.
“It is important to know which insect you are dealing with so you can evaluate which management practices are best so as not to waste time and product,” Symmes said.
This graphic shares the habit of damage caused by the two moths in the nut and the differences:
|Photos of nut damage||Kernel||Frass||Webbing||Boring||Feeding behavior||Other|
|Navel orangeworm||Deep chewing into kernel.||White, often quite a lot.||Yes, often quite a lot.||Yes, into kernel.||Larvae feed in groups.
Many per kernel.
|Shells of heavily infested nuts appear oily.|
|Codling moth||Deep chewing into kernel.||Frass at point of entry into the husk.||Very little.||Yes, into husk and kernel.||Single larva feeds per kernel.||NA|
When there is insect damage in the nut, but worms aren't present, NOW damage can be detected by looking for insect excrement and webbing as multiple NOW will infest a single nut.
“The codling moth typically infests nuts singly,” Symmes stated.
NOW females lay eggs singly on leaves and sometimes on fruit later in the season. The eggs are smaller than a pinhead, disk-shaped, and opaque white when first laid. After about a day, they turn pink, then reddish orange.
Codling moth eggs are disc shaped and opaque white, overwinters as full-grown larvae in thick, silken cocoons under loose scales of bark or in trash on the ground near the trunk.
After hatching, the tiny caterpillars enter nuts through the soft tissue at the stem end and do not emerge until they are adults.
Overwintering and early NOW generations survive in mummies and damaged nuts prior to infesting in-season nuts.
This knowledge helps to understand the need in reducing overwintering populations and reducing early generation development sites.
“If you are in a situation where you had high NOW damage at harvest in 2016, consider that as a potential risk factor going into next year when talking about management options,” Symmes said.
She shared four key elements to management:
- Sanitation—remove and destroy mummies by early March. That includes on the trees, the orchard floor, bins, hulling and drying equipment, and buildings. This practice will limit NOW overwintering sites and reduce the availability of developmental sites for early generations the following season.
“Research has shown the more destroyed the mummies are, the more impact it has on reducing future populations,” Symmes said.
Get orchard as “clean” as economically feasible.
While doing this, crack out a sample of mummies to determine carry-over population potential. Estimating mummy infestation helps provide a ballpark of potential native population going into the season.
Symmes recommends taking nut samples just prior to husk split from early splits or dropped nuts.
“If eggs are detected, harvest promptly to avoid damage and consider insecticide treatment,” she added.
Maintaining ground cover during winter may aid in decomposing trash nuts, but do not rely solely on this, especially in dry years.
Wet weather helps, if nuts are on the ground.
- Minimize damage caused by other sources—such as codling moth, blight, sunburn and hail. Sound nuts are most vulnerable to NOW damage after husk split, thus good codling moth, blight and sunburn management helps to reduce earlier season access and development sites.
“Try to eliminate damage that results in entry points for damage. While there are some situations, such as hail damage, that can't be controlled, it is important to know what entry points for NOW are out there and assessing potential damage,” Symmes said.
- Timely harvest—the longer nuts stay in the orchards after husk split, the more time they are vulnerable to NOW infestation.
Symmes recommended timing harvest to avoid later generation NOW flights.
“Time harvest to avoid late generation flights,” she added.
Also, growers should to consider the possibility of increased damage in the second shake and the use of ethephon to advance husk split to avoid he late generations of NOW.
“Especially in high NOW population years and prolonged dry falls, and based on in-orchard monitoring and potential for immigration from adjacent orchards,” Symmes said.
NOW is considered a strong flier and can develop in a number of fruit and nut hosts, both agricultural and non-agricultural.
- Insecticide treatments—it is also important to know whether or not there is a need for treatment, Symmes said.
One component in determining need for treatment is through continued monitoring options of egg traps, pheromone traps, kairomone traps and crop phenology and egg detection.
Either delta or wing pheromone traps can be used to monitor adult male flights and activity. They need to be hung by early March and counted weekly.
There are currently three female pheramone products on the market—Suterra Biolure, Trece Pherocon NOW L2 (high and low) and AlphaScents AMYTRA, Symmes stated. She said results from research comparing these products and how they work will soon be made available in UCCE agriculture publications.
Kairomone traps, either wing or delta, for attracting and capturing females can be baited with ground nuts (almond or pistachio). This form of monitoring adult female flights and activity helps to establish orchard history.
“While some people find the delta trap is easier to use and cleaner to service,” Symmes said, “the caveat is that they aren't as sensitive and tend to catch fewer moths than the winged trap. My thought is, use whichever is best for your program.”
She recommends, if making changes in the type of trap or lure used, make sure to always document those changes.
Also, the use of traps help to determine the historical pressure in orchards, and immigration potential and treatment thresholds.
Symmes said research is ongoing into the benefits and best implementation of both kairomone and pheramone traps.
“The best current guideline for NOW is to focus protection from husk split through harvest,” Symmes advised.
In the area of codling moth mating disruption, she said what's new in proven technology is the use of aerosols, is the finding of effective suppression at reduced loads and shorter operating times.
“That spells out to more economical options,” Symmes added.
In relations to NOW, good, early codling moth control can reduce NOW damage.
“Flexibility in spray programs can help target other pests,” Symmes said. “Timing for each pest is more critical with increasingly selective pesticides.”