The High Cost of Navel Orangeworm

One of the most serious insect pests of almonds in California is the navel orangeworm (NOW). It poses a high risk to an almond crop because the worms bore into the nut and consume most of the nutmeat. A second risk is that NOW opens the door to aflatoxin contamination.

Life stages

NOW larvae overwinter in mummy nuts either in trees or on the ground. Females begin laying eggs about two nights after emergence from the pupal stage. Eggs are laid on mummy nuts in the trees or on new crop nuts after hull split begins. Larvae bore into the nutmeat and can consume most of the nut, producing large amounts of webbing and frass. NOW larval damage can also lead to fungal infections, such as the mold that produces aflatoxin. Some cultivars are more susceptible to damage, especially later maturing, softshell almonds with a lengthy hull split period or a poor shell seal.

Navel orangeworm management

Growers must enact these critical steps in their IPM program to minimize navel orangeworm damage and risk of aflatoxin:

• Winter sanitation to remove mummies
• Prompt harvest before a third generation of NOW develops
• In-season control of NOW with insecticides or biological control agents

By following guidelines for early harvest and winter sanitation, in-season treatments for NOW may not be necessary. Consider reduced-risk compounds like Intrepid, Delegate, and Success for any in-season sprays to avoid flaring web-spinning mites.

Sampling and monitoring

Treatment decisions for NOW are made on the basis of several sampling and monitoring techniques, including a harvest sample, number of mummy nuts per tree after budswell, degree-day accumulation to predict egg hatch, and egg traps to confirm when hatch begins.

Monitoring and treatment decision guidelines can be found at the UC IPM Web site.  When planning insecticide applications, you should consider the environmental consequences on air quality and water quality.

A five-year study currently under way and funded by the USDA-ARS, is looking at aspects of navel orangeworm damage and management, including a NOW pheromone confusion program and large block trials to discover how newer, softer insecticides best fit in an IPM program.

NOW and aflatoxin

Aflatoxin produced by Aspergillus mold are known carcinogens and mutagens. It is a major concern for the almond industry because of increasingly stringent maximum limits for aflatoxin contamination in key export markets. Navel orangeworm damage in the orchard opens the door for aflatoxin production; therefore, the first line of defense in preventing aflatoxin is to manage NOW in the orchard.

External Links:

Focusing on NOW Management (article in Western Farm Press magazine)

UC IPM Pest Management Guidelines

Seasonal Guide to Environmentally Responsible Pest Management Practices in Almonds