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Winter Sanitation: The Foundation of Navel Orangeworm Control


Keep Rejection Levels Below 2 Percent

The Almond Board’s working goal for the industry is to keep almond harvest rejection levels below 2 percent and to strive for 1 percent, or less. If a grower’s average damage is over 2 percent, it is critical they take a closer look at overall practices and specifically adopt stronger winter sanitation measures, which are the foundation for any NOW control program.

Winter sanitation is key

Remove mummy nuts before bud swell by hand poling or mechanically shaking, or both.

Concerns over rejection rates span beyond direct crop damage and quality because NOW damage is also associated with aflatoxin. In addition to the direct damage NOW causes the kernel, the damage opens the door to fungal infections and contaminants, particularly to the fungi Aspergillus spp. and the aflatoxin contaminant it produces.

The stringent tolerances for aflatoxin contamination in key export markets like the European Union and Japan raises the importance of this yearly integrated management practice.

Mummy Nut Removal Key to Success

Winter sanitation, the cornerstone of NOW pest management, involves the removal and destruction of mummy nuts to prevent overwintering NOW and prevent two-year mummy kernels being harvested the following year. It’s also part of being a good neighbor, as NOW can travel to other almond orchards if many mummy nuts remain.

To reach the goal of 2 percent damage or less, growers should follow the guidelines below, which vary by growing region.

  1. Before January 15, and preferably earlier: Count the mummy nuts and examine 20 trees per block. If an average of 2 or more mummy nuts per tree (and even lower in the southern San Joaquin Valley) are found on or before January 15, get out the shaker or poling sticks and remove mummies in the entire block.
  2. Before February 1: Remove mummy nuts from trees before bud swell, typically before February 1, by mechanically shaking the tree or hand poling, or both.
  3. Before March 1: Blow or sweep fallen mummy nuts to the row centers and destroy them by flail mowing, especially where ground cover is not present or in years with dry winters. This timing is critical as mid-March is when the NOW flights begin.

Growers who have been implementing these cultural practices in their orchards and who still experience rejection levels greater than 2 percent should seriously consider other NOW management practices including more focus on timely harvest, in-season sprays and NOW mating disruption. 

Responsible Practices Maintain Open Markets

The European Union, one of the biggest importers of California almonds, has tight regulations and a low threshold for aflatoxin levels. To maintain open market opportunities in Europe, the Almond Board of California created the Pre-Export Checks (PEC) program as a systems approach to aflatoxin mitigation, based on the handler using specified procedures to sample, test and ship almonds to Europe.

Navel orangeworm

Winter is a key time to practice winter sanitation and prevent NOW outbreak later in the year.

Growers can also do their part to maintain these market opportunities by practicing winter sanitation to ensure strong yields and quality product. 

Mummy nuts have been identified as the link between one season to the next for overwintering NOW. It becomes an insidious cycle if mummies are left in the orchard, as they become a food of subsistence for NOW. Therefore, growers are strongly encouraged to minimize or break down this link to prevent continued pest damage and should continue practicing winter sanitation for years to come.

To learn more about winter sanitation and minimizing navel orangeworm, visit Also visit the UC IPM site,, and click on ‘Agricultural Pests,’ then ‘Almonds.’