Winter sanitation addresses two issues: navel orangeworm (NOW) and aflatoxins.
NOW, named because it was first found on navel orange trees, is a primary pest of California Almonds and can be found on several hosts. The larvae bore into the nutmeat, rendering them inedible, and later, consume most of the nut to produce large amounts of webbing. This damage by NOW larvae not only reduces yield, it can also lead to fungal infections that result in aflatoxin contamination.
Aflatoxin is a chemical compound produced by Aspergillus flavus and A. parasiticus, known carcinogens and mutagens. The mold spores are found in the soil, dust and air. Research indicates that NOW larvae can tolerate high concentrations of aflatoxin, explaining the strong link between navel orangeworm activity and aflatoxin.
A major concern for the almond industry is increasingly rigorous tolerances for aflatoxin contamination in key export markets. One of the largest markets for California almonds – the European Union (EU) – also has one of the lowest allowable limits for aflatoxin contamination on almonds. In response to this, the almond industry is focused on improving NOW management and reducing the potential for aflatoxin contamination.
How to prevent NOW and aflatoxin
1. Winter sanitation to remove mummies
Effective removal and destruction of mummy nuts (almonds left on trees after harvest) during the winter will offer the most effective control of navel orangeworm. Removing mummy nuts to an average of two mummies per tree will reduce damage for the next growing season. Without winter sanitation, the damage to the next crop can significantly increase.
2. Prompt harvest before a third generation of NOW develops
3. In-season control of NOW with insecticides or biological control agents
Application of insecticides or other in-season IPM techniques are reduced when these practices are carried out properly. If necessary, sprays are timed using egg traps, monitoring of hull split and/or degree-days.
Aflatoxin Affects Food Safety
Managing Stockpiles to Prevent Aflatoxin
Post-Harvest Sample Defines IPM Strategies
Post-Harvest Monitoring Guidelines
Deficit Irrigation Strategies to Prevent NOW & Aflatoxin
Focusing on NOW Management (article in Western Farm Press magazine)