Navel orangeworm is the primary insect pest almond growers in California must manage. When it comes to minimizing damage caused by this pest, one technique continues to be recognized as the most effective baseline approach: sanitation. By following proven sanitation guidelines, growers can limit the pest’s ability to overwinter, thereby reducing NOW pressure going into next season. Reduced populations can reduce pest damage as well as reduce pathogen inoculum.
The target for sanitation practices are mummy nuts. These are the nuts that remain on trees post-harvest. Mummy nuts provide the only bridge for navel orangeworm larvae to survive the winter and emerge the following spring to infest the orchard. In addition, last season’s mummy nuts serve as the egg-laying and larval development resource for the early NOW generations in spring and early summer prior to hull split, allowing for further population increase.
While mummy sanitation activities face logistical, environmental, and financial challenges, the practice of removing and destroying the nuts that remain after harvest is an essential component of the almond IPM program. Leaving mummies in trees or intact on the orchard floor has been shown to significantly increase NOW populations and damage at harvest, which can be more costly to growers in the long run. That’s because damage from NOW can reduce both total yield as well as price premiums for high-quality crops, important considerations when growers are calculating the return on investment for sanitation.
Mummy removal can be accomplished using mechanical harvesters, hand-poling crews, or a combination of the two. It is strongly suggested to follow removal of mummy nuts from trees with flail mowing to destroy nuts on the ground. Survival of NOW in ground mummies can be high, especially where there is little ground cover and low precipitation during the winter. Flail mower operators should be advised to pay attention to mower height and speed, checking to ensure that the ground mummies are adequately destroyed.
Timing is also important when determining when to mummy shake or pole in order to get the cleanest removal and return on investment. Mummies are most effectively removed after rain or fog events due to the mummies absorbing moisture and becoming heavier. However, even in years when environmental conditions do not provide these ideal opportunities, timely sanitation efforts should proceed. Mummy nuts should be off the trees by January 15th and destroyed by March 15th.
Sanitation in almond orchards is an important part of the IPM toolkit. Like most IPM strategies, it is most effective when used in conjunction with other tactics. NOW can often be managed to the low industry standard levels for damage when combined with timely harvest, proper use of insecticides, and mating disruption. Mating disruption is a non-toxic, environmentally friendly technique that can be used to protect almonds by preventing NOW adults from reproducing, exponentially decreasing pest populations when used alongside sanitation methods and other IPM tools. There are sprayable mating disruption products that can be used right up until the day of harvest, and aerosols that provide season-long protection when hung up in the spring.
As we head into the post-harvest season, keeping mummy nut removal in the forefront of your mind can help protect your crop in seasons to come.
Sometimes the most effective parts of an Integrated Pest Management program are the most straightforward ones, and removing mummy nuts is no exception. As we head into the post-harvest season, keeping mummy nut removal in the forefront of your mind can help protect your crop in seasons to come. If you have questions about IPM or mating disruption techniques, contact your local Suterra representative or send Suterra a message online through this portal.