A newly developed model that predicts navel orangeworm (NOW) damage under various winter sanitation and harvest timing scenarios, combined with field experience and research, gives evidence that the current guideline to remove mummies to an average of two mummies per tree by Feb. 1, needs to be revised.

The model, developed by entomologist Brad Higbee with Paramount Farms and Joel Siegel, USDA-ARS-Parlier, indicates that the guidelines should be tailored to growing regions based on the amount of rainfall, which reduces orangeworm survival. For instance, in the drier southern region, the model and field experience show the mummy threshold is less than the current standard, while in the Chico area, this threshold could be revised higher. The model, currently being validated, provides a tool that growers and pest control advisers can use to assess expected results and project the outcome of different options in order to take appropriate action.

A teaching tool version of the model, based on Kern County conditions and data, is posted on the Almond Board Web site almondboard.com/nowpredictor for those interested in seeing how different scenarios can impact final NOW damage. Even though this version is specific to the Southern San Joaquin Valley, it underscores and reaffirms a number of longstanding basics; in particular, that sanitation – removal and destruction of both tree and ground mummies – is a priority. After this, harvest timing, early vs. later, is important. Other factors that have an impact on NOW damage include the previous year's NOW damage, and peach twig borer damage during the current season. Also specific to the southern San Joaquin Valley is proximity to pistachios, which harbor higher NOW populations.

This work is being done under a five-year USDA-sponsored Area-wide Pest Management Project with additional funding from the Almond Board of California. Another aspect of the work is being led by UC Plant Pathologist Themis Michailides with USDA's Siegel. They are finding that under field conditions, both NOW larvae and adults carry spores of Aspergillus – the fungus that produces aflatoxin – and introduce it into the hulls, shells and kernels.

For more on recent NOW management research, see the article by ABC's Bob Curtis, "Focusing on NOW Management," in Western Farm Press: http://westernfarmpress.com/tree-nut-crops/now-management-1021/index.html.