Franz Niederholzer, UCCE Farm Advisor, Colusa, Sutter, and Yuba Counties
Sudan Gyawaly, UC IPM Area Advisor, Sacramento Valley

Times change. Weather changes. Manage navel orangeworm accordingly.

For years, discussions about pest pressures in almond production in California have been separated by north/south differences, usually related to weather. The higher average rainfall in the Sacramento Valley means more disease pressure in that region. Generally hotter temperatures in the Central to Southern San Joaquin Valley drive higher navel orangeworm pressure “down there”.

The UC IPM website for almond pest management presents separate thresholds for orchard sanitation for navel orangeworm management – one for southern and central San Joaquin Valley and another for the northern San Joaquin and Sacramento Valleys. Based on mummy counts in 20 trees per block, the current northern threshold was the statewide industry standard beginning in the 1980s and established the target of 2 mummies or less per tree with no mention of number of mummies on the orchard floor. As quality standards and market concerns about Aflatoxin increased, Kern County research produced a stricter southern region threshold — 1 mummy per 5 trees and 8 mummies on the ground under each tree, using data from 2003-06. The researchers developing the southern San Joaquin Valley threshold stated that “in order to meet a new threshold of 2% or less kernel damage in Kern County” the new threshold numbers were needed.

Winter sanitation will be critical to controlling NOW next year given the early reports of 200+% jump in NOW damage in Nonpareil in some counties in the Sacramento Valley this year and the expected high carry-over NOW populations. It could pay growers, here, to sanitize to the lower, tougher standards developed down south.  The decision is yours. Activities on any farm are the decision of the grower. Lower yields and nut prices the last couple of years in the Sacramento Valley have made the decision to do proven practices difficult. However, not sanitizing at all invites potential disaster, for your operation and very possibly for your neighbors.

Also, remember that ‘Winter Sanitation’ is just the first, very effective, of the several lines of defense against NOW damage. Other defenses against NOW include timely harvest, well-timed in-season sprays, and mating disruption practices. Multiple NOW management practices are necessary to lower NOW damage to below 2%, the acceptable damage set for the industry.  The foundation of NOW management is orchard sanitation, but many steps are needed to reduce crop damage, especially when NOW numbers are high.