Sanitation is the basis of a good integrated pest management system for navel orangeworm. UC Integrated Pest Management Advisor Emily Symmes spoke about the importance of sanitation at this year’s Almond Conference and said the 2017 season was a stark reminder about the need to get those mummies out of the trees.
From the UC IPM website:
Two cultural practices —effective removal with the destruction of mummy nuts in fall or winter (sanitation) and early harvest with rapid removal of nuts from the orchard floor— are essential components of an effective navel orangeworm control program. Insecticide treatments are often needed if these practices are not carried out, in situations with high navel orangeworm numbers, or when navel orangeworm may immigrate in from neighboring orchards. When infested trees of alternate hosts are harvested, navel orangeworm moths may migrate into almond orchards. Treating border rows (at least ten rows) may be adequate to prevent the moths from infesting the almond crop when navel orangeworm numbers are low to moderate in a given area. Sprays are timed using egg traps or pheromone traps in conjunction with degree-days, and monitoring hullsplit. Two parasitic wasps may be found in orchards, but they cannot be relied on to provide effective control alone without using other cultural or compatible chemical practices.
In contrast to the mid- and southern San Joaquin Valley, navel orangeworms are typically less abundant in the Sacramento and northern San Joaquin valleys, so nut damage tends to be less severe. However, environmental conditions, proximity to sources of infestation, and effectiveness of sanitation practices impact the potential for damage by this pest, regardless of growing region.
Remove Mummy Nuts (Sanitation)
Remove mummy nuts from trees before bud swell by mechanically shaking the tree or hand poling, or both. Blow or sweep fallen mummy nuts to the row centers and destroy them by discing or flail mowing by March 1, especially where ground cover is not present or in years with dry winters. Moist orchard floor conditions provided by winter-resident vegetation and rain will enhance mortality of navel orangeworms in mummy nuts that have fallen from trees in years with adequate rainfall. Conversely, mummy removal is even more important during periods of drought because the survival of the overwintering larvae in the mummies tends to be greater than in wet years. Nevertheless, mummies remaining in the orchard, even if not infested with overwintering populations, may provide a development site for first flight prior to hullsplit.