Tips for Nut Growers Living with Navel Orangeworm

An infested nut from photo taken in January. There are no larvae visible, but navel orangeworm frass is evident. (Photo: Franz Niederholzer)

Navel orangeworm (NOW) damage in the 2017 almond crop was painfully bad in many blocks in California’s Sacramento Valley.

It cost some growers hundreds of dollars per acre, slowed crop processing (more money lost), and may be an issue in some international markets due to aflatoxin concerns. Ugly, ugly, ugly. While bloom is a “quiet” time for NOW management — other than destroying mummies — it’s a good time to review the pest and your options as the season begins.

Management Options
The following is a chronological menu of management options for NOW management and/or control for growers to consider from now until pollinizer harvest, though not all activities are necessary in every orchard every year.

Navel orangeworm larvae is shown from a mummy cracked open in January. (Photo: Franz Niederholzer)

Know Your Enemy
Remember that not all of these activities are needed in every orchard every year. Work closely with your Pest Control Advisor(s) to evaluate the pressure in your particular orchard blocks and adjust your management plan accordingly. The timing and number of sprays needed to achieve successful — or at least tolerable — control of NOW will depend on multiple factors, and can be informed by a number of risk assessment methods. These methods include monitoring of both pest densities and crop phenology, historical/previous season damage, location of external sources of NOW, etc. Know your enemy.

Mission Impossible
Given the pest, dense orchards, and the tools available, it is not possible to eliminate the pest. The aim is to minimize its damage by using all of the tried-and-true methods available: keeping your orchard clean using winter sanitation until hull split, reducing NOW pest levels with hull split sprays, and harvesting and picking up the crop as soon as 100% hull split arrives. Additional things you can do to reduce NOW damage in tough years: