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

Historically high navel orangeworm damage in almonds last year has caused many growers to commit to aggressively managing navel orangeworm (NOW) this year. Many (most?) growers sanitized their orchards this year with winter shaking, although we’re not sure how many were able to get below the recommended 2 mummies per tree average.

Now that the season has begun, what can growers do to manage NOW? Many growers are adding mating disruption in their orchards this year. Mating disruption is a proven technology with about a 50% reduction in nut damage by NOW when using this tool with other control methods, and cost is justifiable when the damage is above 1%. Dispensers should be up this spring following manufacturer’s guidelines. Likewise, many growers with a high NOW damage last year and more than 2 mummies/tree at the start of the season may opt to use a spring (mummy) spray this year to reduce NOW populations within the orchard. Mummy sprays can reduce NOW pressure within an orchard going into hull split, but should not be seen as an alternative to winter sanitation. If you are considering applying a spring spray to manage NOW, be smart about the product you select and the timing when you apply it.

Selecting the product(s). There are two important facts to remember while selecting insecticides for spring sprays. First, the flights of spring generation can extend over 3-4 months; therefore, using a product with a longer residual effect should be more effective. Also, using higher label rates should extend the insecticide activity. Second, broad-spectrum insecticides (pyrethroids such as Asana, Warrier, Brigade, etc.) applied during this period can flare up spider mites as they can reduce natural enemy populations. Using growth regulators (Intrepid, etc.) or other reduced-risk insecticides (Altacor, etc.) that have relatively longer residual effects and have lower risks to spider mite predators could therefore be a good choice for spring sprays. Keep in mind that these insecticides tend to be more costly.

Timing insecticide spray. New crop almonds are not susceptible to NOW damage until hullsplit. Mummy nuts are the bridge that NOW use to move from crop to crop. The rationale behind insecticide sprays in spring is to target the mummy nuts prevent the NOW population from building up in high numbers ahead of hullsplit. This approach is theoretically correct. However, one application likely won’t cover all the overwintering population and will not control NOW in neighboring orchards. Determining egg-laying biofix using egg traps and spraying insecticides after 100 DD after biofix (or spray timing for peach twig borer) to cover the peak egg laying activities is important for these treatments to have the most impacts in reducing NOW numbers.

Hullsplit Sprays. Finally, applying insecticide 1-2 times at hullsplit is critical in protecting the crop from NOW damage regardless of spring sprays. Doing  hullsplit sprays correctly is crucial for NOW control. Do not wait too long (spray at 1% hullsplit or slightly earlier); early sprays (after blank nut hullsplit) are reportedly better than later. Very good spray coverage is highly critical in protecting the nuts from NOW damage. High volume sprays (150-200 GPA) with a slower spraying speed (2 MPH) provides better coverage. Rotate the insecticide between the generations (i.e., use chlorantrniliprole (Altacor) at hullsplit sprays if methoxyfenozide (Intrepid) was used during spring) to reduce or slow the risk of insecticide resistance development.

Navel orangeworm is impossible to control completely, it must be carefully managed to reduce damage and improve grower income. Growers and PCAs are fighting back to manage NOW this year. Following the steps outlined in this article should help growers land punches and avoid swinging misses.