Navel orangeworm management at harvest: When, what, & how to get the best results

Franz Niederholzer, UCCE Farm Advisor, Colusa & Sutter/Yuba Counties; Emily Symmes, UC IPM Area Advisor, Sacramento Valley

Almond nuts become vulnerable to navel orangeworm (NOW) damage at hull split.  In the south Sacramento Valley this year, Non-pareil hull split is expected in the last week of June, about the same time as last year, based on the prediction model developed by UC researchers (see it on-line at:  http://fruitsandnuts.ucdavis.edu/Weather_Services/almond_hullsplit_prediction/).  Protecting nuts from NOW (and peach twig borer) with hull split sprays and timely harvest are key to delivering a high quality crop to the huller and maximizing grower returns.  If you haven’t already, now is a good time to plan your hull-split spray(s).

Non-pareil (NP) nuts split first – and have the most value.  Not surprising, the primary focus in NOW management is protecting NP nuts.  The worst NOW damage to NP nuts occurs if the nuts are still in the trees when 3^rd generation NOW egg laying begins.  Harvest should occur when 100% of the nuts have split but the hulls are still green (see picture below). If this can be accomplished before 3^rd generation egg laying, a significant portion of NOW damage to NP can be avoided.  Preconditioning of just-shaken nuts accelerates their drying and hastens pickup, reducing nut exposure to protein feeding ants and allowing irrigation ASAP before pollinizer harvest.  Careful orchard monitoring of NOW populations using egg traps and degree days indicate when egg laying should occur.  This can be supplemented with using pheromone traps to follow male flights.  In addition to timely harvest, properly timed and applied hull split sprays can help reduce the overall NOW population in the orchard and thus limit crop damage and income loss from current and future resident NOW generations.

Once hull split occurs, growers can target different NOW generations depending on varieties planted, previous/current pressure, pre-harvest interval (PHI) timings (see table in this post) and when NOW egg laying is expected based on egg trap counts and degree day accumulation.  If making multiple hull split applications, rotate pesticide mode of action chemistries (see IRAC numbers in table in this post) to minimize the risk of resistance development.  The best time(s) to spray depends on egg trap counts and projected egg laying timing, damage history in the orchard, and how many times you can afford to spray.  The following are some points to consider when planning hull split sprays:

• If 3^rd generation NOW egg laying will occur before shaking and you can only make one spray per year, spray to protect the crop ahead of egg laying for the 3^rd generation – usually 1700-2100 DD from spring biofix on egg traps.
• If you can shake your Non-pareil before 3^rd generation egg laying, spray to control the 2^nd Some growers make two applications against this generation, depending on budget and materials  – one spray at first suture crack and another 2 weeks later (if label allows).  This practice protects the Non-pareil crop and suppresses the NOW population, hopefully reducing damage to pollinizers.
• NOW populations can grow very large after Non-pareil harvest and pesticides targeting early generations of NOW last 4 weeks at most. Consider treating pollinizers once Non-pareil pickup has occurred.  Late pollinizers with higher value in-shell options (Monterey) may benefit from additional spraying, especially in small blocks with heavy NOW pressure from outside the orchard.
• Don’t forget B.t. as a stopgap measure if the crop is not protected and shaking is delayed. Effective protection is only lasts a few days, but there is no PHI and if only a few days protection is needed…

Effective pesticides labeled for NOW control in almond range in persistence, PHI, impact on beneficial insects, and price.  Pyrethroids (Brigade®, Warrior®, etc.) have provided excellent control with relatively short PHI and modest price but are hard on beneficial insects (mite and scale predators).  These materials provide about 2 weeks protection.  Pyrethroid resistance is building in NOW populations in the San Joaquin Valley, and is thus likely in other areas of the state, reducing pest control and increasing damage potential.  Chlorpyrifos  (Lorsban®, etc.) is a very effective material, but has a relatively short persistence in the orchard.  Newer chemistries (Altacor®, Belt®, Intrepid®, Delegate®, Proclaim®, etc.) range in persistence and price, delivering good pest control (with good spray coverage) and reduced impact on beneficial insects.  In recent UC research, 3 to 4 weeks of pesticide activity was provided by Altacor® or Belt® and Intrepid®, respectively.  Wherever possible, these newer pesticides should be applied ahead of any NOW egg laying to get maximum benefit.  Dr. Joel Siegel, USDA ARS, recommends that materials such as Altacor®, Belt®, or Intrepid® be applied at the very first hint of hull split (first suture crack) so that if egg laying is occurring at that time, eggs will be placed on treated tissue.  For recent field research results testing different pesticides for NOW control at hull split, see UCCE Entomology Advisor David Haviland’s research report from 2012-13 season at:  http://cekern.ucanr.edu/files/205967.pdf.  The key result graphs are on pages 9-10.   Always consult with an experienced PCA before deciding on any pesticide application.  Read and follow the label.

Finally, a pesticide treatment is only as good as the spray job that applies it.  This is especially true for pesticides that target NOW eggs and larvae such as diamides, Intrepid®, Delegate®, B.t., etc.  Slow sprayer speeds (not more than 2 MPH) to allow good sprayer air+pesticide penetration into the canopy are essential to maximizing pest control under hull split conditions in mature almonds.  Also, avoid spraying when temperatures exceed 75^oF and Relative Humidity is below 40% — especially when using small spray droplets.  Water evaporates fast under those conditions and small droplets become even smaller or evaporate completely, reducing spray deposit by as much 30%.  [That means that 30% of the product you pay for doesn’t end up on the target when sprayed at 11 AM vs 4 AM, for example.]  Early morning or night spraying, when humidity is higher (>40%), will produce the best coverage from a well calibrated and set up sprayer during California summers.

Table 1.  Some common pesticides used at hull split in almond for Navel orangeworm control and details that may influence use planning – IRAC number (for resistance planning), PHI, impact on beneficials and duration of activity (for some materials).  Insecticides with the same IRAC number have the same mode of action.

¹ http://www.irac-online.org/modes-of-action/

² Harvest = shaking, not nut pickup, when calculating PHI

³ For more complete information, see http://www.ipm.ucdavis.edu/PMG/r3900311.html

⁴ Research by Dr. Frank Zalom, UC Davis

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