California Pistachios: A Light NOW Year For Several Reasons

    Pistachio nuts in mid-May.©Sara Savary, AgFax Media

    On the date this was written (September18), we have about 35-40% of the crop harvested. Golden Hills nut quality is reportedly very high, with 85% or more clean open split nuts, and only 5% closed shell. Early harvested Kerman grade sheets have 70% or more clean open split nuts, and about 10% closed shell. Field reports and processor representatives say this is some of the best quality ever.

    Nut size is also very large, even on heavily cropped trees. Large nut size was initiated during Stage 1 (bloom to shell hardening). The soil moisture and heat units must have been optimal for shell expansion, and kernel filling in Stage 3 had to not be limited as well to get the larger nuts to split.

    A system for collecting accurate weather data at various locations throughout the state for comparing possible phenological differences in heat units would greatly assist us in understanding this year’s crop development.

    Too bad the pistachio industry has neglected to accomplish this integrated weather data network.

    The cooler weather predicted will help maintain hull integrity, and slow navel orangeworm (NOW) development. Thus far, NOW damage has been zero or very low on most grade sheets. This is looking like a third year of low insect damage, which would be historical.

    However, a large amount of almond acreage is now harvested, and NOW is migrating to their next ovipositional site. Thus, pistachio growers need to harvest as soon as maturity allows them to. The cooler weather and smoke-filled skies have reduced tree water use substantially.

    The reduced photosynthesis may also slow maturation of the crop remaining after the first shake. It may be three weeks before it is ready. Keep a close eye on it for maturity and hull integrity, since NOW is looking for a new home to complete its life cycle.

    With NOW, We Caught A Break

    As I mentioned earlier in the season, 2020 harvest maturity was estimated at possibly 7-10 days later than “average” due to the False Spring. I still think we are 7 days behind last year. Normally, we are in full swing about September 10.

    The delayed maturity would make me sweat if it was a bad NOW year, but lots of factors we can all guess about seem to have worked in our favor to make this another low insect, high quality nut year.

    I did detailed nut phenology work back in 1983 and 1984 to show when freshly mated NOW females found pistachios most attractive to egg laying. Brad Higbee, Trece Field Research Director, repeated this work about three years ago. We both found that early pea split nuts were attractive, but egg laying on the sound nuts did not increase dramatically until the hull tissue began tearing and breaking down.

    The significance of this in your orchard depends upon what your resident and migrating NOW population is. Although we do not have the much-desired ability to assess the actual NOW population for individual fields, growers and crop advisors develop a “gut estimate” over the season from weekly scouting.

    My “gut estimate” this spring was that 2020 might be another low NOW year, because the delayed maturity might keep the hulls intact longer, and the fourth generation of NOW occurring during harvest might not overlap prime nut susceptibility. The optimist within me wonders if we have actually reduced the overall NOW population with mating disruption? Note: this is the optimists wondering out loud, not a scientific statement, so please don’t go blabbering about that I said mating disruption has kicked NOW’s arse, and our insect problem is solved. NOT..

    The Continued Value Of Sanitation

    I cannot quantify how many growers performed winter sanitation or employed mating disruption, but DECADES of research by some of the world’s best entomologists shows these two important tools as being very effective in reducing codling moth and NOW populations.

    The problem lies in getting everyone to use them. Many growers may think that if 2020 proves to be yet another very low insect year that we have this nasty pest beat. I do not think that for one nanosecond.

    I say it’s time to build an even stronger arsenal to improve our odds of beating the beast back in bad NOW years, which will be back. So, the more we winter sanitize and employee mating disruption over ALL nut crops, the more capable we are of achieving NOW management success.

    The Pea-Split Factor

    The occurrence of early pea split nuts was also much later and fewer than normal in the fields I was visiting. Rather than beginning around July 7, I did not see many until July 24, and they were hard to find.

    It is generally agreed that the early pea splits are an important link between the overwintering NOW population emerging from poor food quality mummy nuts, and the new crop, which can reduce development time from 1200 degree days to as low as 600.

    Did the delay between the beginning of the second flight of NOW in early July and the occurrence of pea split nuts significantly reduce NOW survival? Perhaps the research entomologists can tell us, but I do not know. Research on the botany of early pea split development and factors affecting their occurrence is a high priority, in my opinion.

    Trap Counts Are Up Now

    Several crop consultants report a marked rise in NOW trap catches over the past week. One could say it’s the fourth flight, but at this point in the season, there is a lot of overlap between the current and previous generations, so the occurrence of the fourth flight just adds to the number of NOW that can lay eggs on maturing hull tissue.

    Thus, it is important to continue scouting the fields you have not yet harvested, or plan to second shake to avoid damage that effects your premium payments.

    • Drive the quad around, and then get out and visually scout the open split nuts and nuts with torn hull tissue.
    • Look for eggs in the cracks, and any small amount of frass.
    • Open the nuts suspected of having insect feeding and look for the worm.
    • Record whether it is tiny or large, so you can report your observations to your crop consultant.

    More often than not, pistachio growers are applying insecticides between harvests and on late blocks to suppress the fall NOW population. Discuss this with your crop adviser to determine if the NOW pressure in your orchard justifies it.

    Navel orangeworm management is very complex, so if you are consistently having problems, sit down with your crop consultant, and go over every aspect of your program. Encourage your adviser to be as candid with you as necessary, so weaknesses in the program can be corrected. Also ask your processor for assistance and listen carefully to the researchers when they present their findings.

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