Timing of Hull-Split Spray – IGRs v/s Pyrethroids

There have been a few questions about the timing of hull-split sprays with the various products available. Our suggested timing for the spray depends on the product planned to be used.

Insect growth regulators (IGR) (i.e. Intrepid, Success, Altacor, Belt, etc) should be applied at the onset of hull-split – just as the suture becomes defined and the nut pops open when force is applied. This is about the same time that the blanks begin to split in the tops of the trees on the outside rows. This timing is in contrast to the application of pyrethroids. These products (i.e. Asana, Pounce, Warrior, etc.) should be applied later than an IGR, around 2-5% hull split.

The timing difference is due to the differences in activity and persistence of the products. IGRs tend to be more effective in controlling eggs, neonatal and developing larvae, while pyrethroids do a better job in knocking down adults moth populations. The activity of the IGRs also tends to persist longer in the field. Since the IGR has longer persistence and tends to target the developing larvae, it has to be present on the almond surface before the egg hatches/larvae continues to develop.

Since these sprays are going out earlier than in the past, bracket sprays may be needed within areas with high NOW pressure. This is an important consideration if dealing with later harvesting varieties which will be exposed to the later flights of NOW.

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4 thoughts on “Timing of Hull-Split Spray – IGRs v/s Pyrethroids

  1. Dr. Walt Bentley’s video says that IGRs need to be applied and 1-5% hull split, with the old method explained (2:15-2:35 in the video), but this article says that Pyrethroids need to be applied later than IGRs, around 2-5% hull split. These application timings seem to be identical. Are these chemistries supposed to be applied together or is it IGR then Pyrethroid?


  2. You are right, I can see how this is confusing. Basically, a pyrethroid application should occur later than an application with a growth regulator (IGR). A good timing for pyrethroid application should be when about 5% of the nuts in the orchard have about 1/8″-1/4″ opening. This is a few days later than the timing for an IGR, which is when suture is defined but still closed, and the nuts can be opened by squeezing the ends.

    The confusion on when hull split begins is due to the varying stages of hullsplit – I think we have around 6 stages defined in the IPM guide.

    These chemistries are different, and can be combined in areas of high pressure in order to take advantage of the strengths of each product. Since pyrethroids will “knock” down adult populations, and IGRs will affect developing eggs/larvae, a combination product should have the ability to do both, being a very effective tool for NOW management. These sprays are not needed in all areas, but only in areas of high NOW pressure.


  3. I think the topic is being vastly oversimplified (both in the video and the blog). The NOW dynamics are not the same relative to nut development each year. I believe one must take both into consideration when deciding when to apply what type of material. It may be entirely appropriarte to apply a pyrethroid at an earlier stage of HS if pops are going up.

    By the way, Altacor and Belt are not IGRs, but they are targeting the same stages. I prefer to lump them all into the “reduced risk” category.

    Lastly, I really have not heard a good definition of 1% HS or 1-5%HS. If one waits until the nuts on the interior trees are at 1%, the orchard as a whole may be closer to 50%. If one sees 1% on the south edges, there may be 1% split in the tops of the trees also, but no splitting in the interior. Can you enlighten?


  4. I agree with your comments. Managing NOW changes on a year-to-year basis and I may be over-simplifying it.

    #1 – I agree, the timing of using a pyrethroid or “reduced risk” has been a bit skewed by the videos and entries. A pyrethroid applied early will provide control of larvae – just as the “reduced risk” products. In contrast, any chemistry applied too late, will not provide any protection as the worm will already be within the nut. What the articles were attempting to state were the differences between the types of products. Reduced risk products need to be applied earlier since their strengths are within their ability to provide a persistent control (last about a week longer than pyrethroids) and target eggs and larvae. In contrast, pyrethroids differ from most reduced risk pesticides because they do a nice job of driving down the adult moths but lack the ability to persist. With this in mind, if a farmer is applying a spray at the onset of hull-split, we generally recommend a reduced risk because of the persistence aspect of these chemistries and the lifecycle of the moth attempting to be controlled. If they are a bit delayed on getting out their hullsplit spray, pyrethroids are a little bit more forgiving, and they will provide better control of adults, eggs, and larvae. Then again, if not spraying at night, the whole point of targeting adult moths may be moot.

    #2 – You are correct: Altacor and Belt are calcium channel agonists and target muscle; Intrepid is an IGR.

    #3 – Hullsplit timing is varied among and within orchards, and knowing this, there is not a “one-size-fits-all” timing. If the edges are splitting, in a high pressure situation you must spray the edges by 1%. If you wait for the center to start splitting, you can have infestations as high as 50% within the edge. In other words, if using a reduce risk product, the product must be applied to a tree when that tree is at 1% split — which may not be the same timing as when the whole orchard is at 1% split. This may seem impractical, but partially explains why hull-split sprays are going out earlier than years past.

    I hope this helps, but if not, let me know.


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