Pyrethroid v/s Reduced Risk product usage for Hullsplit/May Spray
A few people have inquired about the differences between spray product choices for worm control during Hull Split and/or "May" Spray. I thought I would highlight some of the thoughts that the UC has developed over the years regarding this decision. Some of this may be redundant, but hopefully some new points will be brought to the table.
Which product is best?
Determining which product is the best treatment option for your orchard depends on budget, pest pressure, timing, and familiarity.
Pyrethroid products are effective in knocking down adult moths and killing larvae that come in contact with the product. Persistence of the product within the field is not as long as the reduced risk products (about 2-5 days less), but they are useful for later hullsplit applications - around 2-5% for optimal timing. The downside with pyrethroids is the assumed mite flare up, knock down of orchard beneficial insects, and water run-off issues. A miticide should be tank mixed with the hull-split application if applying a pyrethroid.
"Reduced risk" products (i.e. Entrust, Success, Delegate, Intrepid, Belt, etc.) target the eggs and larvae of the moths. They do not knock down adult populations as well as pyrethroids, but control developing larvae more effectively and selectively. These products tend to persist within the orchard a little longer, providing longer control and thus can be applied earlier than pyrethroid products (when blanks split). They have a minimal effect on beneficials, allowing the natural predators to help control mite populations, usually preventing a mite flare up, thus not requiring the tank mixing of a miticide. These products are very effective but resistance to the mode of action may occur - so chemical class rotation is important if products are sprayed more than once per season. Water impacts appear to be minimal.
Currently, a pyrethroid treatment is cheaper than reduce-risk products - even including the cost of tank mixing the miticide. If the hull-split spray is delayed due to a spray rig breakdown, late start, etc, and the spray is beyond 5% hullsplit, a pyrethroid is the better product to use to help knock down adult populations. If sprays are being applied before the 2% hullsplit, a reduced risk product should be used. Making use of both products can help increase the window of hull-split sprays. Tank mixing of reduced risk and pyrethroid products is not advised due to the cost and no additive gains in worm control.
Should I ever Spray a pyrethroid in the orchard?
Philosophically, most researchers/entomologists will say "no." Clearly, there are effective options out there for worm control that do not require the use of broad spectrums. It is important, however, to acknowledge that there are more orchard insect pests than moths/worms. Leaf-footed plant bug, stink bugs, and other insects may warrant a broad spectrum spray. In these years where the spray has to be made, it is important to develop a strategy to help re-balance the loss of natural predators within the orchard. The benefits of the reduced risk products are due to the selective nature of their chemistries; they have minimal impact on non-targeted insects and thus allow the orchard to gain a biological balance.
May Spray: Its not just for PTB anymore.
Reduced risk pesticides (i.e. Entrust, Success, Delegate, Intrepid, Belt, etc.) can be applied in May because they do not have the effect on mite predators like the broad spectrum chemistries (Pyrethroids, Organophosphates). For the past few decades, the UC has made a conscience effort to move away from May Spray timing of NOW and PTB due to the flare up potential of the broad spectrum chemistries. This has changed. A spray for NOW and PTB can be made without the expected mite flare up with reduced risk pesticides. This will help reduce the over wintering/first flight population of NOW within the orchard, possibly preventing a hull-split NOW treatment. This spray may be important for orchards with historically low populations, orchards with sub-par sanitation that need more effective NOW control strategies, or for pistachio and almond growers who have these respective crops in side-by-side plantings.