The pesticides used in the conventional dormant spray include oil, an organophosphate or pyrethroid and copper.
The target pests controlled by the oil are San Jose scale (low to moderate populations) and European red mite, the organophosphate controls peach twig borer and San Jose scale, pyrethroids control peach twig borer (not scale), and copper controls peach leaf curl. Delayed dormant spray timing (late January to mid-February before bloom), is more effective than dormant spray timing for controlling San Jose scale, European red mite, and peach leaf curl.
Another benefit to spraying later during the dormant period is more orchard floor vegetation reducing pesticide runoff potential. A good reason to delay the dormant spray this year is to avoid any tree damage from dormant oils because of the very dry soil conditions.
Growers have several dormant spray management options available to them to potentially reduce costs while reducing runoff potential. The first option is to monitor for these pests by taking dormant shoot samples. These samples will help you determine the levels of San Jose scale and European red mite populations and the most appropriate pesticide and rates to use. If San Jose scale is below 10 percent, oil alone should be an effective control.
If over 10 percent, then consider using an organophosphate such as Supracide or the insect growth regulator Seize.
When applying organophosphates, pyrethroids, or any pesticides, they should not be applied 48 hours before a predicted rain event to avoid runoff. Secondly, there are more dormant or bloom time control options available with newer chemistries that have reduced hazard to the environment, greater worker safety, and are replacements for the traditional broad spectrum contact pyrethroids and organophosphates. These include biological insecticides (Bt), Spinosyns (Delegate), or insect growth regulators (Intrepid, Dimilin, Seize) listed in the table below.
For peaches, reduced hazard insecticide programs build from the basic dormant/delayed dormant spray which is oil for scale and copper for peach leaf curl. In the table below are insecticides that have been demonstrated to be effective. Bt, Spinosyn, and Intrepid also control oblique banded leafroller which is an occasional peach pest. Seize applied delayed dormant with the oil and copper spray, has been very effective in reducing or eliminating scale in peach orchards where it was used on blocks with over 10 percent San Jose scale as determined from annual dormant shoot sampling. Alternating with different materials and chemistries every year will help manage insect resistance and help ensure that our insecticide tools remain effective.