A dormant or delayed dormant spray is a solid pest management tool for almond growers. Done right, it will control scale, peach twig borer, peach silver mites, Brown almond mites, European red mites, and delay sporulation of almond scab in the spring. Spray coverage is usually excellent because trees are bare, with no leaves to interfere with spray and air movement. This timing is a good one for a pesticide such as diazinon or Supracide that can harm beneficial insects, because beneficial insects are not active at that time and so are not harmed.
However, a dormant or delayed dormant spray using the proper pesticides and labeled rates is expensive, may not be necessary, and may harm the environment through drift or pesticide runoff. A pesticide that is effective on scale at labeled rates plus 2-4 gallons of oil pushes the pesticide bill/acre into the $30-40+/acre range without adding labor, fuel and equipment costs. Pesticide runoff from orchards into streams and rivers can occur in many parts of California, leading to potential damage to aquatic life including salmon, steelhead, and the small fish and insects they eat. All pests targeted in the dormant spray – excepting scale – can be as effectively controlled at other times.
How do you know if scale is a problem in your orchard? Take a dormant spur sample. Detailed instructions on how to take a dormant spur sample are available from your local UCCE office or from the UC IPM website at: http://ipm.ucdavis.edu/PMG/C003/m003dcdmtspursmpl.html. Use of certain pesticides – particularly pyrethroids (Asana, Brigade, Warrior, Baythroid, etc.) – can harm beneficial insects that help control scale and contribute to buildup of scale in an orchard. If you use pyrethroids in your hull split spray or for peach twig borer control in dormant or spring, a dormant spur sample is especially important. Don’t let scale sneak up on you.
If a dormant spur sample shows a scale problem, what can be done? A high volume (400 gpa), delayed dormant ground application gives the best scale control. A lower spray volume (100 gpa) or the dormant spray timing does give some scale control. Low to moderate populations of scale are effectively controlled by high rates of oil (4 gallons/acre), alone.
Adding a pesticide labeled for scale control (diazinon, Seize, Centaur, Supracide, etc.) plus oil will control high levels of scale. Oil + labeled pesticide provide two modes of action in the same tank and is a good resistance management practice. Getting spray solution into scaffold and trunk bark cracks is essential to effective, long term control. High spray volumes (400 gallons/acre) give better scale control than lower volumes (100 gallons per acre). Expensive, yes, but high volume works best for pre-bloom scale control.
But how can peach twig borer, peach silver mites, and European red/Brown almond mites be controlled if a dormant spray is not applied? There are several, effective options. Peach twig borer control at bloom with bee-safe pesticides (Intrepid, Dimilin, B.t., etc.) tank mixed with fungicides is a research-proven practice. Peach silver mites can be controlled by sulfur or one of many miticides – check the label -- in the spring. Brown almond mites and European red mites are usually not a significant pest in almond and often are good to have in the orchard as they are a food source for beneficial mites in the spring before web-spinning spider mites appear.
A dormant or delayed dormant spray of copper plus oil or lime sulfur can be part of an integrated scab management program.
Check the pesticide labels and consult with your PCA before combining scale and scab control pesticides in the same tank or making separate applications close in time.