Just returned from a field day meeting held near Firebaugh discussing pest and disease management strategies for the upcoming dormant season. I thought I would highlight a few points from the talks by Walt Bentley (UC IPM), Mario Viveros (Emeritus UCCE Farm Advisor – Kern County), and myself – David Doll (UCCE Farm Advisor – Merced County). I apologize for the brevity of the entry as I am preparing for a field trial due to be fumigated next Monday.
Navel Orange Worm (NOW): Winter sanitation is critical to help reduce the overwintering population of NOW. In general, no more than two mummies per tree should be left in the tree. With some growers, complete removal of the mummies is performed.
Most growers remove mummies. This is easily done on younger trees. As the trees mature and become larger in size, the task of sanitation becomes difficult, resulting in more mummies remaining within the upper canopy. This may explain why many growers see more NOW damage in mature blocks.
Even though the trees may appear to be clean, a closer look usually reveals mummies still hanging in the tree.
Peach Twig Borer (PTB): Scouting for hibernacula should be performed. There are several treatment options and timings for PTB. These include dormant oil sprays, bloom sprays with reduced risk products, and May sprays. See the PTB page on the UC IPM website for more information.
Mites: European Red Mite and Brown Almond Mite will overwinter as eggs around the base of spurs. Spur sampling, which should also be done for scale, can help determine if treatment is needed. An oil spray outlines at the Mite page on the UC IPM website will suffice for most locations.
Scab: The scab fungus overwinters on twig lesions. These lesions will sporulate in the spring, infecting the new leaves of the tree. If a bad scab year was experienced this past year, it is advised to make a copper-oil application during the delayed dormant period. Studies by Dr. Jim Adaskaveg have demonstrated that copper and oil applications delay scab lesion sporulation and reduce the amount of inoculum. Sprays 2-5 weeks post bloom will still be needed to prevent the disease, especially if rains persist post bloom.
Rust: The rust fungus overwinters on plant tissue that remains on the tree or on the ground. For orchards with a history of rust, apply zinc sulfate now to hasten leaf fall. If leaf debris is still remaining on the soil surface in the delayed dormant period, broadcast a liquid formulation of nitrogen (10 lbs/acre) to help speed the breakdown of the leaf material. Strobilurins (i.e. Gem, Abound, Pristine, etc.)provide the best control of rust. Apply 5 weeks after petal fall. Sulfur can be used for subsequent rust control sprays. Fungicides can provide some level of control even after the first symptoms of rust appear.
Using a copper-oil spray in the delayed dormant period can provide control for most insects and diseases. Mario Viveros recounted a fungicide study where every treatment that contained a dormant copper/oil treatment out-performed the non-dormant spray treatment. This application should be considered if you experienced any foliar disease or early season mite problems this past year. If other insecticides are needed and are planned to be sprayed, please double check the compatibility with copper/oil.