jan-feb-2020

damage. Recent research by Dr. Adaskaveg has shown the antibiotic kasugamycin (Kasumin ® ) to be very effective on blast and registration is pending with a Section 18 emergency registration requested for spring, 2020. Biological materials such as Actinovate AG and Botector reduced blast damage in Dr. Adaskaveg’s research in cherry, but not as consistently and effectively as kasugamycin. Bloom Protection Timing and Material Selection Varies with Weather Bloom Weather Forecast Spray Timings Elevated Disease Risks and Fungicide Selection Considerations Clear skies 1x; 30-40% bloom FRAC 3,9, and/or 11 (locally systemic fungicides) Warm rain 2x; pink bud and full bloom Brown rot and anthracnose Cold rain 2x; pink bud and full bloom Jacket rot, blossom blast. [FRAC 3 fungicides ineffective on jacket rot.] Frost Protection Irrigation systems and orchard floors should be prepared for frost management. Bare or close mowed, firm and moist orchard floors provide warmer conditions than those with tall vegetation. If freezing temperatures are forecast, and impact or micro-sprinklers available for active frost protection, water should go “on” when the wet bulb temperature is above the critical temperature for the stage of crop development in the orchard. Turn off sprinklers when wet bulb temperature rises above the critical temperature. Why worry about wet bulb temperatures ? All critical temperatures reported by UC are wet bulb temperatures. All field thermometers are dry bulb devices. If relative humidity (RH) is less than 100 percent, irrigating for frost “protection” will result in evaporative cooling of the orchard until wet bulb temperature is reached and possible crop damage. For example, critical temperature for 25 percent loss of Nonpareil nutlets (post-petal fall) is 29 degrees Fahrenheit. If dry bulb temperature is 33 degrees Fahrenheit and RH is 60 percent, orchard temperature will drop to 29 degrees Fahrenheit if irrigation sprinklers are turned on. Knowing critical and wet bulb temperatures are vital to effective frost protection. Hand held weather stations and/ or sling psychrometers can be used to determine wet bulb temperatures. These tools are also helpful in the summer to determine when the air is too dry for effective spraying and spraying stopped or droplet size increased. If current, field dry bulb temperature and relative humidity data are available, national weather service has a free online wet bulb calculator at: weather.gov/epz/wxcalc_rh. When using the online tool, assume barometric pressure of 1013 millibars — that’s what UC tables use. 4 3 J A N U A R Y – F E B R U A R Y 2 0 2 0