With warm conditions projected over the weekend fire blight risk may be marginal to high in areas with open bloom and rain or dew. Watch the model. Risk is present any time blooms are open.
Consider the following reminders as you begin your fire blight prevention programs.
Cankers are active
There are reports of actively oozing overwintering cankers in orchards now. This is a source for new infections.
Risk
After fire blight infections in 2023 there is likely to be more overwintering inoculum. With fire blight more likely to be in the area, if temperatures are warm and wet during bloom we are more likely to have severe infections this year. The risk of severe damage due to infection increases in later stages of primary bloom and petal fall until late bloom is finished.
Use products with high efficacy
Check product efficacy WSU Fire Blight webpage or the Crop Protection guide. A new publication covers efficacy of organic products.
Apply products BEFORE an infection event
Consider how each antibiotic works when deciding which to use. Antibiotics have the highest efficacy when applied shortly before a moisture event. While kasugamycin and streptomycin can also be applied up to 12 hours after a moisture event, efficacy is greatly reduced. Streptomycin has locally systemic activity and kasugamycin is effective on bacteria which have been washed into the floral cup but not yet invaded the flower (for a short time). Oxytetracycline is considered bacteriostatic (inhibits bacterial growth). Thus, to be effective it must be applied prior to rains where it can prevent growth on stigmas.
Do not irrigate during bloom
Running sprinklers right now during bloom increases the humidity in your orchard and contributes to infections.
Optimize your spray by buffering
All WSU antibiotic trials are done with tank water buffered to 5.6. At higher pH antibiotics are not as effective. This is because both the residual of the antibiotic is much longer at a lower pH and because the low pH itself reduces bacterial growth. Research by Ken Johnson at OSU showed that buffering to pH 4 can further improve antibiotic efficacy.
Additional information
Contact
Tianna DuPont, WSU Extension
(509) 713-5346
