By Clint Thompson
A dire situation could get worse for blueberry growers impacted by the freeze event during the weekend of March 12. The crop is susceptible to potential disease pathogens that require immediate action, says Jonathan Oliver, University of Georgia (UGA) assistant professor and small fruits pathologist.
“The blueberries were at green fruit stage for the highbush. If they were under freeze protection, they might still have a crop that they can harvest. But we had pretty severe damage in both fruit and leaves in the field,” Oliver said. “We really get concerned when that happens of diseases setting in like botrytis and botryosphaeria especially, which are fungi that like to latch on to that dead or damaged tissue. Both of them can cause severe problems for growers.
“Right now, after a freeze event and with temperatures in the optimum range for some of these fungal diseases to start ramping up, it really is important that growers be mindful and put out some protective materials for control of those diseases.”
Warm temperatures above 70 degrees Fahrenheit, combined with moisture like rainfall or overhead irrigation provide ideal conditions for botrytis development. Products like Pristine, Switch, and Elevate are recommended for control.
Botryosphaeria fungi can invade cold-injured blueberry shoots where it can cause stem blight symptoms. These consist of a dieback that moves down the canes to the crown. Injured stems are colonized early, and disease incidence increases with time and temperature.
Growers can prune out dead tissue which can reduce disease development. Where feasible, it is recommended that cold-injured shoots higher up on older canes be pruned back to healthy green tissue. Application of a broad-spectrum fungicide like Pristine after each pruning day is recommended to prevent additional infection.
Especially since growers are on the brink of harvest, preserving whatever crop they have left is vital. Producers need to realize how vulnerable their blueberries are moving forward.
“Any kind of stress, for sure, can cause disease to take hold. Think of it like scraping your knee outside. You’re not going to die from that, but if you get an infection in there, for sure that could spread to your whole body and make you pretty sick. You want to clean that up and protect that wound,” Oliver said. “In the case of freeze damage, that’s how I think about it. These are open wounds on the plant, dead tissue where diseases can move in and cause problems.”
Source: UGA Extension Blueberry Blog
