Bacon County Ag Update

Fungicide use to prevent cold damage on Blueberry

Cold damage is a concern for everyone this year, since we have had so much new grow and tender shoots from December’s weather. Below are some comments from Phil Brannen regarding fungicide use to prevent disease damage following cold weather.

Call me with any questions.

I had a question today concerning whether fungicide application(s) would be warranted ahead of or following potential cold damage over the next few days, especially cold damage to southern highbush.  While cold damage can increase both Botrytis and Botryosphaeria infection and subsequent disease issues, it is hard to know whether there will be significant damage (happens mainly when plants have not gone dormant due to a warm fall).   Also, fungicide application is not warranted with the current temperatures, since fungi will not readily infect when it is this cold. However, the optimum temperature for infection by Botrytis is 59-68 F, and the optimum for spore germination is actually 68 F and above.  That means we will be above optimum temperatures for spore germination at some point, and temperatures around 70 F with moisture are generally optimal for Botrytis.  It is really a judgement call as to whether a fungicide should be applied with this freeze damage event, but if I were to apply anything when it does warm up a little, I would go with Captan or Ziram immediately after the cold temperatures pass.  These are relatively cheaper protectants, and if temperatures warm and we have moisture from dew or rainfall, they will help to prevent fungal infections.  If significant cold-damage occurs this winter, producers should prune this out in the early spring to prevent mainly Botryosphaeria infections.  The real question is whether a fungicide application in the next few days will reduce the amount of fungal-damaged tissue that comes in on top of the cold-damaged tissue, and the answer is not likely.