Blueberry growers, the winter weather of March 16-17 2017 will most likely be dates we never forget. In just one night what could have potentially been a record crop load was nearly wiped out. Some fields were hit harder than others, but it was devastating across the blueberry belt of Georgia.
The question is: what do you do now with the blooms left and the plants that lost all their blooms and fruit? This is the advice from Dr. Nesmith, Dr. Brannen, and Extension Agents in Blueberry Counties:
The recommendation of using Gibberellic acid is really a tough call. It may help a few places, but will likely be in vain in many places as well. It will not help those flowers at stage 6 and beyond, especially if temps were below 27 F. Many places around Appling County hit as low as 21 F. As we know, blueberries salvaged will often be much smaller which costs more to harvest and pack. This probably isn’t a year to be optimistic about gibb, but depending on temperature lows experienced, it could work in some situations.
-Gibberellic acid applications can be made when some of the earlier stage blooms like stage 4 and 5 start to push further towards stage 6’s, potentially by the end of this week. Then a second application can be made 7-10 days later.
-If you already applied a gibberellic acid rescue spray, then make another application in 7-10 days.
-It is a tough call whether gibberellic acid will be helpful or not. Mid-to later varieties of rabbiteye may benefit if 60% of flowers are earlier stages and appear salvageable, however, if there is only 25-30% bloom left, gibberellic acid may only save half of those which would leave the grower with a crop that may not be worth harvesting.
-For growers that are looking to simply maintain the health of the bush for next year, hedge the plants (bringing rabbiteye blueberries down to 4-5 ft. tall) and then re-tip them mid-summer to take advantage of all the extra growing time this season.
Where cold-damaged blooms/shoots are observed, Botrytis might be a real issue, since damaged blossoms and buds will provide infection courts for the spores. In addition, it has been warm enough prior to the recent cold events that Botrytis development and sporulation may be more prevalent than normal for this time of year. The optimum temperature for infection of Botrytis is 59-68 F, but the optimum for spore germination is actually 68 F and above. That means we will have perfect temperatures for infection over the next few days. Rainfall is not currently predicted, but if rainfall is heavy and prolonged dews (or overhead irrigation) are associated with the warm temperatures, we may have Botrytis/Botryosphaeria development.
Where freeze damage has occurred, we recommend the following choices and things to consider:
Fully damaged rabbiteyes: Some damage is severe and producers may only want to maintain bushes for next year at this time. Rabbiteyes are generally less likely to have major Botryosphaeria issues, and the same is likely true for Botrytis as well. An application of Captan is recommended, but that might be it. Maintaining leaves is important, so rust management or control of other leaf spots should be part of the plan going forward, but use cheap materials for leaf spot management.
Rabbiteyes in bloom: If maintaining bloom on rabbiteyes, use Indar or Orbit or Quash or Proline for control of mummy berry tank mixed with either Captan, or Captan + Elevate or CaptEvate. Then follow suit with a regular spray program for the remainder of the season and going forward.
Rabbiteye and southern highbush (fruiting): In this case, use an immediate application of Switch + Captan or Abound + Captan or Pristine + Captan. Then follow suit with a regular spray program for the remainder of the season and going forward.
There are always questions regarding the tremendous amount of bark/ground wetting that occurs with overhead freeze protection. Hopefully this will not increase root rot diseases substantially at this time, but the root zones were saturated. Ridomil application through drip tape would work. If there is enough foliage for good uptake of a phosphonate-type product (ProPhyt or Agri-Fos or Kphite for example), then consider foliar application of one of these materials to stave off root rots during the early spring; follow label directions and do not over-concentrate these materials in the final spray volume, as damage can occur with their use if label directions are not carefully observed.