Disease management in tender fruit and grape after a hail event

The severe weather over the weekend resulted in some localized hail damage to orchards and vineyards. This type of injury can activate any early infections that were latent (symptomless) and/or also provide openings for the entry of the brown rot pathogen in stone fruit, fire blight pathogen in pears and Botrytis in grapes.

For brown rot in tender fruit, a tank mix of a locally systemic product with a multi-site fungicide like sulphur at 4-5 kg/ha or half rate of a captan product if fruit thinning is complete and the re-entry works for field work.

For Botrytis bunch rot, a tank mix of a locally systemic Botrytis-specific product plus a folpan product (or captan if it works with re-entry for field work) is recommended.

For pears, if active fire blight was present, streptomycin (or another antibiotic) spray must be applied within 24 hr of the event to prevent trauma blight and Buran has activity up to 450 degree hours over 0^◦C. If you managed to get a streptomycin spray on Saturday morning or Buran before 8 pm on Saturday, it will probably help. Copper is really the only option now and that will just protect from new infections, not eliminate the ones that have already happened.

Monitor for fire blight symptoms and remove infected tissue as soon as possible.  While breaking shoots is faster, research in Washington on apple showed that this approach results in more trunk cankers and thus a greater source of fire blight inoculum the following year. The following is taken from https://treefruit.wsu.edu/article/pruning-fire-blight/:

Breaking off diseased branches by hand provided a rapid removal method, but it can result in a greater number of cankers in the orchard at the end of the season with more cankers on structural wood. In the experiment ‘Washington 2021 Cripps Pink’ where four-year-old trees were trained to the wire, treatment “Breaking” resulted in significantly more re-formed cankers and new symptoms than other cutting treatments, and was similar to the no-treatment control. Pruning 30-46 cm (12 to 18 inches) below the visibly diseased (cankered) tissue into two-year-old wood generally reduces new symptoms and canker reformation caused by systemic movement of fire blight bacteria through the plant. Increasing the amount of wood below cankered tissue to 60 cm (24 inches) did not give significant improvement.

Sanitizing pruning loppers may reduce transfer of bacteria if workers cut through active ooze. However, in situations where there are many infections throughout the block, the speed at which crews can remove blight is critical to reduce the number of trees that die due to systemic infections.  Therefore, the risk of not sanitizing loppers may be less than the risk of going slower. For example, Toussaint and Philion (2008) found that pruning quickly as soon as disease was detected greatly reduced fire blight damage compared to pruning symptoms out starting in August. In Bartlett pear, Covey and Fischer (1990) found that a two-week delay in removal increased the amount of plant material that had to be removed by six-fold.