Low wetting hours, sunburn and heat injury

Accumulated wetting hours (starting April 29, 10 days after petal fall), as of July 5: Winchester AREC, 259 hr. Although we surpassed the 250-hr threshold for presence of sooty blotch and flyspeck fungi on unprotected fruit last week, accumulation of wetting hours has been very slow the past two weeks- totaling only 12 hours. This is the fewest hours accumulated in a 2-week period since we started keeping track of this statistic in 1994. The next closest to this was in 1998 when 14 wetting hours accumulated from Aug. 24- Sept. 6. That year a 3-week period totalled only 36 hours. We have had no extended wetting periods since June 15. In spite of the lack of rainfall, apple fruit size hasn't suffered much yet, but we really could use a good soaking rain.

Heat injury: We have seen an increase in the amount of sunburn and heat injury on apple fruit, as would be expected with the warm temperatures and exposure of fruit to the sun with increasing crop load. The examples of York Imperial fruit shown above were brought to the lab from a commercial orchard today. Internal browning of the flesh correlated with surface discoloration on the more exposed side of the fruit. A cross section through the core showed that the seeds were white and healthy looking, indicating that the surface symptoms were not due to frost injury, and there was no evidence of fungal growth as would be present in a pathogenic condition such as moldy core. Typically, the heat-injured side of the fruit will stop growing while the non-injured side continues to grow, resulting in a disfigured fruit.