Taking an environmentally sensitive approach to pest management
After several years of relatively warm winters, peach floral buds were injured by the low temperature episode on January 6 in some areas of Missouri. At the Horticulture and Agroforestry Research Center (HARC) near New Franklin, -11°F was recorded on this date. On January 20, peach floral buds on the middle portions of terminal of shoots from five year-old trees were collected to assess bud survival. ‘Redhaven’ peach bud injury ranged from 29 to 74%, depending on the rootstock. ‘Redhaven’ buds from trees with Lovell rootstock had a low percentage of bud injury, whereas those on trees with almond hybrid rootstocks had poor survival. While bud loss was significant on trees with some rootstocks, there are still enough floral buds left on all of our trees at this time to produce a full crop of peaches, assuming minimal additional damage occurs later this winter or spring. To look at temperatures recorded in your area, Missouri weather records can be obtained at: http://agebb.missouri.edu/weather/history/index.asp?station_prefix=sfm. When using this information, remember that it is site specific. If your trees are located in a sheltered area or a higher location than the local weather station, the temperatures may be warmer than those recorded at this website.
To assess low temperature injury on your peach trees, cuttings from trees can be collected at any time after injury is suspected. Once cuttings are collected, they should be brought indoors and sealed in plastic bags or basal ends of the shoots can be submerged in water in a container to prevent them from drying. After a few days at room temperature, floral buds (plump outer buds at a node) can be sliced longitudinally with a razor blade. Near the center of the bud, injured floral tissues (pistil and stamens) will be water-soaked and brown (Figure 1). Live buds will have bright green floral tissues.
For our evaluation, buds were purposely sampled so that the basal buds of last season’s growth were retained. These buds are typically hardier than those located nearer the tip of the shoot. Also, large diameter floral buds are generally hardier than smaller buds.
Although peach floral buds have been damaged, the shoots are not. Prune trees before bud growth in the spring. Traditionally, most Missouri peach crops are lost during bloom due to spring frosts. For this reason, delay thinning until fruit is set, leaving small-diameter peaches spaced at least six inches apart on shoots to obtain large fruit at harvest. The earlier thinning is accomplished, the larger fruit will be at harvest. Because it is often hard to see developing fruit in the spring, additional thinning is usually required. If the entire peach crop is lost this winter, do not fertilize trees. When low temperatures eliminate the crop, vegetative growth is abundant during the following growing season. Thus, fertilizing trees without a crop results in excessive shoot growth with more pruning required later.
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REVISED: September 29, 2015