As always, there is a high potential for spring frost damage to fruit crops in Missouri. Unseasonably cool temperatures have been recorded this year and it is predicted that this trend will continue through the spring. With this in mind, there are a few techniques that can be used to protect fruit buds and flowers from low temperatures.
First, delay fruit tree pruning for as long as possible in the spring, but allow just enough time to complete this task before bloom. The hardiest buds are always on the older wood, while those nearest the tips of branches are the most susceptible to damage. Plan to leave a few extra fruit buds when pruning. Once the danger of frost has passed, excess blooms or small fruitlets can be removed by thinning.
For grapes, a good way to protect the crop is to use double pruning, especially for cultivars that are the earliest to break bud in the spring. This technique is only used for cultivars trained to a single curtain cordon system with spur pruning. Like fruit trees, the buds at the base of shoots, nearest the trunk and cordons, are the most tolerant to cold temperatures. To double prune, select the fruiting spurs that will be left on the vine to produce the crop. Next, remove excess wood as usual, except for the spurs. Instead of leaving just 3 to 4 buds per spur, leave as many as 10 to 15 buds on them. These extra buds delay development of the basal buds so they can potentially avoid frost damage. After the frost free date, wood with the extra buds is removed. While this method requires some extra effort, it can save the crop. Also, if primary buds at a node are injured, a smaller crop of grapes can be produced from secondary buds.
Small fruits, such as strawberries, can be re-covered with straw mulch or protected by placing plastic or tarps over the plants during when temperatures fall below freezing in the spring. Brambles and blueberries can also be covered, but this is practical only when there a few plants.
Frequently, the average frost free date is publicized for specific areas. However, with fruit crops, it is often more useful to consider the last frost free date on record. For example, weather data indicate that the average frost free dates for Springfield and Kirksville are April 15 and 20, respectively. However, based on historical data, the latest date that 32°F was recorded in Springfield was May 9. Kirksville has recorded this temperature as late as May 25. Like other years in Missouri, be prepared for erratic spring weather.
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REVISED: March 21, 2014