Managing Fruit Plants after the Historic April 2007 Freeze

Published: February 1, 2008

The unprecedented freeze that occurred last spring will impact fruit harvested in 2008. One of the first things that growers are faced with in preparation for the upcoming growing season is pruning. When temperatures plummeted in April after a very warm March, many growers had already applied fertilizer. In more normal years, nitrogen fertilizer is used for reproductive and vegetative growth. However, with the loss of the fruit buds and/or fruit, nutrients normally diverted to the developing crop were available for the production of more vegetative shoots and leaves. Therefore, any nitrogen applied before (or after) the freeze promoted excessive vegetative growth. For this reason, fruit trees will require more hours of pruning this season. When pruning, the dead and diseased wood should be removed first. Secondly, thinning out unproductive branches and those that shade other fruit-bearing shoots will be necessary to ensure sustained fruit production.

Unlike blueberry, blackberry, and peach, apple trees go into a cycle of alternate bearing (excessive fruit set the year after a season of low fruit production). In 2008, apple trees will likely have a heavy crop load (barring any erratic weather). It will be important to apply adequate fertilizer to produce quality fruit. However, splitting the total amount of recommended fertilizer into two applications (before bloom and after fruit set) or more will help provide better sustained growth and help avoid leaching of the nitrogen if applied as ammonium nitrate. Using multiple fertilizer applications also gives the grower the opportunity to stop fertilizing if another catastrophic frost or freeze occurs. Multiple fertilizer applications are recommended for all fruit crops, starting pre-bud burst and ending by July 1. Fertilizer applications after this date promote late season growth, delay hardening, and increase fruit bud susceptibility to winter injury.

Fruit removal (i.e., thinning) will be very important on peach and apple trees to balance the amount of fruit and vegetative growth. For apple, only one fruit per cluster should be retained. This should be done as early as possible, when the fruit is the size of a dime. For peach, strip off all small fruitlets, leaving 10 inches between each fruit. Peach branches often break when they are bearing too many fruit.

The incidence of pests may also be greater this growing season, depending on the pesticide applications used after the 2007 freeze. Many growers reduced their chemical applications or quit spraying completely after the freeze. Thus, uncontrolled pests from last year may increase pest populations this year. Fire blight on apple and pear trees may be worse this year on trees that were fertilized either before or after the 2007 freeze because of the excessive vegetative growth. Also, canker development may be worse than usual on peach trees after the April freeze and the low winter temperatures experienced recently. There may also be outbreaks of pests not normally seen in Missouri due to the erratic weather. Even though the true consequences of the freeze may not be known for a few years, woody fruit plants are often productive with optimum culture following unseasonable weather events.