Revisiting Fruit Losses Due to the Late Freeze and Fruit Drop in Tree Fruits

Gordon Johnson, Extension Vegetable & Fruit Specialist; and Emmalea Ernest, Associate Scientist – Vegetable Crops;

Losses in tree fruits due to the late freeze are now more obvious. As one grower put it “a light crop becomes even lighter”, that is, the damage is not fully known for several weeks. Fruits that seemed to be set often do not develop because the embryos have been damaged.

Plum, pluot, plumcot, and apricots have 80-100% losses. Peaches and nectarines are more variable depending on location and variety. In discussions with growers, some orchards are carrying only a 20% (or less) crop, others are in the 40-60% crop range. However, certain varieties, such as Redhaven and White Lady, and later flowering varieties are carrying a heavier (near full) crop. What remains to be seen is if there is hidden freeze damage to existing fruit leading to continued drop.

Fruit drop is a result of unfertilized or poorly fertilized seeds, freeze damage to buds and flowers (as in this year 2016), competition between fruits, or shading. In other years, fruit drop may be due to poor pollination as a result of cold, rainy weather during bloom in self-fertile fruits such as peaches, or poor insect pollinator activity during flowering in insect pollinated fruits such as apples. In stone fruit, some fruit that is not fertilized will remain on the plant for 25-50 days after bloom and then will drop before pit hardening starts. This is what we are seeing now in cold damaged peaches and nectarines.

Another cause of fruit drop is cloudy weather during the period 5 to 7 weeks after bloom. A continuous 4 day period of cloudy days during this period will cause fruit to drop. In addition, defoliation due to disease such as peach leaf curl, chemical injury such as copper fungicide damage, or severe storms can cause fruit drop during this critical period.

Another wave of natural fruit drop occurs in late May or early June. This fruit drop is due to competition between fruit for sugars stored and produced by the tree. A tree can only carry a certain load of fruit and will naturally drop smaller and weaker fruit during this period. With the light crops in 2016, competitive drop should be minimal. However, when there are large differences in timing of fruit set (late set fruit on the same twig near to earlier set fruit), the larger fruit will become a sink for resources and the smaller fruit will abort leading to further crop reduction.

In 2016, Asian pears and European pears had some flower losses due to the freeze but still have good crops. Most apples were minimally affected by the freeze.

Sweet cherries in the open have high losses; however, those in high tunnels have full crops if they were covered early. Sour cherries have a much reduced crop. One of the issues with sweet cherries is that cross pollination is needed for many varieties. If a pollinator variety suffered damage, the varieties dependent on the pollinator will have reduced crops, compounding the freeze damage.

Marginally hardy fruits such as figs were killed to the base and persimmons were also damaged.

Strawberries also had some fruit losses in both plasticulture and matted row systems and have a higher than normal amount of deformed berries in early pickings. Brambles (raspberries and blackberries) have more tip dieback this year than usual. Early flowering blueberry varieties (mostly Southern highbush) have some freeze loss in our trials at Georgetown, but it will be difficult to estimate yield loss until closer to harvest.