Why Do Fruit Trees Drop Fruit?
 | Author:
Allison Kosto, MSU Broadwater County Extension Agent
MSU Broadwater County Extension Agent |
Why Do Fruit Trees Drop Fruit?
Allison Kosto
MSU Broadwater County Extension Agent
Fruit trees are a labor of love in Montana, especially in Broadwater County. They take a lot of water and are subject to iron deficiency, wind, insects and disease. If you are successful at getting them to survive, it can sometimes be hit or miss if they even produce fruit. It can be ever so frustrating to have them looking good and then have the tree drop its fruit or not set fruit after bloom. There are a few reasons for this situation.
First, it’s important to note that it’s natural for fruit trees to drop some fruit. Fruit trees can also experience a phenomenon called alternate bearing. While it can happen with any fruit trees, it seems to be more common in apple and pear trees. This is the tendency for a fruit tree to bear fruit in two-year cycles where it will produce a heavy crop one year followed by a light or no crop the next year. This is believed to be related to energy allocation of the tree for heavy fruit production. However, it can also be related to weather, nutrient cycling, environment conditions and cultivar. A light fruit year could be related to alternate bearing, but it could also be due to fruit drop.
There are often several phases of fruit drop. The first is the “pollination drop.” This occurs after the flower petals fall off and may last two to three weeks. You may not even notice this ‘drop’ because the fruit is so small. All of the flowers that were not pollinated will drop their fruit. Apples and pears require cross-pollination. This means that you need at least two different varieties (cultivars) within close proximity for pollination. Most plums, peaches and cherries are self-fruitful which means they do not need to cross-pollinate.
Another reason for the lack of pollination could be the lack of pollinators which are necessary for fruit trees. Bees are the most common pollinator of fruit trees. A lack of pollination can also occur as a result of cold or wet weather during the bloom period, because bees are less active in cool weather. Additionally, freezing weather right before and during flower bud development will result in more pollination fruit drop. Another reason trees may fail to set fruit is excessive growth when trees are focused more on woody growth than fruit development. This is typically the result of excessive pruning or over fertilization.
The next drop is called the “June drop.” It typically happens when the apples are about the size of a walnut. Depending on the variety, this could happen from late May to early July. This is often a natural response of trees if more fruits are formed than the tree can support to full maturity.
Next you might see a “pre-harvest fruit drop.” This can also be normal and is often a sign of a heavy fruit load. However, it can also be a sign of insects, disease or adverse weather conditions. For example, trees not receiving enough water and becoming drought-stressed could cause them to drop extra fruit. Finally, you will start to see fruit drop again when the fruit is mature. This is often a sign that it’s time to harvest!
One way to avoid excessive fruit drop is by hand thinning. Other advantages to hand thinning are to increase the size of the fruit, allow for greater development of buds for next year’s crop (overcoming the tendency for alternate bearing) and to prevent limb breakage. This is most common for apples and should be done within six weeks of full bloom. Earlier is better because it allows the tree to put more energy into the remaining fruit. Remove any damaged or misshapen fruit first. If they all look heathy, then leave the largest apple in each cluster. Ideally, apples should be spaced 8 to 10 inches apart. Do not remove the spur, which is the short, woody structure that is attached to each apple. Spurs can produce fruit for multiple years so if you remove the spur then it will reduce the fruit in subsequent years.
I may have sounded negative when I started this article, but it really is possible to grow fruit trees here! Apple and pears are the easiest to grow. Plums and sour cherries are also feasible, but others are a little trickier, depending on the environment. For questions about fruit trees, you can contact the MSU Extension Office in Broadwater County at 406-266-9242 or allison.kosto@montana.edu.
