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Is The Weather Causing Fruit Drop and Excessive Seeds On Maple Trees?

GARDEN TIPS – written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written June 25, 2015

Earlier this month some gardeners noticed that a number of small apples were dropping off their trees and wondered why it was happening. There are three different types of “fruit-drop” that backyard orchardists may observe.

Fruit drop very early in the season is linked to pollination. Apples and pears require cross-pollination for fruit to form. Cross-pollination is the exchange of pollen from the flowers of one variety to the flowers of a different variety of the same type of fruit.

Cross-pollination is needed for fruit development to occur in many tree fruit, like apples and pears. If adequate cross-pollination does not occur, fruit may start to develop but then drop from the tree. This typically happens soon after the flower petals drop. It occurs because there are not enough viable seed within the fruit producing the plant growth regulating chemicals needed for fruit development.

Lack of pollination can be the result of not having a compatible variety nearby to enable cross-pollination, frost, a deficit of bees and other pollinators, or weather conditions that deter bee activity during bloom, such as rain or strong winds.

Apple or pear fruit may also be observed dropping in early summer. This is called “June-drop.”  The drop is usually due to the crop load of the tree. June-drop is a way for the tree to thin itself because it can not support all the fruit that were pollinated and developing on the tree.

This self-thinning allows more of the tree’s carbohydrate resources to go into the development of fruit left on the tree. Backyard fruit growers can avoid an excessive June-drop by thinning or removing extra fruit early in the season, allowing only one fruit per cluster to develop and spacing these an average of six inches apart on the branches. This results in the development of larger fruit instead of many small fruit or considerable fruit loss from June-drop. June-drop may be extraordinarily heavy if late spring weather is hot.

If fruit drop occurs close to harvest, it is called “pre-harvest fruit drop.” This may be caused by a heavy fruit load, high temperatures, wormy fruit, or drought stress.

Local gardeners are also noticing another phenomenon this year, the production of an excessive  amount of seeds on maples and other trees this spring. I was once told that trees produce copious amounts seed like this when stress triggers them to “think” they are dying and driving them to procreate. This is only a partially correct untechnical explanation.

Abnormally large seed crops may be due to heat or drought stress that occurred the previous year, but it may also be due to spring weather the current year. Maples do flower quite early in the spring and their flowers are subject to spring frost damage. Mild spring weather with no killing frosts allows for good pollination and the development of more seeds than in most years.

Scientists have also discovered that some types of trees normally bear heavier seed crops every other year or every few years.  There is even a phenomena called “masting” where some trees, such as oaks, produce massive seed crops on cycles of three to twelve years. This occurs over large regions and is thought to have evolutionary significance within forest ecosystems.

When it comes the abundance of seeds this spring on local maples and other trees, it could be due to the mild spring weather, stress last summer, or cyclical seed bearing… or maybe all three.


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

The Mid-Columbia Community Forestry Council has named the red maple, Acer rubrum, the Mid-Columbia Tree of the Month” for October. Red maple is the perfect choice to recognize because it has outstanding fall color and performs well in local landscapes. Growing up in the northeast part of the country, I’m a sucker for trees with magnificent fall color. That’s why you’ll find an October Glory, a cultivated variety of red maple, in my yard. The leaves on my tree are just beginning to show tinges of red, so I’m anxiously anticipating glorious color by the end of the month.

Red maple is an excellent shade tree for use in home landscapes. This native North American species grows to from 40 to 60 feet tall and 25 to 35 feet wide, although many of the cultivated species are smaller in stature. In the spring it’s one of the first trees to flower with small clusters of red flowers. While this tree prefers both slightly moist and slightly acid soils, it will tolerate wetter or somewhat dryer conditions. It can exhibit chlorosis in highly alkaline soils, but seems to tolerates most local alkaline soils without any problem.

The red maple is a favorite of many gardeners because of its outstanding fall color ranging from bright reds to oranges and yellows. It’s one tree that can be relied upon for a beautiful autumn display. Some cultivated varieties develop color early in the fall, others a little later. If you live in an area with early fall frost, select one that colors up early.

The other things I like about red maples is that they have few pest problems and have a relatively fast rate of growth, without causing as many problems as some fast growing trees, such as silver maple. This is because their root system is less vigorous and aggressive, but the red maple does have shallow roots that develop into surface roots as it grows older.

The smooth, silvery bark of young red maples contrasts well with the green leaves of summer or the bright fall colors. However, some owners have found that cats find the bark a great scratching post, causing significant damage to the tree. Red maple leaves tend to be a little tougher than those of other maples and less prone to tearing and tattering from windy conditions.

October Glory is one of the favorite cultivated varieties of red maple because of its long lasting intense red fall color. It’s very popular and readily found at local nurseries. It grows from 40 to 50 feet tall, averaging about a foot of growth a year. Another popular variety is Red Sunset which colors earlier than October Glory with outstanding oranges to reds. Autumn Flame is another highly touted variety that colors up with red leaves about a month earlier than October Glory. If you don’t like raking, you might want to know Autumn flame also has smaller leaves .

There are also some hybrids (Acer x freemanii) of red maple and silver maple that are often sold as red maples. One of these is Autumn Blaze with long lasting orange-red fall color. It’s a very hardy, fast grower, but tends to be weak-wooded.

Visit your favorite local nursery and check out their red maples now. Even if you don’t intend to buy and plant until next spring, you can check out the fall color of the different red maple varieties and decide which one you like best. That’s what I did.

Published: 10/9/2010 12:56 PM



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