MIDSUMMER LEAF DROP AND FRUITLESS PLUMS
GARDEN TIPS – Written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Published August 14, 2016
Tree anomalies have a way of occurring from time to time over the years. They are signs of potential problems that justifiably alarm tree owners. Recently, some local tree owners became concerned when a considerable number leaves on their trees started to turn yellow and drop on the ground.
Midsummer leaf drop occurs before the arrival of fall and is usually related to heat stress. As you can imagine, excessively hot days can stress trees, especially species not well suited to hot climates. The root systems of these trees are not able to keep up with the water demands put on the trees by high temperatures. Some types of trees respond to heat stress by getting rid of some leaves, thereby limiting the loss of water through their leaves. Other types of trees develop leaf scorch (brown, dry edges on the leaves) when they cannot keep up with the water demand caused by hot weather.
In our area, sudden yellowing and dropping of numerous leaves due to heat stress has been noticed on birch, cherry, Liriodendron (tulip), linden, sycamore, and willow trees. This year’s midsummer leaf drop was probably more pronounced because of the abrupt change from moderate weather to high temperatures.
Drought stress can also lead to tree leaf drop, especially when paired with heat stress. During hot summer weather, it is important to provide your trees with the water they need via deep watering. Large shade trees seldom receive adequate water when getting moisture only through lawn irrigation. It is important in hot weather to provide trees with a deep watering at least once a week.
How much water do trees need? They need a lot of water because they lose a lot through the pores, called stomata, in their leaves. Adequate irrigation is extremely important. To determine how much water your shade tree needs, go to the WSU Irrigation website and use their Tree Water Management Calculator at http://irrigation.wsu.edu/Content/Calculators/Residential/
A Supposedly “Fruitless” Plum Tree with Fruit: It can be annoying for owners of a flowering plum tree when their supposedly fruitless plum occasionally or frequently produces a prodigious crop of plums. When this happens, I get asked the same two questions. Why did this happen and are the fruit edible?
The production of fruit on ornamental plums is not a reliable occurrence, but it can happen if their bloom overlaps that of other types of plums. Typically, purple-leaved flowering plums bloom in early spring before other plums are flowering, limiting the possibility of cross-pollination and fruit development. Before buying a flowering plum tree, check with your nursery to make sure the cultivar you are selecting is rarely fruitful in our area.
As to edibility, the fruit can be eaten, but are generally of poor quality for eating. The trees were bred for their beautiful flowers, not their fruit. If you are a thrifty gardener, you might try making jam with the fruit and see if it is tasty enough to be worth your time and trouble. Do not use the fruit if the tree has been treated with pesticides not labeled for use on edible fruit trees.
Garden Note: Whenever applying pesticide to a tree with edible fruit, check the label for the “days to harvest” or the number of days after application that you must wait before harvesting the fruit. Also, make sure the type of fruit receiving the application is listed on the label.