Submitted by Krista Harding

Summer is officially upon us now, and it has brought some common plant problems with it. We have had plenty of moisture and to date, our plants haven’t really had to be “tough” yet this growing season. Now that the temperatures have risen and we are not getting rain quite as often, some plants are starting to show environmental stress.

I have started getting calls about Walnut and River Birch trees having problems. The trees have yellow leaves scattered throughout the canopy and some are dropping leaves. How do you know if this is a serious problem for a tree? Generally speaking, it depends on the tree species and if the leaves stay attached to it. If leaves have fallen from throughout the tree and resulted in a general thinning of leaves, this is not a serious problem. Trees will often set more leaves in the spring than they can support during the summer. Heat and drought stress will cause the tree to lose leaves that it cannot support with the available soil moisture. Remember that our plants haven’t had to be “tough” yet. We can have green leaves drop that appear perfectly healthy. As long as the leaf drop results in a gradual thinning of the leaves, this is not a serious problem and the tree should be fine.

Sometimes, virtually all of the leaves drop. Certain trees, such as hackberry, can drop all of their leaves and enter summer dormancy. We are a bit early in the summer for this to occur, but it may happen soon if we turn off really hot and dry. If trees are affected by summer dormancy, they should still have supple twigs and healthy buds. Usually the effect on the health of the tree is very minor and the tree leafs out normally next spring. However, if the buds die and the twigs become brittle, at least part of the tree is dead.

Trees that have leaves that die and remain attached to the tree is a serious problem. Sometimes this happens in what seems like just overnight. In a case like this, the tree couldn’t keep up with moisture demands and died quickly. I have seen one case of this already. I believe it was due to the cold snap last December 18, when we got very close to zero temperatures. Damage to underlying tissues is the root cause of this problem.

Another problem that is starting to appear this time of year is two tomato leaf-spot diseases. Septoria leaf spot and early blight are both characterized by brown spots on the leaves. Septoria leaf spot is characterized by small dark spots whereas early blight spots are much larger and have distorted “target” pattern of concentric circles. These diseases usually start at the bottom of the plant and work up. Mulching, caging or staking to keep plants off the ground will make them less vulnerable to diseases by providing better air circulation so the foliage can dry quicker. Mulching also helps prevent water from splashing and carrying disease spores to the plant.

In situations where these diseases have been a problem in the past (or even this year), rotation is a good strategy. Obviously it is too late for that this year. Fungicides are often helpful. The active ingredient Chlorothalonil is a good choice to use. It can be found in numerous products including Fertilome Broad-Spectrum Landscape and Garden Fungicide; Ortho Garden Disease Control; Bonide Fungonil and others. Be sure to start protecting the plants when the disease is first noticed. It is all but impossible to control these diseases on heavily infected plants. Read labels for harvest waiting periods.

Don’t forget that most of the Extension services are free of charge! If you are experiencing plant problems, don’t hesitate to give me a call for diagnosis.

Krista Harding is a K-State Research and Extension Agricultural agent assigned to Southwind District. She may be reached at 620-244- 3826 or [email protected]