Fungal leaf diseases prevalent

Due to rainy weather throughout the spring, a variety of fungal leaf diseases are showing up on a number of plants including tomatoes, roses, lawns and trees.

These foliar diseases cause various colored spots or brown, blighted areas on leaves, followed by leaf yellowing, browning and dropping.

Here are some key points about fungal leaf diseases to keep in mind.

In most cases, applying a fungicide this late in the season will not provide a lot of benefit to plants. The fungal infections have already occurred and will run their course whether a fungicide is applied or not.

Fungicides are most effective in protecting plants from fungal infection than they are in curing an infection. Fungicides work best when applied to susceptible plants just prior to fungal spore release and when weather conditions are conducive to infection.

Fungal spores require moisture on a leaf surface for a certain period of time to infect the plant. A specific temperature range also is needed for infections to occur. Many fungal spores are released in spring when weather is typically cool and rainy.

On plants with a history of fungal leaf disease, we do recommend applying fungicides as soon as the plant begins growth in spring and repeating applications according to label directions as long as the weather is rainy.

If fungicides are applied now, they can prevent new infections, but because the weather is becoming warmer and dryer, new fungal infections will begin to decline. Since high humidity or heavy dew can provide enough moisture for some types of diseases, there are some situations where we do recommend continued fungicide applications or starting applications this late in the season.

Some diseases, where starting or continuing fungicides application now can be beneficial, include black spot of roses, fungal leaf diseases on vegetables, and leaf spot or brown patch disease on lawns. For most of the leaf spot diseases on shade or ornamental trees, a fungicide application at this time is not needed.

It’s important to keep in mind many fungal leaf diseases are fairly harmless to plants. While they can result in minor to severe leaf drop, otherwise healthy plants usually recover without any long term negative affects.

Also be aware that fungi are host specific so they will not spread between different types of plants. If you have a disease in a crabapple tree, it is not going to spread to your shade trees or evergreens, so there is no need to apply fungicides to unrelated plants to protect them.

In some cases, especially with vegetables, diseases can spread within vegetable families, although this does not occur very often. Common vegetables related to one another are tomatoes, peppers and eggplants. Vine crops such as squash, pumpkins, cucumbers and melons also are related.

If you have a plant whose leaves are yellowing, browning and dropping off, inspect the plant closely. If you find leaf spots or brown, blighted areas on the leaves this is most likely a fungal leaf disease.

As long as your plant is otherwise healthy, it will be fine in the long run.

Contact Kelly Feehan, Extension Educator, at 563-4901 or e-mail her at kfeehan2@unl.edu.