Weather causes leaf spot diseases

Leaf spot diseases are now rampant due to the wet spring weather. You can see them in fruits, vegetables, lawns and ornamentals.

The spots are yellow and/or brown. Fungi cause most of them, and they are not always a serious problem for plants. Many leaf spot diseases look worse than they really are.

Your yard probably has one or more plants with the following leaf spot diseases.

Dogwood trees have more leaf spot diseases than most other plants. Spot anthracnose caused small holes in the leaves during spring, and now the brown blotches typical of septoria leaf spot are showing up. Powdery mildew is another source of brown blotches on dogwood leaves. Discula anthracnose, which actually kills dogwoods, starts out as a brown spot with purple edges.

Anthracnose is expected on the leaves of maple, ash and sycamore whenever the spring is wet and cool. It is now causing blackish-brown blotches on their foliage. Although some of these trees may drop their leaves, no lasting harm will be done.

Irises are cut back in summer to remove leaves sickened and killed by heterosporium leaf spot. It attacks the highly popular bearded iris, and is always most damaging in a wet season.

Lawns thin out and turn a yellowish color when they get a case of helminthosporium leaf spot. Under severe conditions, it can also kill the grass. Lawns fertilized in spring and summer are sure to get leaf spot in addition to other diseases.

Redtip bushes, aka photinia, are looking like plucked chickens right now. The ground under them is covered with dead leaves. They are having an outbreak of entomosporium leaf spot, and it could be fatal to some of the bushes.

Leaf spotting and leaf drop are widespread on roses. The culprit is blackspot disease. Weather was so wet earlier this year that even the highly disease resistant rose known as Knockout came down with blackspot.

The brown spots of early blight first appear on tomatoes as the fruits begin to develop. Leaves die rapidly, starting at the bottom of the plant. Virtually every tomato plant in Virginia has early blight to some degree right now.

For leaf spot, the bottom line is that a preventive approach works better than a curative approach. In fact, there is no great need to control most of these diseases.

Sanitation helps prevent leaf spot disease. This involves raking up and disposing of dead leaves and other plant parts.

Your watering technique can make leaf spot worse. The more you sprinkle your plants’ leaves, the more leaf spot they will have.

Stores have fungicides, which are registered for use on many of the leaf spot diseases. In organic gardens, the item to spray with is liquid copper. In other
gardens, the leaf spot fungicide most widely recommended is Daconil.