Are Those Leaf Spots on My Plants?

No one likes to see leaf spots on their plants, but they are typically minor stresses that will not affect the overall health of the tree. Some leaf spot diseases can cause the plant to lose its leaves, but as long as the plant is healthy, it should grow back new leaves. Leaf spots are mostly caused by fungus, but sometimes, they can be caused by bacteria, which is more serious. Leaf spot diseases favor wet and humid conditions, as the pathogens are able to breed better. That’s why many leaf spots pop up in the spring, summer and early fall.

What does leaf spot disease look like?

Leaf spot disease leaves behind black or brown spots or blotches on plant leaves. The spots vary in size, shape and placement, and some diseases are specific to a particular genus, which means it won’t spread to other nearby plants. In addition to black and brown colors, leaf spots can also be yellow, red, gray and tan, and many have definite margins. Although leaf spots can look deadly, they often affect the leaves but not the overall health of the plant or tree.

There are other types of conditions that can cause similar looking effects, but they are not leaf spot diseases. Bacterial leaf spot is much less common than fungal leaf spot, and the spots tend to have a light colored halo around the rim. Insects may also cause spots since they feed on the top layer of the leaf. Another factor is the physical damage that can occur from extreme temperatures. Since the cold or heat can damage the individual cells in the leaf, you may find blotches left behind.

What are the types of leaf spot diseases?

Since leaf spot diseases can look like other problems, you may want to remove an infected leaf and show the sample to an arborist. Marssonina leaf spot is the most common leaf spot disease and includes dark brown and black specks that grow bigger during the summer and turn into blotches. Leaf and shoot blight are common during the spring months and mostly affect young aspen trees. Leaf rust is also very common, but it’s not deadly to the tree in most cases. The rust looks like yellow-orange spots that pop up in the late summer months.

What can I do if I find leaf spots on my plant?

If you notice leaf spots on your plants, you may have no choice but to tolerate the infestation. Remember, the overall health of the plant should be fine, but the signs of a leaf spot disease mean you need to step up the level of care you’re delivering to your trees.

In the fall, rake up leaves so that they do not settle and create mold around your plants and trees. Prune plants and trees to promote good air circulation, and remove any diseased branches that may be infected from another disease. When watering trees, adjust the sprinkler so that it does not hit the leaves and overwater them. This is especially important in the late afternoon or evening, as you don’t want the plants to head into the cooler temperatures and sunless skies while having wet leaves.

Any type of fungal disease thrives off of wet, cool and humid conditions, so creating these types of environments will only allow fungus to thrive. When planting trees for instance, choose a spot where the plants will get ample sun and not be planted too close together. Air circulation is beneficial in protecting plants from leaf spot diseases and anthracnose.

Should I use fungicides?

Many people believe that fungicides are the cure-all to everything, but this isn’t the case. Fungicides can be used if a mature plant continues to lose its leaves each year, but in the beginning, tolerating the fungus is best. Fungicides will help prevent leaf spot diseases, but they will not restore current spots. The timing of fungicides is also important, as they should be applied in the spring when the leaf buds start to open. It’s much easier to apply fungicides to small plants and shrubs; large trees will best be served by an arborist.