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Landscape Diseases: Fungal Leaf Spots

Fall is a great time to be outside, seeing nature change right before your eyes. With fall, comes a LOT of leaves on the ground. Honestly, myself included, many of us do not really pay attention to our tree’s leaves right now because they are supposed to fall anyway. That being said if we start taking a closer look, odds are there will be several leaves with dark blotches or spots on them. A good chunk of those will most likely be caused by fungi resulting in what we call fungal leaf spot. I have had numerous calls about spots on leaves and trees losing leaves all the way from back in spring until now. I am not saying they were all cases of leaf spot, but a good chunk of them were. We usually see leaf spot worsen in spring and continue being a factor until around now into November. Why is that? Well it has to do a lot with environmental factors, rain in particular. But hold your horses if you are about to go dig up all your trees and shrubs because they have leaf spot. While leaf spot can be extreme on some plants and is very common in landscapes, very few fungal leaf spots actually cause major damage. Typically they create just some aesthetic issues. In other words you will not be winning any prettiest trees or bushes contests if you have leaf spot going on in your landscapes. There are exceptions, do not get me wrong, but for this article we are focusing on the majority of fungal leaf spot disease. Before we SPOT TREAT this problem, let’s talk about the why behind the disease. 

The why is first. Why does any disease happen in our landscapes? Our UGA Extension Publication, Common Landscape Diseases in Georgia, gave three important factors that must be present at the same time for a disease to occur on a plant at any particular time. The publication calls them the “Disease Triangle”. (As a Harry Potter fan, all I could think seeing that was the Deathly Hallows triangle) These factors are:

  1. A plant must be susceptible to the disease
  2. The disease-causing agent (pathogen) must be present and able to infect the plant
  3. The environment must be favorable for disease development.

If any one of these factors is missing, then the disease will not occur. As Sherlock Holmes would say these factors are simply “Elementary.” Common Sense could have told me that, but they are crucial to understanding diseases in landscapes, not just Leaf Spot. This is because if you are not really versed in plant diseases, you may very easily confuse one with another or even just environmental shock (nutrient issues, weather, ect.) with a disease. There are easy management strategies to help kick these diseases to the curb before they become an issue. 1) Keep sickly plants out! When buying plants inspect to make sure the plants you are buying do not have any symptoms or signs of disease. 2) Keep the landscape area clean of plant debris. Keep harmful insects and weeds out as well. The less stress the better! Plus some of those insects can carry diseases. 3) Make sure you are growing healthy plants. How do you do that? Use recommendations for that plant and follow them to a T. A strong healthy soldier can fight off an enemy way easier than a weak one. 4) Keep foliage dry. Do not let water sit on the foliage for long periods of time. Like with Fungal Leaf Spot, the excess water can lead to diseases. Avoid irrigation later in the afternoons because plants will not dry as quickly come evening time. Also avoid areas where you have poor drainage so the plants are not just sitting in a pond. 5) Lastly, you can use chemical control after using the other strategies mentioned above to also get a handle on diseases. For residential landscapes the only chemical control for diseases is fungicides. Make sure you read the label and follow the directions and protocols properly. If you have any questions regarding fungicide recommendations or application please feel free to give me a holler! I will be glad to help. 

Shifting gears back to the disease at hand, Fungal Leaf Spot, the symptoms range from small little specs to big dark blotches on the foliage. The lesions can be tan, grey, brown, reddish, or even have purple tones to them. Fungal Leaf Spot survives on the infected host and are spread through their spores via air or splashing water. That excess moisture on the leaves I just mentioned is a Fungal Leaf Spot paradise. Strategies for handling a Fungal Leaf Spot issue, on top of what I listed above, would be reduce humidity by way of air circulation, rake and remove fallen leaf litter that was infected, and increase spacing or selectively prune branches to improve the plants ventilation. Also those protective fungicides mentioned, also work really well at first sign of leaf spot or as a protective measure. Leaf Spot can be a serious eye sore, but with the proper management practices and identification there are ways to lessen this disease.

Joke of the Day: What kind of tree has leaves shaped like chickens? A Poul-TREE. 

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