Fungus Disease – By Mark Govan, Host “Florida Gardening”

If you grow vegetables, citrus, or even ornamental plants, then you have probably had a fungus disease that you have had to deal with. I get questions daily from homeowners asking me what the problem is on their plants and often this brings up fungal diseases. I have to ask, is the fungus on your lawn, your fruit tree leaves, the fruit, your ornamental plants, your vegetables, or in the soil? For many homeowners, identifying fungal diseases can be very hard especially if you do not know what to look for. How can you tell? In fact when we do not know we have a fungus and the disease goes unchecked, our plants can wither and die. If all fungi looked the same we could easily identify them and control would be easy. Unfortunately, most fungi look different. In this article I am going to try to explain what a fungus is and how to identify the different types. I will also give you a few control methods to help your vegetables, plants, and turf to remain fungus free.   

            What is the role of a fungus? According to the dictionary, “Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange”. Even though this sounds good for the environment, is there a beneficial fungus? In fact there is. For many years fungi have been used as a direct source of food. Mushrooms are an edible form of fungi similar to the leveling yeast used in breads. There are even varieties of fungi used for medicinal purposes. Most of these are beneficial to humans and are used commonly everyday. However, there are varieties of fungi which also attack our food supplies and garden plants. Today, I am going to help you identify several different types of fungi which attack our vegetables, citrus, ornamental plants, and turf grass. If you know what to look for you will be able to spot problems before you lose your plants. There are a few simple techniques you will need to learn and I am happy to help you do this.  

            Powdery Mildews are a very common form of fungus which attacks a wide variety of plants. Vegetable crops like squash, beans, and greens are commonly attacked by mildews. Strawberries and grapes also fall victim to this fungus. Crepe myrtles, just about the time they go into bloom begin fading away to this fungus. The one good thing about this disease is that mildews are easy to identify. Once you have a positive identification control methods can be used. 

            Powdery Mildews attack the foliage and the flowers of plants. What you need to look for is the white powdery spots on the upper sides of the leaves or on the flowers. As the fungus grows these spots tend to coalesce and more of the fruiting spores become visible. Soon entire leaves turn completely white and begin to shrivel up. If you rub your thumb or finger across these white spores they will smear. Some varieties of powdery mildew may not smear to the touch as the damage to the leaf has already been done. At this stage additional leaves or flowers will start to succumb to the fungus. Control of the problem must start soon or you will risk losing the entire plant. Once we go through the differing types of fungus I will give you the controls.

            Leaf spot diseases are very easy to identify by their distinct spots on plant leaves and stems. These spots may either be raised to the touch or flat with a halo or colored border around the spot. Most leaf spots start out as small dots on the leaves or stem. This is the stage you should start controlling the problem. As the disease matures these small spots enlarge to the size of a pea or bigger or these spots may coalesce into larger spots. Many people do not even see these spots. They do notice the leaves turning yellow and falling on the ground. By performing a quick walk through of the garden you should be able to spot these symptoms before they become a larger problem. One thing you need to know about leaf spots is that not all leaf spots are the same and if you just do not know what you have then you should call in a professional pest control applicator or take a sample to the cooperative extension office in your area for proper identification.

            Rusts are one of my worst nightmares. You all know I love Plumerias, the Hawaiian Lei Flower. Plumerias have large beautiful leaves and fragrant blossoms. Their nemesis is rust. Rust appears as orange colored spots on the bottom side of the leaf. If you run your finger across this area you will see a smear of this orange fungus on your hand. Fig trees are also attacked by rust which appears as black spots on the leaves eventually causing their leaves to drop. Rust and leaf spot diseases are spread by the air and overhead watering. When possible try to water your plant from the bottom and keep your leaves as dry as possible. Rainbird and Toro make special sprinkler heads which direct their spray low to the ground away from the plants leaves. These special heads can help for long term control.   

            Brown Patch, Dollar Spot, and Grey Leaf Spot fungi attack lawns when humidity and temperatures are high. Watering at night or having increased thatch in your lawn can cause any of these fungal diseases to kill your turf grass in as little as two to three short weeks. As noted above, look for spots on the leaves with halos around the center. Sometimes, you may even notice a foul smell emanating from the thatch. I will list controls for these problems below but you should be aware that not all fungal problems can be controlled with one product or one application. Control applications should always include a professional pest control application and reinspection to be sure the fungus has been controlled. 

            Pythium, Phytophora, Crown or Root Rots can be some of the most damaging fungal infections you will ever run into. These diseases can kill entire plants large or small in your landscape. Because these diseases normally affect plants root structures or interfere with the uptake of nutrients from the soil, you can not always visually see these diseases. What you need to look for is the early stages of this fungus. Look at the top of the plant for a general dieback or wilting. Because this fungus attacks the roots, the first areas of the plant to die is where the new growth forms, the top of the plant. Small plants infected with this fungus may be hard to diagnose as this fungus may make the entire plant look wilted even though you have watered the plant. Controls of these diseases are very expensive and should only be attempted by a certified pest control company. In most instances, homeowners will merely replace the plant with a different variety because of the cost. Never plant the same type of plant in the same hole as one that has died from one of these fungal diseases as the new plant will probably die as well. 

            Fungicides such as Bayleton, Daconil, Funginex, or Dithane M-45 are good control products for leaf spots, rusts, and mildews. Read the label for each of these products before you use them on your plants. Some of these products are systemic so be sure not to use them on your vegetables. However, systemic fungicides are the products of choice for non-vegetable crops. Products such as Cleary’s 3336, Subdue, and K-Phite work great on hard to kill diseases like pythium or phytophora. They also work well on our turf grass diseases. Remember, these should be applied by professionals.

            If you are treating your vegetables, be sure that you mark your calendar to re-apply every fourteen days as products like Dithane M-45 tend to wash off the plant after a rain or irrigation cycle is completed, you will have to re-apply them. Cultural methods may also have an impact on control. Spacing plants to give them proper air circulation and removing severely infected leaves from the plant and placing them in the garbage will also help with control. Make sure you are properly fertilizing your plants. Plants that are healthy and growing will have fewer problems than stressed plants. Use a well drained soil and choose plant cultivars that are resistant to diseases. This will help to save you money.  

            Even though I only have covered a few of the fungal diseases I run into regularly, these are what I see the most frequent. I hope this will help you identify fungal problems in your landscape and give you an idea of how you can control them. Try to have fun in the garden and remember, without plants we would not be here.      

4 thoughts on “Fungus Disease – By Mark Govan, Host “Florida Gardening”

  1. bonnie primovic says:

    Hi Mark,
    We saw you today at the botanical gardens at USF. Our Plumeria have rust. What was the name that of the chemical you told us to purchase at Shell’s? I thought I would remember but I have totally drawn a blank.
    thanks!

    1. Mark Govan says:

      The product is called Thiomyl or you can try Honor Guard. Hope this Helps!

  2. bonnie primovic says:

    Mark,
    How much honor guard per gallon for plumeria and how much per viburnum, please. The directions only state per 100 gal and I have a 3 gallon spray tank.
    Thanks!
    Bonnie

    1. Mark Govan says:

      I believe it is one ounce per gallon but you have to refer to your label to make sure. If it says x ounces per 1000 sq ft. figure one gal can treat 1000 sq ft.

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