Fungus Among Us

I’ve lost track of how many questions I received this summer that had “fungus” somewhere in the answer. Just in the last week alone, I fielded five questions involving plants suffering a fungi-filled fate.

A side effect of one of the wettest Illinois summers on record is an abundance of fungal diseases on just about any plant in the landscape. Prolonged wet conditions especially when accompanied by cool temperatures are ideal for development of fungal diseases. The heavy, humid conditions that were prevalent in between rainy periods this summer were perfect conditions for a bumper crop of fungal problems.

Dead, dying spots on leaves, stems, flowers and fruits are all symptoms of possible fungal infection. Occasionally infections are advanced enough that you can see signs of the actual fungus appearing fuzzy, dusty, or even mushroom-like.

I’ve read that anywhere from 80-85% of plant diseases can be attributed to fungi. Some gardeners might read that last statement and conclude “well then, we must kill all the fungi before they kill my plants”. Unfortunately, like most things in nature, it is not that simple.

Fungi are everywhere, even in the cleanest homes. Many fungal spores travel by wind; when they fall on a favorable material (like a forgotten piece of stale bread) they grow. There are fungi all over our landscapes and the soil beneath. Keep in mind that fungi have a crucial role in breaking down plant materials through decay, and that helps build nutrient rich soils. Even if there was a way to selectively kill the fungi that infect our plants, new spores would blow or wash into our landscapes regularly.

After discovering a fungal disease in their landscape, many homeowners conclude they must apply a fungicide and that will restore their plant to health, as if the disease was never present. Applying a fungicide might stop the spread of the disease, but the damage to the existing leaves, flowers or fruits is done, at least for those particular ones at that time.

As a rule of thumb, fungicides should be applied to prevent disease rather than treat it. Fruit trees are a great example. Spray guides for different types of fruits trees will recommend application of fungicide at different points in the growth cycle at specific times when fungal infections tend to develop.

Sometimes though, labels can be a bit misleading. The bag of a well-known brand of lawn fungicide promises to “prevent AND control” major fungal diseases of turfgrass. Knowing that fungicides really prevent rather than treat fungal disease, you may think this label is lying about what it can do.

Reading the label, it gives two rates of application: a “preventive” and a “cure” rate. The “preventive” rate is supposed to be used before the disease shows up or in the very early stages, and the “cure” rate when it’s really obvious. But even if you’re applying the higher “cure” rate, it is essentially preventing infection of new turfgrass growth. The dead and dying infected blades of grass are still there. In theory at least you will eventually mow off these affected blades of grass and if the fungicide is effective, you will have “cured” the fungal infection and have nothing but healthy new growth in its place. If the “cure” rate of fungicide was applied too late and the disease had already invaded the entire plant, there would be no new uninfected growth—probably no new growth at all since in all likelihood the plant would be dead.

Like just about any plant, healthy, well-cared for lawns are less likely to develop fungal disease problems than neglected ones. But there are limits to that line of reasoning. A friend commented to me this week that he couldn’t figure why so many lawns in a particular well-kept subdivision appeared to have dead and dying patches of grass. These were lawns that often had irrigation systems and were regularly fertilized. Everyone wants a lush green lawn, but if the lawn is overfertilized with too much nitrogen, that same beautiful lawn is more susceptible to fungal diseases than a lawn appropriately fertilized.

Nitrogen is the fertilizer component that pushes the lush green growth that homeowners long for. Plants generally respond well to nitrogen and can grow very fast when conditions are good for growth. But with this quick growth, the plant’s cell walls are thinner, which makes it easier for fungal diseases to invade the plant. Fertilizer is definitely one of those things where a little is good, but more is not necessarily better.

Lawns aside, what is a homeowner to do when faced with fungal disease in the landscape? Personally, I’ve never used fungicides, only because they require repeat applications to prevent infection throughout the growing season and I have many more things to do than spray fungicide. So it boils down to plant care and selection plus your tolerance for less than perfect plants.

• If you have plants hit hard by fungal disease this year, take extra time this fall to clean up any infected leaves that have fallen around the plant. These leaves are a source of infection for next year’s growth. Get them out of the garden and do not compost them.
• Good air circulation keeps plant foliage from remaining wet for long periods which promotes fungal infections. Fall is a great time to thin out overcrowded plantings to increase air circulation.
• Water plants at their base to minimize wetting the foliage, and use mulch to minimize splashing soil onto the plants when watering since many fungal spores exist in soil.
• In the vegetable garden, rotate the location of your crops from year to year since many fungal diseases can overwinter in the soil. While not foolproof, rotating crops can lessen the severity of many vegetable garden problems.
• Look for plant varieties resistant to common fungal infections. Sometimes this information is listed on seed or plant labels, but it may require some research.
• Either learn to live with the fungal infection or remove the plant from the landscape. We have several variegated dogwood shrubs that my husband loves. They do look nice in the spring and early summer, but by this time of year they are a fungal disease disaster. Thinning out the branches to increase air circulation helped somewhat, but they still look pretty ragged this time of year. They might be good candidates for a fungicide regimen, but there is just no time for that at our house right now. Our compromise was to remove the dogwood shrub that was on the front corner of the house, move a Hydrangea paniculata ‘Quick Fire’ into its place, and leave the others where they are in the back yard for now.

Thankfully most fungal diseases in plants do not kill the plant unless they are severe, and usually it takes multiple years of severe infection to kill larger plantings like trees. Deciding to use fungicides may certainly be the best course of action in some cases, but realizing their limitations and implementing good plant care and selection practices will go a long way in keeping your landscape beautiful.

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