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Rains Bring On Fungus of All Sorts; Here’s Your Organic Treatment Guide

Updated: Feb 14, 2022

Rain. We always seem to either get too much or not enough. This spring is bordering on the excessive side. Along with comes high humidity. Together they create the perfect conditions for fungal outbreaks.

If you haven’t seen them already, you’ll probably experienced mushrooms popping up in your lawn, black spot appearing on your roses, and powdery mildew on your crape myrtles and many of your other plants. Worst of all, if you have Red Tipped Photinias or Indian Hawthorns, you will likely see spots on the leaves of the plant that signal an outbreak of Entomosporium – a fungal disease that can kill your plants if left untreated.

All of these problems can be treated with organic methods and products. We’ll explain what to use in each situation and help you to potentially head off premature plant death.

Photo of a mushroom growing in a lawn
Mushrooms sprout up quickly in wet conditions.

Lawn Mushrooms

Mushrooms sprout up quickly in continually moist lawns and gardens, particularly in areas where you’ve laid mulch or perhaps have an old tree stump or other rotting organic matter. Fortunately, these are harmless to your landscape. (Just don’t eat them! They are poisonous to consume!) The mushrooms will disappear as soon as your garden has a chance to dry out. If you are concerned, you can treat for it by spreading horticultural corn meal on the affected area. Corn meal is a food product and so is safe to use around people and pets. Horticultural corn meal, which is the kind that we sell at Marshall Grain, has garlic added to increase the efficacy of the product. Corn meal and garlic are both non-specific fungicides, which means they will kill both beneficial and harmful fungi in the treated area. For this reason, horticultural corn meal is often used to treat Brown Patch in St. Augustine lawns.

Rose leaves infected with Black Spot
Roses are common victims of Black Spot.

Black Spot

Black Spot primarily affects roses but can affect many other ornamental plants, too. First, make sure you remove any diseased leaves from the plant. Rake up and dispose of any plant debris on the ground as well. Once you’ve done that, you can choose from several organic products to bring the problem under control. These include Neem Oil (either 70% or 100%), Monterey Complete Disease Control, and Ferti-lome’s Triple Action (a blend of Neem Oil and Pyrethrin). Sulfur and Potassium Bicarbonate can also be used as fungicides. Spray the entire plant — make sure you cover both sides of the leaves, the stems, and the trunk (or canes). This should be repeated every 10 to 14 days. Avoid spraying in the middle of the day to prevent the oil from burning the plant. Always spray in the early morning (before 10 a.m.), if possible. Otherwise, spray in the evening around sunset.

Since Black Spot can also live in the soil, a third option is to spread horticultural corn meal around the base of the plant. You may also want to try drenching the soil with 100% Neem Oil. While 70% Neem extract is usually sufficient as a foliar spray, it is not effective as a soil drench.

Sprays and drenches need to be applied regularly during spring and fall to bring outbreaks under control.

Another organic solution is to plant Society Garlic near your roses (within 6 ft). As we mentioned above, garlic is a natural fungicide, so by planting it in the same area as your roses, it works systemically as a natural preventative.

Note: Roses and other plants can also develop spots in response to heat stress, particularly when temperatures soar into the 100’s. This problem should not be confused with Black Spot fungus. Never apply foliar sprays in the heat of the day or you will burn your plants.

Photo: Powdery Mildew on pumpkin leaves
Powdery Mildew

Powdery Mildew

Powdery Mildew can occur almost any time of the year — whether it’s wet or dry. If the leaves of your plants look like they’ve been dusted with flour, you probably have an outbreak. You may also see leaves turn yellow, dry up and crinkle or become disfigured. Crape Myrtles and squash plants are common victims. It’s one of the most prevalent and hardest fungal problems to resolve and takes persistent applications of an organic fungicide to eliminate. As with Black Spot, you have several organic treatment options, including Neem Oil and Monterey Complete Disease Control.

Entomosporium fungus on a Hawthorn shrub.

Photinia Leaf Spot

Commonly known as Photinia Leaf Spot, Entomosporium impacts Photinas and Indian Hawthorns and it is extremely difficult to eradicate. Prevention is the best option, but if caught early and treated aggressively it can be brought under control. The fungus won’t kill your plants immediately, but if left unchecked, each year the problem will become worse until the plant finally dies.

You can recognize it by checking the foliage for black, brown, reddish or purplish spots on the leaves. Generally, the spots appear on the new growth first and then spread to other parts of the plant.

Prevention and containment are the keys. Over-crowding of plants aggravates the disease and encourages its rapid spread, so if you plan to add these plants to your landscape, make sure you allow enough space between them so that when they are at their fully mature size there is room for air to circulate around each plant. Often these two plants are grown as hedges, which only encourages the spread of the disease. If you really want a hedge, consider a mixed hedge that allows for your susceptible plants to be placed further apart. Since the spores can’t travel very far, separating plants will help prevent its spread.

Another key is to ensure that they are planted in well-drained soil. Both Indian Hawthorns and Photinias hate to have “wet feet.” The soil must have time to dry out between waterings. Fungal spores are easily spread by water splashing on the leaves or on the ground under the plant. Of course, you can’t prevent the rain from falling. However, when you water, always try to apply it from below and avoid getting the foliage wet. Mulching can help to prevent water from splashing up from below.

The fungus goes dormant in the winter when your plants are also dormant so limit pruning to the cold season. That way your plants won’t begin to put on new growth until spring.

Finally, never allow plant debris to accumulate under the plant. Rake up any fallen leaves and remove any infected parts of the plant.

Treating infected plants means starting early. At the first sign of leaf spot, begin spraying an organic fungicide every 7 to 14 days. You will need to do this continuously through the spring and then start up the treatment again in the fall and continue through the winter. Treat again the following spring.

Since the fungal spores can remain in the soil it’s important to treat the soil as well. You can do this by spreading horticultural corn meal on the ground around the plants. Use 1 to 2 pounds per 100 square feet. Corn meal is not affected by rainfall or watering. One application per season should be sufficient but more often won’t hurt.


Fungus and most other garden problems are easier to treat if you catch them early. Make a point of inspecting your garden on a regular basis to watch for pests and diseases. Then come see us for the right organic solution.

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