When aloe plants are happy and healthy, their leaves are a vibrant green. However, sometimes aloe plants develop issues that lead to brown spots on the leaves. Keep reading to learn about some of the reasons why your aloe plant may have brown spots.
Causes of Brown Spots on Aloe Leaves
A variety of different diseases can cause brown spots on aloe leaves. Here are some of the most common causes.
Aloe rust is a fungal disease caused by the pathogens Phakopsora pachyfhiza and Phakopsora meibomiae. These fungi attack the outer portion of the leaves, causing discolored spots. They can affect aloe plants being grown indoors and outside.
Spots from aloe rust may start out light yellow or orange before they turn brown or black. Over time, the spots will harden, and the infected leaves may start curling or fall off.
Other signs of aloe rust may include orange masses of spores on the bottom of the plant’s leaves.
Aloe rust is more likely to occur in cool and wet conditions.
Generally, brown spots caused by aloe rust are not a cause for concern. While the infected leaves may fall off, new leaves can remain healthy.
Anthracnose is a general term used to describe a group of fungal diseases that cause dark spots on leaves. One fungus which can cause anthracnose in aloe plants is Colletotrichum gloeosporioides.
Signs of anthracnose in aloe plants include dark green or brown spots of various sizes. These spots typically appear water-soaked and sunken.
As the disease progresses, the spots often darken and develop reddish centers. The number of spots can also increase and form large patches of rotting tissue.
If you spot anthracnose on your aloe plan, it’s best to prune off infected tissue. Dispose of the tissue and ensure to sanitize any tools both before and after pruning.
Anthracnose can remain dormant in the soil. Therefore, you may want to repot your aloe plant in a fresh potting mix after removing infected leaves.
Leaf Spot Disease
A disease simply known as leaf spot disease can be caused by the pathogen Alternaria alternata and species in the Curvularia genus.
Spots caused by Alternaria alternata typically first appear as dark brown, round, and sunken. As the disease progresses, the spots can develop concentric circles with different shades of reddish and brown.
Eventually, the spots will spread, and entire leaves may turn brown and shriveled (and the plant may display signs of drooping).
Fungi in the Curvularia genus cause dark brown spots that appear water-soaked. There may also be a water-soaked appearance around the outer edge of the spots.
As these spots age, they may appear scabby and light brown or gray.
How to Prevent Brown Spots on Aloe
Since a variety of pathogens can cause brown spots on aloe plants, it can be hard to identify exactly what is causing the unsightly spots. The good news is that preventative strategies are the same across the board.
Fungi spread in moist conditions. Therefore, much of your preventative strategy involves controlling moisture.
First, keep the humidity low. Aloe plants prefer dry air with less than 50% humidity.
Next, only water your aloe plant when the top two to three inches of soil is dry. Overwatering can lead to constantly moist soil, encouraging diseases to develop and spread.
You should also ensure that you use a well-draining potting mix and a container with drainage holes.
Along with keeping conditions dry, you should also take care to avoid introducing pathogens in the first place. Inspect new plants before bringing them into your home, and use a trusted aloe potting soil.
How to Treat Brown Spots on Aloe
In most instances, you should prune off the infected tissue and dispose of it. Make sure you are sanitizing any tools both before and after pruning.
After you prune, aim to decrease the moisture in both the air and soil. If you follow these steps, your aloe plant should recover. Aloe plants will also benefit from light fertilizing each season.
Keep Your Aloe Plant Healthy
Fungal diseases are the number one cause of brown leaves on aloe plants. You will likely avoid these issues by keeping the air and soil moisture levels low. With due care and attention, your aloe plants will thrive for years to come.
For more, see our in-depth guide to aloe plant care at home.
Briana holds a B.S. in Plant Sciences from Penn State University. She manages a small market garden where she grows vegetables and herbs. She also enjoys growing flowers and houseplants at home.
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