Money tree plants (Pachira aquatica, USDA zones 10-12) experience relatively few pests and diseases. If you see brown leaves on a money tree plant, check for pests, like aphids or mealybugs. Consider whether the plant has been exposed to too much sunlight or received too much water. If none of these issues seems present, your money tree plant probably has a fungal infection called anthracnose.
Aphids Cause Brown Spots
Aphids and other pests, like mealybugs, siphon the cell sap from many kinds of plants, including the money tree. Each meal results in a tiny nick on the leaf, which turns brown as the tissues dry up. These pests aren't picky about what they eat, so if you notice an infestation on your money tree, chances are that your other houseplants are harboring them as well.
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Both aphids and mealybugs are tiny, which makes them difficult to see at first glance. You can often see a congregation of these pests on the underside of leaves or on the plant's stem. Spray the plant with neem oil to get rid of both aphids and mealybugs as well as most other pests. Before spraying your plant with neem oil, consult the product label and follow all brand-specific recommendations for using this insecticide so that you don't risk damaging your plant.
Sunlight Burns Money Tree Leaves
Sunburn or sunscald occurs when a plant accustomed to full or partial shade is suddenly exposed to full sun. First, the leaves lose their color in blotchy patches. Then, the edges of the leaves turn brown and crispy. Too much sunburn can kill a plant, but it may recover as long as there is a sufficient number of green leaves remaining for photosynthesis.
If you want to set your money tree plant outside, be sure to keep it in a shady area to protect it. If you notice signs of sunburn after moving your money plant to a new window, place it out of direct sunlight and gradually move it closer to the bright window. The slow acclimation can prevent sunburn.
Overwatering Causes Yellow Leaves
Another possible cause of spots on a money tree plant is overwatering or underwatering. Overwatering is more common since the money tree only needs about 3 tablespoons of water per week. However, the leaves will typically turn yellow before they turn brown, and the entire plant will begin to look unhealthy.
The problem starts in the roots: Oversaturated roots cannot take in oxygen, which is crucial for nutrient transport. Soaked money tree roots will also begin to rot. Combat this problem with proper watering and by regularly dumping the pot's drip tray.
Anthracnose Causes Spots on Leaves
If many small brown spots have appeared on the leaves of your money tree, the culprit might be a fungus called anthracnose. These brown spots often have a yellow ring around them. As the spots grow, they eventually merge to form a much larger blotch on the leaf.
Anthracnose can spread from plant to plant and should be quickly addressed before it passes to other plants in your home or garden. Remove infected leaves and branches and discard them in the trash. Sanitize your gardening shears afterward. There are several different chemical sprays to treat anthracnose, including copper-based products like Liqui-Cop.