As a subtropical plant, the golden cane palm (Dypsis lutescens, USDA plant hardiness zones 9a-11) has golden stems and yellow-green foliage, and it does well in the sun, the partial shade outside or bright spots indoors. These trees are also called areca palms and butterfly palms and don't require much maintenance. Like other palm trees, though, the golden cane is susceptible to fungal diseases.
Black Spots on Palm Tree Leaves
All palm trees can succumb to leaf spots and leaf blights, and they are more vulnerable when they are young or seedlings. The leaves can develop small, water-soaked lesions which turn yellow, gray, brownish-red and black; they also have surrounding halos in different colors. The spots can be fuzzy and may also appear as streaks on the bottom of the leaves. If you see this sort of spot, you'll likely want to identify the issue and figure out how to treat it before the problem becomes irreversible.
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These marks on palms can spread and increase in size and can take over trees. They are caused by fungi such as bipolaris, stigmina, phyllachora, gliocladium and cercospora. False smut is another leaf spot disease caused by the graphiola fungus. This type of fungus looks different; the black spots resemble small warts and show up on leaf surfaces. You usually don't see this disease on the younger leaves.
How to Prevent and Cure Cane Palm Fungi
If you see black spots on your golden palm tree, prune away the most infected fronds. After you finish trimming, sterilize the pruning shears because these can also spread fungal diseases. Keep an eye on the palm and trim any other areas that seem problematic. Don't remove too many fronds at once, as this can damage the tree. You can apply a fungicide, but it's best to do this in the spring. This is usually only done as a preventative treatment and won't eliminate the black spots already there.
The best way to prevent black spot diseases is to space out palm trees when planting them to increase their air circulation and avoid getting the fronds wet when watering. The soil should stay evenly moist but not soggy. Whenever you're watering, wait for the liquid to drain and get rid of excess water in the saucer if your cane palm is a houseplant. Choose a fungicide that contains copper and follow the manufacturer's instructions.
Other Areca Palm Diseases
Another fungal disease, Ganoderma root and butt rot, is caused by Ganoderma zonatum, which also infects other kinds of palms. You'll first notice drooping and withering in older fronds and stunted growth on new ones. When things get worse, the trunk can collapse, or the head of the palm can fall off. The trunk can sound hollow when tapped, and the inside will have dark brown tissue; there may also be visible fungal spore-producing structures (conks).
To treat root and butt rot, remove any dead trunks, stumps and root systems of nearby palms. You can trim your affected cane palm if it's still struggling, but there's no chemical control for the disease; this is a bad one. This fungus lives in the soil, so you won't want to plant anything else nearby. Bud rot is caused by bacterial pathogens and Phytophthora and Thielaviopsis fungi and can also lead to tree death, but you may be able to save the tree by using a fungicide in time.