When your palm tree (family Arecaceae) is rotting, it's often too late to save the tree. Palms are susceptible to fungal attacks that often cause the plants to rot. Some disease-causing organisms are very specific, infecting only certain palms with a particular disease. Other organisms produce different diseases on different palm trees, so knowing what type of palm tree you have can help you identify the cause. For instance, the pathogen Gliocladiium vermoeseni causes trunk canker on queen palms (Syagrus romanzoffiana, USDA zones 10-11), and bud rot on canary island date palms (Phoenix canariensis, zones 9-11).
Root Rot Disease
Palms are susceptible to two primary root rot fungi, including Phytophthora and Armillaria. Symptoms of Phytophthora include browning and death of young leaves, discoloration of the stem and a bad smell. Palms that are grown on poorly draining soil are especially prone to developing this fungus. Ensure trees have good drainage, and don't overwater them. Infected palms can be treated with fosetyl aluminum.
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Symptoms of Armillaria root rot include leaves that are stunted, yellow or brown. Carefully peel the bark away from the wood on the lower trunk and trees to reveal a white fungus growth underneath the bark. Honey-colored mushrooms may also grow around the base of the tree. There is no cure for this disease. Remove and destroy all of the root system and the stump.
Pink Rot on Palm Trees
Pink rot fungus is a rose- or salmon-colored fungus that usually infects older palm trees growing in coastal areas where it's humid. It causes spotting and rotting on all parts of the trees, especially the leaves. This fungus produces billions of spores on a single plant, so there's no way to avoid it.
However, typically it only infects stressed palms, usually through wounds. Control pink rot by avoiding injuries to your palm tree. Applications of fungicides like Thiophanate-methyl can help prevent infections.
Bud Rot on Palm Trees
Phytophthora bud rot attacks several species of palm and can infect the roots, leaves, stems and fruit of palm trees. Symptoms include the appearance of brown sunken spots on developing fronds. The fronds turn a light grayish-brown and then darker brown as they collapse at the base. The infection spreads to the bud tissue and to the base of nearby fronds, which turn yellow and fall off the plant. As the disease advances, the buds die, and the decaying bud tissue has a bad smell.
Phytophthora bud rot generally infects trees that are at least 2 years old and often occurs a month or so after a heavy rain period. Occasionally, trees recover from this disease, but they usually die within two years of infection. Trees with advanced symptoms should be removed and destroyed. Fungicides can be applied to healthy neighboring palms or to palms in the early stages of the disease.
Butt Rot on Palm Trees
Ganoderma butt rot causes the lower 4 to 5 feet of the trunk to rot. In addition, the palm can suffer from mild to severe wilting. A definitive diagnosis can be made with the appearance of a hard, shelf-like structure called a conk that attaches to the lower 4 to 5 feet of the trunk, but not all infected palms produce conks.
Reasons why this disease develops aren't known and there are no ways to prevent or cure this infection. Remove infected palms as soon as conks appear, along with as much of the stump and root system as possible. Don't plant any other palms in the same soil.