Prevention is more effective than cure for most palm tree diseases.
When removing an infected tree, get the whole thing, including fallen foliage, stump, and root system.
Watering at ground level with no splashback is the best way to prevent the spread of soil-borne pathogens.
Palm trees are generally pretty easy to care for. But, even though they're low maintenance, they're still susceptible to several palm tree diseases, including both fungal and bacterial infections. One of the best ways to keep your palms free of disease is to keep them healthy by providing the right nutrition and environmental conditions. This helps to reduce the likelihood of disease setting in.
Preventing Diseases in Palm Trees
Aside from providing the right nutrition and environmental conditions, there are a few other things that you can do to reduce the chances of your palms getting infected.
You should also practice proper tool sanitization, cleaning the blades of pruners, for example, thoroughly between uses to reduce the risk of spreading diseases from one tree to another.
When you water, don't let the soil splash up onto the palm foliage, as soil-borne pathogens can quickly infect the trees this way. Irrigate low to the ground or use drip irrigation.
Fertilize your palm trees adequately, using a high-quality product, but don't over-fertilize, as this can cause additional problems.
Give your palms plenty of room. Don't crowd them. Proper palm spacing ensures adequate airflow, which is important because it creates a less hospitable environment for fungal spores that like dark, damp spaces.
Prune palm trees conservatively at the right time of year, and avoid injuring the trunk.
Leaf Spot and Leaf Blight
There are many different leaf spots and leaf blights, but the symptoms and treatments are generally very similar. Fungal pathogens cause leaf spot in palm trees. While all palms are at risk and should be considered potential hosts, juvenile trees and weaker, sicklier trees are most at risk.
You'll notice small, water-sodden, deep green lesions on the tree's leaves that rapidly change color, turning yellow, red, brown, or black. As the disease progresses, depending on the fungus responsible, the lesions may develop an outer ring that's a different color than the lesion and may be necrotic tissues.
The size of the lesions is dependent on the pathogen causing the disease.
Early intervention is critical to successful treatment and recovery. Prune all affected palm fronds, even if a blade only has one or two spots. If the disease is fairly well set-in and widespread, apply a copper fungicide spray. Remember, if you use your palm fruits for food, copper fungicides are the only legal fungicide option.
Ganoderma Butt Rots
Caused by the fungus Ganoderma zonatum, ganoderma butt rot attacks the trunks of palms up to 4 inches above the ground. It inhibits the plants' ability to move water up the trunk by infecting the woody tissue and blocking the structures that transport water.
This is not a soft rot so, although infected, the trunk does not develop soft spots.
Symptoms include a generalized decline in health, withering fronds, stunted new growth, yellowing leaves, paler leaves, a weakened trunk, and root rot. As the disease progresses, the palm trunk may collapse, and the pam head falls off.
This disease is severe, spreads rapidly, and has no cure. The only way to control it is to remove all remnants of the infected trees, including root systems, stumps, and decaying foliage. Remember, too, that Ganoderma zonatum can survive for many years in the soil without a host, so avoid planting any more palms in the same area.
Palm Bud Rots
Bacterial or fungal pathogens can cause bud rots and most commonly attack after heavy rains or tropical storms. The first sign you'll see is wilting and color change in the spear leaf. These symptoms then spread to the next youngest leaves. However, if your palm canopy is above eye level, you may not see these changes. In this case, the first symptoms you'll notice are a lack of new crown growth.
As the disease gets worse, you'll notice that young fronds and buds develop black lesions, the buds become slimy with a foul odor, and the spear leaf is easily pulled from the bud.
Remove and destroy the affected plants, as there's no cure once the disease has taken hold. It's also advisable to apply copper fungicide to any remaining palms that currently show no symptoms.
Caused by the fungus Fusarium oxysporum, fusarium wilt causes bown, wilted fronds. The first signs appear on the lower fronds, and the disease attacks one side of the tree, causing a one-sided death.
The palm eventually loses its striking green coloring and dies as it succumbs to the disease. Depending on the size and health of the palm when it gets infected, it can die within a couple of months or last up to a year.
There's no cure for fusarium wilt, so the only option is to remove all parts of the infected trees, including root systems. Just like other soil-borne pathogens, fusarium wilt lingers in the dirt, so you shouldn't plant any new palms in the same spot.
Lethal yellowing is caused by a microorganism called phytoplasma and is spread by planthoppers, a common palm tree pest.
To accurately identify lethal yellowing, you need to observe the disease progression and combination of symptoms, as no single symptom is enough to give you an accurate diagnosis.
The first signs you'll see are fruit drops. All or the vast majority of fruits fall from newly infected trees.
The fallen fruits have black or brown, water-soaked patches, particularly where the fruit was connected to the tree.
Next comes flower necrosis, with flowers wilting and turning black from the tips before dying off. The male flowers fall off rapidly, so no fruit sets. But remember, the symptoms specific to flowers and fruits only occur if the tree is fruiting at the time of infection.
After the fruits fall and the flowers die, the leaves begin to yellow. This starts with the oldest leaves and progresses up the crown. After half to two-thirds of the foliage has turned yellow, the apical meristem dies, followed by the tree's death.
If the disease is set-in, there's no effective treatment, and you should remove and destroy the tree. If, however, the disease is identified early on, antibiotic injections, specifically oxytetracycline, injections into the roots may provide a cure, although there's no guarantee.
Instead, it's advisable to remove the infected trees and replant a variety that's resistant to lethal yellowing.
Pink rot is an opportunistic disease that tends to attack already weakened or damaged palms. It can also infect areas damaged by aggressive pruning, as palm trees can't repair their own woody tissues.
This fungal disease causes stunted growth, deformations, and leaf spots. You'll see the notorious clumps of pink spores from which the infection takes its name. And, in severe cases, you'll likely notice a brown, syrupy substance oozing from the infected areas.
While there's no cure, you can prevent pink rot by keeping the palm healthy and by applying a copper fungicide and a barrier spray after pruning to protect the wounds.
Caused by the fungal pathogen phaeoisariopsis neowashingtoniae, diamond scale produces large numbers of small, diamond-shaped fruiting bodies on the leaves of afflicted plams. The disease rarely causes tree death, but it does weaken the tree and make it susceptible to other, more dangerous diseases and infections.
Water-soaked lesions on the leaves are the first symptom to appear. Shortly after, the fungal fruiting bodies start to form with a black stroma. As the disease progresses and the stroma continues to grow, the area around the fruiting body starts to turn yellow.
Prune away affected foliage to prevent spread and keep your plants as healthy as possible. If trees are badly infected, it may be worthwhile removing them and replanting diamond-scale resistant varieties.
Sooty mold is a fungal disease that doesn't directly attack the palm. It's caused by aphids, mealy bugs, and scale insects who feed on the palm leaves and leave behind honeydew, a sweet, syrupy substance, on which sooty mold quickly takes hold.
It appears as black, sooty spots on the palm leaves but doesn't cause much harm, other than its unsightly appearance. But it is a good indication that your tree has a significant insect infestation.
Sooty mold washes off easily and you can prevent reinfection by controlling pests.
Root rot isn't strictly a disease. Instead, it's a preventable problem caused by consistent overwatering or poorly draining soil.
You'll notice the tree starting to rot at the base, soft, mushy roots, yellowing leaves, and stunted new growth.
If the palm is small enough to be moveable, you can potentially save it if caught early enough. Dig up the palm and cut away all the affiliated roots as close to the root ball as possible, without damaging the root ball. Then replant the tree in another spot with good drainage and give it a good dose of rooting hormone to encourage new root formation.
Thielaviopsis Trunk Rot
Caused by thielaviopsis paradoxa, this fungal trunk rot causes trunk collapse and tree death. This particular fungus infects wounds in the tree's trunk. The key symptom of thielaviopsis trunk rot is the stem "bleeding." You'll also notice the oldest leaves dying off prematurely. In some cases, you won't see any obvious symptoms on the trunk, but the whole canopy will fall off the top of the tree before the trunk collapses in on itself.
There's no cure for this disease, so if it strikes your palm, remove the infected tree as soon as possible to prevent spread. To prevent the disease from occurring, avoid causing wounds to the tree's trunk. And, if you do cause injury, apply a fungicide over the area to prevent fungal infections.