Sudden oak death (SOD) is a fungal disease caused by a pathogen called Phyophthora ramorum. The disease affects oak trees and other woody plants. Here are six facts Florida tree owners should know about SOD.
1. SOD Is an Emerging Pathogen
SOD was first observed in Europe in 1993 and was initially found on rhododendrons and viburnums that were nursery-grown. Several years later, tens of thousands of oak and tanoak trees succumbed to the fungal disease along the California coast.
Researchers and plant experts continue to study SOD to learn more about the disease, which has since been introduced into Florida via ornamental nursery plants. While no oaks have succumbed to the disease in the state, the pathogen is a risk to plants throughout Florida.
You can help researchers in the state by having any suspect trees examined by your tree service. If your tree care company believes your trees are infected with SOD, contact your nearest County Extension Agency. Your extension agent can explain how to collect and submit samples of infected trees for further study.
2. SOD Can Spread to a Variety of Plants
Over 100 species of cultivated and native plants have shown symptoms of SOD infection. Symptoms of the disease vary according to the type of plant host that’s infected.
Trees that may be affected by SOD include the following:
- Bigleaf and planetree maple
- California buckeye
- Horse chestnut
- Camellia (all species and hybrids)
- European ash
- Bay laurel
- Red tip photinia
- Coastal live oak
- Southern red oak
- Viburnum (all species)
While the SOD fungus has been noted on the above plants, researchers caution that many more tree species may be susceptible to the disease. As related plants are tested, additional trees and shrubs could be added to the list of affected species.
3. SOD Presents Several Symptoms
Many infected plants appear healthy even when their roots are host to the SOD fungus. When symptoms do appear, they often appear first on the leaves of affected plants. Lesions may form on the ends, sides, or mid-lines of leaves.
Leaf lesions look like brown or tan scorch marks. Where a lesion meets the healthy part of the affected leaf, you may see a dark margin that makes the leaf look wet or water-soaked. Lesions often have a bullseye appearance, with darker centers and lighter brown edges.
Leaves may curl or drop off the stems as the disease advances. Entire stems may turn black or brown at any point on the tree. This symptom is called stem blight.
Sunken or swollen spots on the branches and bark of trees are signs of SOD. Called cankers, the lesions may be hard to spot by untrained property owners. If the cankers begin to bleed, the sap will be red and sticky.
4. SOD Is Spread in Several Ways
Researchers believe SOD was brought to the U.S. on infected ornamental plants from other countries. The P. ramorum fungus can move to new host plants by several means.
SOD is spread in the following ways:
- Fungus-infected-plant movement
- Fungus-infected soil
- Fungus-infected irrigation water
- Wind-blown rain
As researchers investigate the habits of the P. ramorum fungus, they may discover insect pests or other vectors of the pathogen.
5. SOD Can Spread on Tools
You can reduce the spread of most plant pathogens on your property by sanitizing your hands, pruners, and other tree tools after you trim or prune woody plants. Most household cleaners will disinfect and/or sterilize hand tools.
Household cleaners that kill SOD fungi and other pathogens include:
- 10-percent chlorine bleach/water solution
- Ethanol or isopropyl alcohol
- 10-percent trisodium phosphate/water solution
Make a 10-percent solution by mixing one part cleaner into nine parts water. For example, mix one cup of bleach into nine cups of water. Protect your hands with gloves when handling the cleaners.
You can either wipe down your tools with the cleaners or dip the blades and handles into the cleaning solution. Disinfect tools between trimming plants to avoid spreading diseases from tree to tree. Wipe away excess disinfectant so you don’t harm the next tree with the sanitizing materials.
6. SOD-Affected Trees Should Be Removed
Until more is known about SOD, preventing the introduction and spread of the disease is the best policy to control the fungus. Plant experts advise property owners to have SOD-infected trees and woody plants removed from their landscape. Trees and shrubs should be removed as soon as possible after the disease is diagnosed in the plants.
Your tree service professionals will burn or deeply bury the infected plant material to reduce the chances of the fungus spreading to nearby woody plants. The infected plant material should not be tossed in the compost pile, since material in the compost heap won’t reach the high temperatures necessary to kill the fungus.
Fungicides have been effective at preventing the SOD fungus in plant nurseries. However, the P. ramorum pathogen has shown some resistance to existing fungicides. Your tree service professional has access to stronger fungicides that may be effective at preventing the spread of SOD on your property.