It can be a little unnerving when you discover gummy deposits all over your trees. It looks like the tree has been wounded and is oozing painfully.
Gummosis is quite common, but that doesn’t mean it’s something growers should accept. It’s a sign something is wrong with your tree, so you need to know what has caused the tree to respond the way it has.
If you have experienced gummosis and want to know how to avoid or treat it, let’s get going on this sticky subject.
What We’ll Cover:
What is Gummosis?
Put simply, gummosis is a generic term used to describe the gummy deposits on your fruit trees (and some ornamental trees) that occur due to one of several causes. It’s most common in stone fruits like cherries, plums, peaches, apricots, and some apple trees.
Stone fruits are sensitive to injury and will release a clear gum when cut or otherwise damaged. This usually happens in the warmer part of spring when they have been damaged externally. These injuries or wounds are caused by various factors we will look at later.
Insect damage is a common cause of small areas of oozing, and the ooze is usually dark or golden in color, but this isn’t gummosis.
Gummosis is caused by fungal pathogens. It can also be caused by bacteria called Pseudomonas syringae. Most commonly, it’s caused by the fungal pathogens Leucostoma persoonii and L. cincta, formerly Cytospora spp.
The overall condition, environment, and growing conditions can contribute to gummosis, but do not cause it.
Leucostoma Canker
Leucostoma species are common in stone fruits and is an opportunist that enters into the tree through damage, and is especially successful in infecting trees that are also stressed for some reason, like drought, pests, or other diseases.
Sunken lesions develop at the site of damage and infection. These may be small and hard to see in the early stages. Over time, the canker expands and can even girdle the branch or trunk.
The gum that oozes out is usually dark brown to light orange and there is a ton of it. If you scrape off the gum, you’ll find cinnamon-colored tissue underneath.
Other common signs besides the canker sites are new shoots and leaves that should be healthy turn yellow and wilt or die. The wood under the canker can die, so whole branches could drop off at the point of infection.
Some people believe that their tree has healed because the gummy area might dry up the following season, but the disease is still present and you might see black fruiting bodies in the place of the gum.
Optimal temperatures for Leucostoma infections are in the spring when daytime temperatures are between 60ºF and 80ºF. The fungus will continue to grow and release spores while the weather remains warm.
Although it’s important to be careful not to damage trees any time of the year, be especially careful in warm spring weather.
Leucostoma cankers are caused by two different fungi that overwinter on deadwood or within lesions on the tree: Leucostoma persoonii and L. cincta.
Bacterial Canker
Bacterial canker is caused by a bacteria called P. syringae. Like Leucostoma, it enters through damaged branches or trunk, and usually looks for a weakened or stressed tree.
A sunken lesion forms on the branch and is tacky to the touch. The lesion forms a canker as it grows, causing the branch to swell and exude golden or amber gum. Typically, the gum is only present in the spring and fall.
Additional symptoms of a bacterial canker are brown holes in leaves, dark spots on leaves, and new shoots dying off. Blossoms may develop and then die off.
The bacteria needs cool, wet weather to thrive. It overwinters in damaged plant areas and waits for ideal conditions to begin reproducing.
What Contributes to Gummosis?
Gummosis is a symptom or sign of wider issues for the tree. First, the tree surface needs to be damaged in some way. Second, the tree is usually stressed or not in optimal health to begin with. Thirdly, a bacterial or fungal pathogen enters the tree through the damage.
1. Mechanical or Tool Damage
Lawn and garden equipment is brutal to trees if you’re not careful. If you accidentally hit the bark of the trunk or branches, it opens the tree to problems.
String trimmers are notorious for damaging the surface of trees at the ground level. The same goes for mowers and other equipment.
When pruning, take care only to cut where necessary. When working around your trees with yard equipment, take special care to avoid hitting the tree.
2. Broken or Torn Branches
Branches can be broken by all manner of circumstances, and although the damage is minor in the life cycle of the tree, that damage can allow pathogens in that are no good for a stressed or unhealthy tree.
Storms, climbing children, wildlife, and many other things can cause broken branches.
If you see these, go in right away and clean up the damage. Cut it away at the nearest branch or trunk.
3. Bad Pruning Practices
Poorly pruned trees are susceptible to gummosis because it leaves an opening in the tree for the pathogens to get in.
A tree will often exude gum as a protective measure after it has been cut. This is the tree’s way of creating its own bandage to protect it from pathogens.
The gum from damage without infection is usually clear or pale. The gum when pathogens are involved is usually gold or darker. Protective sap is totally normal and fine. It’s when there is an excess of it and its darker than you know you have a problem.
4. Environmental Issues
Sunscald can cause the surface of the tree to weaken and crack. This can also be caused by a tree that is in compact soil, is heat stressed, drought stressed, or in very poor-nutrient soil.
Once the tree cracks, it’s left wide open to any pathogens looking for a host, including the ones that cause gummosis.
5. Insect Damage
Insects like peach tree borer (Synanthedon exitiosa) cause a lot of damage to trees and should not be ignored. The damage is caused by the larvae that chew through the bark.
This damage can be extensive, depending on the extent of the infestation. The gum that oozes out of the tree will be clear or pale, but you will see sawdust-like excrement in the sap.
The clear or pale sap isn’t the problem, nor is it gummosis. But now the tree is left exposed to pathogens where the insects left openings. Treating and preventing pest infestations is key, here.
How to Prevent Gummosis
Prevention is better than the cure because if the issue becomes to widespread on a tree, it will die or you may have to remove it to prevent spreading to other trees.
1. Be Careful Not to Damage Trunks
When you mow around a tree or use a line trimmer, be conscious of the tree trunk. Damage in this area is a common infection point for the fungi and bacteria that can cause gummosis. Consider shields around trunk bases for stone fruit in particular.
2. Maintain Healthy Trees
A healthy tree with high vigor helps to prevent infection. Water deeply in the summer so that the tree doesn’t enter fall and winter dormancy drought in a stressed state.
Fertilize in spring and avoid too much nitrogen in summer. This can cause a late growth spurt in fall that doesn’t have time to harden off before winter. The new growth can be deficient in iron (iron chlorosis), and this makes the tree more susceptible to fungal cankers.
3. Insect Control
Consider a spray program to control insects that cause damage to the tree by boring or targeting wood. Organic or chemical sprays work well, and what you choose depends on your personal gardening ethos.
4. Good Pruning Habits and Techniques
Prune regularly so that cuts are small rather than a lot of big cuts.
Prune in late winter or early spring when temperatures are cool. Don’t prune if rain is forecasted or if the wood is wet, as water is one way the fungi and bacteria spread.
When you prune, cut back to healthy wood. If you don’t already know them, learn proper pruning techniques so you don’t make the wrong kind of cuts, like flush cuts, or leave stubs.
5. Protect Trees From Sunscald
Since sunscald can expose the tree to pathogens, do your best to protect your tree from it. During the winter, when the tree doesn’t have foliage to protect it, paint the bark with a half-and-half mix of white latex paint and water.
6. Plant Resistant Varieties
If you know the pathogens that cause gummosis are in your area, seek out resistant varieties. There are stone fruit resistant to gummosis, you just need to make sure they will suit the USDA zone you’re in.
7. Chemical Treatments
When you prune, apply captan, kaolin clay, lime sulfur (Bordeaux mixture) in 50% latex, or thiophanate-methyl to the cuts you made.
Treating Gummosis
Prune any symptomatic branches below the symptoms using clean, sharp tools.
Destroy all pruned off branches, preferably by burning if you can. Otherwise bag up and seal before removing from your property.
Ensure you disinfect your pruning tools to prevent the spread of the pathogens.
For new infections that are small and have not spread too far, you can try cutting out the damaged area if you can’t prune it out. To do this:
- Place newspaper around the base of the tree to catch any debris. You want to remove all of it, or the pathogens will continue to spread.
- Use a good quality boxcutter with a new blade and cut around the lesion or canker. Make sure you don’t cut through the canker. You want to be cutting into healthy wood.
- Scrape out the infected wood. You normally have to get to the heartwood. Although you don’t want to remove too much, try not to leave any infected wood within the circle you cut into the tree.
- Make sure all removed infected wood is wrapped up in the newspaper. Place this in a bag and seal it, and either burn it or dispose of it off your property.
- Spray the wound with captan, kaolin clay, lime sulfur (Bordeaux mixture) in 50% latex, or thiophanate-methyl. Don’t use copper as it can harm the tree.
If you find that the cankers and gummosis take over the tree, you will have to remove it, or it’s likely to spread to any other susceptible trees.
Don’t plant a tree from the same family in that spot.
Gummosis can infect other species, though it’s most common on stone fruit. Be sure to monitor all trees on your property for the signs, and not just stone fruits.
