Growths on apple trees and other deciduous trees are caused by the fungus Nectria galligena. We explain sprays, prevention and diagnosis of fruit tree cancer.
Infection of fruit trees by the ascomycete Nectria galligena (secondary fruit form: Neonectria galligena) is colloquially referred to as "fruit tree canker" because it leads to growths of wound tissue resembling ulcers. Apple trees in particular are affected, while pears, stone fruit and other fruit trees are attacked much less frequently. Fruit tree canker on the cherry is relatively rare. We show you fruit tree canker pictures for clear identification and explain how you can treat and prevent fruit tree canker, for example with fruit tree canker spray.
Fruit tree canker damage: How to recognize the disease
An infestation with fruit tree canker on apples or other fruit trees looks very typical: Ulcers and tumor-like growths appear on perennial branches. The ulcers can be open, showing the bare wooden body, or closed. These thickenings are wound tissue from the tree, which tries to overwhelm the infection with so-called callus every year. Strong branches often take many years to die off completely due to infestation with Nectria galligena. Often only a stripe (ortho bites) starting from the infested site is initially affected, which in some trees also turns, so that a longitudinal, winding, dead zone develops on the branch.
In late summer and autumn, red spore deposits of about 0.5 mm in size (perithecia) can be observed at the edges of the growths. In summer, on the other hand, 1 to 2 mm large, flat, white and rounded spore beds can be seen (Sporodochium). The spores are spread by dripping or thrown water during rainfall. However, the spores formed in winter are also actively released from the spore stores and then spread by the wind.
ToYounger branches do not yet form growths, but the bark sinks in at the infested site and the branch dies above the infected area. Frequently, the first infection occurs on bark cracks, wounds or on bursting buds, where the fungus can most easily penetrate.
In addition to the symptoms visible on the twigs and branches, the fruit tree canker pathogen also causes fruit rot: on the one hand, a black rot in the calyx pit in late summer, on the other hand, a storage rot, which can be recognized by the brownish-colored tissue separating slightly from the releases he althy pulp.
Tip: Fruit tree canker is mainly known from apple trees (Malus) and pear trees (Pyrus ), other important host plants are cherry, maple, horse chestnut, birch, beech, ash, poplar, lime and willow.
Treat fruit tree cancer
Treating fruit tree canker is not easy because there are no fruit tree canker sprays, at least for use in the home garden. In any case, the pathogenic fungus is so deep in the tree tissue that sprays can hardly reach it.
Regular monitoring is important in order to detect canker infections in good time, especially if you have already observed the disease in other trees nearby have.
In the case of small canker sores and individual affected branches, these are simply cut off generously. Wounds on strong branches of the tree or the trunk can be excised or gouged out. You should seek the help of a trained professional for this. Optimally, the cut is made in dry, cool weather, i.e. in the course of the winter cut, in order to prevent direct re-infection of the resulting cuts. The clippings should be disposed of immediately in the residual waste bin or burned.
These measures are also taken in professional, organic fruit growing. In addition, fruit growers may use copper sprays against fruit tree cancer - a suitably trained specialist can help you with this. Useful times for treatment are after a severe frost, when the buds open and after the leaves have fallen. The purchase and use of the funds is prohibited for private individuals because they are extremely harmful to the environment and he alth if used incorrectly.
Summary: Treating Fruit Tree Cancer
- Check trees regularly, especially if infestation is known nearby.
- Cut off affected branches generously; in dry, cool winter weather.
- Cut out or mill out infested areas on the trunk and strong branches.
- Dispose of clippings in the residual waste or incinerate.
- Additionally, a treatment with organic copper sprays by trained gardeners is possible.
Prevent fruit tree cancer
Prevention is much more promising than fighting fruit tree canker. You can prevent fruit tree cancer on apple trees or other trees by only purchasing he althy, high-quality plants, for example from a tree nursery or fruit tree nursery. The most important thing, however, is the choice of variety: while pears are attacked much less frequently overall, there are some highly susceptible apple varieties. These include: 'Cox Orangerenette', 'Gloster', 'Klarapfel' and 'Freiherr von Berlepsch', 'Nicoter', 'Braeburn' and 'Gala'. On the other hand, the apple varieties 'Pinova', 'Santana', 'Boskoop', 'Elstar', 'Jonagold' and 'Topaz' are slightly or very slightly susceptible.
Before planting your apple tree, it makes sense to look around for particularly he althy apple tree varieties for your home garden.
The choice of location also has a major impact on the risk of fruit tree canker infestation. Moist gardens that are shaded through the morning, experience little air movement, and get only mildly cold winters are perfect for fruit tree canker to appear. In these gardens in particular, a low-susceptibility variety should be chosen. On the other hand, fruit tree canker is almost never found in well-ventilated, sunny places and on rather light soils.
Summary: Preventing fruit tree cancer
- Buy high-quality plants, for example from the nursery.
- Choose a low susceptible variety.
- Especially in humid, mild places with stagnant air and shade in the morning, make sure you choose a non-susceptible variety.
Apple trees have low nutritional requirements compared to vegetables. We explain when and how to fertilize your apple trees in the appropriate special article.