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If the crown of the pear tree glows red-orange in summer, there is a very high probability that it is infested with pear rust. Because this fungus nests on the trees from spring and disappears again in autumn. Since it can lead to crop losses and weaken the pear trees, you should act if the infestation is severe.
pear grating
The pear rust is a fungus from the order of the rust fungi (Uredinales). Its scientific name is Gymnosporangium fuscum or Gymnosporangium sabinae. The pear rust is a host-changing fungus that “oscillates” between juniper and pear trees.
damage picture
Pears, or rather pear trees, are the summer host of the fungus, which can also infect quinces. How to recognize the fungus on the pear tree:
- first symptoms from the flowering period in spring
- yellow to orange-red spots on the upper side of the leaves from May/June
- increase over the summer
- formation of summer spores
- Crown of tree more orange-yellow or red than green
- second stage of infestation on the underside of the leaf in late summer
- oval to warty growths with winter spore beds
- brownish color
- up to 1.5 centimeters long
- release winter spores
- infect the juniper
A severe infestation occurs when the pear tree sheds its leaves prematurely. However, you can also recognize a severe infestation by the following characteristics:
- Infection of at least 40 percent of the leaves
- infected leaves with more than three spots
How much the fungus actually damages the pear tree is controversial. What is certain is that the fungus can have a deadly effect on young pear trees. In mature trees, the fungus is considered another stressor that weakens the tree. However, in combination with other factors, this can lead to the death of the tree.
Harmful image of juniper
The juniper is the winter host of the fungus. How to recognize the infection on the juniper:
- from mid-April: wart-like thickening of the branches in the affected areas
- Formation of first brown, then yellow spore layers
- gelatinous when wet
- Size: up to two centimeters
- Spore stores expand or shrink depending on humidity and precipitation
- heavy infestation: whole branches glow orange
notice: Gymnosporangium sabinae is harmless for the juniper, as it does not damage the plants significantly.
causes
The cause of pear rust on pears is ultimately the infestation of juniper plants. Because of these, the fungus is spread by the wind in the spring and infects the leaves of the pear trees. The flight radius of the spores is usually 500 meters. However, they can also be worn beyond that in strong winds. If the fungus has formed summer spores on the leaves, these are spread by wind and insects. Because it is assumed that flies and wasps are attracted by the orange-red color of the spots and excreted "nectar". This can lead to an explosive spread of the fungus.
When the winter spores are ripe, the growths on the underside of the pear's leaf tear open like a lattice. This releases dark brown spores, which in turn infect the juniper plants. However, the pear rust does not settle on all types of juniper. The infestation mainly affects juniper species that come from Asia, such as Juniperus sabina (Sade tree) or Juniperus media. In addition, the susceptibility to the fungus varies between the individual cultivars.
tip: The native juniper (Juniperus communis) is not attacked by pear rust.
control and prevention
Effective control of the fungus is currently not possible on either juniper or pear trees. It is therefore recommended to reduce the risk of infection as much as possible. This in turn affects the juniper and includes two points:
- regular controll
- manual removal of the fungus
To prevent the fungus from spreading to the juniper, you should regularly check the juniper plants in the garden, even if you don't have any pear trees in the garden yourself. If you find an infection, you should cut out the diseased shoots. Since the fungus in juniper is very deep in the wood, it has to be cut very generously. This means that you have to cut far into the supposedly healthy wood, because fungi develop mycelium in the wood that remains invisible to humans. If the infestation is severe, the juniper should be completely removed. Fighting the fungus on juniper with the chemical club is not possible.
notice: However, cutting out and removing the juniper is no guarantee that your pear tree will not become infected with the fungus, as the spores are transported up to 500 meters by the wind.
If the fungus has infected the pear tree, you can only wait until autumn. Because then the tree will get rid of the fungus naturally through the falling of the leaves. A preventive measure for the pear tree is the administration of a plant strengthener, such as a horsetail extract. This home remedy makes the tree more resistant and reduces the risk of infection. To strengthen the tree, you should spray it thoroughly three to four times every 10 to 14 days when the leaves begin to sprout. You can get the extract in good specialist shops or you can order it online. It is important that you dilute the horsetail extract with water according to the package instructions before spraying. In addition, you should only spray the solution on the dry pear tree on an overcast day. The ideal time to fight the fungus is in the morning or in the evening.
Make horsetail manure
To produce your own horsetail manure, you need a kilogram of fresh horsetail, which you can find in waterlogged locations.
- Chop up the stalks with scissors
- in a bucket with 10 liters of water
- stir
- add a hand scoop of stone flour (against the smell)
- stir
- Close the bucket with a cloth
- Leave to ferment in a sunny spot for two weeks
- stir every few days
If no more bubbles rise, the household remedy is ready. To apply, dilute it with 5 liters of water to make one liter of liquid manure.
Treating the tree with pear scab remedies is possible, but not recommended by experts for control.
tip: If you notice a medium to heavy infestation, you should contact your municipality's plant protection office.
Another measure against the fungus is to switch to more resistant pear varieties. These include, for example:
- Clapp's favorite
- Trevoux
- condo
- Colorful July
Pear variety Colorful July pear
tip: Switching to more resistant pear varieties is also possible through grafting.
Pears: edible or not?
Since the fungus only infects the leaves, remain the pears themselves edible. However they are not storable. The latter is related to the degree of ripeness of the pears. If the tree is infected, the pears often fall off before they are fully ripe and pears that are not fully ripe cannot be stored or can be stored less than ripe ones, but they are edible.