Fighting pear rust: sprays and household remedies for pear grating

The pear grate is a fungus belonging to the rust fungus order that attacks plants of the species Pyrus (pears) and Juniperus (juniper). The annual change of host is unique about the fungus, because juniper plants are attacked over winter, while pears are exposed to the pear rust in summer. To put an end to the fungus, special sprays are available that work effectively against the infection.

Infection chain of the pear grid

The pear rust (Gymnosporangium fuscum) is a fungal disease that has a unique course over the year and during which it changes host several times. This process is called an infection chain, which describes exactly which plant species are attacked by the rust fungus and when:

Winter to early spring: the juniper species Juniperus chinensis (Chinese juniper) and Juniperus sabina (sad tree), more rarely Juniperus scopulorum (Rocky Mountain juniper)
Spring to early autumn: pear trees (bot. Pyrus), more rarely quinces (bot. Cydonia oblonga)

The spores specifically attack the juniper trees and bushes of the species mentioned and spread through them. The infection manifests itself in nodular thickening of branches and large spore beds. These are as follows:

Color orange
Consistency: rubbery, gall-like
stand out in individual thickenings
get slimy over the year

The spore beds of Gymnosporangium fuscum can be easily recognized and through these the fungus attacks its next target, the pear trees. Interestingly, the juniper plants are not harmed by the fungus, they only serve as a kind of intermediate host. Basidiospores are formed, which are distributed by winds in a radius of 500 meters from spring and settle on the leaves of the pear trees. There they begin to infect the pear and thus continue the chain of infection:

The top of the sheet becomes blotchy
The spots are orange-reddish
Spots get bigger over the months
summer spores are formed, which attack the tree even more severely
now pollinator insects like bees are attracted by the formation of the wrong nectar
the spores adhere to the animals and carry them on
in late summer the fungus spreads to the underside of the leaf
up to 1.5 centimeters in size, oval spore beds in a brownish color are formed
these break open at the beginning of winter and spores are released, which in turn attack juniper plants

Through this chain of infection, the rust fungus can easily sustain itself and use every season to its advantage. This development must be taken into account when combating the pear grate, as this is the only way to combat the infestation effectively. Especially young pear trees can be severely restricted in their growth by the rust fungus, while older specimens are only weakened. The consequence of this is often stunted growth that intensifies over the years, which results in a poor harvest. Do not confuse the infestation by the fungus with the pearpox mite, this has a similar damage pattern, but without the spore beds.
Tip: Even if your pear is infested with pear rust from top to bottom, you shouldn't just throw the fruit away after harvesting. The fungus only affects the leaves of the tree and not the fruits, which can still be consumed and pose no threat to your health.

Prevent

Fighting pear rust after pear tree infestation is extremely tedious and difficult, so you should contain any possible infestation as early as possible. If the chain of infection described above is interrupted,

the spores cannot identify the trees and your pears are safe with little effort. Various methods are available for prevention:

Treat intermediate host

To prevent the spores from spreading further, it is necessary to contain the infestation and prevent the spores from rising again in the air. For this reason, as soon as a juniper of the above species is in your garden, you should check it for the fungus. If this shows the characteristic growths, you should thoroughly remove all affected areas. Simply remove these with clean garden shears or loppers.

Remove intermediate host

The complete disposal of the host is extremely effective, especially if it is heavily infested. If the infested juniper is removed from the immediate vicinity of the pears, the infection can be largely contained. But always make sure that even junipers that are far away can still distribute their spores, therefore it is possible to remove the pear tree as well, so that the spores no longer spread over the summer host multiply.

Replace intermediate host

If you don't want to do without a juniper in your garden, you should opt for a different species that is not susceptible to rust fungus. This includes:

Wacholder community (bot. Juniperus communis)
Gray shrub juniper (bot. Juniperus media 'Hetzii')
Coastal juniper (bot. Juniperus conferta)
Virginia juniper (bot. Juniperus virginiana)
Scaled juniper (bot. Juniperus squamata)
Creeping juniper (bot. Juniperus horizontalis)

Alternatively, you can also choose pear varieties that are not so susceptible to the fungus:

Condo
Countess of Paris
Stuttgarter Geißhirtle
Upper Austrian wine pear
Trevoux
Gellerts

Even if these pear varieties could still be attacked by the pear rust, they are much more resistant to Gymnosporangium fuscum and therefore need a longer time to become infected. The exchange of juniper species is of course more effective.

Plant strengtheners

It is advisable to treat pears with plant strengtheners as soon as the leaves appear in spring. Horsetail extract, which you can purchase from manufacturers such as Neudorff or Aries, is best for this. If you want to make the extract yourself, you can too. This home remedy is the only one that works effectively to prevent pear rust:

Ingredients: 10 g dried or 100 g fresh field horsetail (bot. Equisetum arvense) per 1 liter of water
cut the blades of grass into small pieces
put them in a saucepan with water
Soak for 24 hours
then boil for 30 minutes
then pour through a sieve into another container
mix the brew with water in a ratio of 1: 5

The finished extract can be stored correctly for several months. Spray these on the pear trees four times at intervals of one to two weeks.

Reduce nitrogen

Use less fertilizers that are high in nitrogen. These weaken the pears for a long time and thus enable an infection that strikes faster and leaves the trees defenseless to the fungi.

Remove leaves

If your pear tree has been attacked by the fungus, you should remove all leaves as soon as possible and dispose of them on the compost. The fewer weakened leaves on the tree, the stronger the plant and the risk of the infestation spreading rapidly is prevented. Do not worry, you can compost the disposed leaves because the spore stores are empty over the winter.
Tip: If one of your neighbors has a juniper in their garden, be sure to check it out Discuss possible disposal or treatment in the event that the pear rust infects the plant is. This is the only way to prevent possible infection.

spray

Once pear rust has attacked a pear tree, it is stubborn and difficult to fight. Home remedies do not work at all with this rust fungus and for this reason you have to switch to ready-made sprays. For home gardeners, there has been only one fungicide on the market since 2010 that is effective against rust fungus:

COMPO Duaxo Universal mushroom-free
available in 75 and 150 ml
Cost: 12 - 17 euros

This universal fungicide can not only be used against the pear grate, but also for other cultivated plants such as roses or herbs. This is administered to the tree in good time before the infestation by the spores and thus they no longer have a chance to infect the pear. A big advantage of the remedy is the depot effect, which protects the tree over a longer period of time. You apply the remedy as follows: