The characteristic, conspicuous damage caused by pear rust makes infested pear trees appear dangerously ill. However, combating the fungal pathogen is not always necessary. This article tells you how to recognize the disease and when and how to take action.

There is no reason to panic with individual leaf spots

Table of Contents

Show all
  1. the essentials in brief
  2. What is pear grating?
  3. damage picture
  4. prevention
  5. Combat pear rust
  6. frequently asked Questions

    7. the essentials in brief

    • Fungus called Gymnosporangium sabinae causes pear rust
    • Infection always takes place via various juniper species as intermediate hosts
    • Fungal spores migrate from juniper to pear leaves in spring
    • In autumn, spore transfer occurs in reverse, since the spores overwinter on juniper
    • Damage is characteristic, control is only necessary in the case of severe infestation

    What is pear grating?

    Pear rust is a plant disease caused by the fungus Gymnosporangium sabinae. The parasitic pathogen prefers to infect already diseased or weakened plants by settling on them or on the soil and from there penetrating the plant tissue and feeding on it. Like all fungi, pear rust spreads through so-called mycelium (i.e. the mycelium) and through spores.

    How is the pathogen transmitted?

    Gymnosporangium sabinae overwinters in juniper

    This section is important in order to be able to fight the disease properly - the fungus not only affects pears, but also takes a detour via an intermediate host. The transmission only works with the help of the host change, which is why you can prevent (re)infection of your pear by eliminating the intermediate host.

    This intermediate host is a variety of juniper species (Juniperus), which must be close to the pear tree and from where the spores spread again and again. The life cycle of Gymnosporangium sabinae is as follows:

    • winters in juniper
    • forms its spurs here
    • Spores are transmitted to pear leaves by wind, insects, or birds
    • The time of this infection is spring, when the leaves begin to sprout
    • here, spores form again in autumn
    • these are again transferred to the juniper
    • With the fall of leaves in autumn, Birnbaum gets rid of the fungus again
    • in the spring the game begins again

    On the pear, the fungus only sits on the leaves, only the affected juniper is permanently diseased.

    Transmission occurs through ornamental juniper

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    However, Gymnosporangium sabinae does not like every juniper. Species such as the native common juniper (Juniperus communis), the creeping juniper (Juniperus horizontalis) from North America and the scaly juniper (Juniperus squamata) are spared from the fungus. Juniperus communis in particular has repeatedly proven to be extremely resilient.

    Frequent carriers of pear rust and therefore problematic are many imported ornamental juniper species, which have been increasingly planted in gardens, parks and cemeteries in recent decades because of their vigour:

    • Moss Juniper or Sadebaum: Juniperus sabina, evergreen dwarf shrub, particularly susceptible to Gymnosporangium sabinae
    • Chinese juniper: Juniperus chinensis, popular ornamental juniper, common intermediate host for pear rust
    • Pfitzer juniper: Juniperus pfitzeriana 'Wilhelm Pfitzer', variety of Chinese juniper
    • Virginian juniper: Juniperus virginiana, also known as Virginia cedar or red cedar, is often touted as a climate change tree

    The species mentioned are commercially available in various cultivars, although not every variety is equally susceptible to infection with pear rust. For you, this knowledge means that you have to make a decision when pear rust appears on your pear trees: either the juniper has to give way or the pear, because this is the only way to combat the pathogen.

    digression

    How dangerous is pear grating really?

    Around 30 years ago, pear trees were already attacked by pear rust. At that time, however, the disease was not yet a problem, instead fungus and affected trees could co-exist. Only after the ornamental junipers mentioned above were imported and planted more often did the pathogen become more dangerous for various Pyrus species and their relatives.

    In principle, however, the infection does not have to be a problem today, as long as the affected pear tree is otherwise healthy and strong and is in an ecological balance. Specimens in suitable locations in naturally cultivated gardens therefore have a better chance of surviving pear rust unscathed.

    Damage - How to recognize an infestation with pear rust

    Small orange spots on the leaves are the first sign of an infestation

    Pear infection with pear rust occurs around the flowering time of the tree between May and June:

    • initially small orange or yellow spots on the upper sides of the leaves
    • increase over the summer
    • different degrees of infection possible
    • sometimes only a few leaves affected, sometimes severe infestation affecting almost all leaves
    • if the infestation is severe, the tree will look orange-red rather than green in autumn
    • later wart-like nodules on the undersides of the leaves
    • these are spore deposits
    • gradually tear open into a latticework and are dispersed by the wind

    However, an infection with the harmful fungus manifests itself differently in the affected juniper. Here you identify the disease by the following characteristics:

    • recognizable from mid-April
    • first, branches of the affected juniper thicken
    • later wart-like growths appear there
    • these bear brown, later bright yellow spore deposits
    • about one to two centimeters tall
    • shine when wet
    • Infection only appears on the branches

    Infected junipers can usually live quite well with the fungal pathogen, only with a very severe infestation and the associated weakening does the wood die after a few years.

    tips

    Since the fungal spores can spread over an area of several hundred meters, the infected juniper does not necessarily have to be in your garden or in your neighbor's. It is therefore not always possible to identify and eliminate the diseased tree.

    Effectively prevent pear grating

    Nutrient-rich, healthy soil is the basic requirement for healthy trees

    "Climate change is one of the most important reasons for the increasingly massive spread of pear rust."

    Once a pear has been infected with pear rust, the infection will recur again and again - in order to fight the disease effectively, you would eventually have to find and eliminate its originator, the juniper tree that is also affected. However, this is not always possible, after all, the culprit can be hiding in an unfamiliar garden a kilometer away.

    In this case, your only option is to strengthen your endangered pear tree. It survives an infection better and is less weakened by the effects of the fungus. Suitable strengthening measures are:

    • Creation and maintenance of a healthy soil
    • Strengthening of soil life
    • both are done by using organic natural fertilizers
    • and by doing without artificial fertilizers and chemical pesticides
    • compost is particularly suitable for strengthening microbial life in the soil
    • Fertilize sparingly with nitrogen, as the nutrient promotes fungal infections
    • therefore, do not lay out beds with plants that eat heavily (e.g. vegetable beds) in the immediate vicinity of pear trees
    • Also, never cut pear trees before they sprout, this weakens them
    • Always cut back in the summer, as wounds can now be closed better
    • Strengthen the defenses of the pear trees with plant strengtheners
    • Homemade horsetail manure is particularly suitable
    • Purchased horsetail or algae extracts are also suitable

    The production of horsetail manure is very simple, even if it is quite smelly. It is therefore best to place the container with the brew in a place where its vapors are not too disturbing during the fermentation process. You can also bind the smell with a handful of bedrock powder.

    To make the herbal-boosting brew:

    1. Pick or cut a kilogram of field horsetail.
    2. Use whole plants, without roots.
    3. Chop the horsetail as finely as possible.
    4. Place the plant matter in a plastic or enamel bucket.
    5. Do not use a metal bucket, as undesirable chemical reactions occur here during the fermentation process.
    6. Fill up ten liters of soft water, rainwater if possible.
    7. Stir well.
    8. Add a handful of bedrock meal.
    9. Cover the container with a piece of fine mesh wire mesh or a piece of burlap cloth.
    10. The cover is intended to prevent animals from drowning in the liquid manure.
    11. Put the manure bucket in a dark and warm place.
    12. Leave it there for about a week.
    13. Stir vigorously daily.
    14. The manure is ready when it becomes frothy.

    Now filter the finished horsetail manure and fill it immediately into a suitable container, preferably made of plastic and closeable. This will keep it for a few weeks. Water the pear tree with a watering can full of liquid manure about every 10 to 14 days from the moment they sprout in spring until the leaves fall in autumn. The tree is not only strengthened, but also supplied with valuable nutrients.

    Which pear varieties are susceptible to infection and which are not?

    Some varieties of pears are more susceptible to the disease than others

    The incidence of infection can also be contained by planting less susceptible pear varieties. The popular varieties of Pyrus communis listed in the table below are considered particularly susceptible or less susceptible to pear rust.

    Susceptible pear varieties Less susceptible pear varieties
    'Alexander Luke' 'Colorful July'
    'Good Gray' 'claps'
    'molle bush' 'condo'
    'Club Dean' 'Double Phillips'
    'Williams Christ' 'Gellert'
    'Countess of Paris'
    'Good Louise'
    'Trevoux'

    But be careful: "Low susceptible" does not mean that the pear trees mentioned cannot still suffer from pear rust - resistant varieties are not yet available on the market. So if pear trellis are prominent around you - ask your neighbors about this before planting a pear tree - another fruit tree might be a better choice.

    digression

    Other endangered plant species

    In addition to the cultivated pear (Pyrus communis), other Pyrus species such as the Japanese Nashi pear (Pyrus pyrifolia), the wood or wild pear (Pyrus pyraster) or the willow-leaved pear (Pyrus salicifolia), popular as an ornamental tree, can also be affected by pear rust . However, these species are less sensitive than cultivated pears, although not resistant.

    Fight pear rust - methods and means

    Pear rust can only be actively combated with a pesticide approved for home and hobby gardens: Duaxo Universal Pilzfrei from COMPO (also known as Duaxo Rosen Pilz-frei or Duaxo Universal Pilzspritzmittel) is the only plant protection product approved against this fungus.

    However, its use has numerous disadvantages and should therefore not be done rashly:

    • it must be sprayed again every year until the offending juniper has been eliminated
    • causes resistance when used repeatedly, i. H. at some point it no longer works anyway
    • gets into bodies of water (including groundwater) and is not broken down there
    • is highly dangerous for many animal and human garden dwellers
    • endangers the ecological balance

    So instead of spraying poison on the pear tree every year (because that's what it's all about), you better find the culprit and eliminate it. Merely pruning the affected juniper, as is often recommended, is usually not sufficient. The fungus sits not only in the visibly infected branches, but also deep in the apparently healthy areas.

    When is fighting the disease actually necessary?

    Only when the infestation gets out of hand is there a need for action

    If your pear tree only has a few leaf spots, you don't have to act - the pear rust fungus and pear trees can get along without any problems, provided the ecological balance is maintained and the pressure of infestation is not too great. Only in these cases should you take action:

    • Infection occurs several years in a row
    • and very pronounced
    • several spots per leaf
    • premature leaf fall
    • Tree is more orange-red than green in summer

    If the disease has broken out acutely, there is nothing you can do - only preventive measures in spring can prevent a renewed infestation. By the way, young pear trees are also endangered. While an older, established specimen has some resistance to the fungus, young, not yet robust trees perish quickly. In this case, you definitely need to act!

    frequently asked Questions

    Are there effective home remedies for pear rust?

    No, once the disease has broken out, neither commercial pesticides (with the exception of the one mentioned in the article) nor any home remedies will help. You can only treat pear rust by finding the carrier of the infection and making it harmless. In addition, the affected or endangered pear should be strengthened with plant manure - spraying with agents containing silicic acid help against the infection in spring.

    Can the typical harmful symptoms of the disease also be confused with other infections?

    For the uninitiated, pear rust can easily be confused with other fruit diseases such as fire blight or pear pox mites. The pear pox mites are pests whose mischief causes a very similar pattern of damage. Fire blight, on the other hand, is a plant disease caused by the bacterium Erwinia amylovora, which primarily occurs in pome fruit plants. Even if the name initially suggests otherwise, affected leaves and flowers wilt and turn brown to black.

    Is pear grating notifiable?

    A detected infection with pear rust does not have to be reported. Since the infection is often confused with fire blight, which is actually notifiable, a report is often sent to the responsible horticultural authorities. Therefore, first check exactly which disease it is actually about. A comparison with the typical damage patterns will help you.

    tips

    As long as no more than about 40 percent of the leaves are affected or the pear tree sheds its leaves prematurely, you do not have to take action. Such a degree of infestation does not harm the tree.

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Trees