The characteristic, striking damage caused by the pear grid makes affected pear trees appear threateningly diseased. But fighting the fungal pathogen is not always necessary. In this article you will find out how to recognize the disease and when you need to take action.
What is pear rust and how do you fight it?
Pear rust is a plant disease caused by the fungus Gymnosporangium sabinae. The fungus attacks pear trees and juniper species as an intermediate host. Affected leaves show orange-yellow spots and wart-like nodules. Control is usually only necessary in the case of severe infestation, for example by removing the infected juniper or strengthening the pear tree.
- Fungus called Gymnosporangium sabinae causes pear trellis
- Infection always occurs via different types of juniper as an intermediate host
- Fungal spores migrate from the juniper to the pear leaves in spring
- Spore transfer takes place back in autumn, as the spores overwinter on juniper
- The damage is characteristic, control is only necessary if the infestation is severe
What is pear grid?
Pear rust is a plant disease caused by the fungus Gymnosporangium sabinae. The parasitic pathogen prefers to attack plants that are already sick or weakened by settling on them or on the soil and from there penetrating the plant tissue and feeding on it. Like all mushrooms, the pear lattice spreads through so-called mycelia (i.e. the fungal network) and through spores.
How is the pathogen transmitted?
Gymnosporangium sabinae overwinters in juniper
This section is important in order to be able to combat the disease properly - the fungus not only attacks pears, but also takes a detour via an intermediate host. Transmission only works with the help of a change of host, which is why you can prevent (re)infection of your pear by eliminating the intermediate host.
This intermediate host is various types of juniper (Juniperus), which must be located near the pear tree and from where the spores spread again and again. The life cycle of Gymnosporangium sabinae is as follows:
- overwinteres in the juniper
- train your spores here
- Spores are transferred to pear leaves by wind, insects or birds
- The time of this infection is spring, at the beginning of leaf shoots
- spores form again here in the fall
- these are transferred again to the juniper
- the pear tree gets rid of the fungus when the leaves fall in autumn
- the game starts again in the spring
On the pear, the fungus only sits on the leaves, only the affected junipers are permanently diseased.
Transmission occurs through ornamental juniper
However, Gymnosporangium sabinae doesn't like every juniper. Species such as the native common juniper (Juniperus communis), the creeping juniper (Juniperus horizontalis) from North America and the scaled juniper (Juniperus squamata) are spared from the fungus. Juniperus communis in particular has repeatedly proven to be extremely resilient.
However, many imported ornamental juniper species, which have been increasingly planted in gardens, green spaces and cemeteries in recent decades because of their vigor, are common carriers of pear rust and are therefore problematic:
- Moss juniper or Sade tree: Juniperus sabina, evergreen dwarf shrub, particularly susceptible to Gymnosporangium sabinae
- Chinese juniper: Juniperus chinensis, popular ornamental juniper, common intermediate host for pear trellis
- Pfitzer juniper: Juniperus pfitzeriana 'Wilhelm Pfitzer', variety of Chinese juniper
- Virginian juniper: Juniperus virginiana, also known as Virginian cedar or red cedar, is often touted as a climate change tree
The species mentioned are available commercially in different cultivars, although not every variety is equally susceptible to infection with pear rust. For you, this knowledge means that if pear rust appears on your pear trees, you have to decide: either the juniper has to go or the pear, because this is the only way to combat the pathogen.
Excursus
How dangerous is the pear grate actually?
Pear trees were also attacked by pear rust around 30 years ago. At that time, however, the disease was not yet a problem; instead, the fungus and infected trees could co-exist with each other. Only after the aforementioned ornamental junipers were imported and increasingly planted did the pathogen become more dangerous for various Pyrus species and their relatives.
In principle, the infection does not have to be a problem today, as long as the affected pear tree is otherwise he althy and strong and is in an ecological balance. Specimens in suitable locations in naturally managed gardens therefore have a better chance of surviving pear trellis unscathed.
Damage pattern – How to recognize an infestation with pear grate
Small orange spots on the leaves are the first signs of an infestation
Infection with the pear grate appears on the pear around the time the tree is blooming between May and June:
- initially small orange or yellow spots on the tops of the leaves
- increase over the course of the summer
- different degrees of infection possible
- sometimes only a few leaves affected, sometimes severe infection with almost all leaves
- If the infestation is severe, the tree looks more orange-red than green in autumn
- later wart-like nodules on the undersides of the leaves
- these are spore deposits
- gradually tear into a mesh and spread out through the wind
However, an infection with the harmful fungus manifests itself differently on the affected juniper. Here you can identify the disease by the following characteristics:
- visible from mid-April
- First branches of the affected juniper thicken
- later wart-like growths appear there
- these carry brown, later bright yellow spore deposits
- approx. 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 in the case of a very severe infestation and the associated weakening does the tree die after a few years.
Tip
Since the fungal spores can spread over an area of several hundred meters, the infected juniper does not necessarily have to be in your or your neighbor's garden. Therefore, it is not always possible to identify and remove the diseased tree.
Effectively prevent pear grids
Nutritious, he althy soil is the basic requirement for he althy trees
“Climate change is one of the most important reasons for the increasingly massive spread of the pear grid.”
Once a pear has been infected with the pear rust, the infection will recur again and again - in order to effectively combat the disease, you would ultimately have to locate and eliminate its cause, the juniper, which is also infected. However, this is not always possible, as the perpetrator can hide a kilometer away in an unknown garden.
In this case, your only option is to strengthen your endangered pear tree. This means it survives an infection better and is less weakened by the effects of the fungus. Suitable strengthening measures are:
- Producing and maintaining he althy soil
- Strengthening soil life
- both are done by using organic natural fertilizers
- and by avoiding artificial fertilizers and chemical pesticides
- compost is particularly suitable for strengthening microbial soil life
- fertilize sparingly with nitrogen, as the nutrient promotes fungal infections
- Therefore, do not plant beds with heavy-feeding plants (e.g. vegetable beds) in the immediate vicinity of pear trees
- also never cut pear trees before they sprout, this weakens them
- Always prune in the summer, as wounds can now be closed better
- Strengthening pear trees' defenses with plant strengtheners
- Home-made horsetail manure is particularly suitable
- Purchased horsetail or algae extract is also suitable
Making horsetail manure is very simple, although it does smell quite strong. It is therefore best to place the container with the product during the fermentation process where its vapors will not be too disruptive. You can also bind the smell with a handful of primary rock powder.
How to make the plant-strengthening brew:
- Pick or cut one kilogram of field horsetail.
- Use whole plants, without roots.
- Crush the horsetail as finely as possible.
- Put the plant material in a plastic or enamel bucket.
- Do not use a metal bucket as undesirable chemical reactions occur during the fermentation process.
- Fill up ten liters of soft water, preferably rainwater.
- Stir well.
- Add a handful of primary rock powder.
- Cover the container with a piece of fine-mesh wire mesh or a piece of jute cloth.
- The cover is intended to prevent animals from drowning in the manure.
- Place the manure bucket in a dark and warm place.
- Leave it there for about a week.
- Stir vigorously every day.
- The manure is ready when it becomes foamy.
Now filter the finished horsetail manure and immediately fill it into a suitable container, preferably made of plastic and easily sealable. It stays here for a few weeks. Water the pear tree approximately every 10 to 14 days with a watering can full of manure from the time it sprouts 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 pear varieties are more susceptible to the disease than others
Infection can also be contained by planting less susceptible pear varieties. The popular varieties of Pyrus communis listed in the following table are considered particularly susceptible or less susceptible to pear rust.
| Susceptible pear varieties | Less susceptible pear varieties |
|---|---|
| ‘Alexander Lukas’ | ‘Colorful July’ |
| ‘Good Grey’ | ‘Clapps’ |
| ‘Mollebusch’ | ‘Condo’ |
| ‘Club dean’ | 'Double Phillips' |
| ‘Williams Christ’ | ‘Gellert’ |
| ‘Countess of Paris’ | |
| ‘Good Luise’ | |
| ‘Trevoux’ |
But be careful: “Less susceptible” does not mean that the pear trees mentioned cannot still get sick from pear gridiron - there are no resistant varieties on the market yet. So if the pear trellis is prominent around you - ask your neighbors for this purpose before planting a pear tree - another fruit tree might be a more sensible choice.
Excursus
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.), which is popular as an ornamental tree, can also be used) be affected by pear grid rust. However, these species are less sensitive than cultivated pears, although not resistant.
Fighting pear grid - methods and means
The pear grate can only be actively combated with a pesticide approved for home and hobby gardens: Duaxo Universal Fungus-Free from COMPO (also known as Duaxo Rose Fungus-Free or Duaxo Universal Mushroom Spray) is the only one approved against this fungus Plant protection products (€17.00 on Amazon).
However, its use has numerous disadvantages and should therefore not be done carelessly:
- it has to be sprayed every year as long as the offending juniper has not been removed
- causes resistance when used multiple times, i.e. H. At some point it will no longer work anyway
- gets into bodies of water (including groundwater) and is not broken down there
- is extremely dangerous for many animal and human garden inhabitants
- endangers the ecological balance
So instead of spraying poison on the pear tree every year (because it's nothing else), it's better to find the culprit and eliminate it. Simply cutting back the affected juniper, as is often recommended, is usually not sufficient. The fungus is not only found in the visibly infected branches, but also deep in the seemingly he althy 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 need to take any action - the pear rust fungus and pear trees can get along without any problems, provided the ecological balance is maintained and the infestation pressure does not become too severe. You should only take action in these cases:
- Infection occurs several years in a row
- and very pronounced on
- multiple spots per sheet
- 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 preventative measures in spring can prevent a new infestation. By the way, young pear trees are also at risk. While an older, established specimen has a lot of defense against the fungus, young, not yet robust trees die quickly. So in this case you definitely have 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 help. You can only treat pear gridiron by locating the carrier of infection and rendering it harmless. In addition, the affected or endangered pear should be strengthened with plant manure - spraying with agents containing silica helps against the infection in spring.
Can the typical symptoms of the disease also be confused with other infections?
For the uninformed, pear gridiron 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 damage. Fire blight, in turn, is a plant disease caused by the bacterium Erwinia amylovora, which primarily occurs on pome fruit plants. Even if the name initially suggests otherwise, affected leaves and flowers wilt and turn brown to black.
Is the pear grid required to be reported?
An established infection with pear gridiron does not need to be reported. Since the infection is often confused with the fire blight that actually needs to be reported, it is still often reported to the responsible horticultural authorities. Therefore, first check exactly what disease it actually is. A comparison with the typical malicious images will help you.
Tip
As long as no more than around 40 percent of the leaves are affected or the pear tree sheds its leaves prematurely, you do not need to take any action. Such a level of infestation does not harm the tree.