Gall mites cause annoying but mostly relatively harmless trouble in gardens. The tiny animals cannot be seen with the naked eye - rather, an infestation is manifested by the typical galls, small horns on the leaves of the host plants. Read below what you can do against the pests.
How do I fight gall mites on plants?
Gall mites are microscopic pests that occur on maple, hazel, plum trees and berry bushes such as blackberries and currants. Horn-shaped bulges, the so-called galls, on the leaves of the plants are characteristic. To combat gall mites, remove infected plant parts, use spray treatments with oil preparations or natural decoctions and keep the soil moist and loose.
What exactly are gall mites?
Gall mites, zoologically Eriophyidae, are tiny mites that appear to us humans primarily as gate pests. They belong to the subclass of mites within the class of arachnids and form a family with 274 genera and over 300 different species (as of 2013).
Appearance
The whitish, brownish or yellow colored mites have a body length of only 0.08 to 0.5 millimeters, which is only possible due to a lack of a cardiovascular system. Larger species can be recognized with a high-magnification magnifying glass, the others can only be recognized under a microscope. Gall mites are worm-like and slightly curved in shape and are armored with dorsal plates on top. Unlike other mites, they only have 4 legs instead of 8.
Lifestyle
Gall mites overwinter in fruit mummies, under bud scales or in the leaf axils of their host plant and move from there to the emerging leaves in spring. They use their jaw claws to suck on the leaves and, by releasing enzymes in their saliva, cause characteristic protuberances, also called galls or poxes, in which they reside and multiply.
The development of the larvae through the nymphal stage to adult gall mites can take place within around 10-15 days, meaning that there can be enormous population growth within one season. The animals spread via the wind. Gall mites reproduce particularly well in dry, warm conditions.
malicious image
The linden gall mite has specialized on linden trees
Gall mites parasitize various plants and cause different damage to them. The trees and bushes most affected are maple, hazel, alder, plum, elm, beech, linden, dogwood, walnut and conifers, as well as berry bushes such as blackberries, currants and raspberries as well as grape vines. Many of the gall mite species are specialized on certain plants and are named after them, such as the linden gall mite (Eriophyes tiliae), the apple rust mite (Aculus meinedali) or the walnut pox gall mite (Aceria tristriata).
| Maple | Conifers | Linde | Hazel | Blackberries | currants | |
|---|---|---|---|---|---|---|
| malicious image | squirrel-shaped, later reddish-colored protuberances (galls) on the leaf surfaces | Hollowing and brown discoloration, then the needles fall off | Felt-like spots on the leaves | Swollen, enlarged 'round buds' that do not sprout and die | Inhibited fruit formation, berries remain completely or partially red and inedible: harvest loss | Swollen round buds, stunted, asymmetrical leaves, growth inhibition, possibly transfer of nettle leafiness, thereby inhibiting fruit formation |
| Combat | Remove affected shoots and leaves | In case of severe infestation, spray treatment with oil preparation or, in extreme cases, cut back | Remove affected plant parts | Break out swollen round buds, remove affected plant parts | Spray treatment with oil preparation or manure, cut back affected plant parts, dispose of fruit mummies | Break out swollen round buds, cut back the affected parts of the plant, dispose of the fear mummies, spray treatment with oil preparation or manure, keep the soil moist |
The so-called galls are typical for damage caused by gall mites. These are everted tissue growths on the top or bottom of the leaves of the forage plant. The mites are also named after these galls. The galls typically have a horn-like or nodule-like shape and can be light green and later brownish or reddish in color.
Gall mites leave horn-shaped galls on maple leaves
But other symptoms can also occur: Swollen, enlarged buds appear on hazel, yew, currants and gooseberries, which serve as a refuge and laying site for entire hordes of mites. Such affected round buds no longer sprout and die. When infested, linden trees show felt-like spots, while hornbeams have their leaves curled up. Bushy or spherical adhesions, so-called witches' brooms or, in the case of willows, tangled heads, form on birch trees and willows.
Fruit formation is also inhibited in blackberries. The berries do not ripen completely, remain partially or completely red and are therefore inedible. Anyone who grows blackberries on a large scale can suffer significant crop loss due to gall mites.
Certain species of gall mites also transmit diseases. For example, currants can become infected with the nettle leaf virus due to gall mite infestation, which in turn leads to reduced fruit production.
Apart from the crop losses for blackberries and, secondarily, currants, the damage caused by gall mites is limited to the visual disfigurement and loss of leaves on the plants. The infestation is not really dangerous, i.e. seriously damaging to them.
Fighting gall mites
As different as the symptoms of gall mite infestation look on different host plants, the possible methods of combating them are just as diverse. As is often the case with pest control, gall mites should be counteracted both preventively and acutely.
Prevention
Preventing gall mite infestation begins with the selection of plants and their planting location. If possible, you should not plant plants that are susceptible to pests in particularly warm, dry and protected locations, because such an environment promotes the reproduction of gall mites. You should also avoid excessive nitrogen fertilization, but the plants should still be adequately supplied with it.
In the case of blackberries, late-ripening varieties are particularly affected by the infestation. So, if it doesn't play a particular role for you, choose an early ripening variety.
Tip
Especially among the susceptible berry bushes, there are now certain varieties that are resistant to gall mites. For example, the blackberry Rubus fruticosus 'Choctaw', the red currant Ribes rubrum 'Rovada' or the raspberry Rubus idaeus 'Willamette'. You can also ask specifically about other resistant varieties at gardening stores.
Acute control measures
If a gall mite infestation has already occurred, you should take phased measures to contain the population throughout the season. The most important measures are the following:
- remove infected plant material
- Spray treatments with oil preparations, decoctions and manure
- Use eating fines
- Keep soil moist and loose
Remove infected plant material
Infected plant parts should be removed promptly
As soon as you notice a gall mite infestation, you should first remove all affected parts of the plant if possible. You can eradicate a good portion of the mites in spring, especially by breaking out the bloated round buds of hazel, currants, gooseberries and yews. It is best to dispose of the broken, infected buds in the household waste, and under no circumstances in the garden. Severely infected shoots and branches should be cut away completely and destroyed. For plants that tolerate cutting well, radical pruning is also suitable.
From the later fruiting phase onwards, the fruit mummies, which are used by the gall mites as overwintering quarters, must be removed.
Spray treatments with oil preparations, decoctions and manure
For plants on whose leaves the gall mites produce the typical galls, the best way to combat the pests is during the migration phase. The migration phase is the phase in which the mites leave their hibernation sites in the fruit mummies or under the bud scales and migrate to the emerging leaves. Here you can then apply a treatment with oil preparations (usually based on rapeseed oil) or homemade plant broths or manures, even weekly during the vegetation phase. With blackberries, the young shoots are treated when they have reached a length of around 10 centimeters, then again after a week and a half and finally shortly before flowering.
The following have proven to be effective, natural remedies against mites:
- tansy brew
- Garlic extract
- Stinging nettle manure
1. Tansy stock
To make a tansy decoction, chop up about 150 g of fresh tansy herb, scald it with about 5 liters of boiling water and let everything steep for 10 minutes. Then filter the broth. Filled into an empty flower syringe, you can then treat the affected plants with it.
2. Garlic extract
You can make a garlic extract by steeping approx. 100 g of crushed garlic cloves in 20 ml of oil for 24 hours. Dilute the filtrate with one liter of water and add 10 ml of curd soap.
3. Nettle manure
Stinging nettle manure helps against a whole range of pests
Stinging nettle manure is generally a proven, ecological plant strengthener and fertilizer and can also help against gall mites. To make nettle manure, chop up about a kilogram of fresh nettles and pour 10 liters of rainwater over them. Cover the whole thing and let it ferment, stirring daily, for about two weeks. When no more carbon dioxide is formed, i.e. no more bubbles appear, the manure is ready and can be filtered off. To use as a spray against gall mites, dilute the carefully filtered broth with water in a ratio of 1:10 and apply it to the plants using a flower sprayer.
Use natural predators
It can also be very helpful to use natural predators against the gall mites. These primarily include predatory mites (Gamasina), which are sold in carrier granules. The granules can usually be spread directly onto the affected parts of the plant. The predatory mites eat both the larvae and the adult gall mites and die themselves as soon as they no longer find any gall mites.
In addition, lacewing larvae can also be used against gall mites. They are sold in cardboard honeycombs in the first or second larval stage. They must be applied according to the enclosed description so that the lacewing larvae do not cannibalize each other.
Keep soil moist and loose
It is also helpful to keep the soil loose and moist when there is a gall mite infestation, especially in the case of infested fruit trees and berry bushes. Every now and then, rake up the soil under the plant and water evenly. To retain moisture, mulching with bark or straw is helpful.
Effect of gall mites on humans
Like many other types of mites, gall mites can also be harmful to humans. First and foremost, allergic reactions are possible. Bites from gall mites usually appear in the form of small pustules with itching and redness. In more severe cases, they can also cause more serious diseases such as Lyme disease, typhus, tularemia or rickettsial pox.
That's why it's important, especially for sensitive people, to wear protective clothing, especially gloves, when combating plants. You should also make sure not to take clothing worn during the measures into the house in order to avoid spreading it to house plants.
Frequently asked questions
What are gall mites?
Gall mites are known to us humans primarily as plant pests. As mites, they belong to the arachnids and form a family with 274 genera and over 300 species. They are microscopic and invisible to the naked eye. Only the damage they cause to maple, hazel, plum trees, blackberries and currants is visible. Horn-shaped bulges on the leaves are characteristic.
How can you recognize gall mites?
Gall mites themselves cannot be seen, their works can be
The animals themselves cannot be seen with the naked eye or even with a standard household magnifying glass, because they are only around 0.08 to 0.5 millimeters in size. Under the microscope you can see their worm-like, whitish, brownish or yellowish body with only 4 legs instead of the 8 legs common to arachnids and mites. An infestation of plants with gall mites can only be recognized by the damage that appears on the plants.
Which plants are affected by gall mites?
Deciduous trees such as maple, linden, hazel, alder, beech or elm are particularly affected, but coniferous trees can also become victims of gall mites. Shrubs such as dogwoods, blackberries, raspberries and currants are also affected.
What does the damage caused by gall mite infestation look like?
Typically, a gall mite infestation is manifested by greenish to reddish or brownish, horn-shaped bulges, the galls, on the leaves of the corresponding plants. However, felty spots, swollen round buds that do not sprout and die, asymmetrical or curled leaves, stunted growth and inhibited fruit formation (blackberries have completely or partially red fruits) can also occur.
How can you combat gall mites?
The fight against gall mites varies depending on the plant. If only the leaves are disfigured by the horn-shaped galls, they should be removed and disposed of. Spray treatments with oil-based preparations or with homemade tansy decoction, garlic extract or nettle manure can also be used. Fruit mummies in which the mites overwinter should be carefully removed and destroyed. For plants that tolerate pruning and are severely affected, radical pruning may be necessary.
Are gall mites also dangerous for humans?
Gall mites can cause allergic reactions in people. These manifest themselves in the form of pustules, itching and redness. In unfavorable cases, the mites can also cause diseases such as Lyme disease, typhus, tularemia or rickettsia pox.
