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Gall mites, although they only have 4 legs, belong to the arachnids. They only reach a size of 0.2 mm and are therefore hardly visible to the naked eye. Depending on the species, gall mites can damage many plants in the garden. The most affected woody plants are called gallstones, from which the name "gall mites" comes from. The pests mostly remain between bud scales or in the leaf axes. Gallmilbs are especially active in spring and summer. Then they often crawl from leaf to leaf.
- Host plants: berry bushes, conifers, deciduous trees
- Distribution: prefer warm, dry locations
- Damage: bile on the leaves
- Prevention and control: remove affected parts of plants
Gall mites prefer berry bushes, for example raspberries, blackberries or red and blackcurrants. The pests live in these plants in the fruit stalls. In infested shrubs, the fruits can not ripen. In many cases, coniferous plants are also attacked by gall mites. The pests colonize the inner needles near the trunk. If the tree is heavily infested with gall mites, the needles turn brown and later fall off. On deciduous trees or shrubs, gall mites are also found. They become noticeable due to shoot deformations or the characteristic bile especially on hazelnut, dogwood, plums, maple, alder or the alpine currant. In very large plants, however, the infestation with gall mites is not too bad as on smaller trees such as soft fruit or ornamental shrubs.
Gall mites feel particularly comfortable in warm, dry locations. Under these conditions, they can multiply optimally. As a rule, these pests overwinter behind the bark or in bud scales. With the foliage they come from their winter quarters and infest leaves and shoots of their host plant. There they induce the galls and live in them until the summer. From about July the hike begins to new winter camps. Gall mites multiply through eggs and develop through a larval and nymphal stage. During the growing season, gall mites spread extensively with the wind.
Gall mites suck plant saps. The resulting excretions of the animals, the neighboring cells of the plant are stimulated to grow. This growth creates the characteristic bile or other deformations. Leaves often develop scarred or nodular protuberances, which are partly red discolored. The bile have a completely different shape depending on the type of mite. In the Ulmengallmilbe and the Erlengallmilbe they are small-pox and pin-like in the Lindengallmilbe. Also, the colors of the bile can vary. In the squirrel gull mite on maple, they are often clearly colored red. Fatty structures on the underside of the leaves can also be caused by gall mites. This is often the case, for example with Pfaffenhütchen, beech or linden. Globular swollen buds on currant Yew or hazelnut may also indicate gall mites. In the hornbeam, the leaves curl and on the linden and beech, the leaf margins curl up. In beeches also the leaf veins can be white-felted.
Prevention and control
In late summer, the leaves are still showing symptoms, but the gall mites are then no longer detectable at these sites. Therefore, it is important to remove infected parts of plants already in the summer. This will reduce the occurrence of gall mites next year. During the flowering period you can inject additionally infested plants with a Rainfarntee Sud dripping wet. This process should be repeated weekly if heavily infested. The settlement of predatory mites can prevent further propagation of the gall mites. To prevent an infestation with gall mites you can buy gallmilk-resistant varieties from berry bushes. It is also possible to use suitable pesticides.
- Affected plants: The gall mites mainly attack maple and linden
- Damage: Leaves affected by gall mites initially show light-green spots, which later become bulging and reddening. Spur tips sometimes deformed during heavy infestations. With the magnifying glass you recognize stretched, maximally 0,5mm large animals, which cause no great damage.
- Most dangerous time: from spring to summer
- Defense: Preventive: no action required to prevent gall mites. Gentle: Not required. However, if the leaves are severely affected by gall mites, this usually puts a lot of strain on the plant: Not required