Hydrangeas are eagerly cultivated shrubs, valued primarily for their beautiful flowers. Although hydrangeas are rarely a problem, they can be attacked by several diseases and pests. It is worth knowing that proper fertilization and conditions in the position where they grow are very important for their he alth. Here's how to deal with diseases and pests of hydrangeas.
Diseases of hydrangeas appear most often as a result of improper care
Non-infectious diseases - errors in the cultivation of hydrangeas
Hydrangeas for he althy growth should be provided with a little shade, and fertile, humus, adequately moist soil with a slightly acidic to acidic reaction.In soils with too high a pH, hydrangeas quickly develop leaf chlorosis, which is manifested by light discoloration or yellowing of the leaf tissue, while the innervation itself remains dark green.
In the event of leaf chlorosis, a soil acidifying fertilizer should be used (it is best to enrich the soil with acid peat), and in the future, the occurrence of chlorosis can be prevented by using mineral hydrangea fertilizers, containing all the macro- and microelements necessary for these plants, but low in calcium. It is also worth mulching the soil under the shrubs with pine bark, which is also acidic and slowly decomposing helps to maintain a lower soil pH. Additionally, the pine bark will play a decorative role.
Sometimes the hydrangea leaves may burnIn this case, in hot and sunny weather, the leaves on the outside turn yellow or brown in their middle parts, some of them may fall. This is because hydrangeas are shade-loving plants, their leaves are very sensitive to excess sun, therefore they can be damaged in very sunny locations, and the soil is also too dry.To prevent leaf burns, provide the plant with more shade and water it regularly.
A common problem is alsolack of flowering of hydrangeasIn garden hydrangeas it may be caused by poorly chosen growing position and exposure of the plant to frosty winds in winter or improper pruning in spring. Well, the garden hydrangea blooms on last year's shoots and if these shoots are frosted over in winter or cut in spring, there will be no flowers on the bush.This problem does not occur in the case of bouquet hydrangea, which blooms on this year's shoots. If hydrangeas bloom poorly, remember that for the proper formation of flower buds and flower development, an abundance of minerals in the soil - nitrogen, phosphorus, magnesium and iron is necessary. Hydrangeas grow well in shade, but excessive shade can also reduce flowering.
Infectious diseases of hydrangeas
Apart from non-infectious diseases, hydrangeas can also be attacked byfungal diseases
Garden hydrangeas (Hydrangea macrophylla) are the most common in our gardens. Of the fungal diseases, they are quite commonly attacked bygray mold of hydrangeas , caused by the fungus Botrytis cinerea. The development of this disease is favored by frequent rainfall and large shading of bushes. The symptom is the death of shoot tips or single leaves. The youngest leaves turn black and the rot extends to the stem. On older leaves, their tips turn brown and blacken mainly. Individual flowers may also turn brown, and a gray coating of mycelium and spores is observed on their surface. Infected parts of plants must be cut and removed on an ongoing basis. For spraying, you can use commercially available fungicides to combat gray mold, e.g. Topsin M 500 SC.
Relatively often, especially on oak-leaved hydrangea,hydrangea leaf blotchIn case of infection with this disease, spots of various sizes are observed on the hydrangea leaves, usually round, initially light brown, then brown and gray-brown, sometimes surrounded by a red border.When the disease is not controlled, more and more stains appear on the leaves and with time the whole leaves die.To prevent the development of the disease, avoid excessive plant density and wetting the leaves during watering (water directly onto the soil). The first leaves showing blotch symptoms should be removed, and in autumn all fallen leaves should be rake out from under the bushes so that they do not become a source of infection in the next season. Of course, we do not compost such leaves, but remove them from the garden. In late autumn, the bushes should also be sprayed with 1% rapeseed oil. If there are a lot of infected leaves in the growing season, you need to use the following fungicides: Baymat Ultra 0.015 AE, Dithane NeoTec 75 WG, Systemik 125 SL, Topsin M 500 SC. Spraying is repeated 2 or 3 times at intervals of 7-10 days, alternating between two preparations. The list of available plant protection products is changing, so before buying it is worth checking if there are any other agents against hydrangea leaf spot.
A white coating may also appear on hydrangea leaves, initially in spots, with time it may cover the entire leaf blade. The tarnished leaf surfaces turn brown over time. Infected leaves grow more slowly and apical shoots deform. Such symptoms indicate that the plant was attacked bypowdery mildew of hydrangeacaused by the fungus Erysiphe polygoni. After noticing the first symptoms, the affected parts of the plant should be removed, and in the autumn all fallen leaves should be carefully rake out from under the bushes so that they do not become a source of infection in the next season. For possible sprays, the same fungicides that are used to control leaf spot can be used.
Hydrangea pests
Besides diseases, hydrangeas can also suffer from pest attacks. However, it must be admitted that the pests do not cause much damage, and only two pests appear on hydrangeas - aphids and spider mites.
Aphids can be observed mainly on the tops of hydrangea shoots and the underside of leaves, where they form large clusters of dark green to black wingless insects. By sucking the sap from the plant, aphids limit its growth and cause deformation of leaves and inflorescences. They also secrete sticky honey dew, which is conducive to the formation of black bloom of seed fungi. When aphids are noticed, spray with an aphidicide, eg Pirimor 500 WG or Provado Plus AE. The latter is a ready-to-use spray, convenient for amateur use.
The second pest to appear on hydrangea is the spider mite. It is a mite that feeds on the underside of hydrangea leaves from May to mid-August. By sucking the sap from the leaves, it causes yellow, mosaic discoloration on their surface. They initially appear along the veins of the leaves, and then may cover the entire surface of the leaves. Heavily infected leaves turn yellow, turn brown their tips, eventually wilt and fall off.To combat spider mites, use one of the spider mite preparations, e.g. Karate Zeon 050 CS.
Note!
Until recently, it was common practice to burn plant debris infested with diseases and pests to prevent the spread of pathogens. However, according to current regulations, smoking leaves and branches, even if they come from diseased plants, is forbidden. From gardens and plots, we should dispose of them in accordance with the principles of segregation and waste return in force in our commune. Cut branches and removed leaves are called green waste.
