How Do You Treat Powdery Mildew On Apple Trees?

In our garden this time a nasty pathogen is spreading: powdery mildew. Several apple trees are affected. The fungus is still only affecting individual branches; the leaves are covered with white coatings, as are the fruit sets. If the disease progresses further, the greenery wilts and dies. Only shears can help here.

How Do You Treat Powdery Mildew On Apple Trees?

Fungus lurks everywhere

Powdery mildew is also called the “fair-weather fungus”. It occurs preferentially in sunshine and warm temperatures and dewy nights. The fungus itself comes in many different forms. It attacks all plants in the garden, from fruit and vegetables to perennials, summer annuals and roses. Everything can be infected. In the case of apples, it is the powdery mildew fungus Podosphaera leucotricha. It attacks some varieties more often than others: ‘Jonathan’, ‘Cox Orange’, ‘White Clear Apple’, ‘Jonagold’, ‘Ontario’, ‘Ingrid Marie’, ‘Boskoop’ and ‘Gravensteiner’ are among the preferred hosts.

In our case, a ‘Boskoop’ is affected, as well as ‘Cox Orange’ and a smaller, unknown apple variety. Initially, only some leaves were covered with a mealy coating. Now the fruit set and several branches are also completely affected. The leaves dry up and die.

First aid for infestation

As an acute immediate measure, we cut off all infested branches down to the healthy wood and disposed of them in the organic waste garbage can. If you quickly remove the infested plant parts, you can limit the source of infection quite well and prevent further spread. This also saves the chemical mace, which could be used in case of very heavy infestation.

Correct pruning in winter prevents infections


Because the powdery mildew pathogen overwinters in the buds, pruning in late winter is especially important. Infected buds and shoot sections are already visible in winter. They seem underdeveloped and dull; they do not shine like the other buds and branches. If you look carefully here, you can directly prevent the infection. We pay attention to it at least next year.

The disease can also be detected immediately in the new shoots. The leaves are covered with the mealy coating immediately after budbreak. The sooner you remove the infected plant parts, the sooner you stop the infection. And if you choose less sensitive varieties when planting new plants, you will have one less garden problem.

By the way: The cut off leaves and twigs must never be put into the compost, otherwise the spores of the fungi will spread in the garden anyway. You always dispose of everything in the residual waste or in the organic waste garbage can.

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