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If the spruce needles turn yellow, this could be due to the sitka spruce. A simple test shows you whether it is infected. Then act quickly.
If you have a spruce tree in your garden, you should check every now and then whether it is infected by harmful lice. There is a louse that can damage some spruce species so much that they die. We are talking about the Sitka spruce louse. It is a pest that can be tasted especially by older needles near the trunk. These then yellow first, but a short time later they turn brown and fall off. Then you should be active at the latest. It is even better if you check the tree regularly for a louse infestation. This is especially advisable after mild winters, because then adult animals can easily survive.
What does the Sitka spruce look like?
The Sitka spruce louse is related to the aphids and therefore looks very similar to them. It is about 2 millimeters in size and green. She also has rust-red eyes. It usually occurs in large populations because it can multiply rapidly even in mild winters. It is also active all year round. She pricks the cells with her proboscis and sucks them out, whereupon the needles change color and fall off. This damage pattern occurs especially in spring.
You can easily check whether your trees are infected with the Sitka spruce. There is a simple trick to detect an infestation.
How to test whether your spruce has lice:
Take a sheet of paper and a stick and use it to knock on the branches. You must hold the paper under it. The 2 millimeter large lice fall on the sheet of paper, on which you can then see them with the naked eye. If more than five of these lice land on paper during the tap action, then you should take action.
This is how the Sitka spruce can be fought
Set up insect hotel:
Combating the sitka spruce is particularly important in spring and winter, as the natural enemies of the louse are then not active. These include e.g. Beneficial organisms such as lacewings and ladybugs. If you offer these beneficials a nesting site or winter quarters, you can fight the Sitka spruce louse faster. Simply set up an insect hotel in your garden.
Use beneficial products:
Otherwise, it is advisable to use rapeseed oil or potash soap-based preparations. They protect beneficials and are still very effective. For example, we can recommend Celaflor Naturen Pest Free (available here). It is a rapeseed oil-based spray. Prepare the spray according to the manufacturer's instructions and spray the branches and trunk thoroughly with it. A two-time spraying every two weeks is usually enough to get rid of the Sitka spruce louse.
Avoid waterlogging and dryness:
Sitka spruce primarily affects conifers that suffer from waterlogging or too dry a soil. Therefore, always make sure that the floor is evenly moist and loose.