The walnut tree with its magnificent leaf dress is a real eye-catcher in summer. It not only provides shade, but also rewards plant lovers with an abundant walnut harvest. However, healthy growth is a prerequisite. Although it is one of the most robust tree species, some pests and diseases can make life difficult for it. You can find out what these are and how to combat them in the following guide.
Better safe than sorry
The real walnut tree or common walnut tree, popularly known as the walnut tree for short, is a strong and robust specimen when healthy. It has a natural defense organism that protects it extensively against diseases and numerous pests. But there is never a 100 percent protection with plants, so that the Juglans regia can also be affected.
At the beginning of every disease and pest infestation, he does all it can to counteract it. But the course of the disease should not be stopped and pests can multiply unhindered as well as them Withdrawing life energy, often not only does the nut harvest fail, but the walnut tree can turn into a life-threatening one In danger.
Tip: For the reasons mentioned, this robust walnut plant should therefore be checked regularly for possible diseases and pests, so that you can act quickly and prevent worse by combating it - unfortunately in some cases there are no effective ones Combat.
Walnut tree diseases
Here are the typical diseases that can affect a walnut tree:
Cherry leaf roll virus
The cherry leaf roll virus is also under the name Walnut Blackline Disease known. It is an infectious disease that progresses slowly and can lead to death, especially in weakened trees.
Recognize
- Yellow line patterns and yellow spots on the leaves and fruits
- Fruits and leaves fall off
- Black lines on lignification
- Dead tissue forms on the refined branches
- Branches dried up
- No more new shoots are formed
Combat
Effective control is not yet known. The virus spreads so quickly inside that even cutting off affected areas at the first recognizable signs is already too late.
Powdery mildew (Erysiphaceae)
The walnut tree is particularly susceptible to powdery mildew in dry months and in warm summer. In contrast to downy mildew, which only prefers the humid climate, powdery mildew is also called
"Fair weather mushroom", although moisture does not deter it. Powdery mildew is a pseudo-fungus that can be dealt with quickly if treated quickly. It is called a dummy mushroom because it optically leaves a corresponding image, but is more related to the brown algae and diatoms.Recognize
- In the initial stage only white, sticky fungus coating on the upper side of the leaves
- In the later course of the disease, a white carpet of fungi can also be seen on the underside of the leaves
- It then migrates to all green parts of the plant
- The surface becomes brownish to greyish over time
- Stunted fruit heads
- Some sheets of paper turn up the side edges
- Leaves dry up and fall off
- If powdery mildew is left untreated, it can penetrate the tree trunk and cause it to die off
Combat
There are various methods to choose from to combat powdery mildew on walnut trees, all of which have proven to be effective.
Soapy water
- Depending on the size of the infestation and the tree, leach the appropriate amount of water with soap
- Only those without chemical additives are suitable as soap
- Pour soapy water into a pointed pump
- Spray the leaves dripping wet with the soapy water
- Make sure that all parts of the plant are sprayed from each side
- If the white mushroom carpets have not disappeared after five to six days, repeat the process
- Do not spray in the blazing sun or in the hot midday sun
- A dry day should be selected for spraying - it is optimal if more dry days follow so that the soapy water can work and is not washed away by rain
Pesticides
A pesticide against powdery mildew is available in every specialist shop. Here you should make sure that night sulfur or other organic active ingredients are included. If you spray the walnut tree with it every year before it blooms, you will keep powdery mildew away. If this has already spread to the tree, a pesticide can be used to combat it. Even if it is in the organic ingredients, a treatment is for existing infructescence less advisable, as the liquid gets into the interior of the fruit and consumption of the fruit is not is recommended. The soapy water, on the other hand, can be used safely.
Fungal infection
There are innumerable species of mushrooms that settle in gardens every year. Some are more stubborn to fight and show themselves with severe and sometimes life-threatening damage, while others have little effect on the
Have walnut tree. But in any case, you should react, because an exact identification of which fungus it is is almost impossible. An expert can certainly help you on site, but an immediate control solves the problem even without knowing the fungus by name. As a rule, walnut trees show more or less the same symptoms when there is a fungal attack.Typical features of a fungal attack
- Brown and grayish brown discoloration of the leaves
- Rolled and / or stunted leaves
- Leaves dry and fall off
- Stunted growth
- New shoots stay away or grow very thin
- Thin branches of green hang limp
- Often smear marks on the leaves and / or on the green branches
- Trees are increasingly thinning
- Fruit clusters do not appear, do not develop properly or fall off immature
Combat
Fungicides
The fastest and most effective are usually fungicides, which are available for purchase from specialist retailers especially for use in fungus treatment. It is recommended to use only organic products here. Most of them ensure that the existing fruits remain suitable for consumption despite spray treatment. In addition, the treatment with bio-fungicides is environmentally friendly. When using chemical products, you must expect walnuts to be polluted. The extent to which these could endanger your health when consuming the walnuts depends on the respective ingredients and dosages. It should also be taken into account that chemical fungicides are also toxic to insects and should therefore only be used under special precautionary measures are used - or just do without them and only use a bio-fungicide to combat fungus use.
Exception: tree fungus infestation
In addition to the tiny fungal spore infestation of various types of fungus, tree fungus infestation can also occur. This can be observed far more often. Real fungal sponges usually form on the tree trunk. These are not always edible and not always harmful to the walnut tree. Nevertheless, you should take action.
- As soon as you suspect the first signs of a possible tree fungus infestation, you should remove them so that the fungus does not spread
- Score the bark / wood with a sharp knife
- If green tissue shows up, control can still be effective
- If the inner fabric has dried up or has a yellowish-green shimmer, the fungus is already inside
- In this case, control with conventional measures is not possible
- It is advisable to consult an expert from the plant protection office if necessary
- This can explicitly assess what needs to be done or what precipitation is necessary
Bacterial infestation
Again and again, bacterial infestations are found in walnut trees, which in the worst case can even kill large, strong trees. Bacteria are usually transmitted through the use of infected pruning tools and large cuts that allow bacteria to enter the interior of the tree.
Recognize
As a result of a bacterial infection, growths usually form on branches or the trunk. These can become immensely large and create holes, especially in the trunk. The so-called tree canker usually results from a bacterial attack.
Fight
In many cases it is sufficient to cut out the growths over a large area. If they are hanging on a branch, cut it back until fresh green appears on the inside. This is a sure sign that the area is (still) healthy. Then the interfaces are to be covered with coal ash or special resin to close wounds in plants. This way no new bacteria can enter.
TIP: Always use disinfected cutting tools when pruning trees. Only cut on dry days and always close larger cut surfaces to avoid bacterial infestation.
Walnut tree pests
With these pests is on the walnut tree too
calculate:Aphids
Damage from aphids can only be expected if an extensive infestation is noticeable and the leaves are severely curled up. Otherwise the Julians regia gets along well.
Recognize
In order to recognize aphids, you would have to get quite close to the leaves, as the small, brown, black or greenish creatures, only a few millimeters in size, can hardly be seen. You can use the following signs as a guide:
- Sticky coating on the leaves (honeydew)
- Rolled up and partly stunted leaves
- Yellow leaves
- Leaves dry up and fall off
- Mostly colonies can be seen mainly on new shoots
Fight
- If the infestation is manageable, cut off the affected branches into the healthy area
- Then spray the tree with strong pressure (wash down any remaining animals)
- In the case of severe, large-scale infestation, use highly concentrated soapy water
- Add around 500 milliliters of rapeseed oil for every ten liters of soapy water (it sticks the aphids' respiratory organs)
- Spray the tree dripping wet
- Repeat the process after about three days
Caterpillars
You are happy to bother blue-sieve, willow borer and butterfly caterpillars on walnut trees. Blue caterpillars in particular often leave massive damage behind. They have a yellowish-white body up to six centimeters in size on which there are so-called point warts. If they have eaten their way into the inside of branches and trunks, they form there like a hollow tunnel system.
Combat
When fighting it, it is important that you do it at an early stage, before the caterpillars have worked their way into the interior of the tree. Once they get there, you can no longer reach them and fight them is impossible.
Collecting
If there are not too many caterpillars and the walnut tree is not yet very high, you can collect the caterpillars by hand. Another variant is shaking it down. To do this, place a sheet of plastic on the ground and either shake the still small tree or work your way from branch to branch with a broom, for example. The caterpillars that have fallen on the foil can then be disposed of with household waste.
Cut
If it is a light infestation in the early stages and the caterpillars are on the branches, you can remove them from the walnut tree by cutting off the affected branches. Telescopic pruning shears are advantageous for tall specimens.
Neem oil
Neem oil plant products are commercially available that can be used to effectively control caterpillars on walnut trees. You can use it to spray the tree or only the affected parts of the plant. The neem oil settles in the respiratory tract of the caterpillars, which then suffocate.
Walnut fruit fly (Rhagoletis completa)
The walnut fruit fly is not the direct problem, but the maggot. From around July / August they lay their eggs in the fruit pods. As a result, they leave black dots on the green fruit peels. The maggots penetrate the fruit walls and eat them. A clear characteristic is a soft, moist fruit that dries out more or less in the further course. Because they only penetrate the pulp, the walnuts can still be eaten as long as they are not completely dry. All you have to do is remove the black pulp from the nut.
Combat
Collect fallen walnuts daily and either remove the nut immediately or dispose of it. This prevents pupation and the walnut fruit fly does not reproduce. Cherry fruit fly traps can be hung in the treetop and should be replaced or cleaned daily. If you put a close-meshed net around the walnut tree from June onwards, you will also prevent walnut fruit flies from getting into the branches and laying their eggs in the fruit shells.
