If the leaves of an apple tree turn brown and curl up, diseases, pests or supply disorders can be responsible. In the worst case, this can lead to death. So that this does not happen, the cause should always be investigated in order to be able to initiate appropriate remedial measures. Possible causes including effective control can be found in the following.
Table of Contents
Root cause research for pests
If brown leaves or discoloration or spots appear on the leaves of an apple tree, the first step in researching the cause is to look for pests.
This is carried out as follows:
- Search the trunk all around for pests and other abnormalities such as possible “stretches” of pests
- Examine shoots and shoot tips
- Examine the tops and bottoms of leaves for pests
- Take a “soil sample” on the trunk and search for pests
- Check several times if none have been seen so far
- A check can also be worthwhile in the dark if the pests are nocturnal
- “Listen” to the apple tree in absolute silence, some pests make noises when they come out of their hiding spots
Possible pest infestation on the roots
There are a number of pests that attack the roots and eat them up. If they are damaged, supply disruptions occur. The leaves dry out, often curling up before they turn brown and fall off.
The main pests that can settle in the root area of an apple tree include:
- Mole crickets
- Maggots of different types of flies
- Root mites
Insecticides are effective against root pests, but not always the first choice. Home remedies can also work in the same way. For years, for example, the use of soft soap solution has proven itself against almost all root pests. Depending on the type of pest, other agents can be added to this solution. Proceed as follows to manufacture and use:
- Mix 30 milliliters of soft soap per liter of water
- For root mites, add an additional 200 milliliters of wormwood tea
- Add 200 milliliters of alcohol to larvae and grubs
- Every three days, water the affected area of the earth generously for a period of around 10 days
- Then stop the treatment and wait until new pests appear from deposited eggs
- In the case of new pests, give a soft soap solution every three days
- Size: about 2.5 millimeters
- The abdomen is black in color
- Body color: blue-gray to dark gray or brown
- Eggs: shiny black
- Colonies form predominantly on leaf rosettes and young shoots
- Damage: yellow, red to dark red-brown leaf spots – rolled up and later whole brown discolored leaves
Control of apple lice is usually not necessary. Usually the damage is limited to small areas of the apple tree.
- Size: 0.16 to 0.2 millimeters and hardly visible to the naked eye (magnifying glass required)
- Body yellow-brown with wart-like structures
- Multiply rapidly from May at the latest
- Damage: Tissue damage with yellow spots on the underside of the leaves, dull leaf surfaces that later turn brown and dry up
Control and prevention:
- Remove the bottom leaves in June – the male rust mites have been on them since May and the female rust mites from June
- Shorten the apple tree in autumn as part of the usual autumn pruning
- Burn the cut off or dispose of it in household waste – never put it on top of the compost
- Use a sulfur-containing preparation in the event of severe infestation
- Size: 1.3 to 2.3 mm
- Body: green, brown-black legs
- Have visible antennae
- Usually settle on the underside of the leaves in colonies
- Shiny black eggs around 0.5 millimeters in size
- Eggs are mostly on the shoot tips
- Sticky leaves from honeydew that the lice secrete
- Damage: first there are leaf curls and curling of the leaves, before they become increasingly brown, growth disorders
- If the infestation is severe, the apples deform
- Natural predators: Aphids serve as a source of food primarily for lacewings, ladybirds and the larvae of 7-point ladybirds. These can be exposed on the tree. They are available in every well-stocked gardening specialist.
- Soap suds: Soap suds have proven to be effective as a home remedy for green apple aphids. This is produced and used as follows:
- Put soap without additives in a container with water
- Let it “steep” until a strongly concentrated soapy water is produced
- Pour lye into a spray pump
- Spray the apple tree dripping wet (don’t forget the underside of the leaves)
- Repeat spraying every two days until no more green aphids can be seen
- Size: up to 3 millimeters
- Color: dark to black
- Dark brown spot on the rump
- Wings twice as long as the body
- Wax-like, white dust on the rump
- Larvae: change from beige to pink, gray and dark brown
- Damage: first yellowish, then black-brown leaf discoloration, stunted and rolled leaves, premature leaf fall
As described under “Green aphid”.
Diseases cannot always be clearly identified. The following characteristics help for various diseases in an apple tree, but a difference is often not noticeable, especially with fungi and viruses / bacteria. A plant laboratory can help here. If you are not afraid of the sometimes high costs, you can find out about addresses from the local gardener or the Internet. However, the most promising control measures are often similar, so that a laboratory analysis is not absolutely necessary.
Apple scab is a fungal disease that is one of the most common on fruit trees. Every year this fungus causes immense damage and destroys entire fruit harvests.
- Young leaves with dark brown to black spots mostly in the center of the leaf
- Discoloration increases in size until the entire leaf has dried up
- Sometimes the leaves curl up, curl and / or show crippled shapes
- Premature loss of leaves
- Later on, jagged spots and cracks on the apples
- Heavily infested apple trees have often lost all of their leaves by August
- Affects neighboring apple trees
If the fruit cluster has already formed, the use of chemical fungicides usually makes the harvest unusable for consumption. Eastern farmers rely on products with sulfur. Baking powder in connection with copper also curbs the fungus and prevents a new infestation.
With this fungus, preventive measures are of great importance in order not to lose apple trees and harvests. Therefore, the following measures should be carried out every year and are an absolute must in the event of a fungal attack:
- Regularly collect all fallen leaves from infested trees, burn them or dispose of them with household waste
- As a preventive measure, remove all leaves in autumn so that the apple scab fungus cannot overwinter on them
- Cut off heavily infested parts of the tree generously
- Thinning out the treetop so that there is better ventilation
Fire blight (Erwinia amylovora bacterium)
Fire blight is one of the most dangerous diseases of plants because, if left untreated, it leads to death and can spread like an epidemic. For this reason, the fire blight is subject to notification.
- Rapid withering of leaves and flowers
- Brown to black discoloration on the leaves
- Leaves mostly remain on the apple tree
- Curled leaves are seldom seen
- External shoots bend down
- Young trees can die within two weeks
- In older apple trees, the clinical picture extends for a few years until it dies
In the case of very young apple trees, the chance of successful control is almost zero. Here it is only a matter of damage limitation, which prevents it from spreading to neighboring fruit trees by immediately planting the affected apple tree and burning it or disposing of it in some other way.
Rigorous cutting of affected tree parts from older trees can provide a remedy against the bacterium. Otherwise, no approved and effective pesticides against fire blight are known to date.
Bad soil conditions
In addition to pests and diseases, the soil can also cause brown leaves on an apple tree.
In many cases, wrong fertilization is to blame for brown leaves, which can lead to a disturbed supply of nutrients. This can happen both with over-fertilization and with too little fertilizer. Brown leaves are not uncommon, especially when using too much nitrogen. Nitrogen is often used to increase the size of the crop.
For the reasons mentioned, your own fertilization behavior should always be checked and, if necessary, corrected if the leaves on the apple tree are rolled up and / or brown. The apple tree usually recovers afterwards.
In many cases, a lack of a substance in the soil is enough to make an apple tree sick and to form brown leaves. A soil analysis shows whether other nutrients are missing or whether there is an unequal ratio. This has to be compensated accordingly if there is a nutritional deficiency.
When brown leaves show up on apple trees, it should not be ignored. This can be due to a serious disease or a pest infestation that can damage neighboring plants to the point of death. Pest can be combated effectively. Diseases caused by fungi and viruses or bacteria are often difficult to distinguish from one another. In any case, good prevention is important.