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When the leaves on cucumber plants turn yellow, you should usually act quickly. The reasons for this can be of various origins, which it is necessary to find out. The plant expert explains clearly how you can identify the cause and how you should act to save the plant and prevent it from spreading.
cucumbers
Cucumbers in the greenhouse/open ground turn yellow - what they lack
Both outdoor and greenhouse cucumbers are equally affected when it comes to yellow leaves, which in the worst case can kill the plant. The most common reason for this is incorrect care, although cucumber plants are not resistant to fungi and parasites. The first step is always to identify the problem so you can choose the right response to help your cucumbers recover.
Glasshouse
While in outdoor cucumbers diseases and parasites are usually to blame for the yellow leaves of the cucumbers, in greenhouse cucumbers this is mainly limited to care errors and/or an incorrect room climate. The latter, for example, leads to yellow leaves if the following is not the case.
- consistent and constant air circulation (avoid draughts)
- constant high humidity
- opening the ventilation ducts in the morning and closing them in the evening
- Ground temperatures of at least 10 degrees Celsius
- germ-free soil (avoid waterlogging)
- sufficient planting distance
infections
greenhouse infections
In many cases, greenhouse cucumbers are only threatened by fungal infestation if they have been cared for incorrectly, as already described in the "Greenhouse cucumbers" section. As a result, two types of fungi in particular can develop on the cucumber plants:
cucumber wilt
If cucumber wilt is caused by the soil fungi Verticillium or Fusarium, you currently have no choice but to dispose of the plant, as there is currently no effective way to combat it. The leaves of cucumbers starting to turn yellow from the stalk. The coloring takes over the entire leaf relatively quickly and it then falls off. The plant looks very limp overall and the wilting process is progressing quickly.
Verticillium wilt
Verticullium wilt is also a harmful fungus that spreads rapidly and affects countless plant species. This disease is recognizable by the following manifestations.
- Wilting despite sufficient watering
- rapidly yellowing leaves
- Cracking and dying of stems or wooden parts of plants
- overall ill appearance
The infection occurs from the ground, where the roots are weakened and an infestation is usually only recognized after a long time. Like cucumber wilt, Verticullium wilt is untreatable. It must be removed from the rows of plants immediately and disposed of with household waste.
leaf spot disease
Leaf spot causes a bacterial infection. You can usually recognize them by the yellowish spots on the upper side of the leaves. In addition, drops of slime can be seen on the undersides of the leaves. In the advanced stage, the yellow leaf spots become larger and larger and take up the entire leaf until it tears, withers and the yellow color changes to brown.
The causes are usually too high humidity and an injury through which the bacteria can get inside the plant. The pathogen can get into the soil with seeds and remain there for a very long time.
mildew
Powdery mildew is a fungal disease that is divided into two different types: powdery mildew and downy mildew. In both cases, the harmful fungi cause yellow leaves and, if left untreated, the affected plants die. Both types of mildew can be recognized by a whitish and sticky fluffy film. With powdery mildew, this is on the upper side of the leaf, while with downy mildew it is only on the underside of the leaf. If the fungal infection progresses, the leaves are completely covered with this carpet of fluff and the leaves turn yellow at the latest.
countermeasures
infection treatment
With the exception of cucumber and Verticillium wilt, the infectious diseases mentioned are relatively easy to get under control if they are recognized early and treated accordingly. Basically, the more advanced the fungal infestation, the lower the chances of survival.
home remedies
Spraying with skimmed milk generally helps to treat fungal diseases. The advantage of skimmed milk is that it is in no way harmful to health and the cucumbers are still suitable for consumption and there is no waiting period.
Proceed as follows for the production and application:
- mix one cup of fresh, low-fat milk with three cups of water
- alternatively mix whey in a ratio of 1:1
- Pour the mixture into a spray bottle
- Spray plants dripping wet once a day
- After about a week the fungus should be dead
- only use freshly prepared
fungicides
The market offers a wide range of fungicides, both biodegradable and with chemical ingredients. The latter is not recommended as it involves treating food and making it inedible for at least a year. But even with ecological products, you have to pay close attention to the ingredients, because even if they are named as suitable for vegetable plants, a waiting period may be necessary. Therefore, fighting fungal infections in cucumbers with home remedies is always the better choice and only resorting to fungicides if the stock is threatened over a large area and rapid control is required.
pests
Greenhouse Pests
The typical pests affecting cucumbers grown in greenhouses are one particular species. If these are seen or even suspected, immediate action is required to prevent the affected plant from dying and to prevent widespread spread to the soil to avoid additional vegetation.
spider mites
These pests are difficult to see with the naked eye because of their small bodies, which can measure up to a maximum of one millimeter. Red eyes can be spotted with a magnifying glass, as well as their eight legs. Depending on the season and temperatures, they have body colors of green, orange or reddish brown. They feel particularly comfortable in dry climate conditions. In a warm greenhouse, they will colonize cucumber plants all year round if you let them. The damage usually looks like this:
- small bright spots on the leaves
- Formation of fine webs on leaf axils and leaf edges
- brown spots appear
- after that the leaf turns completely yellow
- Leaf stock decreases continuously
countermeasures
pest control
If there is a parasite infestation, chemical products should generally be avoided in the vegetable plant. With almost the same effect, but much less harmful to health, are organic herbal remedies that contain, for example, so-called neem oil as the main ingredient. This lodges in the respiratory tract of spider mites and other pests, ultimately leading to death by asphyxiation. Neuendorff and BAYER, for example, offer these in their product range.
home remedies
Moisture application is even more optimal than BIO fungicides, but with a longer effect.
- Shower plants with high water pressure
- Wrap individual plants in plastic wrap while they are dripping wet
- If an entire table is infested, pull plastic film over it completely
- In any case, make sure that it is reasonably airtight
- Keep foil seal for about three to four days - DO NOT OPEN!
- then examine the plants carefully for any remaining spider mites
- repeat the process if necessary
beneficials
Effective against spider mites and many other pests is the use of beneficial insects. Ladybugs, in particular, consume vast quantities of countless types of mites every day and, depending on the number of beetles, can even rid large stands of these parasites within a few days.
TIP: By the way, you can easily get beneficial insects from a well-stocked garden store. This saves you a lot of time for luring the animals and you can start fighting them correspondingly faster.
outdoor
Since cucumbers outdoors are exposed to different weather conditions than cucumbers in a greenhouse, they show typical outdoor diseases or pests, such as the following three in particular:
infections
Cucumber powdery mildew and downy mildew
As already described in the “Greenhouse Infections” section, powdery mildew and downy mildew are also a serious problem for outdoor cucumbers. The fungal infestation manifests itself in the same way as in the greenhouse and can also be combated with appropriate organic pesticides or, even better, with appropriate home remedies with whey or low-fat milk.
cucumber mosaic virus
This virus usually enters vegetable gardens via seeds and weeds, where it is mostly spread via garden and cutting tools and via aphids. He mainly prefers cucumbers and pumpkins, but also takes numerous other plant species. The name is based on the typical mosaic appearance that it causes on the cucumbers or the fruit. Although the virus cannot be transmitted to humans, the cucumber plants affected by this virus are not approved for sale in Germany.
Other identifying features include:
- Sheet deformations and compressions
- young leaf foliage shows yellow spots
- older leaf foliage turns light yellow
- leaves wither
- Cucumbers take on unusual shapes
- restricted growth behavior
Combat:
If the cucumber mosaic virus is recognized as such, infected specimens must be disposed of immediately. It is advisable to separate the cucumbers that have already grown from neighboring plants and throw them in the household waste. In addition, virus-free specimens in the immediate vicinity should be provided with organic green manure and an extra portion of magnesium to strengthen their immune system. A new planting in the same place should only be done after a large-scale soil change.
aphids
Aphids are typical of outdoor cucumber plantations and less common in greenhouses. They sneak in there only occasionally and mostly only during the seasons when they are looking for warmth from the cool outside temperatures. Their body usually reaches a maximum of three millimeters in length, with some specimens also being up to eight millimeters in size. Depending on the species, they are green, yellowish or brown in color and usually gather in colonies on the stems. Classic signs of an aphid infestation are the following.
- crippled leaves
- sticky leaf coating (honeydew)
- yellow leaves falling off
Combat:
The same methods with neem oil or beneficial insects can be used as control measures as described for parasites in the greenhouse. Only when using an effective home remedy against aphids does a spray solution made from milk provide a quick solution to the problem. Proceed as follows during preparation and use.
- Mix 200 milliliters of water and 100 milliliters of milk
- Pour the solution into a spray bottle
- spray affected cucumber plants dripping wet from all sides
- Don't forget the leaf bases, stems, shoots and undersides of the leaves
- Apply solution once a day
- After about four days, the aphids should be gone
- always use fresh milk
Conclusion
At the latest when yellow leaves or the first yellow discoloration on the leaf of a cucumber become noticeable, there is usually a serious illness behind it, a pest infestation or it is a sign of incorrect care or poor housing conditions. In any case, the result is usually the death of the plant if no action is taken quickly. With the help of this guide you will be able to identify the problem with certainty so that you can react correctly and, above all, protect other plants nearby.