Yellow leaves on your cucumber plant are a sign of poor care, disease or pest infestation. Once you know the various causes, you can counteract the problem with the appropriate solutions.

In a nutshell

  • yellow leaves can result from a lack of water or excess
  • a lack of nutrients can lead to yellowing of the leaves
  • Diseases are caused by fungi and viruses
  • Verticillium wilt is especially dangerous, which can endanger the entire cucumber crop
  • Among the most common pests on cucumber plants are aphids and spider mites

Watered wrong

If you discover yellow leaves on your cucumber plant, you should always check the substrate at the location first. One of the most common causes of leaf yellowing on Cucumis sativus is improper watering. While overwatering rarely results in yellow leaves, these are a direct indication of a lack of water. Check the substrate for dryness with your thumb. If it's too dry, you'll need to add water to rehydrate the cucumber plant. Only use low-lime water for this:

  • rainwater
  • filter water
  • stagnant water

The plants are watered daily in the morning so that not too much moisture evaporates. If the location is constantly struggling with drought, mulch. The mulch layer protects the soil from drying out.

Notice: Be careful not to pour the water over the leaves as this can also cause yellowing. Only water the substrate.

Missing nutrients

Cucumbers are among the heavy consumers and must therefore be supplied with sufficient nutrients. If they lack food, this is reflected in yellowing of the foliage and poor vitality of the plant. Ideal fertilizers for cucumbers are organic long-term fertilizers that are already incorporated during planting. Are suitable:

  • well-ripened compost
  • rotted horse or cattle manure

powdery mildew

Yellow leaves on your cucumber plant are often caused by fungal infections, especially powdery mildew (Erysiphaceae). The causes of this are spores that get onto the cucumbers through spray water, wind or damp fallen leaves and spread there. Powdery mildew can be recognized by the following symptoms:

left: powdery mildew right: downy mildew
  • white coating on leaf surface
  • powdery
  • yellow discolouration occurs
  • leaves dry up
  • Leaves curl up

In the worst case, the entire cucumber plant can die. Especially in warm weather phases, powdery mildew should not be underestimated. For this reason, you have to use your own sprays and use them to wipe off the mildew. The following mixtures are suitable:

  • 1 part milk and 2 parts water
  • water and a few drops of washing-up liquid
  • 1 part baking soda and 10 parts water

Mix up one of these remedies and apply it at regular intervals. As an alternative to these, you can make a decoction of field horsetail or nettles and use it diluted.

Tip: Downy mildew (Peronosporales) also occurs in cucumbers and shows up on the underside of the leaf with a white-greyish to brown fungal coating and yellowed, blotchy leaves. You can use the same solutions as for powdery mildew to combat downy mildew, which tends to increase in damp weather.

cucumber mosaic virus

The cucumber mosaic virus (cucumovirus) causes leaf discoloration that resembles a mosaic, as the name suggests. The leaves are covered in yellow spots and will wilt until you fight the virus. If the infestation is advanced, warts form on the skin of the fruit and they no longer mature properly. Since the virus is transmitted by aphids, you must remove them, as well as the yellowed leaves and infected fruits of the cucumber plant. As with other diseases, you should never compost the plant parts, as this could allow viruses and fungi to spread again in the garden. The residual waste is better suited for disposal.

Notice: Leaf spot disease can be controlled in the same way as cucumber mosaic virus, but has different symptoms. Individual leaves turn yellow locally, then brownish and finally they die.

Source: DieterO, Cucumber Mosaic Virus, Edited from Plantopedia, CC0 1.0

Verticillium wilt

One of the most dangerous fungal diseases of the cucumber plant is Verticillium wilt, which is caused by the fungi of the same name. Unfortunately, there is nothing you can do about Verticillium wilt, as the fungi can spread too quickly and destroy your entire crop. For this reason, you must sort out and dispose of infested specimens. If there are still fruits on these plants, you must also dispose of them, as they are inedible. If your plants are affected by wilt, you can tell by the following symptoms:

  • Leaves turn light green
  • initially affects lower leaves
  • Leaves turn yellow
  • Infestation spreads to the entire plant
  • leaves wither
  • die off
  • Plant weakens to the point of death

The symptoms are more severe in the heat. The fungi are introduced either via contaminated tools or plants.

Tip: Do not use the location of infested specimens for susceptible growth for a period of ten years. The Verticillium fungi can remain in the soil during this period.

aphids

As described above, aphids are the cause of cucumber mosaic virus. The pests are often found in larger colonies on the cucumber plants and can cause yellow leaves even without transmission of the cucumber mosaic virus. Aphids can appear suddenly on your Cucumis sativus plants, making them a dangerous pest. In contrast to other pests, care errors are not the only reason for colonization. Symptoms of an aphid infestation are:

  • Aphids recognizable on cucumber plants
  • Foliage stunted
  • yellow leaves
  • honeydew visible

Since Aphidoidea often attract ants, you have to reckon with them as well. Luckily, there are plenty of home remedies you can use to get rid of lice. If you do not want to use beneficial insects such as lacewings, ladybugs or gall midges, you still have sprays based on the following:

  • milk
  • neem oil

While you can spray the neem oil directly on the lice, you need to mix the milk with low-lime water in a 1:2 ratio. Treat your cucumber plants with the sprays until the aphids are no longer present. Remove affected shoots and leaves.

spider mites

Spider mites are also common cucumber pests, the damage pattern of which is similar to that of aphids. The most striking symptom are the webs, reminiscent of cobwebs, that appear between the leaves and stems. The causes of an infestation with the Tetranychidae are varied:

Spider mite infestation
  • low humidity
  • planted too tight
  • lack of water

Especially cucumber plants in the greenhouse have to struggle with the annoying insects. Effective solutions include spraying with neem oil, using a strong jet of water, and removing the affected leaves and shoots. You can prevent spider mites by not letting the plants dry out. That would encourage another infestation.

frequently asked Questions

Can removing the leaves stop the spread?

No, removing the yellow leaves will not protect the remaining foliage from yellowing. You need to fix the problem to get the cucumbers back on their feet. It only makes sense to cut off the leaves if there is a pest infestation or a disease. So the fungi and insects cannot spread so quickly.

How can fungal diseases be prevented?

One of the most important points that is often overlooked is that the planting distance is too small. Cucumber plants should never be planted too close together, otherwise not enough fresh air can reach the foliage. This in turn promotes the spread of fungi and associated diseases. There should always be a distance of 40 centimeters between the plants. Optionally, you can rely on one of the numerous F1 varieties that have better resistance to fungal diseases.

How Does Humidity Affect Leaves?

If the humidity in the greenhouse is too low, the cucumber plant can develop yellow leaves despite sufficient watering. As they are generally sensitive to prolonged drought, they yellow. If this is the case, you must carefully increase the humidity until you see an improvement. A value of at least 60 to 70 percent is aimed for.

What should be considered when cultivating in a greenhouse?

Be sure to check that the cucumber plants are not exposed to cool drafts. Ventilate during the day and close the greenhouse at night.

Category:

Vegetable garden