In the process of caring for cucumber seedlings, gardeners may notice that the tops of some plants lose their rich green color, and the vine itself becomes lethargic over time. Why do cucumber leaves turn pale, and what could this effect be associated with - the quality of soil fertilizers, the frequency of watering, or an unsuccessfully chosen seed variety?
Why do cucumber leaves turn pale?
The main reason for pale foliage in cucumbers is a lack or, on the contrary, an excess of certain micro- and macroelements.In most cases, an imbalance of nutrients entails a deterioration in the growth and presentation of cucumbers, but after taking appropriate measures, the fruiting of damaged bushes is completely restored.
The blanching of cucumber leaves occurs when there is a lack of the following elements:
- Nitrogen. The deficiency of this substance is reflected in the development of seedlings and modification of all elements of the tops - weak formation of lateral shoots and leaves, falling of inflorescences without the formation of green ovaries, but the most significant point is the spread of yellowness on mature leaves of seedlings. If you do not apply nitrogen fertilizing in a timely manner, the top leaves begin to turn yellow and, last of all, those that are located above the first two shoots. The lack of nitrogen in cucumber seedlings can be differentiated by the peculiar pattern of pale yellowness covering the leaves - the veins remain green until the last moment and lose color before falling off.
- A decrease in photosynthetic activity due to iron deficiency is immediately detected in the form of a loss of green color in young plants. Further inaction is reflected in the appearance of a dry edge along the perimeter of the damaged leaves, and the “washing out” of the intense green color transfers to mature leaves. The yield of cucumbers does not suffer from iron deficiency.
- Calcium. Already formed leaves almost do not react to a lack of calcium, but young leaves that are released turn out to be very small and have an unnaturally dark shade of green. After a short time, the new leaves begin to lose color along the edges and from the center. The pallor spreads in stripes over the surface of the leaf, without affecting the veins, then these areas die off, and the damaged edges bend downwards.
- Light green and then almost colorless tops of the leaves, with parallel wilting of the entire plant, indicate a lack of copper.
- The fact that the leaves on the plant first began to turn yellow, and then acquire a brownish tint and shrink, will indicate a potassium deficiency. The presence of a large amount of peat in the soil composition will aggravate the progression of leaf damage due to potassium deficiency.
- Phosphorus starvation stops the growth of a cucumber bush - the vine stops stretching upward, and the leaves on it become small and hard, as if leathery. Soon the modified leaves become covered with pale green spots, similar to water stains, and fall off.
If the gardener is overly enthusiastic about boron-containing fertilizers, he or she runs the risk of causing irreversible changes in the plantings and the destruction of the entire crop. The first sign that you should immediately stop using boron is that the mature leaves turn a deep yellow color around the edges. Soon the yellowness spreads towards the center in the form of spots that begin to dry out and wrinkle the leaf. Feeding the plant with any type of fertilizer should be temporarily stopped.
Why cucumber seedlings lose their green color - other reasons
What to do if the leaves of cucumbers become pale during the period of active growth and development of the bush? First of all, determine the cause, and then act in such a way as not to reduce the fruiting of plants:
- Planting cucumbers in open ground too early. If you transfer cucumbers to a permanent growing place when the soil has not warmed up to the required temperatures, the leaves on the seedlings may not only lighten, but also fall off. The only measure to eliminate the problem is to make a mobile tunnel greenhouse on arched stands directly above the bed until the earth warms up enough.
- Excessive amount of organic matter in fertilizer. Fertilizers such as chicken manure should be temporarily abandoned. How to feed cucumbers in this case? It is best to use neutral mineral fertilizers - ash or bread solutions.
- Lack of moisture in the soil or cold watering. The reason for the paleness of plants may lie in irregular watering or freezing of the roots under the influence of cold tap water. The situation can be corrected by setting an exact watering schedule and using insulated and settled water for these purposes.
- Excessive number of ovaries on the lashes. Green fruit formations drain vitality from the plant, causing the seedlings to become lethargic and the entire plant to lose color intensity. The number of fruit units should be reduced, distributing them evenly among the vines, decreasing towards the top.
Pinching the ovaries is a very important point in the formation of a fruit bush. On average, it is believed that one plant should not have more than 23 ovaries at the same time, otherwise it will not cope with the load and will begin to turn pale.
Causes of leaf blanching - seedling diseases
Seedling diseases leading to loss of color in the green part of the plant occur more often in cucumbers in a greenhouse, since fungal and viral infections spread faster in a stuffy and humid atmosphere. Caring for plants in a greenhouse is also complicated by the fact that it is necessary to monitor a constant flow of fresh air.
There are five most common cucumber diseases seedlings that cause plant leaves to turn pale:
- Mosaic disease. With this disease, which affects cucumbers both in greenhouses and in open ground, the leaves of cucumber seedlings become covered with a spotted pattern of yellowish or pale color.Then the cucumber leaves turn up at the edges and shrink. The disease spreads when infected seed is planted or when diseased plants come into contact with healthy ones. It is impossible to heal the damaged part. If the area covered by the disease is not large enough, the damaged areas are removed, and the entire plant is irrigated with milk of 1% fat content. Severely affected cucumber seedlings should be removed and the soil disinfected.
- Powdery mildew is a whitish, lime-like coating that covers the green leaves of cucumbers, mostly in open ground. The disease becomes active in damp weather with strong wind, watering or rain, and spreads not only to the leaves of the plant, but also to the stem of the vine and even to nearby crops. If the leaves of cucumbers characteristically turn pale in greenhouse conditions, it means that excess moisture or poor soil treatment before planting is to blame. Plants are healed with a composition of mullein and urea, taken in a ratio of 1:50.
- Downy mildew. The principle of covering a leaf with a coating during peronosporosis resembles the signs of powdery mildew, only the color of the coating is not white, but yellowish on the upper leaf plate and grayish on the lower one. When the gardener is inactive, the spots typically darken, and the leaf becomes deformed and dries out. Causes of the disease: firstly, excessive watering, secondly, unstable air temperatures or irrigation water. The fight against fungus includes: limiting soil moisture up to complete cessation of watering, removing damaged leaves and spraying the entire cucumber with Oxyx solution (two tablets per bucket of water).
- Root rot.The fungus spreads to the plant from the roots, and first covers the lower tier of leaves with a pale yellow color, and then moves to the subsequent ones. Following the defeat of the leaves, the entire vine begins to die off, and the plant dies - rots at the root. The causes of the disease are excessive watering, thick planting, in which fungal spores pass from a diseased cucumber to a healthy one, as well as high humidity and stuffiness in the greenhouse. Pale leaves should be removed immediately, and diseased plants should be sprayed with Infinito 61 SC solution.
- White rot is another reason why the leaves on cucumbers have turned pale. The fungus can be found under the lower vines of cucumbers, closer to the roots - jelly-like wet spots appear there, which are later covered with white fluff. White rot quickly spreads throughout the vine, affecting the stem and most of the leaves. Green ovaries can also turn white, especially those hanging on the lower vines. The fight against rot begins with removing damaged areas of the plant that have turned white, and, if the affected area is small, sprinkling the cucumber bush with a dry mixture of chalk and lime. Plants completely affected by the disease will have to be removed.
In close plantings typical of greenhouse cultivation, not only diseased plants are inspected and treated with solutions, but also all those in the immediate vicinity.
In the case when the disease is soil-borne, that is, all types of fungal infections, special attention is paid to disinfecting the soil at the site of the removed bush.
