Seedlings can change color for various reasons, healthy strong seedlings are the key to a future excellent harvest. That is why every gardener is very attentive to it, so responsibly follows the rules of watering, lighting, fertilizing. But sometimes something “goes wrong” and young plants clearly show signs of ill health.
Kiev. Ukraine. Ukraine Gate – April 05, 2021 – Agriculture
Today we will talk about those cases when the green shoots suddenly change color or are covered with spots. What is the reason and how to fix the situation? We understand together the possible scenarios.
Seedlings turn yellow
The most common variant of “trouble” with seedlings – is that it suddenly turned yellow en masse.
The good news is that in most cases this condition is reversible and without consequences. The bad news is that yellowing of leaves in seedlings can occur for a variety of reasons, and to correct the situation you will have to find out which ones:
too bright lighting (direct sunlight);
excess nitrogen (too abundant application of organic fertilizers to the soil before planting);
improper watering/lack of watering;
increased soil acidity;
potassium deficiency (seedlings turn yellow from the top);
early stages of some diseases – fusarium wilt, chlorosis, or downy mildew.
To avoid yellowing of seedling leaves, protect it from direct sunlight, ensure a stable daytime temperature, not higher than 25 ° C, and night, not lower than 15 ° C, water it no more than twice a week in a tray and only with warm water.
Seedlings should be planted in the soil only after a week of adaptation and try to maintain conditions (temperature and humidity) in the new place, which are not very different from those to which it is accustomed.
If the edges of the leaf blades become brown and they die, timely application of potassium fertilizer (potassium sulfate, etc.) should help.
Lack of nitrogen in the early stages is also characterized by slow growth, reduced size, and a pronounced “fading” of the seedling leaves, which turn yellow below. Seedlings can be helped in this case by easily soluble nitrogen fertilizers (ammonium nitrate, urea, etc).
Seedlings turn black
If the young weak shoots turn black and thin the lower part of the stem, the lower leaves turn yellow and lose turgor, as a result of which the seedlings collapse and die – these are signs of blackleg, a dangerous disease caused by fungi and some bacteria.
Blackening and rot of the root neck are contributed by many factors:
the presence of pathogens in the soil;
infected seed;
excess moisture and heat;
thickened crops;
lack of ventilation;
sharp fluctuations in temperature.
Therefore, to prevent the appearance of blackleg, it is first necessary to disinfect soils and seeds. If you are not sure about the quality of the soil, it is not superfluous to add to the soil a biological product for the prevention of root infections Trichodermin (5 g per 5 liters of soil).
It is very important to adhere to the timing of sowing, to prevent violations of humidity, temperature, and light during the cultivation of seedlings, as well as to avoid thickening of plantings.
You should not immediately try to correct this situation. Check – if, in addition to darkening the stems, the plants have no other signs of disease, then perhaps they simply belong to the species or varieties in which dark stems of seedlings are the norm (for example, red cabbage).
If the disease occurs, it is necessary to replace or disinfect the soil with fungicides (Phytosporin, 1% Bordeaux mixture or raspberry manganese solution), destroy affected plants, apply fertilizers that increase resistance to disease, establish irrigation systems and aeration for crops.
Seedlings turn red or blue
A red, blue, or reddish-purple tinge on the underside of seedling leaves or stems may indicate a serious lack of nitrogen, potassium, or phosphorus in the soil. At first, parts of the plant usually turn pale (yellow), and then painted in such unusual colors that it is often accompanied by growth retardation. This can be especially evident during cold rainy weather when the small roots do not have time to fully absorb the useful elements. The way out is timely fertilization.
Also, seedling stems can begin to darken (blue) due to temperature stress – for example, when the air in the greenhouse and the top centimeters of soil undercover have warmed up a bit, and in the depths of the soil is still cold. If the temperature does not equalize, the young plants may become noticeably weaker.
Seedlings turn white
The white plaque on the leaves of seedlings, which over time becomes denser, indicates that they are affected by powdery mildew. Subsequently, the affected plants change the shape of leaves and stems. Then the affected leaves dry completely and fall off.
Diseased plants should be sprayed with 0.5% soda ash solution or the drug Skor. Such treatment will be required once a week for 2-4 weeks.
Seedlings are covered with spots
Spots of any shape, color, and size on the leaves of seedlings – most likely a sign of the disease.
For example, powdery mildew (downy mildew) is a fungal disease characterized by the appearance of grayish-yellow spots with a plaque on the lower leaves of seedlings.
Small brownish-black spots on cabbage leaves can be a sign of mosaic infection (viral disease) or Alternaria (black spot) – a fungal disease.
Yellow spots that grow over time may be evidence of progressive chlorosis – the presence of this disease is evidenced by the veins of the leaves, which remain green.
Drying gray and brown spots with black spots may indicate phimosis (dry rot).
Black concentric indented spots, which “grow” from small greens, can be an indicator of the presence of black ring spots.
How to deal with fungal and bacterial diseases?
Treat seeds and soil before sowing, strictly follow the cultivation techniques of plants and, if necessary, use appropriate drugs. Unfortunately, there are no effective remedies against viral diseases – damaged plants must be destroyed.
Sometimes spots on seedlings – a sign of lack of nutrients.
Thus, small white (rarely black) “marble” spots, which appear first on the tops of the lower leaves and then spread to the entire leaf blade, may indicate a lack of magnesium. Brown spots indicate a lack of potassium, blue-green – phosphorus, red – nitrogen.
In this case, the only way out – timely and balanced fertilization of plants.
Finally, some pests can leave stains on seedling leaves.
Thus, the rusty tomato mite is manifested by brown spots on the leaves, onion octopus, tobacco whitefly, bedbug-soldier, and watermelon aphids – yellow, thrips – silver or yellow stripes and strokes.
If you suspect the presence of pests, carefully inspect the plants and take certain measures if they are detected.
Do not forget about the basic measures for disease prevention and in general about the rules of cultivation of seedlings.
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Source: Ukrgate