Onions are a vegetable crop that literally grows in every vegetable garden, and sooner or later almost every gardener faces the problem of onion leaves turning yellow.
There are many reasons for this phenomenon, but only one can be perceived quite calmly by gardeners — when the bulb matures, the feathers turn yellow and fall off. All other causes of yellowing onion shoots are unacceptable and must be understood and dealt with before harvest.
But before we address those causes and start learning how to eliminate them, let’s talk about how to protect your onions from leaf yellowing as reliably as possible.
SIMPLE RULES TO PREVENT ONION LEAVES TURNING YELLOW
Therefore, in order to keep Onion leaves in a healthy color before harvest, it is necessary to treat the plots correctly, to water them in time, to use modern means to control pests and diseases and to consider other rules of their cultivation.
1. Observe crop rotation system
Remember that it is not recommended to plant onions in the same place more than once every four years, otherwise, pests and diseases will accumulate on the plot and onions will consume enough nutrients from the soil.
2. Fertilize correctly
Fertilizer needs to be applied correctly and in optimal amounts, remembering that neither lack nor excess fertilizer will bring any benefit.
3. Water properly
Onions like to be watered moderately, but let’s just say, constantly. You shouldn’t let the soil get too dry or over-water it.
4. Don’t ignore the plot
If you find that Onion leaves have started to turn yellow, it is best to take them out and burn them. This way you can stop the spread of infection or pests.
5. Dig deeper
It is recommended to dig the soil of the Onion to the full snag of the spade, turning it with the layers to minimize the number of harmful microorganisms in the soil.
Arguably, these are the most important measures to prevent Onion leaves from turning yellow, but there are cases where these measures do not help and the onions still turn yellow. What are the reasons and what can be done?
As we have already mentioned, there are many reasons for Onion leaves turning yellow, it can be the manifestation of pests and diseases, improper tillage techniques, the influence of weather, or lack of nitrogen in the soil.
PESTS THAT CAUSE ONION LEAVES TURNING YELLOW
There are quite a few pests that cause onions to turn yellow: Leek moth, Onion thrips, onion spiders, Ditylenchus dipsaci, and of course, the onion fly.
1. Leek moth
The Leek moth is usually most active when the weather is hot when there is little rain, and when the soil is dry. This is when the Leek moth butterfly appears, not much different from the domestic moths we are all familiar with. Its larvae hatch from the eggs laid by the moths and cause damage.
The presence of the larvae leads to the fact that first, the tips of the onion leaves begin to dry out, and then the entire feathers dry out.
To know how to control the Leek moth, you need to understand its biological characteristics. For example, the egg-laying apparatus of the Leek moth brings the part near the bulb into the soil. The caterpillars that hatch from the eggs have a light yellow body color and are about 0.4inch (1cm) long.
After hatching, they move to the feathers, enter them and begin to nibble on the tissue from the inside, which causes the feathers to turn yellow and wilt.
Before using insecticides, you can try traditional methods to control the Leek moth: treat the feathers and surrounding soil with well-dispersed cooking ash and tobacco (possibly directly with cigarettes), or spray the soil and plants with a garlic infusion (a few cloves per 0.26 Gal of water).
2. Onion thrips
Onion thrips, or Onion thrips, also causes Onion leaves to turn yellow. onion thrips are smaller than aphids and feeds on the same cell sap as they do, causing onion leaves to turn yellow and dry out.
Onion thrips overwinters in the soil and in the bulbs left for the next year’s planting, so even if you plant your seedlings in an area that is perfect in every way and follow all the agricultural techniques, onions can still suffer from this pest.
To prevent Onion thrips from coming to your area without getting with the sowing, you need to drop the sowings in water at a temperature of 110–120°F a quarter of an hour before planting and then soak them in cold water for 10 minutes.
If the pests are already evident, then folk remedies are unlikely to help, and then you need to use an insecticide. To control Onion thrips, you must use an insecticide that follows strict instructions.
3. Ceutorhynchus suturalis
Its activity is another reason why onion leaves may turn yellow. the larvae of Ceutorhynchus suturalis literally eat Onion leaves, which first change color to light, then turn yellow, wilt, and die. If this pest is not controlled, it can kill most onion plantations.
The most frustrating part is that this beetle moves quickly and even if you take into account crop rotation, fertilization, and watering, and take good care of the soil, it can still appear on your plots and migrate from neighboring plots.
To minimize the risk of beetles on your plots, you need to dig up the soil, remove and burn plant debris, and observe crop rotations. The soil around the beds should be sprinkled with wood ash or mustard or pepper, which will repel the beetles.
If the beetles do not appear in large numbers, these individuals are likely to be picked up manually. However, if there are many pests, it is necessary to apply the insecticide strictly according to the instructions on the package. Earlier, medicated biocide (an organophosphorus compound used as an insecticide) helped to be effective, but later it was banned and you need to look for other authorized analogs.
4. Ditylenchus dipsaci
Another cause of the atypical color of onion leaves is the stem nematode. Basically, it is a small worm that penetrates the bulb and causes cracks at the bottom of the head, it starts to rot, the leaves plate — yellow and die.
The nematode is usually very small, no more than 1.5 mm, but the damage it causes can be enormous. Once the nematode is introduced, crop rotation may not help; it can live in the soil for up to 10 years, sometimes even longer.
To exclude nematodes through onion seedlings, they should be placed in water heated to 113°F (45°C) above zero for a quarter of an hour, then in saltwater — for half an hour — before planting.
Gardeners say that if nematodes are present in the soil, infusion of marigold solution can help get rid of it — 4–6Lb of nutrients per bucket of water infusion of marigolds is the standard for 20–30 square feet of soil.
There are also insecticides for fighting complex pests.
5. Delia Antiqua (onion fly)
Almost the most common pest of onions, its larvae are happy to eat any variety of onions. You can usually tell that it’s the onion fly that’s causing the yellow feathers by the way the leaves deteriorate: they first turn yellow and then shrivel up.
To prevent Delia Antiqua (onion fly), alternate onion beds with carrot beds. The smell of carrots repels Delia Antiqua (onion fly) and the smell of onions repels carrot flies — a double benefit.
If the number of individuals is small and they are not yet very harmful, then the affected plants can be treated with a solution of salt and ammonia alcohol, but remember that salt is dangerous for the soil and it is best not to carry out this treatment more than once a season.
To obtain this solution, you need to dissolve 200 grams of salt in a bucket of water (no more!) and one tablespoon of ammonia alcohol. The solution can then be applied to the soil and the affected plants, using this amount per 50 square feet of the seedbed.
A mixture of ash and tobacco, pepper and mustard in equal proportions is more beneficial to the soil but less effective against pests. 25–30 grams of these substances are needed per 11 square feet.
If folk remedies do not help, which often happens, you will need to use insecticides.
In addition to insects, bacterial rot, wilt, rust and a number of other less common diseases can cause onion leaves to turn yellow. Usually, diseases on onions are fungal or bacterial and can be introduced on-site with the planting material or can emerge through insects.
With this in mind, when planting onion seeds, they should be thoroughly inspected to remove any bulbs that show signs of insect infestation. The remaining bulbs should be placed in water at 113°F (45°C) for 10–15 minutes and then soaked in brine (one tablespoon per 300 g of water) for 8–10 minutes.
Don’t forget that diseases are more active in soil with too much moisture and in shady areas, so water your onions frequently, but moderately, and choose a level and well-lit area under them.
In addition, diseases can be spread by pets, so even if there are few pests in the area, you still need to deal with them.
If you don’t want to use chemicals to combat the disease, then at least treat the affected plants with a copper-containing preparation: Bordeaux mixture, etc. If this is not appropriate in your area either, then remove the affected plants and do not allow the disease to spread further.
ONION BED CARE MISCONCEPTIONS
Any plant can suffer from improper care, and onions are no exception here. The most common mistakes are growing onions in the same place for many years, fertilizing and watering them improperly.
1. Little or too much nitrogen in the soil
Onions are one of the most sensitive vegetables to nitrogen. onion leaves can turn yellow from lack of nitrogen and too much nitrogen, so you must be careful to add trace elements.
If the feathers have yellowed, dig up a bulb. If you find no signs of pest infestation and the bulb looks intact, chances are that the feathers are yellowing due to a lack of nitrogen.
To replenish it, foliage feed: dissolve 45–55 grams of ammonium nitrate in a bucket of water enough and apply the resulting solution to a few dozen square feet of onion beds.
As a rule, the onions of the season can be fertilized only a few times, the first time when new shoots appear, and the second time after 12–14 days. For this purpose you can use nitroaminophos, dissolving one tablespoon of fertilizer in a bucket of water, an amount sufficient for a 10-foot bed.
Due to the high nitrogen content in the soil, signs of decay will be evident on the dug-up bulbs. In this case, calcium superphosphate and potassium sulfate should be added to the soil.
A teaspoon of water is needed for each bucket, which is the standard for a bed of several dozen square feet. After a week, you can loosen the soil and add 100–150 grams of wood ash per 11 square feet.
Applying organic matter under onions is not recommended, especially in the summer when it is wet and cold, as this can lead to fungal disease outbreaks.
2. Incorrectly watering onions
If onions are underwatered or overwatered, their feathers will begin to turn yellow. Onions should be watered daily, preferably in the evening, with settled water at room temperature. A bucket of water every 11 square feet is sufficient, but only if it is not raining and the weather is hot.
If it rains lightly during the day, you should not water either. If it does not rain, but it is cold 68°F (20°C), then the watering rate can be halved.
As you have learned, there are quite a few reasons why Onion leaves start to turn yellow. Before resorting to chemical methods, assess the condition of the onion, try to find pests, assess the soil condition, etc., before deciding whether to resort to chemical methods.
Sometimes, simply removing some atypical plants from the plot and following some simple rules of care can save the situation. And don’t forget about prevention, especially if you are sowing unfamiliar material.
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