Causes of Wheat Yellow Leaf Disease and Its Treatment Methods with Medication

After the beginning of spring, wheat leaves show varying degrees of yellowing, commonly known as wheat yellow leaf disease. Symptoms generally begin to appear at the end of February and the beginning of March. So what medicine should be sprayed for wheat yellow leaf disease? What causes the yellowing? How should it be prevented and controlled?

Wheat yellow leaf disease is a soil-borne viral disease, namely wheat yellow mosaic virus disease, also known as wheat spindle streak mosaic disease. The disease spreads mainly through infected soil, diseased root residues, and water flow from diseased fields, and can also be transmitted by sap rubbing inoculation. The natural transmission vector of wheat yellow mosaic virus is Polymyxa graminis. The disease infects during the autumn seedling stage but shows no symptoms; it begins to develop when the wheat seedlings turn green the following year. The suitable air temperature for disease development is 5-15 degrees C, and when the soil temperature exceeds 20 degrees C the disease stops developing.

After wheat is infected, the stages of turning green, jointing, heading and maturity are delayed, the plants are dwarfed, the ear-bearing rate is low, the ears are small and the grains are shriveled, generally causing a yield reduction of 10-30 percent, and in severe cases a reduction of more than 50 percent or even total crop failure. This disease spreads extremely quickly; from scattered cases to patchy death takes only 3-4 days. Therefore, after a cold wave, wheat is in a “weakened” stage with poor immune levels, and as temperatures gradually rise, the pathogens hidden in the soil begin to invade at suitable temperatures. If the duration of disease-favorable temperatures is too long, the probability of wheat developing the disease greatly increases, creating a huge risk of yield reduction.

There are many causes of wheat yellow leaf disease, mainly the following situations:

1. Drought and lack of soil moisture

When the subsoil moisture is insufficient and sowing is done by seizing whatever moisture is available, the water that the wheat root system absorbs from the soil is difficult to compensate for consumption, affecting growth and development and causing leaves to turn yellow, and in severe cases to die. In the field, the entire wheat field turns yellow rather uniformly, tillering is slow to emerge, growth is slow or stagnant, new leaves are short and small, and roots are small and thin. For management, 7-8 kg of urea per mu can be applied in combination with watering.

2. Soil tending toward acidity

At present, farmland generally uses excessive chemical fertilizers, causing the soil to tend toward acidity. Acidic soil causes the root system to turn black, reducing its ability to absorb water and nutrients, which in turn causes wheat seedlings to turn yellow. You can apply 50-70 kg of quicklime or 50-100 kg of plant ash per mu to neutralize soil acidity.

3. Incomplete straw crushing or insufficient plow layer when returning straw to the field

Returning straw to the field can improve the soil and build up soil fertility. If the plow layer is less than 20 cm when returning straw to the field, and the returned straw is not thoroughly crushed, the wheat root system after emergence sits on the loose straw, becomes suspended, and finds it difficult to absorb nutrients from the soil, causing the wheat seedlings to turn yellow. You can water to firm the soil and apply additional nitrogen fertilizer to accelerate straw decomposition, and at the same time allow the seedling root system to fully penetrate downward. At the same time, when preparing the land, it is recommended to crush thoroughly and deepen the plowing and deep turning; deep plowing should be carried out once every 3 years, with a depth of 25 cm.

4. Nutrient deficiency

Deficiency of nitrogen, phosphorus, potassium, calcium, iron, magnesium and other elements in wheat can all cause yellow leaves at the wheat seedling stage. The more common ones are nitrogen deficiency and phosphorus deficiency. When wheat is yellow due to nitrogen deficiency, the plants are short and weak, with few and weak tillers, and the seedling leaves then turn yellow. About 5 kg of urea per mu can be applied as a top dressing during the green-turning stage, and another 12-15 kg of urea per mu can be applied as a top dressing during the standing-up or jointing stage. When wheat is yellow due to phosphorus deficiency, it shows very few secondary roots, few tillers, dark green leaf color and yellow leaf tips. At the same time, yellowing of wheat due to phosphorus deficiency can also lead to small ears and few grains, a decrease in 1000-grain weight, and a serious impact on yield. You can apply 10 kg of diammonium phosphate or 45-50 kg of superphosphate per mu in furrows. For nutrient deficiency symptoms, once the diagnosis is accurate, the principle of supplementing whatever is lacking can be followed, using soil application or foliar spraying methods to supplement.

5. Excessive wheat sowing density

High wheat sowing density affects wheat photosynthesis, and competition for water and fertilizer becomes intense, which in turn leads to yellow, weak seedlings. Therefore, sowing should be done in appropriate amounts according to the season and temperature.

6. Continuous low temperatures and freezing damage

Continuous low temperatures and few sunlight hours make the overall wheat seedling condition relatively weak, and the effects of low-temperature freezing damage show symptoms of yellow leaves. Management should be strengthened when a cold wave arrives, and foliar fertilizer should be sprayed.

7. Causes related to pests and diseases

Underground pests, wheat aphids, red spiders and other pests can all cause wheat seedlings to turn yellow. For aphids, 5 percent imidacloprid 1000-1500 times solution can be used for control; for red spiders, 1.8 percent abamectin 3000 times solution can be used for control; for underground pests, 48 percent chlorpyrifos emulsifiable concentrate 1000-1500 times solution or 40 percent phoxim emulsifiable concentrate 1000 times solution can be sprayed and drenched at the roots.

The main wheat diseases are sheath blight, take-all and root rot. They are all fungal diseases, and all can show yellow leaves in the early stages, but the sites where the lesions occur and the shapes of the lesions differ. Sheath blight mainly damages the leaf sheath; take-all mainly damages the stem base and roots; root rot occurs only on the roots. They are all diseases transmitted through the soil, and tebuconazole and propiconazole can control all three diseases at the same time.

8. Herbicide damage

The most common is yellow wheat seedlings caused by herbicide damage. Regulators, foliar fertilizers or detoxifying agents should be sprayed promptly to stimulate wheat seedling growth and reduce herbicide damage. You can also combine this with one irrigation and apply additional tillering fertilizer, which can likewise help alleviate herbicide damage.

9. Effects of adverse climate

Yellow leaves are caused by meteorological factors such as low temperatures, strong winds and frost. Their occurrence is often closely linked to weather changes, covers a relatively large area, and appears fairly uniformly across the whole field. When symptoms are mild, no control is needed; in severe cases, quick-acting fertilizer can be applied as a top dressing to promote growth.