Growers may recently notice that some wheat seedlings in the field are not looking right - leaf tips are drying up and leaves are turning yellow. What is causing this? Will it affect yield? Should pesticides be applied immediately?
Don't panic. Yellowing and tip burn in wheat are actually very common during cultivation, and there are many possible causes - both management issues and pests/diseases. Only by identifying the correct cause can you take the right measures.
This article breaks it down into two parts: first, find the cause; then, find the solution.
Part 1: Why Does Wheat Turn Yellow and Develop Tip Burn?
1. Lack of Water
As the farming saying goes, "Whether you get a harvest or not depends on water." This is absolutely true. The greening and jointing stages are when wheat grows fastest and has the greatest demand for water. If the field is dry during this period, wheat growth is inhibited, and yellowing and tip burn will appear.
This is especially true for wheat that was sown late, has weak growth, insufficient tillering, or has suffered from freezing damage - these plants are more prone to yellowing and tip burn.
2. Nutrient Deficiency
Wheat mainly needs nitrogen, phosphorus, and potassium, followed by trace elements such as zinc, iron, selenium, and copper. After the standing stage, wheat grows rapidly and consumes a lot of nutrients. If the supply of nitrogen, phosphorus, and potassium is insufficient, yellowing and tip burn will occur.
Nitrogen deficiency: Nitrogen is a key component of proteins and chlorophyll in wheat. When nitrogen is deficient, leaves turn yellow from the bottom up, leaf tips dry first, plants are short, tillering is reduced, and growth is weak. The greening and jointing stages are peak periods for nitrogen demand - if nitrogen is insufficient at this time, yellowing and tip burn will be very obvious.
Phosphorus deficiency: Phosphorus promotes root development and tillering and improves cold and drought resistance. When phosphorus is deficient, leaves are dark green or purple, leaf tips dry up, root development is poor, tillering is reduced, and maturity is delayed. Phosphorus deficiency before winter makes seedlings more vulnerable to freezing, and growth after greening is also poor.
Potassium deficiency: Potassium strengthens wheat stems and improves lodging resistance and disease resistance. When potassium is deficient, leaves begin to yellow from the tip and edges, gradually spreading toward the middle of the leaf. In severe cases, leaf tips dry up and die. The jointing to booting stage is the peak period for potassium demand - potassium deficiency at this time makes yellowing and tip burn particularly obvious.
In addition to nitrogen, phosphorus, and potassium, wheat also needs trace elements such as zinc, iron, selenium, and copper. Although the amounts required are small, deficiencies still cause problems.
Copper deficiency: Copper participates in the synthesis of various enzymes in wheat and is important for photosynthesis and respiration. When copper is deficient, leaf tips turn yellow and dry up, leaves become distorted, tillering increases but heading does not occur, or seed-setting rate is low after heading. This is an easily overlooked cause of yellowing and tip burn in wheat.
Zinc deficiency: Zinc affects auxin synthesis in wheat. When zinc is deficient, internodes shorten, leaves become smaller, leaf tips turn yellow, and plants are stunted.
Iron deficiency: Iron is essential for chlorophyll synthesis. When iron is deficient, new leaves turn yellow, leaf tips dry up, and in severe cases the entire leaf turns white.
Selenium deficiency: Although selenium is needed in extremely small amounts, it participates in the antioxidant process in wheat. When selenium is deficient, stress resistance declines, and leaves are prone to premature aging and yellowing.
The main reason for trace element deficiency in fields is that some growers only focus on high-efficiency chemical fertilizers and apply too little or no organic fertilizer. Long-term reliance on chemical fertilizers reduces soil organic matter, trace elements are not replenished, and soil structure deteriorates. Combined with continuous wheat planting, soil nutrients are continuously depleted, making nutrient deficiency problems increasingly prominent.
3. Improper Fertilization
Fertilization is a good thing, but the wrong method can cause problems. For example:
- Using only nitrogen fertilizer;
- Applying large amounts of fertilizer concentrated on leaf surfaces;
- Applying too much fertilizer when the field is dry.
These situations can easily cause fertilizer burn, leading to yellowing and tip burn. For wheat with good growth and excessive pre-winter fertilization, applying fertilizer too early or too much can also create excessive vegetative growth, making plants less resistant to pests and diseases and more prone to problems.
4. Herbicide/Pesticide Damage
Pesticides are often needed to control pests, diseases, and weeds. At normal concentrations, there is no impact on wheat growth, but excessive concentrations can cause pesticide damage. The main cause of pesticide damage is that growers do not mix solutions according to the concentrations specified in the instructions.
5. Pests and Diseases
As temperatures rise in spring, wheat enters the greening and jointing stages, and pests and diseases become increasingly active in the field. When pest numbers reach a certain level, or when diseases occur severely, wheat may develop yellowing and tip burn. Some pests and diseases have yellowing and tip burn as their main symptoms - for example, wheat yellow dwarf disease, rust disease, and wheat aphids.
6. Root Exposure
Wheat has a fibrous root system, mainly distributed in the 0–40 cm soil layer. Many farms now use straw return. If straw is unevenly distributed or buried too shallow, wheat roots may not contact the soil, resulting in root exposure. In this case, root growth is weak, and the ability to absorb water and nutrients is poor, leading to yellowing and tip burn in seedlings.
Part 2: How to Prevent and Control Yellowing and Tip Burn?
Prevention and control mainly involve three aspects: strengthening field management, scientific pesticide use, and pest/disease control.
1. Establish a Reasonable Tillage System
Soil is the foundation of wheat growth. Selecting fields with deep soil layers and good structure and establishing a reasonable tillage system are essential to keep wheat growing in a good soil environment.
During land preparation, achieve: early, deep, clean, thorough, firm, level, fine, and sufficient.
Pay special attention to straw return: control the amount returned, ensure proper depth, ensure even distribution, and press the soil promptly after return to avoid root exposure. Residual crops from the previous season and large soil clods should also be dealt with promptly, and field edges should be tilled properly as well.
2. Scientific Fertilization and Reasonable Irrigation
Wheat has different fertilizer and water requirements at different growth stages, and different fertility levels require different amounts of fertilizer and irrigation. Decisions should be based on the growth condition of wheat in the field and soil fertility.
Fertilization:
- Base fertilizer: Mainly organic fertilizer, combined with nitrogen, phosphorus, and potassium. Base fertilizer should be applied deeply and incorporated into the soil during land preparation - avoid surface broadcasting. Organic fertilizer must be fully decomposed, otherwise it can burn seedlings.
- Seed fertilizer: Mainly a small amount of chemical fertilizer such as urea. It should be separated from the seeds to avoid direct contact and prevent seed burn. When soil moisture is poor, seed fertilizer should be reduced or omitted.
- Top dressing: Divided into winter and spring applications. Before winter, mainly nitrogen fertilizer to promote tillering, cultivate strong seedlings, and enhance cold resistance. During winter, organic fertilizer is suitable to provide insulation, moisture conservation, and nutrients. After greening in spring, top dress according to seedling growth - weak seedlings can receive more, while vigorous seedlings should receive less or none to prevent excessive growth. The jointing stage is the peak period for nutrient demand, so top dressing must be maintained. At the booting stage, an appropriate amount of nitrogen fertilizer can improve seed-setting rate.
- Foliar spraying: When wheat shows deficiency symptoms, root absorption capacity declines, or rapid nutrient supplementation is needed, spray potassium dihydrogen phosphate, urea solution, etc. For zinc deficiency, spray zinc sulfate; for iron deficiency, spray ferrous sulfate; for copper deficiency, spray copper sulfate - follow the instructions for concentration. Spray in the afternoon or evening on sunny days, avoiding high temperatures and dew. If it rains after spraying, reapply.
Fertilization precautions:
- Top dressing should be combined with irrigation - water promptly after fertilization to promote dissolution and absorption.
- Avoid using only nitrogen fertilizer; ensure balanced nitrogen, phosphorus, and potassium.
- Avoid concentrating large amounts of fertilizer on leaf surfaces to prevent fertilizer burn.
- Do not apply large amounts of fertilizer when the field is dry, to avoid burning seedlings.
- For wheat with good growth and excessive pre-winter fertilization, do not top dress too early or too much to prevent excessive vegetative growth.
Irrigation:
Main irrigation stages include pre-sowing water, winter irrigation, greening water, jointing water, and booting water, arranged according to wheat growth stages, temperature, and seedling condition.
- Apply base fertilizer during land preparation, then irrigate with pre-sowing water.
- After sowing with seed fertilizer, irrigate to promote germination and fertilizer dissolution.
- Irrigate promptly after top dressing, especially at jointing and booting stages.
- Irrigate before winter - this conserves moisture and promotes nutrient absorption.
- Greening water and jointing water should be applied together with top dressing.
While ensuring water supply, also manage drainage to prevent waterlogging. Avoid excessive irrigation that causes soil compaction and nutrient loss. Low-lying fields should be drained properly.
3. Pest and Disease Control
Major wheat diseases include: rust disease, fusarium head blight, smut, sheath blight, dwarf virus disease, yellow dwarf disease, and soil-borne mosaic disease.
Major pests include: wheat aphids, armyworms, wheat blossom midges, and wheat sawflies.
When pests and diseases occur, they first harm wheat growth; secondly, pesticide use increases production costs; and improper pesticide handling can cause pesticide damage and unnecessary losses. Therefore, when controlling pests and diseases, strictly follow the instructions on the product label and apply at the correct concentration.
Summary
The core issue with yellowing and tip burn in wheat is: identify the cause correctly and keep management on track. To solve the problem, focus on:
- Adequate water: Ensure water supply during greening and jointing stages, while managing drainage.
- Complete nutrition: Sufficient base fertilizer, precise seed fertilizer, timely top dressing, combining organic and inorganic fertilizers, and balancing macro and trace elements.
- Scientific fertilization: Avoid sole use of nitrogen, avoid fertilizer burn, avoid excessive vegetative growth.
- Proper pesticide use: Strictly follow label instructions to prevent pesticide damage.
- Pest and disease control: Timely control in spring to reduce damage.
- Reasonable tillage: Even straw return, proper depth, and pressing to prevent root exposure.
By getting these points right, wheat can grow well and strong, and yellowing and tip burn will naturally be less of a problem.
