Causes of Yellowing Wheat Seedlings and Control Methods
AbstractCauses of yellowing wheat seedlings: land preparation not fine enough, base fertilizer not fully decomposed, seed-dressing pesticide concentration too high, sowing density too high, no base fertilizer applied or insufficient fertilizer, too much waterlogging in the soil, occurrence of pests and diseases, encounter with cold wave and temperature drop, etc. Control methods for yellowing wheat seedlings: first, accurately determine what cause is leading to the yellowing seedlings, then take remedial and control measures according to the specific cause of the yellowing.
1. Rough yellowing seedlings
Cause: If land preparation is not fine enough, with many large clods in the soil and the soil being too loose and soft, the roots cannot penetrate well, which makes the seedlings grow slowly, with yellow leaves, shrunken hearts and weak seedlings.
Control method: Crush the covering soil early, then water and hoe finely.
2. Fertilizer burn yellowing seedlings
Cause: If the base fertilizer is not fully decomposed, the seeds and seedlings are prone to burn injury after contacting this fertilizer, causing the leaves and leaf tips to turn yellow.
Control method: Water immediately for remediation; during this period, water once a day for several consecutive days.
3. Pesticide damage yellowing seedlings
Cause: If the concentration of the seed-dressing pesticide is too high, the root tips become injured and swollen, resulting in yellowing seedlings.
Control method: If the yellowing is not serious, no treatment is needed; when secondary roots grow out, the seedlings will gradually turn from yellow to green. For more serious yellowing, water immediately for remediation, and loosen the soil after watering.
4. Overdense yellowing seedlings
Cause: In wheat fields sown too early and with a relatively large sowing rate, seedlings often grow excessively and the density is too high; because nutrition cannot keep up, the seedlings grow and develop poorly and turn yellow.
Control method: Press the soil in time so the seedlings grow more slowly and become sturdy, and deep plow to cut roots, control the increase of tillers and the excessive growth of small tillers. At the same time, thin the seedlings in time and apply topdressing at the appropriate time. In serious cases, paclobutrazol can be used for chemical control.
5. Nutrient deficiency yellowing seedlings
Cause: At sowing time, if there was no time to apply base fertilizer or the fertilizer was insufficient, and no timely topdressing was done later, the seedlings will turn yellow due to long-term lack of nutrients.
Control method: Apply chemical fertilizer before winter; per mu, 25-30 kg of ammonium bicarbonate and 15-20 kg of phosphate fertilizer can be applied as topdressing, which helps promote early tillering and early growth of secondary roots.
6. Drought yellowing seedlings
Cause: When encountering dry climate or lack of soil moisture, the seedlings suffer from insufficient water, leading to slow growth, gray-green leaf color, delayed growth of the central leaf, yellowing of basal leaves, few secondary roots and difficulty in tillering.
Control method: Water and fertilize in time, which helps promote normal seedling growth, sturdy seedlings and more tillers.
7. Waterlogging yellowing seedlings
Cause: In fields located in low-lying areas with poor ditching and drainage, because they remain waterlogged for a relatively long time, organic matter decomposes slowly and nutrients cannot be absorbed in time, causing the seedlings to have yellow leaf color, slow growth, blocked root growth and shallow rooting; in serious cases, root rot and dead seedlings may occur.
Control method: Carry out ditch clearing and drainage measures well, dredge the field drainage ditches in time, lower the groundwater level, and then apply a small amount of quick-acting nitrogen, phosphorus and potassium fertilizer to help the seedlings recover vitality.
8. Pest yellowing seedlings
Cause: When wheat aphids and wheat spiders occur, they suck leaf sap and cause leaves to turn yellow. When underground pests such as mole crickets and wireworms occur, they bite the seedling roots and stems, causing leaves to turn yellow; in serious cases, they directly bite through the root-stem part and cause seedling death.
Control method: Per mu, 65-75 ml of 40% omethoate emulsifiable concentrate can be used, diluted with 50 kg of water for spray control, or 50% phoxim emulsifiable concentrate, or 40% isofenphos-methyl emulsifiable concentrate at 1000 times dilution for root drenching.
9. Disease yellowing seedlings
Cause: Damage from rust, take-all disease, sheath blight, etc. can all cause seedlings to turn yellow and become weak.
Control method: Chemical agents can be used for control. For sheath blight, per mu, 150 g of 20% triadimefon emulsifiable concentrate, or 50-75 g of 50% carbendazim wettable powder, or 150-200 g of 5% jinggangmycin aqueous solution can be used, diluted with 50-75 kg of water for spraying. For rust, 15% triadimefon wettable powder at 1000 times dilution can be used for spraying. For take-all disease, 150-200 g of 15% triadimefon emulsifiable concentrate can be used, diluted with 50-60 kg of water for spraying.
10. Cold damage yellowing seedlings
Cause: When wheat emerges, if it encounters a cold wave and temperature drop, cold damage easily occurs, causing the tender tips and leaf tips to suddenly turn yellow, or some leaf tissues to be damaged, and later gradually wither and yellow.
Control method: Water before the cold current arrives; after the cold current passes, strengthen management work and spray foliar fertilizer.
11. Salt damage yellowing seedlings
Cause: When soil salt content is relatively high, wheat plants tend to grow thin, small and stiff, with few tillers, narrow leaves, many yellow leaves at the base, yellow-green leaf color and purple-red leaf tips.
Control method: Cultivate and loosen the soil in time to reduce surface water evaporation and avoid salt return. Where conditions permit, methods such as irrigation to wash salt or ditching to drain salt can be used, which helps reduce soil salt content.