Science and Technology Department of the Ministry of Agriculture: “8 Questions and 8 Answers” on Spring Wheat Management—Early Application of Humic Acid Water-Soluble Fertilizer

　　Recently, the Science and Education Department of the Ministry of Agriculture and Rural Affairs, in response to key spring‑management issues raised by farmers on the science‑education cloud platform, convened an expert advisory group for the “Science‑Based Seedling‑Strengthening” campaign for winter wheat. The group has compiled an “8 Questions and 8 Answers” guide on spring wheat management, emphasizing the principle of “early application and early care, with a focus on promoting growth.” It recommends promptly applying foliar fertilizers, suggesting options such as water‑soluble fertilizers containing humic acid.

　　1. This year’s weather is expected to bring a “late spring cold spell.” What’s the most effective way to prevent it?

　　Answer: Rational growth regulation: Before jointing, apply 30 grams of 15% paclobutrazol per mu diluted in 25–30 kilograms of water, or mix 5 grams of brassinolide (0.1% concentration) with 100 grams of potassium dihydrogen phosphate and dilute in 15 kilograms of water for foliar spray, to promote robust plant growth, enhance wheat’s cold tolerance, and reduce low‑temperature damage to the developing spikelets. Timely irrigation and topdressing: Prior to the arrival of a cold wave, irrigate promptly to regulate the microclimate near the soil surface and protect against early‑spring frost damage. If wheat suffers frost injury in early spring, immediately apply a quick‑acting nitrogen fertilizer in conjunction with watering. Within 2–3 days after low temperatures, carefully assess the extent of frost damage to the young spikes; for fields where tillers and stems have been killed by frost, apply additional fertilizer promptly to encourage regrowth. Generally, fields with only leaf frost damage or a main stem–spikelet mortality rate of 10% or less do not require fertilization; for fields with a tiller–stem mortality rate of 10%–30%, apply 45 kilograms of urea per mu along with irrigation; for fields where tiller–stem mortality exceeds 30%–50%, apply 7–10 kilograms of urea per mu; and for fields with a mortality rate exceeding 50%, apply 12–15 kilograms of urea per mu. In addition, standard jointing–booting fertilization should still be carried out to promote the development of upper‑position tillers into productive spikes and minimize yield losses. For late‑frost damage occurring in mid‑April, when further tillering cannot produce additional spikes, foliar applications—such as urea, potassium dihydrogen phosphate, or plant cell‑membrane stabilizers and sodium nitrophenolate—can help alleviate frost injury and improve grain set and kernel filling. Moreover, in frost‑damaged fields, plant resistance declines and the likelihood of pest and disease outbreaks increases, so strengthened pest and disease management is essential.

　　2. Can the same type of pesticide or fungicide be applied multiple times for disease and pest control?

　　A: Repeated use of the same pesticide can occur in two scenarios: first, applying the same product multiple times within a single wheat-growing season; second, using the same formulation repeatedly over many years in a given field. In the former case, if the initial application is effective, subsequent applications are likely to perform similarly. However, if the first application proves ineffective, resistance to the active ingredient may be developing, necessitating the rotation to pesticides with different modes of action—either insecticidal or fungicidal. In the latter scenario, long-term, repeated use of the same product in a wheat field can lead to the development of resistance among local pests, pathogens, and weeds that complete their life cycles there, making rotation essential. For regionally widespread diseases in the Huang–Huai wheat belt—such as wheat rust—and for migratory pests—such as the cereal aphid—it is generally more difficult for resistance to emerge. Accordingly, triazoles can be used for sustained control of stripe rust, while pyrethroids and second‑generation neonicotinoids are suitable for managing the cereal aphid. Overall, to prevent the emergence of resistance in target pests and pathogens due to repeated use of the same product, it is advisable to alternate between different formulations or to employ combination products, allowing for flexible and strategic application strategies.

　　3. How can we strengthen wheat seedlings that have become weak due to various causes?

　　A: Sowing too deeply can result in excessively long underground stems, slender seedling leaves, and poorly developed root systems, leaving the wheat seedlings weak and stunted. For such seedlings, early on, rake the soil to remove some of the covering, reducing the depth of soil over the tillering node; combine this with shallow cultivation to improve soil aeration and encourage lateral root development, thereby strengthening the seedlings. If coarse tillage has left many clods and resulted in compacted soil, hindering deep rooting and slowing seedling growth—leading to stunted growth, heart‑shrunken shoots, yellowing leaves, and weak, spindly plants—promptly break up the surface crust and apply water, followed by fine hoeing and shallow cultivation. For yellow seedlings caused by excessive seeding rates—exhibiting overly vigorous growth, nutrient deficiencies, poor development, and limited tillering—timely deep hoeing to sever roots can help promote robust seedling establishment. In fields where the soil is excessively clayey, poorly textured, poorly drained, and waterlogged, leading to root hypoxia, stalled root growth, browning of primary roots, reduced tillering, and stunted, yellowing or browning seedlings, it is essential to dig deep drainage ditches to relieve waterlogging, perform inter‑row cultivation to loosen the soil, enhance aeration, raise soil temperature, and stimulate root development.

　　4. How should wheat diseases and pests be monitored and managed?

　　Answer: When conducting monitoring of crop diseases and pests, priority should be given to wheat‑related threats such as rusts, Fusarium head blight, wheat aphids, armyworms, and locusts, as well as second‑category wheat pests and diseases including smut, stem base rot, powdery mildew, underground pests, and grain‑sucking insects. The monitoring scope encompasses the types, timing, geographic extent, and severity of pest and disease outbreaks; the species, distribution, and population dynamics of key natural enemies of pests; field climatic conditions influencing pest and disease occurrence; and other relevant factors requiring surveillance. In managing crop diseases and pests, the guiding principle is prevention first, coupled with integrated pest management. Strategically, this requires site‑specific approaches, prioritization of critical issues, and tailored guidance. Operationally, a three‑pronged technical strategy should be adopted, combining non‑chemical control with chemical treatment, emergency response with sustainable management, and unified, coordinated control with community‑based, collective efforts. Regarding the selection of control agents, emphasis should be placed on promoting biopesticides and highly effective, low‑toxicity chemical pesticides. For the same active ingredient, preference should be given to high‑concentration formulations and environmentally friendly dosage forms such as suspensions and emulsifiable concentrates.

　　5. Which herbicides are effective for controlling weeds in wheat fields?

　　A: Wheat fields typically harbor a mix of grassy and broadleaf weeds. For control, you can apply 60 mL per mu of an 8% diflufenican–dichlorprop–clodinafop‑propargyl dispersible oil suspension, plus a 1,000‑fold dilution of the synergist Jijian (or Runfei), or use 17 mL per mu of a 6% diflufenican–dichlorprop dispersible oil suspension. Alternatively, depending on the specific weed spectrum in your field, you may formulate a tank mix by combining a single‑active‑ingredient product—such as carfentrazone‑ethyl, diflufenican, bensulfuron‑methyl, or chlorflupyroxypyr‑isooctyl ester—with one of the following single‑active‑ingredient products: clodinafop‑propargyl, mesosulfuron‑methyl, or zoxazolyn. The number of active ingredients in the tank mix should be 2 to 3, with the exact combination determined by the weed species present in the field.

　　6. How should fertilization be applied scientifically to wheat fields with varying growth stages?

　　A: For late-sown, weak wheat fields with few tillers, limited secondary roots, and a small plant population, early spring cultivation to raise soil temperature is recommended; avoid irrigating too early. During the jointing and booting stages, apply 6–8 kg and 7–10 kg of urea per mu, respectively, along with an appropriate amount of diammonium phosphate, to stimulate the growth of secondary roots, promote tillering, and ensure adequate spike formation. For third-class wheat fields, early application and management are key, prioritizing growth promotion. On irrigated land, apply nitrogen and supplement phosphorus during the green-up stage; the fertilizer rate should be adjusted according to seedling condition and soil fertility. Based on soil moisture and irrigation needs, generally apply 5–8 kg of urea per mu for high-fertility fields, 8–10 kg per mu for medium-fertility fields, and 10–15 kg per mu for low-fertility fields, while appropriately increasing quick‑acting phosphate fertilizers to encourage early spring tillering and spike formation, thereby increasing the number of productive spikes. Apply foliar fertilizers promptly to boost wheat growth—typically spraying 100–200 g of potassium dihydrogen phosphate per mu—and consider additional applications of amino acid‑ or humic‑acid‑based water‑soluble foliar fertilizers. For first- and second-class wheat fields, tailor fertilization to local conditions, combining growth promotion with yield control. For second-class fields with normal growth and an appropriate plant population, apply 8–12 kg of urea per mu after emergence but before jointing if soil fertility is high; for fields with average fertility, apply around 15 kg of urea per mu at the green-up stage in conjunction with irrigation. For first-class wheat fields, adopt a strategy of early control followed by later promotion to encourage tillering and spike formation; for fields with average fertility, apply 8–10 kg of urea per mu at the onset of jointing, while higher‑fertility fields may benefit from applying 8–10 kg per mu during mid‑to‑late jointing, combined with irrigation. For vigorously growing fields, suppress excessive vegetative growth during the green-up stage and delay fertilization, reducing the application rate to prioritize control. Delay fertilizer and irrigation management until mid‑to‑late jointing, applying 10–12 kg of urea per mu in combination with irrigation; alternatively, conduct moderate soil compaction or deep plowing to sever roots between green-up and emergence, or spray growth inhibitors (such as paclobutrazol, mepiquat chloride, or chlormequat chloride) during the emergence stage to curb excessive growth and prevent lodging. For fields sown at high densities with relatively weak individual plants exhibiting false vigorous growth, apply 8–10 kg of urea per mu at the jointing stage.

　　7. If no herbicide was applied before winter, how should weeds be controlled?

　　A: For wheat fields that were not treated with herbicides before winter, the optimal window for chemical weed control is during the green-up to tillering stage; once the wheat has jointed, chemical weeding is no longer advisable. However, given the significant temperature fluctuations in early spring, it is best to adhere to the “360+10” chemical weeding guideline: before applying herbicides, monitor the weather forecast to ensure there will be no severe cold spells within three days before and after treatment, with an average daily temperature above 6°C and a minimum daily temperature no lower than 0°C. During application, the air temperature should remain above 10°C, and it is ideal to carry out chemical weeding on a clear day between 10 a.m. and 4 p.m.

　　8. How should wheat diseases and pests be managed at different growth stages?

　　Answer: During the green-up and jointing stages of wheat, the focus should be on early prevention of epidemic and outbreak‑type pests and diseases. In the southern part of the Huanghuai wheat region, in spring, pay close attention to controlling early‑onset stripe rust in affected fields, aiming to contain disease foci. When the average incidence of stripe rust reaches 0.5%–1% of leaf area, or when powdery mildew affects 10% of leaves, promptly organize large‑scale emergency control measures to prevent widespread damage. Triazole fungicides are recommended for such applications. If the incidence of wheat sheath blight reaches 10%, apply fungicides such as jinggangmycin or triazoles by spraying the base of the stems every 7–10 days, repeating three times. For red spider mites, when the average density is 200 mites per 33 cm of row length, or six mites per plant, use abamectin, bifenthrin, or similar agents for foliar application. In fields without seed treatment, if post‑green-up soil‑borne pests cause seedling mortality at a rate of 10%, combine hoeing with the application of phoxim mixed with fine soil (at a ratio of 1:200) to prepare poisoned soil; spreading first, followed by hoeing, yields better results. During the booting to flowering stage, when multiple pests and diseases occur simultaneously, vigorously promote the “one spray, three protections” technique. For single‑pest or single‑disease situations, implement targeted control measures. If the aphid population exceeds 800 per 100 panicles and the ratio of natural enemies to wheat aphids falls below 1:150, consider using selective insecticides such as pirimicarb, neonicotinoids, or pyrethroids for spray applications. At the early heading stage, if more than one adult grain‑sucking fly is observed on every 10 yellow or white sticky traps (120 mm size), or if, during heading, 10–25 adults are found in every 10 sampling nets, or if, upon gently parting the wheat rows, 2–3 adults can be seen at a glance, apply cypermethrin or chlorpyrifos via spraying to protect the ear and concurrently control wheat aphids, armyworms, and other pests. For red spider mites, when the average density reaches 200 mites per 33 cm of row length, or six mites per plant, use abamectin, bifenthrin, or similar agents for foliar application. When powdery mildew affects 10% of leaves, or stripe rust affects 0.5%–1% of leaves, promptly apply triazole fungicides; if the condition is severe and persists, reapply after an interval of 15 days. From heading through flowering, if cloudy, rainy, dewy, or foggy weather persists for more than three consecutive days, or if there are five or more rainy days within ten days, carry out comprehensive control of Fusarium head blight, employing fungicides such as cyproconazole, tebuconazole, prochloraz, carbendazim, or thiophanate‑methyl. If rain occurs 3–6 hours after application, re‑spray promptly after the rainfall. At the same time, conserve and utilize natural enemies, carefully monitor chemical control thresholds and natural enemy utilization rates, and actively promote the use of selective pesticides and formulations with lower toxicity to beneficial organisms, such as pirimicarb and pyrethroids. Adjust application timing appropriately based on the dynamics of natural enemy populations.

　　Source: China Agricultural Science News Network (March 2, 2022)