Key Technical Points for Current and Late-Stage Wheat Management

In some wheat fields in our province, due to earlier drought, the secondary roots are few and short, the population is insufficient, and drought conditions still persist in some plots. In response to this situation, at the provincial spring agricultural production work conference held on April 7, Yu Zhenwen, academician of the Chinese Academy of Engineering, head of the Wheat Expert Guidance Group of the Ministry of Agriculture, and professor at Shandong Agricultural University, introduced the key technical points for current and late-stage wheat management in our province.

Do a good job in fertilizer and water management

Do a good job in fertilizer and water management and chemical control at the standing-up stage. At present, wheat in parts of eastern Shandong, central Shandong, and northern Shandong in our province is still at the standing-up stage. For these plots, fertilizer and water management should continue to be carried out according to local conditions. In particular, for second-class wheat fields, third-class wheat fields that have not received topdressing earlier, or first-class wheat fields with poor soil fertility, fertilizer and water at the standing-up stage should be taken as the focus. The standing-up stage of wheat is also an effective period for using chemical control agents to control excessive growth and prevent lodging. For plots with an overly large population, or with a normal population but relatively high soil fertility, attention should be paid to spraying chemical control agents at the appropriate time.

Do a good job in fertilizer and water management at the jointing stage. The jointing stage is a critical period for wheat field management. In particular, high-yield wheat fields must apply jointing fertilizer well and irrigate jointing water well. The period from Qingming to April 20 is the key period for applying jointing fertilizer and irrigating jointing water across the province. This round of water and fertilizer plays an important role in increasing the number of wheat ears and the number of grains per ear. First-class seedlings that have not undergone spring fertilizer and water management should especially receive topdressing and irrigation at the jointing stage.

When applying jointing fertilizer, the law of wheat fertilizer demand in spring should be followed. Fertilization should be mainly urea. Compound fertilizers have low nitrogen content and are not suitable for spring topdressing. Applying additional potassium fertilizer at the jointing stage has an obvious effect of preventing lodging and increasing yield. For high-yield plots, when topdressing at the jointing stage, 6-12 kg of potassium fertilizer per mu can be applied together with nitrogen fertilizer.

Do a good job in fertilizer and water management at the flowering and grain-filling stages. After wheat heading, the number of ears per mu is already fixed, but the number of grains per ear and grain weight can still change considerably, because about two-thirds of the starch accumulated in the grains comes from photosynthesis after flowering, so this stage is the key period determining grain weight. The management direction is to protect roots, protect leaves, extend the duration of high-value leaf photosynthesis, delay senescence, and increase grain weight.

First, irrigate flowering water or grain-filling water well. Water consumption from wheat flowering to maturity accounts for one quarter of the total water consumption of the entire growth period, and supply must be met through irrigation. Drought will not only affect grain weight; drought at the heading and flowering stages will also affect the number of grains per ear. Therefore, on the basis of having irrigated jointing water, according to the soil moisture condition of the wheat field, irrigating once from flowering to the grain-filling stage can meet the requirements of late wheat growth. However, excessive soil moisture before maturity will affect root vitality and reduce grain weight, so irrigation should be stopped 10 days before wheat maturity.

Second, spray foliar fertilizer. Foliar fertilizer can not only make up for the deficiency of root absorption and meet the nutrients needed for wheat growth and development, but can also improve the field microclimate, reduce the harm of dry hot wind, enhance leaf function, delay senescence, increase the grain-filling rate, increase grain weight, and raise wheat yield. Therefore, foliar spraying can be carried out from the flag-leaf booting stage to the early grain-filling stage. Foliar topdressing is best carried out after 4 p.m. on sunny days. Spray once more at an interval of 7-10 days. If rain occurs within 24 hours after spraying, it should be sprayed again. To simplify operations, it can be combined with other field operation measures, such as mixing insecticides, fungicides, and foliar fertilizer into a mixed solution for foliar spraying, which can simultaneously achieve the "one spray, three preventions" effects of disease prevention, insect prevention, and dry hot wind prevention.

Prevent late spring cold

In recent years, frost damage has often occurred in April in our province. After wheat jointing in April, it completely loses the ability to resist low temperatures below 0 degrees C. When a cold wave arrives and the surface temperature suddenly drops below 0 degrees C, early spring frost damage occurs.

The preventive and remedial measures for early spring frost damage are as follows:

First, irrigation to prevent early spring frost damage. Because the heat capacity of water is greater than that of air and soil, watering before the arrival of an early spring cold current can increase water vapor in the near-surface air, release latent heat when condensation occurs, and reduce the range of ground temperature variation. At the same time, after irrigation, soil moisture increases, soil thermal conductivity increases, and temperature rises.

Second, the remedial measures after early spring frost damage are supplementary fertilizer and watering. After wheat suffers frost in early spring, quick-acting nitrogen fertilizer should be applied immediately and water should be irrigated. The coupled effect of nitrogen and water will promote early tillering of wheat, help small tillers catch up with large tillers, increase the rate of tillers becoming ears, and reduce the damage from frost.

Integrated control of pests and diseases

Drought is favorable for the occurrence of wheat spiders, wheat aphids, and others. Before winter, wheat aphids and wheat spiders occurred relatively seriously in northern Shandong, southern Shandong, and other places, and have already caused damage locally. The overwintering bases of wheat sheath blight, powdery mildew, underground pests, and small brown planthopper in rice-stubble wheat fields in southern areas are also relatively high. After wheat jointing, as temperatures rise, various pests and diseases gradually enter a period of high incidence. Attention should be paid to good forecasting and timely control. The focus of control is wheat aphids, wheat spiders, underground pests, sheath blight, powdery mildew, take-all disease, root rot, leaf rust, and simultaneous control of small brown planthopper and various other pests and diseases, while guarding against epidemics of wheat stripe rust.

To control wheat spiders, 0.9% abamectin emulsifiable concentrate can be sprayed at 3000 times dilution. To control wheat blossom midge, in early to mid-April, 1-1.5 kg per mu of 5% isofenphos-methyl granules or 150-200 ml of 40% isofenphos-methyl emulsifiable concentrate can be mixed with 30-40 kg of fine sand or fine sandy soil and spread on the ground, followed by hoeing. The control effect is better if watered after application.

To control underground pests, 40-50 ml per mu of 40% isofenphos-methyl emulsifiable concentrate or 50% phoxim emulsifiable concentrate can be sprayed on the wheat stems.

To control wheat aphids, 10-15 g per mu of 10% imidacloprid emulsifiable concentrate can be sprayed, which also controls small brown planthopper.

To control wheat blossom midge, during the peak occurrence period of adults from wheat heading to early flowering, 20-30 ml per mu of 50% beta-cypermethrin emulsifiable concentrate can be sprayed with water, which also controls the first generation of cotton bollworm.

To control sheath blight, 150-200 ml per mu of 5% validamycin aqueous solution can be mixed with 75-100 kg of water and sprayed on the base of wheat stems, then sprayed again at an interval of 10-15 days.

To control powdery mildew and rust, 50-75 ml per mu of 20% triadimefon emulsifiable concentrate can be sprayed.

To control gibberella, leaf blight, and glume blight, 75-100 g per mu of 50% carbendazim wettable powder can be sprayed. When the above pests and diseases occur together, appropriate agents can be mixed and applied once for combined control.

For plots with many weeds, manual pulling should be used. Herbicides must absolutely not be used for control, because using herbicides after wheat jointing has poor weed control effect on the one hand, and on the other hand easily causes phytotoxicity to wheat.