How to manage corn at the ear stage? Key technical points explained

The life of corn is divided into three stages: seedling stage, ear stage and flowering-grain stage. The ear stage refers to the growth period from jointing to tasseling, and it is the period when the corn plant's vegetative growth and reproductive growth proceed together. The ear stage is the key period in the life of corn with the fastest development, the largest growth amount and the greatest demand for fertilizer and water. The demand for nitrogen, phosphorus and potassium accounts for about 65%, 55% and 85% of the whole growth period, and the water demand accounts for about 30%. The central task of field management at this stage is to promote leaves and strengthen stalks, with many and large ears, ensuring both robust growth of the plant's vegetative body and good development of the ears, achieving strong individual development and moderate, uniform population growth with a high-yield appearance.

In mid-July, most enter the ear stage growth period. In order to fight disasters and secure a bumper harvest, the following field management points for the ear stage are proposed:

I. Timely and appropriate topdressing. The ear stage is the period of maximum fertilizer use efficiency for corn. Therefore, for all plots where ear-stage topdressing is scheduled or the base fertilizer application rate is insufficient, corn ear fertilizer should be applied in a timely manner. Especially under the current conditions of straw return, topdressing should be advanced as much as possible, and it can be applied right after corn jointing. The topdressing amount is determined by the nitrogen application rate set according to the target yield. Generally, about 20 kg of urea is applied per mu, applied into the soil by manual banding or mechanical banding. After fertilization, water supply should be met in a timely manner to facilitate the exertion of fertilizer efficiency.

II. Timely irrigation and drainage. Corn should be irrigated well twice during the ear stage. The first time is around the large trumpet stage, which is exactly the suitable period for applying ear fertilizer. Irrigation should be carried out in combination with topdressing to facilitate the exertion of fertilizer efficiency, promote the growth of aerial roots and enhance photosynthetic efficiency. The second time is around tasseling, and the irrigation amount should be appropriately increased. Around tasseling, high-temperature summer drought weather is very likely to occur, and "neck-strangling drought" is likely to appear, and pollen abortion caused by high temperature and drought is likely to occur. Therefore, once drought occurs around tasseling, irrigation should be carried out promptly. Although the ear stage requires more water, excessively wet soil affects corn root growth and reduces yield. Therefore, in case of waterlogging, drainage should be carried out promptly to keep soil moisture at 70%-80% of the field maximum water-holding capacity.

III. Integrated control of diseases and insect pests. The main insect pest at the ear stage is the Asian corn borer, etc. In our city, the second generation of Asian corn borer begins to cause damage in mid-to-late July, when most summer corn is at the large trumpet stage. During the ear stage, the Asian corn borer mainly bores into and feeds on leaves in the heart leaf (inside the trumpet), bores into and feeds on the female ear from tasseling to silking, and after corn begins to set grain, it bores into stalks, the ear rachis and the ear stalk. Therefore, the best period for controlling the Asian corn borer is the large trumpet stage. Control after tasseling will be very difficult. The control method for the Asian corn borer is to apply medicine into the heart at the large trumpet stage. The chemicals used are mostly granular formulations such as phoxim or 100-150 ml of Bt emulsion plus 5 kg of fine sand, scattered into the heart leaf for control. Drill 5-6 small holes in the cap of a plastic Cola or Sprite bottle (suitable for letting the pesticide granules leak out), fill the bottle with the granular pesticide, then tighten the cap; when applying into the heart, invert the plastic bottle and aim it at the corn trumpet, and gently shake the pesticide down by hand. Where conditions permit, high-pressure mercury lamps can also be used to trap and kill adults, or Trichogramma can be released in the field for control. Spraying with kangkuan or tebufenozide, etc., can also be used to control the Asian corn borer. The main diseases at the ear stage of summer corn include brown spot and stalk rot, etc. For brown spot, when corn has 6-8 leaves, 20% triadimefon can be selected and added to foliar fertilizers such as potassium dihydrogen phosphate for spray control. Note to spray the top cover and heart and spray the leaves evenly; for stalk rot, in the early stage of the disease, spray with 4,000-5,000 times dilution of agricultural streptomycin or 600 times dilution of 77% keshade wettable powder.

IV. Remedial measures after lodging. Lodging before and after jointing generally does not require manual lifting. Corn that lodges before jointing is mostly lodged after being soaked by rainwater due to excessive rainfall and waterlogging. Since its recovery ability is very strong at this time, it only needs the field water to be drained. If lodging occurs after jointing, the plants can also naturally recover to an upright position without affecting normal pollination and grain setting in the future, so they can be allowed to recover on their own. Corn that lodges around tasseling and pollination has tall plants, and after lodging the plants press against each other, making natural recovery difficult. This not only affects photosynthesis, but also affects normal growth and development, silking, pollination and grain setting, so manual lifting is needed. When lifting, it should be done early, slowly and gently, and combined with earthing up for fixation. After lodging occurs, it should be lifted promptly within 1-2 days. When corn lodges, some roots have already been damaged. When straightening, prevent further root damage. It is best for two people to operate together, with one person grasping the upper part of the corn plant and gently pulling it up, and the other person earthing up at the base. Once the plant bends and grows upward, it can no longer be lifted. Also apply topdressing in a timely manner so that corn growth recovers as soon as possible, with 5-10 kg of urea applied per mu.

V. Other field management. Due to sowing, disease and insect damage and other reasons, after corn jointing, some small and weak plants appear in the field. They usually do not set ears or set very small ears, and not only consume fertilizer and water but also affect the growth of healthy plants. Therefore, small and weak plants should be pulled out early to ensure population uniformity. For plots where weeds grow luxuriantly in the field because weed control was not timely in the earlier period, timely intertillage and weeding should also be carried out in combination with topdressing; alternatively, paraquat can be selected and applied with a protective shield for directed spraying between rows. The equipment selected should minimize dripping, spurting, running and leaking as much as possible, so as not to affect corn.