Problems to Watch for in Late-Stage Corn Management and Countermeasures

In 2016, the climate in Dali Prefecture was the opposite of previous years, with relatively abundant rainfall. In all regions, the rain came early, frequently, and fiercely. Corn planting in mountainous, semi-mountainous, and flatland areas was generally earlier, and the area planted also expanded compared with the previous year. As of June 20, the corn planting progress across the prefecture reached 1.7127 million mu (1.6679 million mu in 2015). At present, corn growth in most areas has entered the jointing-booting to tasseling-shedding pollen stage, and some has entered the grain-filling stage. Growth and development are generally good and the plants are robust, laying the foundation for a bumper corn harvest across the prefecture this year. However, precisely because of excessive rain, there are also certain unfavorable factors: first, corn in flatland areas basically did not go through seedling restraint at the seedling stage, so growth is too tall and vigorous; second, field humidity is too high, and low-lying fields accumulate water and become waterlogged, which can easily lead to premature senescence and the occurrence of various diseases; third, during the corn growing period, sunlight is generally insufficient, affecting photosynthetic efficiency; fourth, temperatures are generally low, accumulated temperature is insufficient, and the corn growth period is correspondingly prolonged. The Dali Experimental Station of the Yunnan Modern Agricultural Corn Industry Technology System, starting from the Dali City corn core demonstration area and reviewing the seedling conditions across the prefecture, proposes the following measures or suggestions for corn production management in the middle and late stages for reference.

1. Cultivate between rows and hill up soil to prevent lodging; clear ditches and drain water to prevent waterlogging

Because there is a lot of rain, seedling restraint was skipped at the seedling stage, and vegetative growth is fast. Now, while the plants enter reproductive growth, they also rapidly grow taller, and both plant height and ear position are noticeably higher than in previous years. According to survey and comparison results from 7 varieties including Yunrui 505, Yunrui 999, and Yunrui 407 in the 100-mu core demonstration area at Wanqiao of the Dali Corn Experimental Station, for the same variety in the same area (not the same field), plant height increased by 28-68 cm compared with last year, and ear position increased by 6-37 cm. The overall average plant height increased by 45 cm, 16.4% higher than the previous year, and ear position increased by 24 cm, 20.7% higher. This situation is somewhat representative, so attention should be paid to preventing the risk of lodging if continuous overcast rain occurs in the late grain-filling stage. At present, to enhance the lodging resistance of the plants, three measures can be focused on: (1) For fields still in the jointing stage, such as varieties that are inherently taller or fields with high fertilizer and water levels, appropriately spray chlormequat before tasseling to reduce plant height and ear position, make stalks thicker, and enhance plant lodging resistance; (2) Cultivate between rows and hill up soil heavily. For plastic film cultivation, remove the film promptly, hoe weeds, and, in combination with applying ear fertilizer, focus on making deep furrows and heavy hilling to strengthen the soil around the base of the stems and help prevent plant lodging; (3) Clear ditches and maintain field ridges, keep field ditches unobstructed and field ridges intact, prevent field waterlogging, keep the soil permeable, ensure drainage and irrigation capacity, and facilitate deep root growth so that roots do not suffer premature senescence.

2. Remove ineffective plants, tillers, and diseased plants so healthy plants can grow fully

During inter-row cultivation, pull out stunted plants, inferior plants, and diseased plants within the population. Most of these seedlings do not form effective ears, and even if they have ears, the ears are very small, with a negligible contribution to yield. On the contrary, they compete for fertilizer and light in the field and affect the growth of nearby normal plants. Some varieties, due to their own characteristics and sufficient fertilizer and water, produce large numbers of ineffective tillers, consuming soil fertility and plant nutrients, and these should be removed promptly to ensure robust growth of the main stem. In addition, remove obviously seriously diseased plants, bury them deeply or carry them out of the field, to avoid the breeding and spread of disease.

3. Apply more fertilizer to ensure nutrient supply, promote strong stalks and large ears, and increase grain weight

1. Apply heavy jointing-booting fertilizer. The corn booting stage (jointing to tasseling-shedding pollen) is the period when corn plants carry out vegetative growth and reproductive growth simultaneously, the peak period of fertilizer demand, and the key stage that determines ear size and grain number. By increasing fertilizer application, many important goals can be achieved, such as thick and numerous roots, sturdy stalks, wide and thick leaves, deep green color, large ears, and many grains. This period can be judged according to the number of plant leaves: for early-maturing varieties, 8-9 expanded leaves; for medium-maturing varieties, 10-11 expanded leaves. During this period, management should emphasize timely heavy application of ear fertilizer. According to the principles of applying more to poor fields and less to fertile fields, and more to weak plants and less to strong plants, mainly apply N fertilizer supplemented with K fertilizer. Generally, apply 25-35 kg urea + 10-15 kg potassium fertilizer per mu, or 35 kg-45 kg high-efficiency compound fertilizer, to ensure sufficient nutrient supply for the plants.

2. Supplement with flower-grain fertilizer. For fields that have entered the pollination stage, supplement an appropriate amount of flower-grain fertilizer according to seedling growth conditions. Generally, apply 10-25 kg urea + 10 kg potassium fertilizer per mu to prolong the functional period of the leaves above the ear and the grain-filling rate, reduce bare tips, and increase grain weight.

4. Strengthen field surveys of diseases and insect pests, and carry out timely unified prevention and control

The main corn diseases in the middle and late stages of corn production in our prefecture are: corn gray leaf spot, northern corn leaf blight, southern corn leaf blight, rust, and ear rot. The main insect pests are corn borer, aphids, and others. This year's climate is objectively favorable for the occurrence of various diseases, especially gray leaf spot, rust, and ear rot. All localities should pay attention, frequently go deep into the fields to investigate, grasp changes in disease and pest conditions, promptly adopt general control measures, and keep diseases and insect pests under control in the early stage. The specific control measures are as follows:

1. Corn gray leaf spot: This disease has a long incubation period, so control should be carried out early. In areas where gray leaf spot is relatively severe, or where varieties susceptible to gray leaf spot or with poor disease resistance are planted, at the initial stage of gray leaf spot infection (from the large trumpet stage to the early grain-filling stage), use 25% propiconazole, or difenoconazole, 50% carbendazim wettable powder, thiophanate-methyl, mancozeb, etc. for control, once every 10 days, for 2-3 consecutive times.

2. Northern corn leaf blight and southern corn leaf blight: At the initial stage of disease onset, use 50% carbendazim wettable powder, or 70% thiophanate-methyl, mancozeb, 80% xinwansheng, iprodione, Score, etc. for spray control 1-3 times, with the second application 5—7 days later.

3. Corn rust: At the initial stage of disease onset, use 20% triadimefon emulsifiable concentrate, or 50% fenxiuqing, 12.5% diniconazole, 25% triadimefon wettable powder, for continuous control 2-3 times, once every 10 days.

4. Corn ear rot: At the tasseling-silking stage, use 25% propiconazole emulsifiable concentrate, or 50% carbendazim wettable powder, 70% thiophanate-methyl wettable powder, and spray the female ear and lower stems and leaves.

5. Corn borer: At the large trumpet stage, use 10% cis-cypermethrin emulsifiable concentrate, 12% emamectin benzoate-chlorfenapyr emulsifiable concentrate, and spray into the leaf whorl.

6. Corn aphids: From the jointing-booting stage to the tasseling-silking stage, use 40% dimethoate emulsifiable concentrate, or 50% pirimicarb wettable powder, 10% imidacloprid wettable powder, etc. for spray control 1-3 times.

5. Harvest at the appropriate time, dry and thresh promptly, and ensure increased yield and income

When the corn husks begin to turn yellow, it indicates that the crop has entered the mature stage. After maturity, if the weather is good, the variety is resistant to ear rot, and it does not affect the following crop, harvest can be appropriately delayed by 5-7 days to allow the grains to complete filling, which helps increase 1000-grain weight. After harvest, dry with good ventilation and thresh promptly to prevent mildew and insect damage that could cause yield loss, and ensure increased yield and income.

Finally, the middle and late stage management measures can be summarized in six sentences:

Control height and hill soil to resist lodging, clear ditches and protect ridges against waterlogging;

Remove all tillers and diseased inferior plants, so healthy plants can grow freely;

Apply heavy ear fertilizer and supplement flower fertilizer, supply enough nutrients to promote ears and grains;

Disease and pest surveys must go deep, save costs and improve efficiency with early broad control;

Harvest at the right time and dry frequently, watch out for mildew and insects to reduce losses;

Farm management lies in diligence, scientific and technological measures ensure “three increases.”