Key Technical Points and Management Notes for Growing Sweet Corn

SummarySite selection: choose a plot with good drainage and irrigation and medium to above-medium soil fertility, and plow and harrow during the suitable tillage period to make the soil loose. Sowing: sow in late April; the seeds do not need soaking, and dry seeds can be sown directly, giving a higher emergence rate. Density: about 3500-4000 plants per mu. Fertilization: apply sufficient base fertilizer and seed fertilizer, and topdress with compound fertilizer before tasseling. Management: thin seedlings at the three-leaf stage, leaving two plants per hill, and remove weeds in time. Pest and disease control: mainly prevent underground pests and rodent damage.

I. Preparatory work before sowing

1. Site selection: the land should have good drainage and irrigation, good uniformity, and medium to above-medium soil fertility.

2. Set up isolation zones: because sweet corn pollinated by non-sweet corn will form non-sweet kernels. Therefore, different types of corn planted in the same field must be isolated; within 200 m around the land used for sweet corn, ordinary corn cannot be planted, and enhanced sweet and super-sweet corn should also be 200 m apart. Time isolation measures can also be adopted, that is, staggering the sowing dates of different types of corn with similar maturity periods by 15-20 days so that their flowering periods do not coincide. Fields harvested for sweet corn shoots do not need isolation.

3. Land preparation: plow and harrow during the suitable tillage period to make the soil loose. Make beds with a bottom width of 140 cm (about 4 chi) and a bed surface width of 110 cm (about 3.5 chi), and dig 30 cm deep drainage ditches around the field.

4. Seed preparation: before sowing, sun-dry the seeds for two days and remove impurities. Sweet corn seeds do not need soaking; dry seeds are suitable for direct sowing and give a high emergence rate. Unsuitable conditions or improper methods for soaking and sprouting will cause the germination rate to drop rapidly.

5. Control of underground pests and rodents: sweet corn seeds are easily damaged by underground pests and rodents. At sowing, apply a small amount of broad-spectrum insecticide 3% phorate-methyl granule into the holes beside the seeds; the strange odor it releases can prevent underground pests and rodents from eating the seeds. Or use 3% Miral granule at 4 kg per mu and scatter it on the bed surface.

II. Sowing and seedling raising

1. Sowing time: generally in late April; with plastic film mulching, sowing can be 10-15 days earlier; with film seedling raising and transplanting technology, sowing can be 20 days earlier. The latest sowing time is preferably before July 10 to ensure timely harvest before early frost. In early spring, where heat preservation facilities are available, it can be appropriately earlier, but sowing between late May and mid-June should be avoided, because corn sown in this period has its flowering and pollination period during the summer drought of July-August, which easily causes bald tips, missing kernels, or empty stalks.

2. Planting density: use a two-row plot design, with each plot row length 5 m, randomly arranged, with three replications. Plant spacing 25 cm, planting density about 3500-4000 plants per mu. Use direct sowing with hill sowing, 2-3 seeds per hill, covering with 3 cm of soil (preferably mushroom residue), and after sowing maintain field capacity at about 80%. Note: after sowing sweet corn, the soil cover should be shallow, because sweet corn seeds are flatter, have less starch, and have poor soil-penetrating ability.

3. Spraying herbicide: spray herbicide on the same day after sowing for weed control, using 40% atrazine 100 g plus 48% Lasso 150 ml per mu, mixed with 100 jin of water, and evenly spray the bed surface and ditch surface. When spraying, soil moisture should be good to ensure the effectiveness of the pesticide.

4. Sowing methods: for cultivating sweet corn, choose sandy loam fields with relatively high fertility and sufficient fertilizer and water, and finely prepare the land before sowing. Sweet corn sowing rate is 1-1.5 kg/667 sq m. Sowing methods include mechanical sowing, seedling raising and transplanting, plastic film mulching, and staged sowing. Planting density is generally controlled at 3000-4000 plants.

III. Field management of sweet corn

1. Apply sufficient base fertilizer and seed fertilizer: heavily applying base fertilizer and sufficiently applying seed fertilizer are key measures for high yield of sweet corn. The base fertilizer is made by composting 2 tons of farmyard manure per mu plus 50 kg of superphosphate with an appropriate amount of water until decomposed. Before sowing, open two shallow furrows on the bed surface, apply the decomposed organic fertilizer in bands into the furrows, then apply compound fertilizer at 40 kg per mu on top of the organic fertilizer as base fertilizer and seed fertilizer for root absorption, cover with 6 cm of soil, then sow seeds according to plant spacing, and cover with another 4-5 cm of soil.

2. Thin seedlings early at the three-leaf stage, leaving two plants per hill.

3. At the five-leaf stage, finalize the seedlings in time, leaving one plant per hill, shallow intertillage and loosen the soil, then topdress, applying 10 kg of urea per mu, and do small hilling. Sweet corn seedlings are relatively tolerant of drought, but are afraid of waterlogging; if submerged overnight, the seedlings may die, so drain water in time. The five-leaf stage is the period that determines the total number of leaves; sufficient water and fertilizer can increase the total number of leaves. The root system of sweet corn has a high oxygen demand and requires loose soil with good aeration. Timely intertillage and soil loosening at the seedling stage and small hilling are important measures to promote the root system to extend deeper.

4. The expansion of the 7th-8th leaves is the stage when the female and male growing cones begin to differentiate, also called the large trumpet stage or booting stage. Intertill and loosen the soil in time, then topdress, applying 20 kg of compound fertilizer and 15 kg of potassium chloride per mu, and hill up the soil. This growth stage determines ear size and the number of kernel rows; sufficient water, fertilizer, and light can promote the normal development of pollen grains, increase the number of spikelets, reduce degenerated spikelets at the top, and increase the area of functional leaves above the ear position. At this stage, the water requirement is greater than at the seedling stage; the suitable soil moisture content is 70-80% of field capacity, and irrigation and drainage should be done in time.

5. Before tasseling, topdress with 20 kg of compound fertilizer and 7.5 kg of potassium chloride per mu, and do large hilling, which can prevent lodging and suppress large weeds. Silking begins 2-4 days after tasseling; female ear silks usually emerge 1-2 days after the male flowers begin to shed pollen. If there is too much water or drought, or high temperature, or planting is too dense, silking will be delayed; if delayed too long, pollination will be affected. The milk-ripening stage is the main period for increasing grain weight; applying potassium fertilizer can also increase it appropriately, while nitrogen fertilizer should be avoided; phosphorus deficiency can cause bald tips, and phosphorus is mainly supplied in the base fertilizer. The tasseling and flowering stage is a sensitive period for sweet corn's water requirement, requiring soil moisture content to reach 80% of field capacity, and it is the period of greatest water demand in its life. “Drought at flowering reduces yield by half”, and may even prevent male flowers from emerging; sufficient water at the tasseling stage is extremely important for high yield.

IV. Control of pests and diseases

1. Poor management, abundant weeds, weak plants, continuous cropping, or excessive rain make sweet corn prone to infection by large and small leaf spot diseases; applying phosphorus and potassium fertilizers can enhance plant disease resistance.

2. At the early stage of leaf spot disease, spray 2-3 times, once every 7 days. Commonly used pesticides include 50% carbendazim 500-fold solution; 70% thiophanate-methyl 600-fold solution; 90% mancozeb 1000-fold solution; spray 100-150 kg of solution per mu.

3. Sheath blight is the same as rice sheath blight; planting sweet corn in rice fields can transmit this disease. For chemical control, use 1 liang of daojiaoqing or 2 liang of daoning per mu plus 100 kg of water; or use 1% validamycin 500 g plus 200 kg of water, and spray coarse mist on the lower part of the plants.

4. For armyworm control, use 2.5% trichlorfon powder at 4-5 jin per mu for dusting, with good insecticidal effect; or use 90% trichlorfon or 50% dichlorvos 1000-1500-fold solution, spraying 100 kg per mu.

5. For corn borer control, granules can be applied into the leaf whorl. Use 3% Miral granule applied into the leaf whorl, with long efficacy and good effect. Or use 1 part Beauveria bassiana powder containing 5-10 billion spores per gram to make a 10-20 fold granule and apply it into the leaf whorl with good effect. Or use 1 jin of Bacillus thuringiensis powder containing more than 10 billion spores per gram, add 750-1000 kg of water, and pour it into the leaf whorl, with good effect against borers.

6. Pest control measures by applying or pouring into the leaf whorl should be carried out at the large trumpet stage. If pests on the female ear silks are severe, after the silks wither, use biological insecticide B.T. emulsion or shachongshuang or padan or dashengong, etc., for control.

7. For aphid control, use 40% dimethoate or 50-80% dichlorvos emulsion 1500-2000-fold solution, or use 50% pirimicarb at 20-30 g per mu.

V. Timely harvest of fresh ears

1. The green ears for market are sweet corn ears from the late milk-ripening stage to the dough stage. The best harvest index is 70% moisture in the kernels; at this time sweetness is high and flavor is good.

2. Harvesting too late gives thick skin and more residue, and sweetness declines. Harvested fresh ears should be processed in time and should not be left overnight, otherwise sweetness declines and flavor is poor.

3. After quick freezing, fresh ears can be stored in cold storage for a relatively long period and supplied to the market out of season.

VI. Crop rotation and stubble change

1. Sweet corn is not suitable for continuous cropping.

2. Rational crop rotation can reduce pests and diseases, reduce weed infestation, and restore soil fertility.