Agronomy

Description

A popular Missouri summer vegetable crop, sweet corn originated in the New World. Sweet corn earned its name as a “sweet” corn because of a mutation. Relative to field corn, corn varieties that express the “sweet” mutation store roughly twice as much sugar in the seed endosperm. The extra sugar gives the corn its sweet flavor.

Site Selection

Well-drained soil that can hold water well creates a good sweet corn planting site. The site should also have a pH level that ranges from 5.5 to 7.0. If a site has soil that can warm quickly and has a southern exposure, then it may be well-suited to support early sweet corn production. A field already growing fescue generally has good characteristics for sweet corn production. Before sweet corn production can begin, however, the sod requires plowing several weeks prior to planting.

Fertility

Producing sweet corn involves applying nitrogen, phosphorus and potassium. Nitrogen supports corn stalk and ear growth. Sweet corn benefits from nitrogen applications before planting and during sweet corn growth. The pre-seeding nitrogen requirement is 65 pounds of actual nitrogen, and producers should use a 35-pound nitrogen sidedress application after sweet corn plants have grown 6 inches high. As another option to supply nitrogen to sweet corn plantings, producers may rotate sweet corn with plants like alfalfa, vetch or clover that can fix nitrogen.

Phosphorus and potassium application rates will depend on soil test results. However, producers can may broadcast as much as 100 pounds of phosphorus and as much as 150 pounds of potassium.

If producers plant sweet corn during cool weather, which is considered a 60 degree F temperature, then they may consider applying a starter fertilizer. The starter fertilizer could support seedling vigor, good establishment and early growth.

Variety Selection

Sweet corn varieties may be distinguished by kernel color, sugar content and maturity. With respect to kernel color, sweet corn varieties may produce white, yellow or bicolor kernels. A bicolor corn ear would be 80 percent yellow kernels and 20 percent white kernels. Kernel color doesn’t influence sweet corn sweetness.

With respect to sugar content, the first sweet corn varieties had the Su-1 attribute. Today, the processing market absorbs most Su-1, or standard, sweet corn. Otherwise known as sugar-enhanced sweet corn, SE varieties yield kernels with more sugar and kernel tenderness characteristics. Sugar-enhanced sweet corn sells well in local markets, and it has more sweetness than Su-1 varieties. The SH2 gene leads to producing supersweet sweet corn. These varieties have tougher kernels and record longer shelf lives; however, they can’t tolerate soil temperatures cooler than 60 degrees F. Overall, supersweet varieties lack the vigor typical of other varieties, so they may have thin or uneven stands. Relative to SE sweet corn, supersweet varieties also tend to be sweeter. Synergistic sweet corn, also recognized as SY or triple-sweet sweet corn, produces corn ears with three-quarters SE kernels and one-quarter supersweet kernels.

Because pollen can spread between sweet corn varieties, producers may need to isolate plantings of different varieties. The isolation intends to stifle cross-pollination. Without isolation, cross-pollination may affect the sugar content and color of sweet corn varieties. As a guide for variety isolation, yellow or bicolor sweet corn requires isolation from white sweet corn; yellow sweet corn requires isolation from bicolor sweet corn; and SH2 supersweet varieties require isolation from Su-1, SE and SY varieties. Additionally, growing areas must isolate sweet corn from field corn and popcorn. To isolate varieties, producers may allocate a 250-foot distance between areas that grow different varieties, or they may stagger variety plantings by 14 days.

Maturity represents another factor that may differ by sweet corn variety. Early varieties mature within at least 70 days. For mid-season varieties, they mature in 70 days to 84 days, and late-season varieties require at least 85 days to mature. Varieties with mid- to late-season maturities generally yield better quality sweet corn. Because consumers might want sweet corn early, however, they may recognize lower quality as a tradeoff for having sweet corn available early.

Several sweet corn varieties work well in Missouri climates. The following table lists a few varieties recommended by University of Missouri Extension. Before selecting varieties, producers should test their options and choose those that satisfy local preferences.

Recommended Varieties in Missouri

Planting

In most cases, postpone sweet corn planting until soil temperatures warm to at least 60 degrees F at 2 inches below the soil surface. Choose seed that is flat and heavy. Fungicide- and insecticide-treated seed may germinate better and establish a better stand.

Generally, space rows 30 inches to 42 inches apart. Producers may adjust row spacing to account for equipment size. When designing the planting area, consider allocating space for an access lane. Positioned at every 12th row, the access lane would improve harvesting and spraying ease. Within a row, plants may grow at 8- to 10-inch spacing. If sweet corn plants are too close, then nonheading may become a problem, and if they’re too far apart, then wind damage and excessive tillering could be issues.

Alternative production strategies may facilitate sweet corn production earlier in the year. With early plantings, producers may earn a premium when they sell sweet corn, and pests may present a less significant challenge. To produce early sweet corn, producers may select varieties with early maturity dates, or they may apply row covers to provide shelter from frost. A plasticulture model is another option. After planting sweet corn seed in double rows with a 14- to 24-inch spacing, producers can spray herbicide and cover the planting area with clear, perforated plastic, which would have a 1- to 1.25-millimeter thickness. For an estimated 30 days, the plastic would cover the sweet corn planting area. Remove the plastic when seedlings have grown 6 inches to 12 inches tall. Although transplants can encourage early sweet corn production, producers would need to take special care to ensure that transplants have success. As a result, sweet corn transplants are relatively uncommon. They tend to lack viability for planting areas that exceed one acre.

As a monecious plant, sweet corn has a male flower, which is the tassel that generates pollen, and a female flower, which is the corn ear, on a single stalk. Pollen must transfer from the tassel to the corn ear silk. Typically, the wind facilitates this transfer. Considering that sweet corn pollination relies on the wind, plantings that use several short rows, not one long one, may experience improved pollination. At a minimum, sweet corn plantings should generally have three rows per variety.

Water Management

With a shallow root system, sweet corn may require supplemental moisture. Each week, production areas need 1 inch of water. If using irrigation, then producers could choose from traveling gun irrigation, solid set irrigation or drip irrigation. Traveling gun irrigation tends to be common. However, drip irrigation could easily meet irrigation and fertigation needs. Moisture availability would be especially important during sweet corn silking, tasseling and ear development stages.

Weed Control

Ideally, planting sites will not have a noxious weed problem. If weeds compete too heavily with young sweet corn stands, then the crop may not yield as well. Weed-free fields are preferred until plants reach 24-inch heights. To control weeds, producers can consider applying herbicides or cultivating the area. Rotating crops is another strategy for minimizing weed competition.

Producers may choose Roundup Ready sweet corn varieties that can withstand glyphosate applications. Before adopting genetically modified sweet corn varieties, however, ensure that the genetically modified characteristic won’t affect marketing opportunities.

Insects and Diseases

When growing sweet corn, several insect pests may challenge production. Those that would most commonly affect Missouri sweet corn producers include the corn earworm, European corn borer, seed corn maggots, cutworms and corn rootworms. To track pest presence and assess control needs, regularly scout planting sites or use traps.

Applying insecticides could help control pests. Rotating crops would also help. After sweet corn has tasseled, regular insecticide applications may be necessary to discourage insects from damaging the crop. Depending on the variety, sweet corn may possess Bt protection. When included in sweet corn genetics, the Bacillus thuringiensis protein would help to control corn earworms and European corn borers.

For sweet corn producers, insects aren’t the only pests that could create concerns. Other problematic species include raccoons, groundhogs, birds and deer. These pests may be especially damaging in planting sites located near wooded areas or thick hedgerows. To minimize bird-related damage, producers may choose varieties that produce a tight husk, or using propane cannons is another alternative. To deter raccoons, groundhogs and deer, consider constructing a fence that surrounds the planting area or keeping a dog nearby.

Sweet corn generally doesn’t experience strong disease pressure compared with other vegetables. However, a few diseases, such as Stewart’s wilt and corn smut, may arise. Stemming from bacteria, Stewart’s wilt may occur if flea beetles carry the bacteria into the stand. As a fungal disease, corn smut forms as galls on corn ears. To reduce disease incidence, strategies include selecting disease-resistant varieties and rotating crops.

Harvest and Storage

When sweet corn is ready to harvest, ears will feel full, and silks will have dried. Kernels should appear plump and contain milky fluid. As a general rule, sweet corn will silk and can then be harvested about 20 days later. Hand labor or mechanical harvesters can harvest sweet corn. Unless harvesting supersweet varieties, however, harvesting sweet corn by hand at three- or four-day intervals is common. Ideally, producers will harvest sweet corn when field temperatures are cool. Mornings present good conditions.

After harvest, producers should view sweet corn cooling needs as a three-step process: precooling, cold storage and in-transit cooling. First, sweet corn requires precooling with hydrocooling or package icing. With hydrocooling, cold water immerses sweet corn, or the sweet corn undergoes a cold water shower. At packaging, package icing involves sending crushed ice through sweet corn containers. The ideal precooling temperature would be near 32 degrees F. Cold storage conditions should have temperatures near 32 degrees F and at least 95 percent relative humidity levels. During transit, producers may circulate finely crushed ice throughout the truck to keep the sweet corn cool. Cold storage discourages sucrose found in sweet corn from converting to starch.

Shelf life varies by variety. In most cases, assume a four- to six-day shelf life. Supersweet varieties, however, may store for 10 days.

Sources

Fritz, Vincent A., Cindy B. Tong, Carl J. Rosen and Jerry A. Wright. 2010. Sweet corn (vegetable crop management). University of Minnesota. St. Paul, MN 55108-6068.

Jett, Lewis W. 2006. Growing Sweet Corn in Missouri. University of Missouri Extension. Columbia, MO 65201.

Kaiser, Cheryl and Matt Ernst. 2014. Sweet Corn. University of Kentucky. Lexington, KY 40506.

Mayberry, Keith S. and Herman Meister. 2003. Sample Cost to Establish and Produce Sweet Corn. University of California. Davis, CA 95618.

Orzolek, Michael D., Lynn F. Kime and Jayson K. Harper. 2011. Sweet Corn Production. Penn State Extension. University Park, PA 16802.

Schultheis, Jonathan. 1998. Sweet Corn Production. North Carolina Cooperative Extension. Raleigh, NC 27695-7602.