Corn, Sweet

Introduction

Sweet corn is a warm-season crop and one of the major vegetables grown in New England.  It is an extremely popular crop for roadside stand and farmers' market sales as well as for wholesale markets.

Sweet  corn grows on a wide range of soil types.  Early planting should be on light, well-drained soil in a warm, sheltered location.  Heavier soils are best for the main crop.  Plowing under corn stalks and cover crops to maintain high levels of organic matter in soils is recommended for best crop production.  Irrigation may only be necessary in dry weather, particularly on light soils, and especially as silking starts.

Types and Varieties

Sweet corn varieties are categorized by their genotype.  The most common types are normal/sugary (su), sugar enhanced (se), and supersweet/shrunken (sh2).  Other newer varieties include sweet breeds, synergistic, sweet genes, or improved supersweets which have a combination of genes.

su           "Normal or Sugary"

Standard hybrid sweet corn is a mutant type of corn that differs from field or dent corn by a mutation at the sugary (su) locus. This type accumulates about 2x more sugar than field corn.

se           "Sugary Enhanced" or "Modified Sugar" or "Everlasting Heritage" (EH)

se +        Homozygous Sugary Enhanced  

There are two distinct groups within the cultivars containing the "se" gene, which increases sugar levels above those found in "su" varieties.  The "homozygous se" or se+ cultivars have higher sugar levels in 100% of their kernels.  Cultivars containing the "heterozygous se" gene have higher sugar levels in 25% of their kernels; the other 75% contain the normal "su" gene with lower sugar levels.  So "se+" cultivars are usually sweeter than "se" cultivars.

  • Sugar conversion to starch is about the same rate as standard sweet corn.  Refrigeration is essential to maintain quality.
  • Isolation not required, but desirable. Note directions on seed tag label.
  • Kernels tender and creamy.
  • Tip cover weak on some varieties

sh2           "Super Sweet" or "Extra Sweet" 

  • Sugar content twice as high as standard sweet corn.
  • Slow sugar conversion to starch so quality will hold 7 to 10 days. Refrigeration suggested to extend quality.
  • Isolation is required from all other types of corn. Note directions on label.
  • Kernels can be somewhat tough or crunchy.
  • Does not germinate well in cold, wet soil.  Plant after soil temperatures exceed 65°F and be sure there is adequate soil moisture.  Adjust planting depth for soil conditions and soil type.  Seed of the "sh2" type is light-weight, wrinkled, and fragile and should be handled gently to prevent damage.

syn          "Synergistic"

These include synergistic or improved supersweets such as Sweet Breed and Sweet Genes.  These varieties have combinations of su, se, se+, or sh2 genes.  Synergistic varieties having the sh2 gene may be grown with other "Super Sweet" varieties, but must be isolated from "se" and "su" types to achieve best quality.

aug          "Augumented Shrunkens"

Augmented Shrunken sweet corns are a new type of shrunken corn types. They contain the "sh2" gene, but kernels of augmented shrunken are more tender, like "se" varieties.  Augmented shrunken varieties should be hand harvested because their tender kernels will likely be damaged by machine picking. These varieties need to be isolated from normal, "se" and synergistic hybrids. Additionally, they have the same seed vigor problems as supersweet varieties and should only be planted under optimal conditions.

MiraiTM    

MiraiTM sweet corn varieties carry two copies of all three sweet corn genes: su, se and sh2. They have all tender supersweet kernels and, like the augmented shrunken varieties, need to be hand-harvested. Mirai varieties also need optimal soil conditions for seedling establishment. Mirai types do not require isolation to avoid starchy kernels, but isolation from other sweet corn types will assure best quality.

Bt Hybrids

These are genetically-modified (GM) varieties that are protected from European corn borer, and to a lesser extent, fall armyworm and corn earworm caterpillars because they express the protein toxin of the bacteria Bacillus thuringiensis. They are currently available as super sweet (sh2) or as synergistic "TripleSweet" varieties, composed of 75% "se" and 25% "sh2" kernels. In the synergistic varieties, the Bt toxin is expressed in the "se" kernels, the stalks, leaves, tassels and fresh silk. Bt varieties are still susceptible to attack from flea beetles, cutworms, aphids, sap beetles, high levels of corn earworm and soil-dwelling insects. Bt seed costs more than the seed of other sweet corn varieties and currently comes with a list of resistance management strategies with which to comply. These varieties may reduce the time, energy and expense associated with insect control and may simplify sweet corn pest management. There are many other less obvious potential risks and benefits that may be associated with the use of this technology. GM sweet corn is not allowed in organic production. Growers in Maine must be certified to grow Bt corn. Contact the Maine Board of Pesticides Control for more information. 

Sweet Corn Varieties.

VARIETY TYPE COLOR WILT RUST MDMV
Sweet Chorus (67) syn Bi L M M
Sweetness (68) syn Bi - - -
Latte (68) syn Bi M M -
Vitality (68) se Bi - - -
Espresso (70) syn Bi M M -
Mirai 308BC (70) mirai Bi - - -
Harris 1001 (72) se Bi M - -
Temptation (72) se+ Bi - - -
Reflection (72) syn Bi - M -
Cuppa Joe (73) syn Bi M M -
XTH 2170 (73) sh2 Bi M - -
Mirai 336BC (73) mirai Bi - M M
Sweet Rhythym (73) syn Bi M L -
Anthem XR (73) sh2 Bi L H -
Charisma (74) se Bi M M -
Fanstastic (74) sh2 Bi - - -
XTH 274A (74) sh2 Bi M - -
Sweet Ice (74) syn W M L L
Kristine (74) syn Bi M M -
Mystique (75) se+ Bi H M L
SC1102 (75) syn Bi - - -
Sparkler (75) syn Bi - - -
Mirai 301BC (76) sh2 Bi M M -
Awesome (76) sh2 Bi M - -
Luscious (77) se Bi - - -
Accord (78) se Bi - - -
Legion (78) sh2 Bi M M M
Pow Pow (78) syn Bi - - -
Essence (78) syn Bi M M -
Providence (79) syn Bi - M -
Montauk (79) syn Bi M - -
Delectable (80) se+ Bi M H L
Precious Gem (80) se+ Bi M M L
Primus (81) sh2 Bi M M -
BC 805 (82) * se Bi - H -
Jackpot (82) se+ Bi M M -
Silver King (82) se+ W M M -
Argent (83) se W H M L
Incredible (85) se+ Y H - -
Cameo (84) se Bi M M -
Silver Queen (94) su W H L L

The number in parentheses is the approximate number of days to maturity from seeding.

H, M, L: High, medium or low resistance or tolerance to the following diseases - Wilt: Stewart's wilt, Rust: Common rust, MDMV: Maize dwarf mosaic virus.

Other codes: mirai: mirai, su: normal sugary, se: sugar enhanced, se+: sugar enhanced homozygous, sh2: supersweet/shrunken, syn: has some combination of su, se and sh2 genes, Y: yellow kernels, W: white kernels, Bi: bicolor, *: Bt hybrid