Coatings enhance seed handling and identification and seedling health
By Elizabeth Ashby
There are more to seeds than meets the eye these days.
Many varieties come coated with polymers—think gel coatings used in the pharmaceutical industry and the candy coatings used in the candy industry. These coatings help them flow easier through mechanical planters, an advantage that is almost taken for granted by growers.
But the role of seed coatings is changing. Chemical companies are working with Incotec, Seed Dynamics, Germains Technology Group and even some seed companies, such as Harris Moran, that apply seed coatings to add nutrients, germination aids and crop protectants.
As with most technology used in agriculture, seed coatings and treatment shouldn’t be viewed as a silver bullet but rather another production tool, says Keith Kubik, a seed physiologist with Harris Moran Seed Co. in Modesto, Calif.
“We take the top seed and make it even better,” Kubik says of treatments and coatings.
But there is no substitute for quality seed and good germplasm—treatments or coatings will not bring poor quality seed or a weak variety up to par, he says.
History behind the coating
Seed coatings have been used in agriculture for more than four decades. Glen Kaufman, president of seed distributor Paramount Seeds Inc. in Plant City, Fla., says large-scale commercial use of coatings began in the 1960s for the European greenhouse transplant industry. In the mid-1970s when California outlawed the short handled hoe, coatings were needed for precision planting.
Kaufman, who has been in the seed business for 30 years, says field precision sowing allowed for accurately placed seeds, which led to easier and less damaging thinning with the long-handled hoe. This, of course, was before the development of mechanical planters.
Types of coatings
Many seeds in their raw form are too small, light or misshapen to use in today’s mechanical planters. Coatings make seeds larger, smoother, heavier and more uniform.
One of the original coating methods, which still remains the most common, is film coating. Kevin Lane, director of operations at Seminis in Oxnard, Calif., says film coating gives the seed a high-gloss appearance, provides excellent flow through planting equipment and is a good platform for incorporating actives that enhance seed performance and yield.
The next step up is encrustment, where Kaufman says more material than even what is in a film coat is added. Encrustments make the seed even smoother, filling any hollows in the seed and reducing friction during planting. Kaufman says encrustments are primarily used in sweet corn.
“They are putting such a cocktail of chemicals, four or five different active ingredients in it, so this can cover it over a bit as to not dust off or break off,” he says.
Further down the line of coating options is pelleting. This method makes the seed almost perfectly round and an even better option for precision planting.
“If you have a row a half-mile long and you want to put three seeds and inch apart, 12 inches on center, as with lettuce for example, you can do that,” Kaufman says. “Machinery can place seeds more accurately even when driving equipment faster.”
At Harris Moran, pelleting gets even more detailed, Kubik says.
The company recently introduced the Opticoat family that offers growers three pellet density choices—light, medium and heavy.
“The reason we have three different densities is because of the lettuce market,” says Kubik, who developed many of the company’s seed coatings. “Heavy for the Southwest and desert, light for the [Central California] coast. Some prefer the heavy in the East and in Canada, but we do have that medium density, which is kind of the best of both worlds, for places such as Florida and up the [East] coast. Some people use that medium density as a utility pellet.”
Although the light and heavy density pellets may look similar, the high density has a coating-to-seed ratio of about 35:1 compared with 17:1 to 15:1 for the low-density line.
Not only does Kubik have to consider densities when developing a pellet, but he also must consider the industry standard seeding rates. With lettuce, for example, that’s 12,500 seeds per pound.
In addition, he has to consider the different materials used in the pellet coatings and how they may affect water retention or repulsion, porosity and oxygen exchange.
Kubik may ask himself, “What is the particle size, and how do they go together to form pores? But they can’t be so tight that they restrict oxygen, and are they hydrophobic or hydrophilic?”
A rainbow of seed colors
After these coating options, seeds move into the realm of enhancements, or techniques used to condition them in some manner. One type of enhancement is adding pigment to the seed so it is more identifiable. Becker Underwood of Ames, Iowa, is known as a leader in the industry for its creation of specialty bio-agronomic and colorant products with a broad range of applications, one of which is the seed industry.
Federal law requires any seed treated with a pesticide to be colored to prevent treated seed from entering the food market, which could lead to accidental consumption. The company says its seed colorants identify treated seed and reduce mishandling of seeds treated with active ingredients. Pigments also allow a seed producer to brand its seed by using a custom color.
Ready for prime time
A second form of enhancement is seed priming, which means starting the physiological process of germination under controlled conditions to accelerate seed germination and enhance vigor. Lane says priming is particularly effective for seed planted in harsh environments.
Kaufman says celery, endive, escarole and lettuce tend to have problems with heat dormancy or light dormancy, which can be overcome with priming.
“It can be likened to putting horses in the starting gate and pulling that starting gate half-way around the track,” he says.
Priming helps seedlings germinate sooner and can keep the seeds from being exposed to soil organisms that they might otherwise encounter in the soil. Kaufman says priming could lead to problems, particularly if the seed it taken too far in the priming process, thus reducing its shelf life.
Chemical companies put emphasis on seeds
A trend that Kubik says he sees continuing is the addition of small amounts of pesticides during the coating process.
The chemicals protect the seed from soil-borne diseases and insects during germination, increasing stand health and establishment. In many cases, the treatments provide long enough residual control that growers may be able to eliminate a foliar spray early in the season.
Until recently, most vegetable growers weren’t able to chose the products applied to the seed—lthe seed companies made those choices.
Take cucurbits, for example. The industry standard was Thiram, Apron and Losban, and nearly all cucurbit seed came with the same package, Kubik says.
The exceptions were sweet corn and snap beans, where growers were typically able to choose from a menu of seed treatments.
The increased choices were mostly due to the larger number of chemicals registered as seed treatments for those crops, he says.
Many of the sweet corn treatments were labeled as part of field corn registrations. The companies also piggybacked green bean registrations onto soybean product labels.
As more major chemical companies receive seed treatment registrations for other vegetables, Kubik says growers should see the menu of options expand.
Four years ago, Syngenta Seed Care, a division of the Syngenta Crop Protection Inc. in Greensboro, N.C., introduced FarMore for Brassica, bulb, cucurbit, leafy and fruiting vegetables.
Tom Harris, a FarMore specialist for Syngenta Seed Care based in Phoenix, says it is a comprehensive program for vegetables that provides early seed protection against diseases, insects and nematodes. It is designed to protect a plant’s initial growth through the first three to five weeks, he says.
Harris says the disease protection portion of FarMore, which protects against general damping off and seedling blight and all four major classes of fungi, has been available since October 2006.
He says the nematode product—Avicta—is registered, but the company isn’t actively marketing it yet as it still works out specific formulations. Harris expects the third component—the insect protection piece—will be registered in the fourth quarter of 2008.
Nine companies are licensed to apply the FarMore technology, including Seminis, Harris Moran, Incotec and Seed Dynamics, he says.
BASF Corp. in Research Triangle Park, N.C., entered the seed treatment business when its Coronet fungicide seed treatment received Environmental Protection Agency approval in mid-June. It is registered for use on Brassica, bulb, cucurbit and legume vegetables.
Coronet contains two active ingredients—boscalid and pyraclostrobin—to protect against seed-borne fungi causing seed decay, seedling damping off and three seed-borne pathogens, according to a news release.
Additional reporting by Grower editor Vicky Boyd
