Ottawa Citizen, Canada
06-02-07
The corn solution
A new, natural (and safe) weed killer is catching on in the garden
Mike Gillespie, The Ottawa Citizen
Call it the accidental herbicide, but Nick Christians and Iowa State University
are still cashing in on its growing popularity as one of the few natural weed killers
on the market.
Christians had a "eureka!" moment while working with corn gluten in 1985. While
researching turf grass disease, he discovered that the by-product of wet-milling
corn to make cornstarch (and corn syrup) worked wonders as a pre-emergent
herbicide -- and a safe one at that.
While also used as an animal feed, corn gluten meal contains substances that
stop many weeds (such as crabgrass and dandelions) dead in their tracks by
shutting down their seeds' tiny feeder roots.
As Christians discovered, seedlings exposed to corn gluten cannot absorb
enough water to survive, and die before they can take hold. The meal's proteins
act much like a silver bullet, breaking down the roots' cell walls. It only works on
seeds, not established plants. And it will not kill dandelion plants, only the seeds
that they leave behind as they mature.
What evolved from Iowa State was a series of patents that led to the licensing of
20 companies to sell corn gluten as a natural pre-emergence herbicide.
Corn gluten meal comes either as a fine yellow powder or in golden pelletized
crumbles and can be used throughout the growing season, but primarily in spring
and fall. It can be spread safely on lawns, flower beds, bulb beds and vegetable
gardens, even up to the day of harvest. It will not harm beneficial insects, soil
organisms, or pond or stream life, Iowa State studies have shown.
For weed control, broadcast (scatter) the meal as you would any fertilizer, from
about mid-April (for crabgrass) to mid-May (for dandelions). Timing is critical. You
want to catch weed seeds three to four weeks before they sprout in the spring,
and then again in early fall when the weather turns cooler. Most annual and
perennial weed seeds sprout in spring or early summer, but the seeds of some,
like winter annuals chickweed and shepherd's purse, sprout in fall and their roots
survive the winter.
The City of Ottawa, one proponent of corn gluten, recommends applying the first
treatment before tulips go dormant. It reports 80 to 100 per cent effectiveness in
reducing crabgrass germination.
The city's website (ottawa.ca) also recommends a summer application from the
middle to the end of June to reduce weed seeds that blow in during late May.
This would hold true in gardens from one end of the country to the other.
Researchers say corn gluten won't burn your lawn like a synthetic fertilizer will. It
releases tiny amounts of protein material every time it gets wet.
Spread the gluten evenly over lawns, but avoid bare spots that have just been reseeded. It can also be sprinkled on cracks in driveways and sidewalks without
fear of harming children or pets (unless they have allergies triggered by dust
inhalation). Pellets are easier to use than the powdered form of gluten meal,
which some users say tends to clump when watered.
After spreading, water the gluten to release its proteins. The seeds will seek the
water, which, "poisoned" with the protein, will kill them. Be sure to water lightly; if
the ground is too wet, it will take longer for the gluten to work, and if you happen
to get a downpour just after you've applied the meal, you may have to do it again.
A secondary benefit of corn gluten meal, which can be bought for about $20 and
up for a nine-kilogram tub, is its fertilizer attributes. The gluten meal has 10-percent nitrogen by weight and acts like a 10-0-0 fertilizer, feeding your lawn and
inhibiting weeds just as a chemical-based weed-and-feed herbicide would do.
Plan on spreading five to 10 kilograms of gluten per 100 square metres (or about
20 pounds per 1,000 square feet) of lawn or gardens. It will remain active in the
soil for five or six weeks before naturally decomposing. It comes in a variety of
brands such as TurfMaize, WOW, Dynaweed and A-Maize-N. At least two stores
in the Ottawa area stock it (Make It Green Nursery, 5200 Flewellyn Rd., Kanata,
and Rona Home & Garden, 585 West Hunt Club Rd.).
While some gardeners report immediate success with corn gluten meal,
horticulturalists generally point to longer-term success with successive
applications over three years and with a high level of weed control by year four.
One word of caution that springs from Iowa State research: Wait until your
seedlings have emerged in flower gardens, vegetable gardens or lawn patches
before applying corn gluten meal. It will stop the pre-emergent plants cold, just
like it does weeds.
City of Ottawa research into natural herbicides has popped up a number of other
environmentally friendly agents that use pelargonic acid, a fatty acid found in
plants and animals. The city's website says such herbicides rapidly lower the pH
of any plant sprayed, weakening the cell walls and killing the plant in about two
hours. It adds that they are not systemic nor selective so cannot be used on
lawns, which would take them off most gardeners' wish lists.
It also suggests a product called Natures Glory Fast Acting Weed and Grass
Killer, which contains acetic acid (vinegar) and lemon juice. Another brand, it
adds, is sold by Ecoval Company, and uses a commercial formula made up of
25-per-cent acetic acid.
Mike Gillespie is editor of the Citizen's Arts & Books section and a commercial
market gardener.