Horticulture/Corn Gluten Meal

Corn Gluten Meal (often simply called CGM) is a byproduct of corn (maize) processing that has historically been used as an animal feed, but was discovered to have pre-emergent herbicidal effects in 1985, by Dr. Nick Christians, during a turf grass experiment being conducted by Iowa State University.

The use of corn gluten meal as an herbicide is patented, but like many food-related substances used for gardening is not regulated in the US

Uses
Target plants include primarily small-seeded annual and perennial herbs. It is most frequently used in lawns, but may be applied to gardens and fields as well.

The corn gluten meal breaks down over time as an organic nitrogen source (NPK value of 10-0-0).

Action
Proteins in CGM inhibit root formation on newly germinated seeds, killing the plant. Applications must be timed so that the CGM is present and effective as seeds are germinating.

Application
Applied using a spreader or even by hand (the material is pretty much harmless if not inhaled, and in fact is edible but not particularly palatable).

On lawns, CGM is applied in early spring (usually timed phenologically by the blooming of ../Crocus/ or ../Forsythia/), and again in the autumn. If the lawn is overseeded, CGM should either be applied at least 6 weeks before sowing, or 2 weeks afterwards.

Precautions
Very safe to use, non-toxic. Should not be applied to areas where it's likely to wash directly into watersheds (it is a nitrogen source), but otherwise ecologically safe.

Resistance
Large-seeded weeds seem unaffected.

Species affected
Testing for affected species is ongoing, but confirmed species include :
 * Velvetleaf (../Abutilon theophrasti/)
 * Quackgrass (../Agropyron repens/)
 * Creeping bentgrass (../Agrostis palustris/)
 * Redroot pigweed (../Amaranthus retroflexus/)
 * Common lambsquarters (../Chenopodium album/)
 * Orchard grass (../Dactylis glomerata/)
 * Smooth crabgrass (../Digitaria ischaemum/)
 * Large crabgrass (../Digitaria sanguinalis/)
 * Barnyardgrass (../Echinochloa crusgali/)
 * Quackgrass (../Elytrigia repens/)
 * Wooly cupgrass (../Eriochloa villosa/)
 * Catchweed, Bedstraw, Goosegrass (../Galium aparine/)
 * Perennial ryegrass (../Lolium perenne/)
 * Black medic (../Medicago lupulina/)
 * Annual bluegrass (../Poa annua/)
 * Buckhorn Plantain (../Plantago lanceolata/)
 * Purslane (../Portulaca oleracea/)
 * Curly dock (../Rumex crispus/)
 * Giant foxtail (../Setaria faberi/)
 * Yellow foxtail (../Setaria lutescens/)
 * Green foxtail (../Setaria viridis/)
 * Black nightshade (../Solanum nigrum/)
 * Shattercane (../Sorghum bicolor/)
 * Dandelions (../Taraxacum/ spp.)