Is corn gluten really effective in controlling lawn weeds before they germinate? Can I use it to prevent crabgrass and when is the recommended time to apply it?
Corn gluten (CG) is promoted as an organic substitute for conventional preemergent herbicides. CG is a by-product of the commercial corn milling process. However, it is not recommended by the University of Maryland Extension for weed control in lawns for three reasons:
- University research data shows mixed results regarding its effectiveness in preventing crabgrass. It is ineffective where weed pressure is high.
- CG is 10% nitrogen by weight. Some experts think that this large amount of nitrogen increases lush, dense growth which crowds out some weeds. But nitrogen is converted into nitrates which can move into surface and groundwater and eventually into the Bay. Also, spring nitrogen applications can increase turf susceptibility to lawn diseases like brown patch.
- The amount of the product needed to suppress weeds violates the Maryland Fertilizer Use Act of 2011 which states that no more than 0.9 lbs. of nitrogen per 1,000 sq. ft. can be applied to lawns at each application. According to some CG product directions, you should apply 20 lbs. per l,000 sq. ft. twice a year in spring and fall. Each application contains 2 lbs. of nitrogen. This is well over the per-application rate of 0.9 lbs. and exceeds the total yearly limit of 2.7 lbs. set by law.
Corn gluten products can be found on Maryland store shelves and are labeled as an organic fertilizer, an organic herbicide, or both. CG can be used as an organic fertilizer as long as the application rate is 0.9 lbs. of nitrogen per 1,000 sq. ft. and no more than three applications are made to your lawn per year.
Crabgrass can be a prominent summer lawn weed in Maryland. A thick, dense lawn is your best defense against weeds. Lawn weeds are opportunistic and fill in bare spots or areas where turf is thinning. Proper mowing, fertilizing and planting a good quality seed will reduce weed pressure. Use a standard preemergent lawn herbicide as a last resort.