Applying Pre Emergents
Hi, Rule of thumb for applying pre emergents is "before the last bloom on the forsythia falls", but since forsythias were already blooming before this snow and freezing weather is it to late to apply, if not when should it be applied? I am speaking specifically of Espoma's Organic Weed Preventer (Corn Gluten). Thank you,
Corn gluten has been sold for many years as a preemergent herbicide. It can suppress annual weeds but not as effectively as traditional herbicides.
Corn gluten is a source of nitrogen. Applying it at the recommended amount to control weeds may exceed the amount of nitrogen allowable in Maryland per the Fertilizer Use Act of 2011. Check the label to make sure. Some products are labeled as both an herbicide and a fertilizer.
We recommend fertilizing in the fall, not the spring. Excessive nitrogen applications in spring and summer increases disease problems and reduces stress tolerance.
We do not know what weeds you are trying to control. If you are referring to a crabgrass preemergent look for a preemergent that contains no fertilizer. See our website for timing and Tips for Application http://extension.umd.edu/hgic/crabgrass