By Jean Gramlich | March 17, 2020
Dr. Erin Hill, Weed Science Diagnostician for MSU Plant and Pest Diagnostics was our speaker for March. She specializes in weed identification and control, as well as herbicide injury and resistance in a wide variety of Michigan environments.
She says that winning the war against weeds requires a comprehensive understanding of the enemy and an integrated approach for control. What makes a weed a weed? It’s a human designation: a weed is out of place; it’s a plant not valued where it is growing; it’s competitive, pernicious and persistent. Ralph Waldo Emerson said, “A weed is a plant whose virtues have not been discovered.” (Hmm…what if he met Japanese knotweed, phragmites or black swallow-wort?)
Knowing thine enemy means we have to identify the weed using an accurate description. Several websites are useful: michiganflora.net, plants.usda.gov, and weedid.missouri.edu/weedkey.cfm and Picture This (she said not to pay for this site). Books include Weeds of the Northeast by R. Uva et. al. and Weeds of Midwestern United States and Canada by C.T. Bryson et. al. MSU Plant and Pest Diagnostics will identify 3 plant photos for free and also physical specimens.
The majority of weeds come from other geographic regions through natural seed dispersal by wind, water and migratory birds and by human intervention through seeds, nursery stock, soil attached to plants, ship ballasts and domestic animals. They spread along roadways, railroad tracks, power lines and river banks.
Knowing the life cycle of the enemy is imperative. Most weed management concentrates on killing seedlings, so it is important to know whether they germinate in the spring or the fall and what conditions are required for germination. Some seeds can be dormant for years before they germinate, so reducing the seedbank can be effective. Animals eat seeds so increasing predator habitat can help as can reducing tillage. Make sure that crop seed, cover crop seed and soil amendments are free of weed seeds. Barriers such as various kinds of mulch help to prevent weeds. Preparing the seedbed two weeks in advance allows the weeds to germinate so that you can destroy the seedlings before planting. Mechanical weed control methods include mowing, hand pulling, hoeing and tillage. Getting rid of weeds before they flower or fruit can save a lot of labor later on.
Herbicides can be part of our armamentarium. It is important to protect plants we want from the ravages of any herbicide we decide to use. Avoid spillage on leaves, exposed roots and injured bark. The labels on pesticides specify directions, applications and protective gear required. Human and wildlife toxicity and the effects on air and water are specified. Horticultural grade vinegar, clove oil and soaps are non-toxic alternatives. Corn gluten meal is a pre-emergent herbicide.
Online research can be helpful: Roundup.com, Bioadvanced.com and Scotts.com are examples of websites which give more information. Of course these companies want you to buy and use their products so buyer beware. The active ingredient in the original Roundup was glyphosate, but now Roundup is a brand and may have other ingredients. Don’t take advice from store personnel! According to Dr. Hill, glyphosate is relatively safer than other herbicides and does not leach through the soil.