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The Homeowners Column
Waging War on Weeds with Organic and Inorganic Herbicides
State Master Gardener Coordinator
In the continuing saga of weed wars, let's delve into the world of herbicides. My column published on August 2 included all the other tactics to prevent and manage weeds. Last week's column I highlighted information about herbicide terminology. Ok, here's the quiz: what is the difference between contact or systemic; selective or non-selective; and pre or post emergent? If you are not sure, it's time to revisit my columns from August 2 and August 9, 2014. Dig through your newspaper recycling bin or go to our University of Illinois Extension website http://web.extension.illinois.edu/cfiv/
Herbicides also differ in origin. Herbicides may be inorganic (synthetically produced in a lab) or organic (originate from naturally occurring chemicals). Each offers advantages and disadvantages depending on your intended purpose, needs and desires.
Read pesticide labels before and after purchasing products and follow all label directions. Here are a few things to consider before purchasing organic or inorganic herbicides.
Properties of inorganic herbicides vary widely in how they kill plants and in environmental persistence. They may be contact or systemic; selective or non-selective and pre or post emergent. Systemic herbicides such as glyphosate and triclopyr are particularly useful with perennial hard-to-kill weeds such as poison ivy and mulberry because the herbicide can move into and kill roots. Products such as 2,4-D and triclopyr selectively control broadleaf plants without harming grasses. Inorganic herbicides may be combined into one product to control a variety of weeds with one application. For example Trimec® contains 2, 4-D; MCPP; and dicamba to control hard to kill lawn weeds such as thistles, white clover or creeping Charlie.
Organic herbicides at present are limited in their herbicidal properties, but can be useful in some situations. Organic herbicides are generally non-selective (no inherent capability to detect desirable and undesirable plants), contact (do not move within the plant) and postemergent (plant must be actively growing).
Common ingredients in organic herbicides include: vinegar (acetic acid), d-limonene (citrus oil), eugenol (clove oil) or fatty acids (soap). As contact herbicides they require full plant coverage of spray. Organics strip away the waxy plant cuticle or disrupt cell walls so the plant loses too much water and dies. If you are in to quick revenge, on hot sunny days young weeds will often quickly show damage from organic herbicides.
Organic herbicides generally breakdown rapidly in the environment after application, have no residual activity and many have low toxicity to people and animals. However organic does not equal perfectly safe. Herbicidal vinegar is 10-20% concentration as opposed to the 5% concentration of kitchen grade vinegar. Acetic acid concentrations above 5% can cause severe injury to skin and eyes.
Corn gluten is organic that is a preemergent that prevents sprouting seeds from developing normal roots. Seedlings quickly die once soil gets dry. Established plants are not affected.
Postemergent organic herbicides are particularly effective on young weeds (less than four inches tall). Mature perennial weeds will likely require multiple applications of organic herbicides. Leaves may be killed, but plant quickly resprouts from roots.
Be careful with home mixtures and home remedies. Boiling water will indeed kill young annual weeds. However my tendency toward klutziness keeps me from walking around with a tea kettle full of boiling water. Borax and salt are often listed in home herbicide mixtures. Yet borax and salt at high levels can damage soil until virtually nothing with grow.
Read the label for borax and it details how to clean clothes not how to kill plants. Legally products must be labeled and registered with EPA to be recommended as an herbicide. Registered herbicides have been studied extensively and come with label directions, including use rate and required personal protective equipment.
Three columns dedicated to weeds. Sometimes I think in the war on weeds, we should just call a truce and relax.