Large scale control refers to the redress of areas with huge, continuous, garlic mustard colonies. These areas usually have well established seed banks. Colonies may be of mixed age, but often appear as one generation. Colonies that appear mostly as second year plants are best combated with string trimmers during May. Colonies that appear mostly as first season rosettes are best combated with herbicide during the ‘dormant’ season. In addition to these two methods described below, please review the section on Small Scale Control for advice on hand removal. Hand removal of satellite infestations is an integral recommendation for any large scale control.
May 5 - May 12 Optimal window for string trimming
As a general guideline, April 25 - May 1 is when second-year plants are about to bloom in Rock County. Tight green flower heads are poised on top of stems everywhere, ready to turn white. These budding plants, or those with the first few white flowers, will not recover much when cut at this stage. Trimming plants close to the ground level at this period is an excellent strategy for anyone wanting to dramatically curtail an infestation. A great deal of potential mustard seed can be utterly eliminated with this technique. The timing must be precise. Cutting earlier (before budding) may leave enough energy in the plant to flower again, though producing much fewer blooms and seeds. Cutting later (midway through the flowering season or later) is helpful and strongly urged if you missed the optimal window, but as the season advances there is increased chance of dispersing some viable seeds. Once the plant has begun flowering you can cut for a week and not worry you are leaving new seeds on the ground. After that plants cut, broken, or snapped by hand should be raked up and bagged for removal from the woods. It will take but a week for the first seeds to form once flowering has begun. County-wide the blooming period will stretch from April 25 to at least the end of May. We really would like to mow the mustard down before the flowers are in full force, and before seeds start to develop.
Garlic mustard can be cut with hand scythes, mowers, or anything that breaks off the plant low to the ground with a minimum of soil disturbance (disturbing the soil promotes mustard germination). The highly recommended tool for mass destruction is the power string trimmer (as opposed to blade trimmers or lawn mowers). String trimmers can cut down more mustard, faster, at this stage than most other tools or techniques. Many Rock County woods are cluttered with dead fall. String trimmers allow close cutting to logs or obstacles. Some muscular exertion is definitely required. Always wear a full-face shield, long legged and long sleeved clothing, and leather gloves. String trimmers splatter around a lot of plant juice, including poison ivy.
Poison ivy is common and may be forming leaves (hard to spot) when you are string trimming. If you find yourself trimming in a poison ivy patch, leave it. Address the mustard later with herbicide. Wash any exposed skin with soap and water immediately. You have six hours before you die (just kidding). You have six hours before the oil bonds to your skin and the next day you will start to itch. The rash may last up to three weeks depending on exposure and sensitivity.
Many people are naturally immune to poison ivy. Most will eventually become sensitive after repeated exposure. If you are so blessed, maintain your immunity by doing what the rest of us do: wear protective clothing and wash often.
Trimming native flora
When string trimming garlic mustard, other flora will be cut too. This is unavoidable. Chances are, cutting will have a short-term negative effect on desirable plants. Most native woodland plants are perennial and should re-sprout.
In general, herbicide should be applied to garlic mustard only when most native flora is dormant. In Rock County this would be November through March. One has to be prepared to run out and apply herbicide on a sunny, snowless day when temperatures are abnormally warm (>50° F) and winds are calm. These conditions are most likely to occur in March or November.
The recommended herbicide is 2% glyphosate (in water). The familiar brand is Roundup© by Monsanto. Always read the label and follow directions. Generic formulations are also available at forestry or landscaping supply agencies. Brightly colored dye added to the herbicide will help keep track of where you spray. Water-soluble dye is often available through forestry suppliers. The spraying unit can be hand-held or a backpack type. Keep the nozzle at a fine setting and the sprayer pumped to high pressure. A fine mist is ideal for this delicate and plentiful target. Low pressure produces big droplets and wastes herbicide. Garlic mustard likes to hide in leaf litter. Kick or rake leaves to fully expose the targets.
1) First year rosettes, November through March.
2) Newly germinated seedlings in very early April.
Herbicide victims in April should turn brown in a week. Spraying in winter will not change the color of most green plants until growth resumes in April.
If new seedlings emerge after treating areas, repeat the treatment about a week later. Please be judicious and spare as much non-target flora as possible. Watch especially for bloodroot (Sanguinaria canadensis) and hepatica (Anemone acutiloba). These are two of our earliest, native risers.
Clearing brush and debris
Persecuted mustard often takes refuge under fallen branches. It receives protection from tangled vines, prickly raspberries, or logs. Protective clutter of this sort keeps us from reaching the mustard. Clearing brush is an essential component of an overall eradication effort. Clear the brush only in winter to avoid damaging native flora and stirring up the soil. Stirring the soil always favors the garlic mustard.
1) Removing fallen dead debris.
2) Cutting and piling brambles, prickly ash, gooseberry, European buckthorn or tartarian honeysuckle.
3) Painting all freshly cut stumps immediately with 20% glyphosate in water with dye.
Some deadwood is normal for woodlands. No need to clear it all. Pick up enough to enable addressing the infestations. Piles of brush tend to snuff out whatever lies under them, so try to pile where there is little native flora to start. Always check upwards, and pick a location that won’t scorch tree limbs if the pile is burned a winter or two later. If you elect not to burn (or remove) the pile, it will make a fine home for a red fox.
Prescribed burning (a.k.a. controlled or conservation burning) during the dormant season promotes native flora by exposing the soil for faster warm up and by scorching low shrubs resulting in higher light. This is true both in prairies and woodlands. Burns are helpful in that they make all plants emerging from the dark earth more visible. Be warned: burning woodlands temporarily promotes garlic mustard for the same reasons it promotes native flora. It opens the soil to more light. Burning is great to promote as much garlic mustard as possible, in order to kill as much as possible. It can be disastrous if there is no follow-through the next March or April with herbicide or mid May with pulling and trimming. Do not burn after April 25 in Rock County woodlands because there is too much native flora out. Burning may also damage populations of beneficial insects, reptiles, or amphibians. When considering burning your woodland, consult with experts about both wildlife and safety. Wisconsin DNR should be of assistance here. Feel free to contact Wildlife Biologist Brian Buenzow at the Janesville Service Center. The phone number is (608) 743-4832.
Please keep in mind that wildfire is potentially lethal. The heat of oak leaf litter can be enormous. Always burn under safe weather conditions and with a trained, responsible crew. Check with local fire departments for rules and regulations. Check with local fire departments for permission or permits first and then courteously notify the 911 non-emergency Dispatch prior to ignition. The 911 non-emergency dispatch number is (608) 757-2244.
Garlic mustard will fill any suitable neighborhood to capacity right up to the treated area. Legions will breathe seeds onto the free zones. All Rock County woodlands are inviting to garlic mustard.
It is advisable to take the mustard point of view, temporarily, and locate desirable and undesirable habitat. Identify conditions that promote and deny the invasion. Figure perimeter lands into your long-term plans. Work with neighbors to maintain or increase mustard-resistant landscapes. This is not a suggestion to clear away existing woodlands. It is a call to recognize that every parcel is part of a larger continuum, and to use your knowledge of garlic mustard ecology to define blocks that can be reasonably defended. Landscapes that deter mustard migration may be called ‘buffers’. These include lawns, agricultural fields such as corn, soybeans, alfalfa, or brome grass, prairie plantings, wetlands, rivers, roads, and parking lots. Beware of stream banks and fencerows. These often provide corridors for mustard to migrate through.
When woodlands go bad
In certain cases, utterly degraded sites like railroad rights-of-way (not those with prairie remnants), industrial fields, or aggressively logged woodlots have little or no native ground flora left. Abandoned agricultural fields often succeed into contemporary groves of box elder, black cherry, Siberian elm, or mulberry. These may have very little or no native ground flora. Such places are ideal breeding grounds for garlic mustard.
Consult someone knowledgeable about landscapes and plants. Be certain you have these conditions. It is possible to apply herbicide to kill abundant mustard and prevent the seed crop. But this will empty the stage and leave it open for more garlic mustard. Introducing competing seed is one possibility. The preferable route is to work toward changing the habitat. The site can be gradually converted to a different habitat that is less conducive to mustard. This may require the assistance of someone able to diagnose and devise treatments. The WDNR maintains a list of environmental consultants that may be of help.