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A Brief Introduction to Integrated Pest Management Part 1: Dealing with weeds
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This is where Integrated Pest Management (IPM) is useful. There are essentially four steps in IPM. Here we'll focus just on unwanted plants or weeds.
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First, prevent weed problems from occurring. Garden cultural practices from site preparation to general maintenance can all impact weed growth. Choose plants suited to site conditions. Use mulches, where appropriate, to prevent weed seed germination. Healthy lawns and gardens can usually outcompete weeds.
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Second, identify and learn about your weeds. When an unwanted plant appears find out why. What conditions are required for its growth? What is its life cycle? How does it spread?
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Third, know when you should act. When a plant is simply growing in the wrong place, weed tolerance can be a matter of taste (like dandelions). However certain weeds are not simply a nuisance but are considered noxious and can threaten livestock health (like milkweed), human health (like poison ivy) and or ecosystem health (like garlic mustard). These noxious weeds should be treated more aggressively.
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Finally, when weeds exceed acceptable levels, take action.
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Begin with simple mechanical and physical controls. There are excellent tools for weeding from simple garden forks and hoes to more complex weed whips and weed burners, (Lee Valley always has a fun assortment of gadgets).
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Some weeds can be smothered with mulches, solarizing plastics, geotextile fabrics, and paving stones/gravel.
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Change cultural practices that may be supporting weed growth. For instances, dandelions love potassium rich limey soil, so use potassium-free fertilizers on your lawn and don't add lime unless you are trying to correct an acidity problem.
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As a last resort, herbicides like acetic acid (quite effective on dandelions and plantain) and corn gluten meal (applied in early spring to prevent weed seeds from germinating) should be used before such things as glyphosate, 2,4,D, dicamba and mecoprop. Herbicides are toxic. Misuse or misapplication of herbicides can damage plants and injure people, pets and wildlife.
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Let us go through an IPM for garlic mustard, (Alliaria petiolata).
What do we know about garlic mustard? It is a highly invasive biennial herb that is posing a severe threat to native plants and animals in our forest communities. Unfortunately, Alliaria appears to be popping up just about everywhere there is open soil and even in some well mulched areas..
When should you act? First-year plants appear as pretty rosettes of wavy round leaves close to the ground. These are easily pulled in spring (throw the tender leaves in a soup or salad along with young dandelion leaves). If you miss it during its first season's growth, there is no real harm. However, allelochemicals exuded by this member of the mustard family, may sicken neighbouring plants and reduce germination of seeds.
While
it may be okay to let a few first year plants survive, you should have zero
tolerance for second year growth. The Alliaria rosette stays
green throughout the winter making it easy to spot them. Before the following
April, pull it out. Otherwise, it will begin to shoot up 25-100cm stalks with
alternate, toothed, triangular leaves. Clusters of four-petalled white flowers
will appear in late spring (and often again in late summer). At this time,
cut it close to the ground. While perennial dandelions will grow back if
simply cut back, Alliaria's tap root will die after it has set flower. Make
sure to clean up, because cut flower stems can form seeds and garlic
mustard's prolific seeds remain viable for at least five years. While,
herbicides, like glyphosate, have been used in forest areas with high
infestation (in late fall, when native plants are dormant), this enzyme
disruptor can impact a range of plants, bacteria and fungi potentially
reducing trees' winter hardiness. (Note also that herbicides like glyphosate
contain other ingredients like surfactants (often
protected as "Trade Secrets") and certain formulations are more toxic to
wildlife than others.) Such herbicides should only be used as a last resort
for forest restoration and have little or no reason to be used by home
gardeners.
Learn about your weeds. Make removing highly invasive plants a priority. These include garlic mustard, leafy spurge, purple loosestrife, japanese knotweed, oriental bittersweet, dog-strangling vine, autumn olive and glossy buckthorn. Develop a variety of ecologically sound methods that work for you and share them with your neighbors. Let me know if you would like specific information or would like to share your successes. Next time - IMP Part 2 Fighting Fungal Disease.
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May toads nestle in your flower beds and help you tend your beauties in the spring.
Tidbits and Resources
| Dandelions The dandelion belongs in the genus Taraxacum (derived from the Greek 'taraxos' meaning disorder and 'akos' meaning remedy) in the family Asteraceae. Our common North American dandelion (Taraxacum officinale) probably originated in west central Asia during the early Cretaceous (144 to 65 million years ago) before being dispersed to the northern and temperate regions of Europe during the Tertiary (64 to 1.6 million years ago) and again to North America with post-Columbian settlement (beginning in the16th century), (Collier & Rogstad, 2003, Clonal Variation). According to efloras database, Taraxacum varieties occurring in Ontario include: T. officinale spp. officinale (the common dandelion), T. .ceratophorum (the most widely occurring North American native also designated T. officinale spp. ceratophorum or horned dandelion), T. erythrospermum (red-seeded dandelion), and T. palustre (marsh dandelion), and according the USDA database Taraxacum spectabile (showy dandelion). The name dandelion is derived from the Old French, dent-de-lion, which describes how the leaf edges resemble the teeth of a lion. The dandelion is also referred to as piss-en-lit, pee-the-bed, lion's tooth, fairy clock, blowball, cankerwort, priest's crown, puffball, swine snout, white endive, wild endive. The French name pissenlit, or piss in the bed comes from the fact that Taraxacum is a diuretic (increased urination is likely the result of the sesquiterpene lactones found in both leaves and roots). Dandelions are also a rich source of vitamins and minerals. The leaves have a high content of vitamin A as well as moderate amounts of vitamin D, vitamin C, various B vitamins, iron, silicon, magnesium, zinc, and manganese. If dandelions are a problem in a lawn. Researchers in England found on experimental park land, "Taraxacum abundances were highly dependent on potassium fertilization and on liming, but not on addition of other nutrients. Potassium fertilization led to a 17-to 20-fold increase in Taraxacum abundances in the classical Park Grass data, and to a 4 to 7-fold increase in the modern data. Liming led to a 2- to 3-fold increase for classical data and to a 3- to 4-fold increase for modern data." (Tilman et al. 1999). There conclusion, reducing potassium and lime should reduce dandelion growth. In addition, hand weeding dandelions is as cost effect as spraying with herbicides. "Experience shows that dandelions can be removed at a rate of 5 to 10 plants per minute, using simple tools that cut the taproot. This means that on a site that has an average of 5 weeds per m2, one person can weed over 100 m2 per hour, at a cost comparable to spraying. ...It is a good idea to drop turfgrass seeds, or a mixture of soil and seed, into each hole created by weeding to speeds closure of the turf and prevent weeds from germinating." (NBHTA "Sustainable Turf" Chp7.)
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