Getting a Handle on Pesky Garden Weeds!
By Rakesh S. Chandran, WVU Extension Service integrated pest management specialistWeeds can compete with the garden vegetables for water, nutrients, and sunlight. If weeds are not controlled in a timely fashion, they can take over a garden. Lack of adequate weed control, especially when the crop is young and actively growing, can weaken the garden and result in significant reductions in yields.
Annual weedsAnnual weeds, including common purslane, hairy galinsoga, common lambsquarter, pigweed, horseweed, bur-cucumber, nightshade, jimsonweed, velvet-leaf, crabgrass, goosegrass, and foxtails, can establish rapidly, taking advantage of the moist, rich garden soil.
By the time these weeds become conspicuous, they may have already competed successfully with the crop! Preventing such weeds from getting a foothold in the garden is the best management strategy. The best time to control such annual weeds in gardens is when they appear as harmless seedlings.
Perennial weeds, such as Canada thistle, docks, plantains, mugwort, pokeweed, bindweed, Johnsongrass, and quackgrass, reproduce through seeds and underground perennating organs and may become a nuisance once established. Effective control of such weeds calls for completely removing or killing roots or other vegetative propagules. Late summer or fall application of a systemic herbicide such as glyphosate during the year prior to establishing a garden is effective in controlling perennial weeds.
Herbicides are typically used to control weeds in larger commercial operations. Although herbicides are considered to be safe in general, people having smaller backyard gardens could easily adopt methods that would not require spray equipment or knowledge about using chemicals.
Mulches, covers, and other methodsMulches provide adequate season-long control of most weeds in vegetable gardens.
Black plastic provides excellent weed control in small gardens.
Plastic mulch could be spread and anchored into soil using landscape pins. Plants may then be planted into holes punched on the mulch. Although it may appear to block the entry of water into soil, plastic mulch has been shown to better conserve soil moisture.
Straw mulch (2 to 4 inches) spread over newspaper also provides good weed control. However, do not apply it too early because it may keep the soil cool and affect plant growth.
Do not use pine needles since certain chemicals present in them may interfere with plant growth.
If using mechanical tools such as hoes, make sure the blades are sharp.
If using vinegars, be aware of the caustic nature of the fumes. Also, it may injure desirable plants upon contact. Contact from drift may not be apparent till the crop lodges later on. Vinegar is effective on young broadleaf annual weeds but ineffective on grasses and perennial weeds.
Other practices – leaving the soil fallow and subsequent cultivation to kill the weeds, keeping the vicinity free of weeds in bloom, and uprooting or cutting back perennial weeds repeatedly – will help deplete weed propagules in the soil.
- Planning the year before planting a garden can help you to control perennial weeds. Applying a nonselective systemic herbicide such as glyphosate in late summer or early fall when there is adequate moisture in the soil will control perennial weeds effectively.
- A stale seed bed strategy can partially deplete weed seeds in the garden soil. Till the soil and let it stay fallow for a few weeks to encourage weeds germinate in spring while the soil is warm and moist. Once weeds emerge, carry out a secondary tillage to prepare the bed for planting.
- Use organic matter that is well-composted and free of weed seeds for gardening. Till the compost into the soil before applying black plastic mulch for weed control.
- In tree fruits, weed control is critical during the years of establishment (2 to 4 years) and thereafter during the months of April through June (in bearing trees).