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carolyn leaf seeds versus weeds

Organic no-till transplanting of tomato and other summer vegetables into roll–crimped or mowed winter cover crops can control light-to-moderate pigweed populations. Rye residues release natural plant growth inhibitors (allelochemicals) that suppress pigweed and some other annual weeds (Barnes and Putnam, 1983; Putnam et al., 1983) without affecting transplanted vegetables.

Erect pigweed species can rapidly overtop short crops like broccoli or snap bean. In taller crops like corn, pigweeds respond to canopy shade by increasing stem growth and deploying leaves higher on the plant, thereby intercepting a larger fraction of available light (Massinga et al., 2003; McLachlan et al, 1993). One to three pigweed plants per 10 feet of row emerging with corn or soybean can cause significant yield losses (Klingman and Oliver, 1994; Knezevic et al., 1994; Massinga et al., 2001) Pigweeds that emerge several weeks after the crop has emerged exert much less effect on yields.

Figure 11 Cultivation left a dust mulch around these young squash plants, thereby discouraging germination of pigweed and other small-seeded weeds. However, foot traffic recompacted the soil enough to re-establish seed–soil contact near the surface, thereby allowing weed seeds to imbibe moisture, germinate, and grow in the footprints. Photo credit: Mark Schonbeck, Virginia Association for Biological Farming.

Crop Competition and Cover Cropping

Also called amaranths, pigweeds are native to parts of North and Central America. Crop cultivation and human commerce have opened new niches, allowing pigweeds to invade agricultural ecosystems throughout the Americas, and parts of Europe, Asia, Africa, and Australia. Most amaranths make nutritious green vegetables or grain crops, and deliberate planting for food has helped some weedy species spread around the world. However, none of the pigweeds discussed here is grown commercially for grain, and modern grain amaranth varieties are not considered major agricultural weeds.

Published December 20, 2019

Competitive summer cover crops such as buckwheat, sorghum–sudangrass, cowpea, and forage soybean are often used to suppress weeds between spring and fall vegetable crops. In Florida, cowpea, sunnhemp, or velvetbean cover crops seeded at high rates reduced but did not eliminate smooth pigweed growth (Collins et al., 2008).

Use in-row drip irrigation to provide water and liquid organic fertilizer directly to the crop without feeding and watering between-row weeds. Subsurface drip lines can provide moisture to the crop and leave the soil surface dry, thereby minimizing within-row weed emergence.

Try to pull out this weed before it flowers!

Creeping Charlie (ground ivy) and also wild violet are common in shady lawns. Native to Europe, it has become an invasive lawn weed in North America. The plant has bright green leaves with scalloped edges on creeping stems that root at the nodes. It tends to form a dense mat over the ground.

Is Pigweed Edible?

9. Pigweed (Amaranthus spp.)

As an annual, crabgrass dies at the end of each growing season, usually at the first frost in the fall, and it must produce new seeds every year.

Is Buckhorn Plantain Edible?

The reason Creeping Charlie is so challenging is the way it spreads—by both seeds and by creeping stems (called stolons) that grow along the ground. If you try to dig it out and leave behind a fragment of rhizome (root), even a tiny piece can grow up as a new plant!

With these techniques, you’ll soon find that you won’t spend much time weeding the following years!