INVASIVE PLANTS - Technical Learning College

Common Lambsquarters is a broadleaf summer-annual weed that can be found anyplace the
soil has been disturbed. The growth habits of the common lambsquarters vary with its location. If
growing along the road or in an open field, it may reach three or four feet in height. Yet those
plants found in lawns may produce seeds when only a couple of inches tall. Lambsquarters prefer
rich soil and are often found in vegetable gardens. The first two true leaves that appear are
opposite and ovate with smooth edges. Later leaves are alternate, arrowhead-shaped, and with
unevenly-toothed edges. At the top of the plant, the leaves become long and narrow. All of the
leaves are pale green and covered with white, mealy granules that give the appearance of frost.
Stems are erect and often have light-green or red lines. Flowers are small, inconspicuous, yellowgreen,
and occur in clusters at the tips of branches and upper leaf axils. These flowers occur from
July to September. Black seeds are contained in an utricle by a thin papery covering.
Control The best methods of weed control in the home vegetable garden are mulching, hand
pulling, rototilling, hoeing and preventing the weeds from going to seed. Because of its short,
branched taproot, lambsquarters can be easily hand-pulled from moist soil. Prevention by use of
good cultural habits should be the first line of defense in eliminating broadleaf weeds such as
lambsquarters from lawns. Pre-emergent herbicides such as trifluralin (Preen) can be used to
prevent germination of weed seeds. Post-emergent herbicides effective against broadleaf weeds
are 2,4-D, MCPP and dicamba (sold under many brand names) and combination formulas
(Trimec). Read labels to be sure the herbicide is effective against the weeds you want to
eliminate and follow the directions carefully.
Purslane is a summer annual, found only in newly seeded or thinning, non-vigorous lawns and
sidewalk cracks. It has thick, succulent, rubbery leaves and small yellow flowers. The plant is
sprawling and prostrate. It is easily pulled when the soil is moist.
Control Post-emergent herbicide use is more effective when plants are young as purslane is
difficult to kill with an herbicide when larger. Always read the label before applying any pesticide.
Crabgrass is a summer annual grass with wider blades and a lighter green color than bluegrass.
It is low growing, prostrate, and often has reddish-purple stems. It forms seedheads below
mowing height. The seedheads are composed of slender, fingerlike spikes. Crabgrass is less
prevalent when turf has good density. In particular, mowing too low promotes crabgrass seed
germination. Maintain mowing heights of 2.5 - 3 inches.
Control A pre-emergent herbicide (benefin + trifluralin, dithiopyr, DCPA, oxadiazon,
pendimethalin, or prodiamine) applied correctly and at the proper time should provide control. Do
not use a pre-emergent herbicide on a newly seeded or sodded lawn or when overseeding a
lawn. Fenoxaprop and other post-emergent "crabgrass killer" (MSMA, DSMA, MAMA) sprays are
not effective unless crabgrass plants are immature, young seedlings. Always read the label
before applying any pesticide.
Poison Hemlock (Conium maculatum), also known as poison parsley or spotted parsley, is an
erect biennial weed that can grow 6 to 10 feet tall. Originally imported from Europe as an
ornamental plant, its spread across North America has been rampant. All parts of this plant are
poisonous. The leaves and flowers of Poison Hemlock are similar to those of parsnips and
carrots. In fact, many deaths have occurred as a result of people mistaking it for the edible
species of the carrot family. The use of hemlock as a poison goes back many years in history. It
is said that the ancient Greeks used it to poison their enemies and political prisoners. Socrates,
condemned to die as a political prisoner in 329 B.C., drank the juice of the hemlock plant and
committed suicide. Native Americans were known to dip their arrows in hemlock. Poison Hemlock
is an erect plant with smooth, hollow stems that are covered with purple spots. Its shiny green
leaves are pinnately compound, multi-stemmed and fern-like in appearance. Flowers are showy,
white umbrella-like clusters that occur during June to July. The fruit is small, flat, grayish-green,
and matures in August to September.
Control The large, fleshy white taproot can be easily pulled from moist ground when plants are
small. Several herbicides are effective in controlling Poison Hemlock. Glyphosate (Roundup) can
be used on newly emerged sprouts. Other post-emergents that are most effective in early spring
are 2,4-D, 2,4-DB and MCPA. 2,4-D should be combined with a wetting agent when applied.
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