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How to Identify Different Grass Weed Types

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How to Identify Different Grass Weed Types

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Overview

People have created weeds by carrying plants in boxes or as seeds in the soles of their shoes as they traveled. Thousands of types of green herbaceous plants with long slender leaves carpet lawns, feed grazing animals in pastures and provide ornamental accents in landscapes. Weed grasses do exactly the same thing except that, for one reason or another, people have identified them as invaders.

Step 1

Begin identification by first eliminating sedges, because grass herbicides will not work on them. Sedges have triangular stems and long, narrow blades that grow in three rows up the stem, while grasses have round or flat stems.

Step 2

Find summer annual weeds when they germinate in very early spring; they will grow all summer and die with the first hard frost. Crabgrass, foxtail, barnyard grass and goose grass are coarse summer annual grasses. Although most of the summer annual grasses grow throughout the U.S., some sub-groups have limited range. Large crabgrass, for example, does not grow well in the Deep South, crowfoot grass grows in the South and along the East Coast and foxtails favor fertile soils like lawns. Most annual grasses are difficult to control after germination; pre-emergent herbicides like MSMA (monosodium methyl arsonate) prevent seed germination.

Step 3

Identify winter annual or biennial grasses as they begin growth in the fall and die the following fall. Italian ryegrass, often called annual ryegrass, crowds out perennial grasses. Jointed goat grass has a tall, jointed stem and poses problems in wheat fields because of its resemblance to the grain. Cheat grass is an invasive weed in the Western U.S. Urban dwellers may notice winter annual grasses along roadways, which also require pre-emergent control.

Step 4

Identify perennial grasses by the fact that they regrow each year, developing larger crowns and deeper roots each season. Quackgrass is often mistaken for crabgrass; it is found across the U.S. except for the Deep South. Knotgrass grows only in the South and along the West Coast. Nimblewill resembles a fat Bermuda grass and forms dense mats in lawns. Tall fescue, creeping bentgrass and Zoysiagrass, all lawn grasses in the right place, become weeds in Kentucky bluegrass turf. Pre-emergents have limited effectiveness on these grasses.

Step 5

Classify the grass using its growth habit, height, number of nodes, construction of collar and ligule and height and shape of seed head. Some grasses have folded leaves and others are curled leaves. Some, like tall fescue, grow in clumps; others, like Johnson grass, develop rhizomes from a crown. Crabgrass spreads above the ground, putting down roots from stolons and branch nodes.

Tips and Warnings

  • You'll need to have a plant or a good idea of how it looks to answer questions about the weed because there are thousands of varieties, all with their own unique collection of characteristics.

Things You'll Need

  • Sample of grass weed
  • Weed identification guide

References

  • BASF Professional Turf: Weed Identification Guide
  • Herbi-systems: Weed Facts
  • Quote Garden: Quotations About Weeds
  • Virginia Tech Extension: Lawn and Turfgrass Weeds

Who Can Help

  • Texas A and M University: Weed Control for Turf with Weed Database
  • Virginia Tech Extension: Weed Identification Guide
  • Colorado State University Extension: Annual Grassy Weeds
  • University of Illinois Extension: Managing Grass Weeds in Lawns
Keywords: grass weeds, identify weeds, lawns and pastures, lawn grass

About this Author

Chicago native Laura Reynolds has been writing for 40 years. She attended American University (D.C.), Northern Illinois University and University of Illinois Chicago and has a B.S. in communications (theater). Originally a secondary school communications and history teacher, she's written one book and edited several others. She has 30 years of experience as a local official, including service as a municipal judge.

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