Weed control in the landscape is a tough business. You have to know a lot about the weed in question just to get started!
As in most situations, a picture is worth a thousand words.
Preen has terrific weed photos and a map that shows the most common weeds where you live: Weed ID from Preen
The University of Georgia has pictures of weeds at the Turfgrass Weed Management.
The University of Minnesota has a nifty identification feature: Is This Plant a Weed?
PBI Gordon Corp. sponsors an excellent weed identification website at WeedAlert. The germination notes on the weeds are particularly helpful.
The University of California has great drawings of plant parts that are easy to understand: Weed Photo Gallery
The University of Missouri lists lots of weeds and features nifty close-up pictures of the weed leaves, which really help.
Auburn University’s Weed Science department has good “in the field” photos of weeds. Look at the nutgrass photos – - – they show specifically how to tell yellow nutgrass from purple nutgrass.
The Virginia Tech Weed Index has lots of pictures, but you have to know the common name of the weeds before it will show them to you.
I found Weeds of Mississippi in a state 4-H weed contest study guide. It too requires you to know the common name and doesn’t have a thumbnail sketch of weed pictures.
In addition, I like
Common Broadleaf Weeds of North Carolina
Weeds of the South by Charles Bryson and Michael DeFelice
Weeds of the Northern U.S. and Canada: A Guide for Identification
by France Royer and Richard Dickinson
Color Atlas of Turfgrass Weeds
(Ann Arbor Press)
With one of these in hand, you can wander down any sidewalk in your neighborhood and identify most weeds by sight!
Once you know exactly what weed you have, control gets so much simpler!