Crabgrass is a familiar summer annual grassy weed. Examples of summer annual broadleaf weeds are knotweed, spotted spurge, purslane, ragweed, mallow and black medic. Knotweed is one of the first summer annuals to be seen, germinating in March and occurring primarily on compacted dry areas along driveways and sidewalks. Knotweed has a low-growing or prostrate growth habit and very small oblong leaves, arranged alternately along a wiry stem. Spotted spurge has a pink, fleshy, hairy stem with leaves oppositely arranged.
Leaves have a purple to brown spot along the center vein and milky sap is exuded from broken stems.
Generally, summer annual broadleaf weeds become problems in dry lawn areas with poor soil conditions. Illustrations by Barb Long, from the MU Extension guide, Home Lawn Weed Control . May. Although fall is the best time to control perennial broadleaf weeds with herbicides, spring is the second best time. During the spring, dandelions and other broadleaves are translocating energy upward to produce flowers, implying that herbicide may be less efficiently moved into the roots at that time. Another reason that fall is preferable for herbicide application is that bare spots left by weeds killed in the fall will have more time to be filled in by creeping bluegrass or planted seed.