All of the following are examples of summer annual weeds except:

• A. Crabgrass
• B. Common lamb's quarter
• C. Hairy bittercress
• D. Giant ragweed

Answer: (B)

Summer annual weeds complete their life cycle in one growing season, germinating in spring or early summer, thriving through the warm months, and producing seeds before frost ends the season. Crabgrass follows this pattern: it pops up with the warming weather, grows vigorously during summer, and sets seed by late summer, then naturally declines as temperatures drop. Common lamb’s quarter does the same, germinating in warmer spring conditions, growing through summer, and seeding before fall. Giant ragweed also fits, starting in spring, growing through summer, and setting seed before winter.

Hairy bittercress does not fit the summer-annual pattern. It is a winter annual weed, typically germinating in fall, surviving through winter in a rosette, then bolting and flowering in early spring before dying as temperatures rise. So it completes its life cycle outside the hot summer period, making it not a summer annual weed.