Common Weeds Found in Indiana

Giant Ragweed

• This summer annual has been ranked No. 1 on Purdue University's list of Indiana's most problematic weeds three times in a row. It grows in areas all over the state, emerging in March and germinating through spring and early summer. It is fast-growing, persistent and resistant to many herbicides. Giant ragweed is similar in appearance to common ragweed, though it can grow considerably larger. It has rough, deeply three-lobed leaves.

Canada Thistle

• Canada thistle can be problematic throughout Indiana, but is most common in the northern part of the state. According to Purdue University, this perennial weed spreads both by seeds and with creeping roots, and can be a problem for many crops. Highly competitive, Canada thistle grows in dense, spreading patches; it displays the crinkled, spiky leaves and purple flowers typical of thistles.

Lambsquarters

• Lambsquarters makes regular appearances on Purdue University's Top 10 Most Problematic Weeds lists. It is a Triazine-resistant weed, and often grows in areas that have been treated with triazine herbicides in previous years. A summer annual, lambsquarters has smooth leaves when young and eventually develops triangular leaves with ragged, uneven margins. The leaves are covered with white frost-like granules.

Common Cocklebur

• Another summer annual weed, common cocklebur moved up from No. 10 to No. 4 on Purdue University's list from 2000 to 2004. It grows throughout the state, and grows from seeds in clinging burs. The plants have triangular or lance-shaped leaves with a rough texture. Common cocklebur can be controlled with a number of herbicides.