A weed associated with runny noses and watery eyes also makes life miserable for Indiana farmers.
Producers surveyed by the Purdue University Cooperative Extension
Service said the giant ragweed is both the most common and most difficult weed to control. The 2000 survey asked farmers to name the most troublesome weeds and the herbicides they use most.
Purdue weed scientists conduct the survey about every four years, and last polled farmers in 1996. Farmers from every region of Indiana participated in the 2000 survey.
Giant ragweed is a summer annual which, left untreated, can grow to 15 feet tall. The leafy plant produces pollen that contributes to hay fever. Farmers suffer aches and pains of a different variety.
"If not controlled, giant ragweed can be a problem in soybeans and corn," said Glenn Nice, Purdue Extension weed specialist. "It's a tough common weed that sticks around. In corn and soybeans, there are herbicides that control giant ragweed well. However, not all of them have the same efficacy with giant ragweed as with other weeds."
Farmers said Canada thistle was the second most difficult weed to control, the same position it occupied in the 1996 survey.
"Canada thistle is a perennial that has an extensive root system," he said. "When you apply herbicide to the weed you often have to apply it more than once, due to regrowth."
The rest of the top 10 most difficult weeds list includes: Johnsongrass, common lambsquarters, shattercane, hemp dogbane, burcucumber, velvetleaf, common ragweed and common cocklebur
Velvetleaf was second on the most common weeds survey, followed by common cocklebur, common lambsquarters, green foxtail, common ragweed, Johnsongrass, Canada thistle, fall panicum and hemp dogbane.
A weed's movement up or down in the surveys helps Purdue specialists measure where weed populations are shifting, Nice said. For example, marestail fell out of the top 10 most difficult weeds after placing fifth in 1996.
Environmental factors or changes in weed control practices may cause weed population shifts, Nice said.
"Most years, the same weeds will be problems in Indiana," he said. "However, the southern part of the state may have a larger problem with Johnsongrass, while the northern part may not."
In the herbicide survey, Roundup was mentioned by farmers almost three times as often as No. 2 Atrazine. Others in the top five were Bicep/Bicep II, Accent and Harnes Xtra.