Marestail is a major weed problem for Indiana and Ohio.
By Amanda Gee, Purdue University
WEST LAFAYETTE, Ind. - Producers need to make burndown applications on winter annual weeds quickly once weather conditions allow them to get into fields, two Purdue Extensions weed specialists say.
Eliminating weed cover helps soils to dry more quickly to allow earlier planting and creates a better seedbed for corn and soybean crops.
Bill Johnson and Travis Legleiter said the weather cycles of cold temperatures, abundant rain and short spurts of warmer, sunny days have allowed weeds such as chickweed, purple deadnettle, henbit, wild garlic, dandelions and marestail to flourish in the last few weeks.
"The big thing when it comes to spraying is that it will help with crop establishment by minimizing other plants," Johnson said. "Although these annuals may already be flowering and nearing the end of their life cycles, a timely burndown application will speed up the drying processes for quicker soil drying and timely planting."
Marestail has been the biggest weed problem in Indiana for the last couple years and this year won't be any different, Legleiter said.
"Marestail is starting to bolt now and will be difficult to control if not treated soon," he said. "The majority of marestail populations are glyphosate-resistant and must be controlled with other herbicides."
More information about controlling marestail can be found at http://agcrops.osu.edu/specialists/weeds/marestail/marestailfact09_000.pdf.
But it's not just marestail that's been building up resistance to the popular herbicide glyphosate. Johnson and Legleiter said they've seen a widespread increase in the number of acres infested with glyphosate-resistant weeds.
Many producers will have to change their regular burndown applications to other herbicides or tank mixes. Legleiter said some popular tank mixes that could work are those that include contact herbicides such as paraquat and saflufenacil.
When applying these contact herbicides, which only kill the parts of the plant where the chemical is deposited, farmers should ensure they're using the proper amount and mix.
"When applying a contact herbicide, producers need to keep in mind that complete spray coverage is essential," Legleiter said. "A lot of producers apply about 10 gallons per acre, but to ensure complete coverage with contact herbicides, producers need to use carrier volumes of at least 15 to 20 gallons per acre."