sealPurdue News

January 22, 2003

Wet and cold, bad news for drivers but good news for farmers

WEST LAFAYETTE, Ind. – Indiana's recent snowfall should help eliminate herbicide carryover into next spring, said a Purdue University expert.

While the snow increases herbicide breakdown in the soil, the colder weather does slow down the process.

"Herbicides still in the soil from last season can damage crops the following spring if the herbicide doesn't break down properly," said Glenn Nice, weed science professional assistant.

A wet winter is the first step in the breakdown process, but spring weather is the biggest deciding factor of herbicide carryover and weed issues that farmers will face. Microorganisms also play a part in the breakdown of herbicides. Warm, wet weather is the ideal situation for the successful breakdown, Nice said.

A wet spring helps break down herbicides, but it also could allow for many of the same problems that occurred last spring, Nice said.

One problem is the difficulty of getting into fields to do burn-down or tillage. Both of these methods help farmers get rid of winter annuals such as common chickweed, purple deadnettle and henbit. These plants prevent the soil from warming up in the spring, which could inhibit planting.

Another problem associated with a wet winter is the fear that fall-applied herbicides won't last until the spring. A plant that affected farmers last season was the cress-leaf groundsel or butterweed (sometimes referred to as ragwort in Indiana).

"This yellow plant canvassed the ground last spring and may not have even been noticed if farmers were able to get into their fields and do burn-downs or tillage," Nice said.

Farmers can expect to experience the usual weed varieties his year as well. These include Canada thistle, giant ragweed, foxtail, velvetleaf and common lambsquarters.

To effectively control Canada thistle, farmers should spray herbicides containing glyphosate. Glyphomax Plus, Roundup, WeatherMax and Touchdown are few examples of these herbicides. Canada thistle should be sprayed in the spring between budding and flowering time. However, don't expect to never see the weed again – it will inevitably have to be sprayed for more than once, Nice said.

Giant ragweed may have been worse in the past than it has in recent years – possibly due to introduction of the Roundup Ready weed management system, Nice said. Foxtail also is not a large concern, due to the Roundup Ready system. Common lambsquarters, on the other hand, has shown resistance to some families of herbicides, Nice said. This means farmers will need to use herbicides with modes of action to which the weed has not shown resistance.

Writer: Michelle Betz, (765) 494-8402,

Source: Glenn Nice, (765) 496-2121,

Ag Communications: (765) 494-2722; Beth Forbes,;

Related Web site:
Purdue Department of Botany and Plant Pathology

* To the Purdue News and Photos Page