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Farmers will have to spray right weed at right time

By Janet Kubat Willette

Date Modified: 04/11/2013 9:13 AM

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NORTH MANKATO, Minn. — For the past 15 years, farmers have been able to spray glysophate and kill weeds.

But before that, they had to spray the right weed at the right time with the right product.

Those days are here again, said Bryce Nelson, a crop consultant and owner of Advantage Crop Consulting in Rose Creek.

Farmers must get back to knowing what pre-emergence herbicide works on what weed, he said, speaking at a Weed Resistance and Grain Management Seminar held March 28 in North Mankato.

Giant ragweed and foxtail became resistant to ALS in the 1980s, and now common waterhemp and giant ragweed are resistant to glysophate.

The era of total post-emergence herbicide is over, Jeff Gunsolus said. Gunsolus is a University of Minnesota Extension weed scientist.

Prior to 1996, farmers used a great diversity of tools to control weeds. Aside from herbicides, people walked beans and farmers used cultivators.

Diverse chemistry is needed now if Minnesota farmers hope to avoid the fate of their southern neighbors who have limited options when it comes to controlling Palmer pigweed, he said.

Lest farmers here grow confident that Palmer isn't a problem in the north, it has been found in Dane County, Wis. Speculation is that it was transported north along with cottonseed for dairy rations. It seems to grow well in the north once established.

Minnesota farmers already have their own resistant weeds.

An issue the next generation of farmers will be dealing with is multiple resistances, Gunsolus said. The loss of herbicides is critical in high-value crops including sugar beets, canning peas and sweet corn.

From 1940 to 1960, four new herbicide modes of action were introduced. From 1960 to 1980 and from 1980 to 2000, three new modes of action were introduced, respectively, said Byron Hendrix, an Enlist launch specialist.

There hasn't been any new mode of action released since 2000 and he doesn't see anything coming in the near future. It will be at least the next decade, Hendrix said.

Gunsolus cautions farmers not wait and instead make changes now.

If they use the new technology like they used the old technology, it won't work for long.

And as the frequency of herbicide resistant traits increase, the likelihood of migration increases. The resistant weed genes move via forage, manure, combine, pollen, water, ditch banks and field margins.

Long-term, solutions will require a more extensive approach to diversification of crops and weed management tactics, Gunsolus said.

One of those tactics will be keeping weed seed banks down. Another will be the use of pre-emergent herbicides.

Companies are taking note, with expanding herbicide line ups, he said.

Take note that poor early season weed control reduces the time period for effective post-emergence weed control, Gunsolus said.

Farmers are also going to have to read labels, checking for interactions with insecticides.

It's going back to what farmers did before ALS and Roundup, when timing mattered.