Download The Prairie Star, MT 03-05-07

The Prairie Star, MT
03-05-07
Sprayers can add flexibility, risk management to weed management
By TIM HOSKINS, For The Prairie Star
Sprayers can often be used by farmers to add some flexibility and risk
management to weed management. The timing of application is critical.
If farmers rely on a custom applicator, their fields may not get sprayed in a timely
fashion.
Bob Hartzler, Iowa State University Extension weed specialist, and Mike
Owen, Iowa State University Extension weed specialist, say timing is the
most critical part of any weed control program.
Owen says putting those sprayers to use at a different time can allow farmers to
get more out of their weed control programs.
He says the program could start with an early pre-plant herbicide application. He
says that can be done when conditions are not right for planting.
With using a pre-plant herbicide, he says a farmer is just trying to add some
flexibility into the schedule in case there are any weather events, such as rain
that would delay his next spraying application.
It also extends the window from one week to three to four weeks to get the next
herbicide application done during a time close to planting.
“You have already killed most of the weeds,” Owen says.
He further explains as weeds get larger, they grow faster and then they get more
competitive with crops. Therefore, he says using a pre-emerge herbicide kills
weeds, and when the farmer returns to spray his post-emerge herbicide, the
weeds are short and less competitive.
The size of the weeds allows some flexibility since the critical period has not
been reached.
“Research has shown up to 1 percent of yield can be lost per day application is
delayed once the critical period is passed,” says Hartzler.
The critical period is the point of time when weeds that emerge with the crop first
begin to affect yields.
“Since we can't predict precisely the critical period, there is always risk of yield
loss when relying on total post products and not having total control of when
fields get sprayed,” Hartzler says.
Owen says using sprayers to add a pre-emerge herbicide application to the crop
focuses attention on the need to have a strategy in any weed management
system.
“It is not simple,” he say of any total post-emerge weed control system.