Winter wheat weed control is more important in 2009 than most years.
The late planting last fall means that weeds have less competition from wheat than most years. Many fields have some killed-out spots or thin areas that will be a good place for weeds to grow.
The actual yield loss in wheat from weeds is not as big a deal as the other problems weeds cause in wheat fields:
• They will make harvest more difficult especially under wet conditions.
• They will lower the value of straw because no one wants to buy straw with weed seeds.
• The biggest reason to control weeds in winter wheat is to reduce the weed seed bank. If a ragweed plant goes to seed it will set hundreds of seed that will be around for years. Most growers have challenges controlling annual broadleaf weeds in soys. For this reason you cannot allow weeds to set seed in winter wheat.
There are limited options for weed control in wheat. If wheat is underseeded to red clover a combination product like Buctril M that contains bromoxynil and MCPA is the product of choice. The label says that you must wait until the first trifoliate to spray. Research from University of Guelph indicates that spraying earlier than this can set the clover back but it will grow out of it. You should not spray this product or any wheat herbicide if you are expecting temperatures to drop below 5 oC in the 12 hours after spraying.
To control chickweed you have to use a product like Refine. For hard to kill weeds like vetch, Lontrel is a good choice. For specific weed control ask your supplier.
One often asked question is “should I add a fungicide to my herbicide.” The answer varies.
There are areas in Ontario where disease pressure is high and grower experience has shown it pays to add a fungicide for protection. In other areas where wheat diseases are not as common it may not pay. Ask your retail supplier what they think. There are some restrictions on which fungicides can be tank mixed with which herbicide. Many are safe but there are exceptions. Enquire as to the safety of these tank mixes before you do one for the first time.
There are some weeds that cannot be controlled now but must be controlled with either a pre-harvest spray or September spray or maybe both. These weeds include perennial sow thistle, Canada thistle and bindweed. BF