Three tips for weed management this fall

Reflecting on some of the weed control issues that came up this past spring, below are three key items where management activities this fall can significantly improve control and/or financial return next season.

1. Fall management provides better dandelion control.

In the fall, resource allocation of perennial weeds shifts and carbohydrates move towards the root system, building root mass for overwintering. When dandelions are managed in the fall, whether it be by tillage or herbicides, resource allocation to the roots is disrupted and control is significantly better when compared to management in the spring. A better seed bed is also established when dandelions are managed in the fall since all the vegetative growth has been desiccated by planting time (see photo at top).

2) Consider fall management in winter wheat if Canada fleabane is present.

Although winter wheat yield loss from weed competition is typically small, there are exceptions. High densities of weeds that emerge with, or shortly after the crop will have the most impact on yield loss. A recent study conducted by the University of Guelph (Ridgetown Campus) found that Canada fleabane interference reduced winter wheat yield by as much as 27 per cent. Managing Canada fleabane in the fall, improved winter wheat yields by 10-15 per cent when compared to waiting until the spring to manage Canada fleabane.

3. When killing off an old stand of alfalfa with herbicides, make sure that the two-week weather forecast after application has warm air temperatures.

A study conducted at the University of Guelph (Elora Research Station) demonstrated that warm air temperatures after herbicide application, quantified by growing degree days, appeared to negatively effect the control of alfalfa. Since alfalfa has a base growing temperature of 5 C, when air temperatures following herbicide application rarely exceeded 5 C, alfalfa growth was stagnant, thereby reducing herbicide uptake and movement within the plant, and leading to unacceptable control.

– To view the full Ontario Field Crop Report (with tables) for Sept. 21, please visit the Ontario Field Crop News website.