Early Season Weed Control

 
  From the June 5, 2017 Issue of Agri-News
Subscribe to our free E-Newsletter, "Agri-News" (formerly RTW This Week)Agri-News
This Week
     Agri-News HomeAgri-News Home
 
 
 
 Early weed control has many benefits as weeds compete with crops for nutrients, water and light.

“Research on weeds germinating before the crop emerges as compared to crop emerging before the weeds shows a very significant drop in yield loss when the crop emerges prior to the weeds,” says Harry Brook, crops specialist, Alberta Agriculture and Forestry. “A pre-seed burnoff with a herbicide or final cultivation should be as close to the seeding activity as possible to prevent weeds getting the jump on the crop.”

All crops have a critical weed control period, which is the time when the crop is susceptible to significant yield loss from weed competition. The critical weed control period for canola is around 17-38 days after emergence. Peas can be as early as two weeks after emergence. “Other, more competitive crops, like the cereals, have a less defined critical period,” says Brook. “Corn’s critical period depends more on nitrogen availability than anything else. If you can keep the weed pressure down until the critical period is passed, you minimize yield losses from weed competition.”

Field scouting is essential to give an edge battling weeds, notes Brook. “Field scouting tells you what weeds are present and their density. Once a field has been scouted and a weed problem identified, the degree of threat needs to be assessed. An example of an early, non- yield threatening weed is whitlow grass. It’s a very slow growing, small plant that bolts and goes to seed, usually before seeding. It’s not a direct threat to the crop. However, if other weedy plants are also present in sufficient numbers and are a threat to yield, you can choose an appropriate control measure.”

Winter annual weeds like stinkweed, narrow-leaved hawk’s-beard, shepherd’s purse, scentless chamomile and many others can start growing in the fall. They overwinter as a small rosette but are then quickly able to go to seed once spring arrives. “Control of them in the spring requires very early action. You need to know the weeds present to choose the best control method. Crop volunteers from previous years are also an increasingly problematic weed obstacle. Volunteer canola is one of our top weed control issues every year. These and other problem weeds will require additional products when applying a spring burnoff with glyphosate.”

To get the best result from any early herbicide application, Brook says the herbicide must be applied when the weeds are actively growing. “Under cool or cold conditions you can expect poor results from the spray as the target weeds are either dormant or growing too slowly. They cannot absorb and translocate enough active ingredient to kill them. Weeds also have to be large enough to absorb enough herbicide to be killed. Low spray volumes and coarse sprays can lead to insufficient herbicide landing on the plants. Best temperatures for application should ideally be above 12⁰-15⁰ C, when the plants are actively photosynthesizing. If it was frosty in the morning, waiting until a warm afternoon will improve efficacy.”

Another tool in weed control is the competitive nature of the crop itself. “Highly competitive crops can reduce the effects of weeds on yield. Once a crop canopy has covered the soil, sunlight no longer can penetrate to the ground and weeds stop germinating. Heavier seeding rates can also squeeze out weeds. Hybrid canola and barley are our two most competitive crops. You still have to choose a competitive variety. Semi-dwarf barleys are less competitive than regular barleys. Heavier seeding rates always increase the crop’s competitive nature against weeds. Thin crops allow light to hit the ground, stimulating more weed growth.”

For more information, contact the Alberta Ag-Info Centre at 310-FARM (3276).

Contact:
Alberta Ag-Info Centre
310-FARM (3276)

 
 
 
 
view Agri-News RSS FeedAgri-News RSS Feed      Share via AddThis.com

For more information about the content of this document, contact Harry Brook.
This document is maintained by Ken Blackley.
This information published to the web on May 11, 2017.