| | Despite the cool spring and slow plant growth, weeds are growing and germinating. Once again, crop producers have to wage war against yield-sapping weeds.
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“It’s probably a good time to review the process of weed assessment and control,” says Harry Brook, crop specialist with Alberta Agriculture and Rural Development, Stettler. “One of the best uses of time and effort is scouting your fields. A regular field walk helps keep you informed as to what is going on in the field. For example, if the crop emerges before the weeds, impact of weeds on yield is greatly reduced. This only emphasizes the importance of controlling weeds as early as possible so they can’t rob the crop of nutrients, moisture and yield. It demonstrates the principle of the critical weed control period. The critical weed control period is the time when weed growth and competition can seriously damage your crop’s yield. Weeds emerging before or after this period will not have an appreciable effect on crop yield. As it turns out, the time of weed emergence relative to the crop is more important than the density of weed population.”
Another issue to consider is the competitive nature of the crop being grown. Twenty years ago, canola was not a very competitive crop, and it was often seeded on the cleanest land. Now, with hybrid canola and more vigorous genetics, canola is used as a cleanup crop and is rated the second most competitive crop, behind barley. Barley is still Alberta’s most competitive crop, as long as a competitive variety is chosen. Semi-dwarf barleys are less competitive than regular barleys. Heavier seeding rates always increase the crop’s competitive nature against weeds, as thin crops allow light to hit the ground which stimulates more weed growth.
“Once you’ve field scouted and identified the weed problem you have to assess the degree of threat they represent,” says Brook. “An example of an early, non- yield threatening weed is whitlow grass. It is a very slow growing, small plant that bolts and goes to seed, usually before seeding. It is not a threat to the crop except indirectly, through the use of spring moisture. If other weedy plants are a threat to yield, in sufficient numbers, then appropriate control measures can be chosen.”
Using herbicide is the most common control measure, but there are others. Under certain circumstance, cropping systems or crop types (row crops), cultivation is still a valid way to kill weeds. Biological controls that can target specific problem weeds are being developed and registered. A crop rotation with a mix of spring- and fall-seeded crops can also be effective in managing weed populations. Weeds must be immature enough to be controlled by the method chosen. Once weeds are making seed, the damage to crop yield has been done and you end up with more weed seeds in the soil.
There is a large selection of herbicides available for weed control or suppression of many weeds. In almost all cases, the best results come from spraying early, before the weeds are competitive with the crop. A comprehensive list of herbicides with up-to-date information is available in Crop Protection 2009 (Blue Book), a dependable resource that can help producers make decisions concerning herbicides, pesticides and fungicides controls. The Blue Book is available from Alberta Agriculture’s Publication Office by calling toll-free 1-800-292-5697. It can also be ordered on-line at www.agriculture.alberta.ca/publications. The cost of the Blue Book is $12, plus GST, plus shipping and handling.
“After spraying you should also be scouting the field again to assess the success of the control measure,” says Brook. “This gives you information on how effective the control measure was, what other problems may be arising in the field and how the crop is developing. Think of it as quality time with your crop. It avoids any nasty surprises that can lead to a crisis response.
“Weeds are always going to be with us. With regular field scouting and assessment, you can deal with these small problems before they become large, costly problems. It’s a case of an ounce of prevention being better than a pound of cure.”
Contact:
Harry Brook
310-FARM (3276) |
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