Wild Buckwheat and Oats Most Prevalent Weeds

REGINA - Jan 19/04 - SNS -- The results of the 2003 survey of weeds in Saskatchewan found the most common weeds were: wild buckwheat and wild oats, present in 51% of the surveyed fields; green foxtail, in 44% of the fields; Canada thistle, in 35%; and lamb's-quarters in 22% of surveyed fields.

"In general, however, the results of the 2003 weed survey showed that weed populations were very low at the time of counting. This demonstrates that most producers are managing their weeds effectively," says Clark Brenzil, weed control specialist with Saskatchewan Agriculture, Food and Rural Revitalization.

The overall ranking of individual weeds in the survey, however, is not based solely on the proportion of the province's fields in which a particular weed grows. Weeds are ranked according to their "Relative Abundance," which also takes into consideration the evenness of their distribution and the density of the weed in the fields in which it is found.

Overall, the 2004 ranking of each weed, based on its Relative Abundance, changed little from the last survey in 1995. Still, says Brenzil, there were a few exceptions. Some of the weeds that became greater problems were, for example: redroot pigweed, which moved from 10th in the ranking to 6th; kochia, from 13th to 8th; barnyard grass, from 28th to 11th; narrow-leaved hawk's-beard, from 29th to 20th; and volunteer wheat, from 20th to 9th.

"Several of these, such as redroot pigweed, barnyard grass and kochia, are warm-season plants, and their increases may be a response to the recent hot, dry seasons in Saskatchewan," explains Brenzil. "Volunteer cereals, narrow-leaved hawk's beard, cleavers and field horsetail have been documented in other studies as being more common in low-disturbance seeding systems."

Brenzil says weeds with a lower ranking than in past surveys were stinkweed, shepherd's-purse, wild mustard and quackgrass. Other weeds that dropped substantially in ranking included scentless chamomile and stork's-bill. Because scentless chamomile and stork's-bill are common in wet areas, this reduction is most likely due to the same weather conditions - hot and dry - that encouraged the warm-season plants.

"Other notable changes, and weeds to watch for in the future, are spiny annual sow-thistle and American dragonhead in canola. These weeds had not been observed in 1995. Because of a similarity in appearance, however, spiny annual sow-thistle may have been recorded as perennial sow-thistle in the past. Prickly lettuce and black medic made substantial jumps in the rankings as well.

"Interestingly, for all the concerns raised in recent years, dandelion and wild buckwheat changed their ranking very little. Dandelion was actually found in fewer fields, but at higher densities in those fields, while wild buckwheat was found in fewer fields and at lower densities than in 1995," says Brenzil.

He goes on to point out that the relative abundance of a weed in Saskatchewan fields does not necessarily represent the overall impact of that weed on the crop. For example, he says, 10 wild oat plants in a canola field will result in about 10% yield loss, while 200 green foxtail plants are needed to cause the same yield loss in the same field. Yield-loss values also vary according to the emergence of the weed relative to the emergence of the crop: a weed that emerges early, for example, will cause more yield loss than the same weed emerging later.

The 2003 Saskatchewan Weed Survey Project is made up of three parts. The first involved counting the weed species in select fields in July and early August 2003, a time that is typically after spraying and so assesses how well the weed-control strategies had worked. The second portion is the herbicide resistance survey, in which a second team traced the original surveyor's path to find patches of surviving weeds, sampled them and submitted them to test for resistance to the herbicides used on the fields, which may take a couple of years. The third part is the field management questionnaires currently being completed by producer cooperators.

"The management questionnaire addresses crops, varieties, seeding rates, fertilizers, chemicals such as herbicides and other pesticides, and even the equipment used and the number of passes on a particular field. This information, when combined with the field counts and resistance results, will give clues as to what crop management strategies favor specific weed problems. Until we receive these completed questionnaires, we can only look at the weed counts and try to put some reasons to why the trends occurred.

"So we are anxiously waiting for all the 2003 field management questionnaires to come back so we can begin to explain why certain weeds are where they are, and how to correct the problem. I urge anyone who has received a questionnaire in the mail to take 15-30 minutes to fill it out and return it. The information provided on individual fields is kept in strictest confidence and is critical to understanding how farm management influences weed population," says Brenzil.

He suggests producers consult with their local extension agrologist on changes occurring in their area.

The 2003 Saskatchewan Weed Survey was carried out by the Agriculture and Agri-Food Canada (AAFC) Saskatoon Research Centre and SAFRR. It was funded by several agricultural chemical manufacturers and distributors, and matched through AAFC's Matching Investment Initiative.

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