Weed characteristics

B. Frick, E. Johnson - Scott Research Farm

Problem
Knowing what weeds are common on a particular farm will help to determine what lessons can be learned and what management strategies might be effective against them. What can we learn about common weeds to help with weed management?


Background
Most weeds have some characteristics in common. Weeds generally produce large numbers of seeds. Weed seeds can often germinate under a variety of conditions, but some portion of the seed population remains dormant. Dormant weed seeds are insurance against conditions that might destroy growing plants. Even though 95% of the weed seeds in the soil ‘seed bank’ may be lost to germination or death, the seed bank can often recover in a single year. Many weeds develop rapidly, are able to self-pollinate, disperse widely and tolerate a wide range of environmental conditions. A study in 1980 indicated that despite enormous effort, weeds have steadily increased from 1900 to 1980. This trend probably continues.

Weeds have characteristics unique to each species, so recognizing weed species can be important. Many sources are available to help with weed identification.

Several weed characteristics have been summarized in Table 1. Let’s compare wild oats and green foxtail as an example of what we can learn from these characteristics.

Green foxtail (commonly known as wild millet or pigeon grass) is an annual grass with small seeds that birds seem to love. As with most weeds, seed production can be prolific. Seeds that germinate on the soil surface, or in surface chaff, often have trouble rooting, so these species can be less abundant in zero-tillage systems. Root development, even within the soil is not extensive. Therefore, harrowing is often an effective means of control. Green foxtail is a warm season grass. It germinates more quickly and is more competitive at higher temperatures. Thus, it is more aggressive in late-seeded crops, common in organic systems, and is less vigorous in cooler situations such as in zero-till, or early seeding. Mature plants vary in size from one inch to three feet. Large plants can be quite competitive. Small, very dense plants can reduce surface moisture supplies.

Wild oat is an annual cool season grass. It has larger seeds, and thus is less prolific. Because the seeds are large, they tend to dry out on the soil surface, making wild oats more common in wet areas, or low spots. Wild oat germinates quickly in cool soils, and is more competitive at lower temperatures. Thus, it can emerge before the crop and become very competitive. Pre-seeding tillage will remove many early germinating plants. Later seeded crops may be relatively free of wild oats. Wild oats can be quite competitive. Seeds can remain dormant for long periods, making wild oat management a perennial task.


Conclusions
Weed management can be made easier and more effective by considering the characteristics of the most common weeds.


Funding
Provided by the Canada-Saskatchewan Agri-Food Innovation Fund


Contact information
Brenda Frick, Ph.D., P.Ag.
Prairie Coordinator
Organic Agriculture Centre of Canada
c/o Department of Plant Sciences
University of Saskatchewan
51 Campus Drive, Saskatoon
Saskatchewan, Canada S7N 5A8
Tel: (306) 966-4975
Fax: (306) 966-5015
Email: brenda.frick@usask.ca


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