Week of May 16th - Weed Emergence in Winter

Crop Staging and Weed Emergence - Week of May 16th, 2005

This is the second last report that I will provide information on weed emergence patterns in winter wheat. Next week I will summarize the crop growth and weed emergence that has occurred in those six fields (Figure 1) scouted over the past 4-6 weeks.

Figure 1 - Map of winter wheat locations scouted for weeds
throughout central and south-western Ontario.

Crop Stage: The wheat crop continues to grow at a steady pace although it hasn't really advanced in terms of Zadok's scale. The majority of wheat ranged in height from 29-50 cm and was at the first node visible growth stage (see Table 1).

*For more information on Zadok's scale refer to the OMAF Publication 811,
Agronomy Guide for Field Crops

New Weeds Emergening- Week of May 16th, 2005:

No new weeds have emerged at the two locations that received herbicide applications. Site 5 received an herbicide application this week but no visual activity to the weeds has been observed yet. Emergence of new weeds at the other 3 sites has been low, with small populations of lady's thumb, lamb's-quarters and prostrate knotweed emerging. Barnyard grass and green foxtail have also emerged at two of the locations, but certainly not at populations that would warrant any concern for weed management (see table 2). Perennials weeds, in particular field horsetail, have grown steadily (by 5 cm) over the past week.

Table 2. Weed species, density and growth stage
at 6 winter wheat field locations on May 17th, 2005.

* Indicates newly emerged seedlings since the previous week of scouting

Implications for Weed Management:

The density of weeds at the remaining 3 untreated fields is not significant enough to warrant an herbicide application. The wheat crop is also growing at such a fast pace that the increased tramping injury coupled with the increased chance of crop injury from late herbicide applications would virtually eliminate any potential benefits from weed control.

I acknowledge that 6 field locations does not provide a basis for generalizing weed control in winter wheat for the entire province. However this exercise does illustrate that weed management in winter wheat, like many other field crops is field specific. Most importantly, there is an opportunity to avoid applying herbicides in those fields with very low weed pressure.

Related Links

• OMAF Publication 811 - Agronomy Guide for Field Crops

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