I was driving down a long country road and noticed two large fields where winter wheat had been harvested almost eight weeks earlier. Each had a beautiful thick canopy of oats.
Figure 1 (at top). An oat cover crop planted almost eight weeks ago following winter wheat harvest.
That same day, when I came across a field that had been left fallow, it became clear why so many farmers had chosen to plant an oat cover crop. There were significantly more annual weed species with mature seed heads in the field left fallow.
Figure 2. A field left fallow almost eight weeks after wheat harvest. Notice the abundance of annual weed species with mature seed heads.
Out of curiosity, I decided to harvest the weed species in 20 random areas (each area was a square metre) in each field to quantify the difference in weed seed produced. Below is a good representation of the amount and types of weed species found in each field.
Figure 3. Field No. 1 with oat cover crop had lamb’s quarter, common ragweed and pigweed.
Figure 4. Weeds harvested within a square metre in field No. 2 with an oat cover crop. There was annual sow thistle and lamb’s quarter.
Figure 5. Weeds harvested within one square metre of the field left fallow. From left to right: lamb’s quarters, pigweed, Canada fleabane, spiny annual sow thistle and common ragweed.
Figure 6. The reduction in weed seed produced in each field by taking dry weight of seed heads and comparing each field as a percentage of the fallow field.
Bottom line: Farmers who are utilizing cover crops after wheat harvest are seeing a reduction in the amount of annual weed seeds produced and returned to the soil. Perennial weeds can be managed throughout October at the same time that the volunteer wheat and oat cover crop is retired.