Herbicides work best when weeds are small. Period. Exclamation mark. You get the gist…
There’s perhaps no better example of this than cleavers. Take a quick flip through the Guide to Field Crop Protection and you’ll notice that most herbicides with activity on cleavers only guarantee control/suppression of this weed when applied between the 1 to 4 whorl stage. Although this staging is most common, application timing may be limited to as few as 2 whorls or extend up to the 8 whorl stage, depending on the product. There are also herbicides that are somewhat ambiguous as to cleavers staging but research and experience have shown that, when it comes to herbicide application to cleavers, the smaller the better.
It makes sense then that a recent question on CropTalk Westman was: ‘How do you stage cleavers?’
Whorled leaves, one of cleavers most distinctive features, results in a herbicide application staging unique to this weed. Staging cleavers is similar to other weeds with a few simple tweaks:
- Find the main stem. Identifying the main stem is an important step in staging crops and weeds. But this is often easier said than done with cleavers because of its creeping habit and similar sized branches. If you can’t find the main stem, just be sure to pick the stem with the highest number of whorls present.
- Don’t count the cotyledons. Only the true leaves count when staging plants. The cotyledons of cleavers are oval to oblong with a notch at the tip and are easy to distinguish from the true leaves.
- Each whorl counts. Unlike most other weeds, cleavers have a whorled leaf arrangement, with each whorl having ~4 to 8 leaves (usually 6). In this case, simply count each whorl along the main stem rather than each leaf (see figure & example below).
Submitted by: Jeanette Gaultier, Provincial Weed Specialist, Manitoba Agriculture
Find the 2016 Guide to Field Crop Protection online: www.gov.mb.ca/agriculture/crops/guides-and-publications/#gfcp