Tom's Blog

Wednesday, November 25, 2009

Sweet clover: last fall spraying

As readers if these posts know, sweet clover (Melilotus albus and M. officinalis) is one of our major scourges of the summer. It has a very long-lived seed bank and the seeds are stimulated to germinate by burning. We spend a lot of the June-July period hand-pulling it.

Sweet clover is a biennial, and like many other nonnative species (garlic mustard, for instance) it has a long fall regrowth period. These first-year plants will overwinter and become the large flowering plants that we will be pulling next summer.

Late fall is an ideal time to spray these sweet clover plants with glyphosate. Since they remain green, they will take up the herbicide and will be killed. And since virtually all native species have died back for the winter, there is no worry about killing any "good" plants. Also, glyphosate has no soil-residual, so there will be no herbicide present next spring. (The glyphosate concentration recommended on the label should work fine.)

I did a study where I marked a large patch of sweet clover during this fall regrowth period and sprayed it with glyphosate. There was no growth the following spring/summer, and the area continues to remain free of sweet clover four years later.

Today, Susan, Marci, and Amanda cruised our major sweet clover areas and sprayed all visible plants. On the south slope, where sweet clover has been especially bad, the green plants are small but reasonably visible among the clumps of little bluestem grass (see photo). Although not as easy to spot as fall regrowth of garlic mustard or hedge parsley, they can be found, and every sprayed plant will be one less plant to have to pull next summer.

How about hand-pulling now instead of spraying? Unfortunately, it does not work. The root crowns of these sweet clover plants are still very delicate, and the stems break off if hand pulled. You have to dig them up, using a sharp knife, a rather time-consuming job.

Our fall foliar spraying activities are now over for the year. When the temperature drops below freezing, aqueous spraying is difficult to do. We are now tooling up for winter herbicide work, using Garlon 4 dissolved in bark oil to control woody invasives, either as a cut stem treatment or by basal bark.


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