Garlic Mustard Results

by Carl Strang

In mid-May I returned to my garlic mustard study plotsĀ  to harvest the second year plants, counting the survivors in each square-meter subplot to learn what had happened. The second year plants had developed flower buds,

GM flower buds b

then flowered.

GM flowers b

Meanwhile the seedlings were adding leaves.

GM seedlings 3b

When the time came to count and remove second year plants, the contrast between treated and control square-meters was clear cut beyond expectation.

GM plot 2 overview 14MYb

The plant count on untreated (control) squares ranged 100-223 per square meter, with a median value of 159. In some of the treated squares I had uprooted all of the second year plants I could see in March. A few remained in May, probably ones that were so small in March that I mistook them for seedlings. Their numbers ranged 1-4 on the square-meter subplots, with a median of 3. I was most interested in the other treatment, in which I pinched or clipped plants at ground level, leaving the roots. There had been indications in the literature that this would be sufficient to kill the plants. Such was not entirely the case here.

GM plot 2 NW to SWb

Some clipped plants had enough stem buried beneath the ground that they recovered and their new shoots were producing fruits. Their numbers were much lower than in the controls, but also distinctly greater than in the pulled plant treatment: range of 21-47, median of 23. These differences were statistically significant. Clipping in March killed most but not all plants.

I also was interested in seedlings. The claim has been made that uprooting plants disturbs the soil and so increases the number of seedlings. Seedling numbers increased between March and April in control squares as well as in both treatment types, but there was no statistically significant difference among the three different square types. I will need to return next year to see if there is a difference then, but so far I find no support for the claim that uprooting garlic mustard has undesirable effects.

On the other hand, when I removed the second-year plants in May, I saw that seedlings in treatment squares were robust and healthy looking.

GM plot 2 W central post treatment b

In contrast, the ones in control squares were puny.

GM plot 2 S central post treatment b

Clearly they had been suppressed by the second year plants. Time will tell if they catch up with the ones in the treatment squares.

I will want to see if the ground-level clipping of control plants in May succeeded in killing them. Also, next year I am thinking of applying the initial treatments in April rather than in March, and doing the clip treatment at a more realistic level of a short distance above the ground.

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