Garlic Mustard Seedling Survival

by Carl Strang

In the spring I began a study of how garlic mustard, a harmful exotic biennial, might best be controlled by manual means. In small areas where the plant is just beginning to invade, and where use of herbicides is undesirable, it is possible to uproot or clip the second-year plants. Results so far indicate that pulling is more effective than clipping, but there is a timing variable to investigate, and I need also to determine whether pulling stimulates an increased germination of seedlings in the following year.

GM October 1b

Last week I returned to my study plots to count seedlings at the end of their first season. As the above photo shows, some tree and shrub leaves had fallen, so I carefully removed these to make sure my seedling counts were complete.

GM October 2b

I had expected some attrition through competition, but was surprised at the numbers of seedlings that had died. Every single one of the 27 square meters in the study plots showed big drops in numbers of seedlings, even in cases where there were so few that competition between them would seem to be negligible. Where in May seedling counts ranged from 12 to 345 in the square meter areas, in October the counts were 0 to 55. Especially dramatic were the control squares, in which second-year plants had been allowed to proceed to fruiting before I clipped them. There, seedlings had looked weak, but plenty still remained in May. However, the total of 214 seedlings in May had dropped to only 3 seedlings in the 9 square meters of the control treatment by October. Apparently their inhibition by the second year plants had been too great for them to overcome. Attrition in pulled treatment squares had been from 747 to 236 between May and October, and the corresponding numbers for clipped treatment squares were 1002 and 107. Statistical computations supported the difference between controls and both treatments in October counts, but indicated no statistical significance between the two treatments.

GM October 3b

Now I wait for spring. I plan to set up new study plots next year, but will apply the same treatments a month later, to see what difference timing makes. I also will return to this year’s plots. I want to follow this year’s seedlings through to their fruiting times, and to see if the numbers of new seedlings in those squares support or reject the notion that pulling increases seed bank germination.

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