Date of Award

Spring 5-13-2017

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Eric Gallandt

Second Committee Member

Gregory Porter

Third Committee Member

Mark Hutton

Additional Committee Members

Andrei Alyokhin

Jianjun Hao

Abstract

Many farmers target weeds at the seedling stage, aiming to control weeds with the minimum amount of labor necessary to avoid crop yield loss. Other farmers with a more long-term, seed-focused approach aim to prevent weeds from setting seed so that emergence will be decreased in subsequent crops. These strategies likely vary in short- and long-term effects on farm ecological and economic health. In 2014–2016, I compared these strategies in a test crop of onion. Unexpectedly, due to high yields, the more labor intensive, seed-focused strategy was the most profitable. Case-study interviews of farmers who have adopted each approach indicated seed-focused management improves over time, whereas seedling-focused management becomes more challenging. A key obstacle for both seed- and seedling-focused management was the control of weeds directly in the crop row, where mechanical cultivation tools are only marginally effective due to the need to avoid crop damage. In 2015–2016, I tested the hypothesis that rather than using just one tool, “stacking” on a second or third type of tool would increase efficacy. Indeed, for most tool combinations tested, efficacy increased in an additive manner when more tools were used. One particular combination of three tools exhibited a synergistic increase in efficacy, even over a range of conditions, suggesting that farmers could improve intra-row weed control by adopting this technology. Weed seedling control could be further improved by decreasing the burden on cultivation through a more diverse set of ecologically based weed management practices. Such tactics could be benefited by improved knowledge of the timing of weed seed germination and emergence. In 2014, I recorded the timing of emergence of weed species at Rogers Farm in Old Town, ME and found that many weed species had peak emergence periods that could be targeted by ecologically based management tactics. Overall, my research results provide farmers several ways to enhance effectiveness of ecologically based weed management by encouraging more thoughtful selection of preventative, suppressive, and reactive tactics, increased efficacy of weed seedling control, and improved timing of management activities.

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