By: Dr. Jason Ferrell, UF/IFAS Center for Aquatic and Invasive Plants Director
Invasive plants are a constant problem in the environment. Whether they are blocking navigation and access, or damaging native plant communities, invasives have to be managed. However, debate about the means of management is an old and often passionate conversation. Mechanical harvesting in a great option, but current funding does not allow for the luxury of harvesting as a standalone management strategy. Biological control is an amazing science and while many of our worst weeds can be slowed down by these insects, they are rarely eliminated by this practice alone. So often, herbicides become the clean up crew or the main tool in a manager’s toolbox. Although, herbicides are controversial, most everyone can agree using less is best. So, what are the options? How can scientists make strides toward maximizing control of invasive plants while using as little herbicide as possible?
This question has been asked for decades and the best solution to date is the adoption of a maintenance control strategy. Maintenance control is a practice that aims to maintain an invasive plant population at the lowest feasible level. This control technique is accomplished by frequent herbicide applications to sustain very low invasive plant populations. Though it is counterintuitive, frequent applications will lead managers to a result of less overall herbicide use. This reduction is because fewer plants require less herbicide to keep the population low. On the other hand, when the population grows, the amount of herbicide will likewise increase.
This scenario has been proven over and again in both invasive plant management research and in real world applications. In 1985, Dr. Joe Joyce showed this experimentally with a simple and elegant study. He started with 10 water hyacinth plants in large tub and allowed them to grow. In one tub, when the plants covered 5% of the surface area, he would spray – but leave the original 10 plants. He did this over and over, recording how much herbicide was used. In other tubs, he did the same thing, but after they reached 25%, 50%, or 100% cover. At the conclusion of his one year study, he found keeping plants at 5% cover required him to spray eight times, but only used 136 ml of herbicide. Allowing the plants to reach 100% cover meant he only needed to spray twice, but it required 350 ml of herbicide. As stated previously, it seems counterintuitive that spraying eight times used only one-third of the herbicide vs spraying two times. However, this experiment just goes to show, keeping plant populations low results in less overall herbicide in the environment.
Well-meaning stakeholders see spray boats on their lake and sincerely ask for less spraying. Unfortunately, this results in more plant growth and eventually translates into significantly higher herbicide requirements. Invasive plants like water hyacinth do not provide good wildlife habitat and actually degrade native communities. If we, as a society, can come to terms with frequent herbicide management, the end result will be fewer invasive plants, less herbicide in the environment, and healthy native plant communities.
Dr. Jason Ferrell, UF/IFAS CAIP Director, wrote this piece. Any questions should be directed to Shelby Oesterreicher at firstname.lastname@example.org. For more information about the UF/IFAS Center for Aquatic and Invasive Plants, please visit http://plants.ifas.ufl.edu. Be sure to follow us on social @UFIFASCAIP.
UF/IFAS CAIP, Turning Science Into Solutions.
 Benefits of Maintenance Control of Waterhyacinth. Aquatics Magazine, 1985 Winter Issue. P 11-13. https://fapms.org