Discussion

from Dudley Pond Aquatic Plant Survey 2021 by ARC

by Wayland Surface Water Quality Committee

Results

As mentioned in the prior report, Dudley Pond has ample light and desirable sediment to support rooted plant growth and therefore something will grow. The pond will not sustain a plant-free littoral zone without dredging (and even that is limited) or excessive chemical application. The best achievable goal is to strike a balance of valuable aquatic habitat and human use by selecting a desirable native plant that will cover the pond bottom but that does not have a growth morphometry that allows the plant to reach the water surface impairing boating and swimming uses. Herbicides have become more selective over the years for control of non-native species, but none are known to effectively control tapegrass.

Tapegrass is a resilient plant that has multiple mechanisms for reproduction and expansion. Generally, tapegrass is considered a desirable species and is not often a target plant for management. For these reasons there is not a lot of information on plant control remedies and very few tested solutions other than winter water level drawdown (not applicable for Dudley Pond), mechanical removal and herbicides, which have shown only fair results.

The mechanical harvesting pilot program implemented in 2021 was successful in reducing tapegrass density based on the observation data and photographic documentation (Appendix –Photographs). Tapegrass can be difficult to harvest because of its ribbon like morphometry with leaf blades moving easily along with water movement. Blades can be swept away from the harvester teeth leaving spots of tall growth within a recently harvested area (see photo in Appendix). It also grows rapidly in ideal warm sunny conditions. Multiple passes with the harvester and multiple harvesting events per growing season are required to limit plant growth topping out at the surface. While mechanical harvesting will not reduce the overall plant coverage in the pond, continual harvesting will reduce the plant biomass lessening entanglement with swimmers and boating.

EWM is found within the beds of tapegrass (see photo in Appendix). Unlike tapegrass, EWM can spread from fragments. Small fragments of EWM can sprout and root in the sediment upon settling. As mentioned in the 2020 evaluation, mechanical harvesting can exacerbate EWM density and a carefully planned plant management program is needed in order to avoid trading the tapegrass nuisance for a more severe EWM condition. The herbicide applicator will need to assess conditions (distribution and density of EWN in relation to tapegrass) early in the growing season and devise a treatment plan appropriate to decrease EWM density significantly prior to mechanical harvesting to avoid spreading EWM fragments. The herbicide applicator will need to carefully select an herbicide that will provide sufficient contact time with EWM as tapegrass blades may prevent the herbicide from making good contact with EWM. As with any aquatic plant management program, it is important to ensure that all appropriate permits are in place, nontarget impacts are minimized, and the contractor adheres to label restrictions and any permit special conditions.