aquatic weed | Panhandle Outdoors

Now is the Time to Address Aquatic Weeds

by Mark Mauldin | Apr 9, 2020

Monitor your ponds closely throughout the spring and make any necessary herbicide applications before weed growth becomes too excessive.
Photo Credit: Mark Mauldin

Even though the calendar says we are only a few weeks into spring, recent weather has been more like summer. The early arrival of sustained warm weather has water temperatures in local ponds high enough that aquatic vegetation growth has really taken off. This early growth period is the ideal time to evaluate ponds and address any aquatic weed issues that may be present, since aquatic weed infestations tend to become worse through the summer. Getting an early start generally helps control efforts to be more successful and less expensive, so get started sooner rather than later.

As plants grow, they are able to build up energy reserves, making them more difficult to control. The longer they are allowed to grow, the stronger and more difficult they are to control. Controlling weeds earlier in the growing season reduces this problem.

Similarly, as the growing season progresses plants produce more and more biomass. If a herbicide is applied and the weeds are killed, large amounts of decomposing plant material in the water can cause problems. The decomposition process uses oxygen; dissolved oxygen in the pond can drop to levels that are hazardous to fish and other aquatic species. The more plant material that is present when herbicides are applied the bigger concern this becomes. Applying herbicides earlier in the growing season, before large amounts of biomass are produced, can help lessen this problem.

Further compounding the issue, warm water is physically able to hold less dissolved oxygen than cooler water. Late in the summer, pond water can be very warm with low concentrations of dissolved oxygen even before large amounts of decomposing plant material are added.

To help reduce the risk of oxygen depletion never treat more than ½ of a pond at one time, if weed growth is already substantial treat no more than 1/3 of a pond at one time and always allow 10 -14 days for oxygen recovery between treatments. Also, avoid treating on cloudy days, another factor that can lead to lowered dissolved oxygen. Photo Credit: Mark Mauldin

Evaluating the vegetation in a pond is always the first step in the management process. Figuring out what kind of weeds you have, and if the population warrants control might seem simple, but it can be somewhat challenging. This is particularly true for submerged weeds – those that grow beneath the surface of the water. Unfortunately, submerged weeds are often the most troublesome weeds for pond owners to deal with. All submerged vegetation is not necessarily a bad thing, but there are several aggressive and/or invasive species of submerged aquatic plants that grow very rapidly and can be quite problematic, making proper evaluation critical.

While emergent and floating plants are easier to evaluate than their submerged counterparts, proper identification of all aquatic plants can help determine their potential for spread and, if warranted, the most effective control measures. If you had problem weeds in your pond last summer, you probably still do; get them identified and under control before they have time to spread. If you did not have problem weeds last summer, be on the lookout for any new/different kinds of weeds to head-off any potential issues.

Due to the current situation with COVID-19, generally speaking, County Extension Agents are not permitted to make field visits, but we are still here to help identify and provide control recommendations for your aquatic weeds. Floating and emergent weeds can generally be effectively identified using pictures. Submerged weeds can be much harder to identify using only pictures. For the best results, special care should be taken when photographing aquatic weeds. Collect a small sample of the weed, place the sample in an opaque container (preferably white in color), cover the sample with clean/clear water just deep enough for the sample to completely spread out and be supported by the water. Take multiple, well focused pictures of the sample. Some pictures should be of the entire sample, while other need to focus on the leaves and the attachment of the leaves to the stem(s). The pictures need to be emailed (not sent via text message) so the image size/quality is not compressed.

A good image of a submerged weed sample. In addition to this image close-ups of the leaves and attachment points will likely be needed for identification. Photo Credit: Nikki West

Now is the time to start managing aquatic weeds. The current situation in the world will make the process a little different, but with some effort and patience your County Extension Agent can help you get your weeds identified and develop a plan for control. On a positive side-note, most of the commonly recommended herbicides used to control aquatic weeds are available to order online, so it is quite possible you can address your aquatic weed issues all while staying “safer at home“.

Invasive Species of the Day: Cuban Tree Frog and Hydrilla

by Carrie Stevenson | Feb 28, 2015

Cuban Treefrog (Osteopilus septentrionalis):

Image by Dr. Steve A Johnson 2005.

The Cuban Treefrog: was introduced into Florida as a stowaway on vehicles and plants in the 1920’s. As of 2013, breeding populations have been recorded as far north as Georgia. Cuban Treefrogs have larger toepads and eyes than any of the native species. Being larger in size, the Cuban Treefrog out-competes other treefrogs for resources, to the point that they are predators of Florida’s treefrogs and inhibitors of native tadpoles.

Juvenile Cuban Treefrogs can be distinguished from natives by their red eyes and hind legs with blue bones. Three-foot-long sections of 1.5 inch diameter PVC pipe can be placed in the landscape to monitor for treefrog species. Should Cubans be found, they should be reported and euthanized. For additional details visit: http://edis.ifas.ufl.edu/uw259.

Would you like to be a Citizen Scientist? You can help Dr. Steve Johnson at the University of Florida Department of Wildlife Ecology and Conservation by reporting suspected Cuban Treefrog sightings. For more information on how you can become a Citizen Scientist, visit The Cuban Treefrog Citizen Scientist Project.

For more information contact the author Sheila Dunning, UF/IFAS Extension Okaloosa County Commercial Horticulture Agent 850-689-5850.

Hydrilla (Hydrilla verticillata):

Hydrilla is a perennial submerged plant that grows in dense mats up to the surface of freshwater habitats, including ponds, lakes, springs, and rivers. Growing at the rapid rate of an inch a day and up to 25 feet long, hydrilla shades out beneficial native plants and clogs waterways, preventing flood control, boating, and fishing. In dense populations, the plant can alter oxygen levels and water chemistry and survive in a wide variety of nutrient conditions, sunlight availability, and temperatures.

Hydrilla Photo Credit: Vic Ramey, UF/IFAS Center for Aquatic and Invasive Plants.

Originating in Asia, it was introduced to Florida (likely through Tampa and Miami) in the 1950’s as part of the worldwide aquarium trade. Hydrilla has become a very expensive problem for the state. Millions are spent annually on chemical and mechanical treatment simply to maintain the plant. Adding to the problem is the fact that it is still available commercially, even though it has been placed on the US Federal Noxious Weed List. In the United States, the plant is found as far north as Connecticut and west to California and Washington.

Methods of control include mechanical harvesters and chopping machines (although fragments of hydrilla left in the water can regrow), introduced insects and fish (particularly the Chinese grass carp), aquatic herbicides, and lake drawdowns. Hydrilla is often transported from one body of water to the other by unknowing boaters moving fragments of the plant left on boats, trailers, or live wells, so learning to identify the plant and cleaning boats before leaving the ramp are helpful in prevention. Visit the Extension Hydrilla IPM site for more helpful tips.

For more information contact the author Carrie Stevenson, UF/IFAS Extension Escambia County Coastal Sustainability Agent at 850-475-5230.