IPM programs must also consider the many shared and often competing uses of areas to be managed. Additionally, conditions change throughout the year and programs designed for one season may be unsuitable for others. Some examples:

• Summer treatments of submersed plants may require higher rates of herbicides if they are broken down microbially (microbes are more active in warmer waters). Winter treatment rates would need to be adjusted for cooler water with less microbial activity.
• Summer drawdowns may allow the spread of transitional species such as cattail (Typha spp.) to deeper areas of the water body. During winter, these plants are dormant.
• Grass carp release is more successful in fall or winter than in summer because there is less temperature stress and more dissolved oxygen, and target plant growth may be lower so fewer fish are needed.

More than 60 biological, chemical, mechanical and physical tools are available to manage aquatic plants in Florida waters. FWC biologists consider each of these and integrate them into strategies that:

• provide cost-effective control of the target plant
• conserve or enhance the uses and functions of the water body, including native plant and animal habitat; and
• are compatible with current conditions in the water body.

Example: 20,000-acre Lake Toho in Osceola County is part of a Federal Flood Control and Navigation Project. It supports a world-class largemouth bass fishery; is an important recreational source for boating, ecotourism, and water-fowl hunting; and provides critical habitat for the endangered Everglades snail kite. In the past, hydrilla has covered the surface of more than 15,000 acres of Lake Toho. Hydrilla management programs in Lake Toho must address herbicide resistance issues; as well as annual flood control regulations, irrigation requirements, recreation, and fish and wildlife habitat, especially endangered snail kite nesting and foraging. This example shows how the various uses and functions of Lake Toho influence the window of opportunity to conduct large-scale hydrilla control. Because of the multiple uses of Lake Toho, hydrilla and hydrilla management will always have some level of impact on these uses.

The best time to initiate large-scale hydrilla control using herbicides is in cooler winter and early spring months, when hydrilla is actively growing and most native plants are dormant. Oxygen content is higher (which accommodates plant decomposition), and rainfall is generally less than late spring and summer (when tropical storms and hurricanes could flush herbicides from the system). If hydrilla is not controlled in winter or spring, it may cover the surface of thousands of contiguous acres by late summer. This level of hydrilla interferes with flood control, navigation, and recreation, and also creates conditions where dissolved oxygen could reach critically low levels and cause a catastrophic fish kill. Yet winter and spring months are also peak waterfowl hunting, fish spawning and fish tournament months.

Water levels can be lowered to reduce the volume treated with herbicide, which in turn reduces the amount and expense of herbicide use. It also increases the capacity to store excess rainfall and stormwater runoff. If water level dams in the reservoir are opened during herbicide treatments, application cost and control are diminished, and additional risks are posed to non-target plants downstream. Likewise, releasing herbicide-treated waters for irrigation can threaten commercially important plants; for example, sod, vegetables, and citrus. Timing and amount of water-level reduction must also consider impacts on the nests of endangered snail kites and apple snail reproduction (the kite's main food source), as well as sportfish bedding and accessibility to shallow shoreline and marsh areas for water-fowl hunting.

See these links for Mechanical, Physical, Chemical and Biological Control Considerations for invasive plants.