EPA Workplan: Demonstration Project on Hydrilla and Hygrophila in the Upper Kissimmee Chain of Lakes

Element 1: Development and Testing of New Aquatic Herbicides

Objectives Addressed by Element 1

1) To evaluate the effectiveness of Experiment Use Permit (EUP) herbicides in the treatment of hydrilla and hygrophila.

2) To evaluate new technology processes or practices, or a new combination or uses of technologies, processes or practices for the control of hydrilla and hygrophila using small-scale field work.

3) To implement and monitor successful practices and processes identified in objectives 1 and 2 using large-scale field demonstrations.

Introduction

Within the past few years there has been renewed interest in the agrichemical industry to develop new herbicides for registration for aquatic use. Many of these new products have reduced risk to humans, short residual in water and low toxicity to aquatic fauna. Presently, flumioxazin and bispyribac-sodium are approved for use under Experimental Use Permits (EUP) by the Florida Department of Agriculture and Consumer Services (FDACS) and the U.S. Environmental Protection (EPA) (see Table 1). There are an additional five products in which Section 3, 18, 24C, or EUP (see Table 1) petitions have been submitted for approval permitting limited testing in Spring/Summer 2006.

The primary information needs for aquatic plant managers who intend to use these new aquatic products are:

1. Weeds controlled and selectivity on native plants

2. Proper rate and timing of application

3. Residual in water, typical half-lives and potential impacts on irrigated plants. (landscapes, sod farms, citrus, pastures)

Table 1. New aquatic herbicides under consideration for use in Osceola County waters for aquatic plant management.

Trade Name & Manufacturer

Generic Name

Label Status

Primary use/ Potential use & Herbicide Family

Renovate by SePRO

Triclopyr

Section 3*

Broadleaf weed control, floating plant control, possible activity on hygrophila – Auxin mimic

Habitat by BASF Corporation

Imazapyr

Section 3*

Floating/emergent plants only, torpedograss control. More cost effective than glyphosate? Selectivity? ? Acetolactate Synthase Inhibitor (ALS) – inhibits protein synthesis

Stingray by FMC Corporation

Carfentrazone

Section 3*

Water lettuce, full range of activity unknown? Protoporphyrinogen Oxidase (Protox) Inhibitor – rapid cell membrane disruption

Trade Name Unknown - SePRO

Penoxulam

Section 18*

applied for

Hydrilla control, whole lake treatments, selectivity. Timing and rates not well understood? Acetolactate Synthase Inhibitor (ALS) – inhibits protein synthesis

Clearcast by BASF Corporation

Imazamox

Section 24C* applied for

Hydrilla control, whole lake treatments, selectivity. Timing and rates not well understood. Acetolactate Synthase Inhibitor (ALS) – inhibits protein synthesis

Trade Name Unknown – Valent Corporation

Flumioxazin

EUP

Contact herbicide for hydrilla control, selectivity and timing, rates not well understood. Acetolactate Synthase Inhibitor (ALS) – inhibits protein synthesis

Trade Name Unknown – Valent Corporation

Bispyribac - sodium

EUP

Hydrilla control, whole lake treatments, selectivity. Timing and rates not well understood. Acetolactate Synthase Inhibitor (ALS) – inhibits protein synthesis

*Section 3 label = is the EPA approved label for national use.

*Section 24(c) label = a provision for Special Local Needs - States may register an additional use of a federally registered pesticide product or a new end-use product to meet special local needs. EPA reviews these registrations and may disapprove them under certain circumstances.

*Section 18 Label = label for Emergency Exemptions - Section 18 of FIFRA authorizes EPA to allow States to use a pesticide for an unregistered use for a limited time if EPA determines that emergency conditions exist.

This information is critical for managers to determine which herbicides to apply for weed control giving consideration to water use (irrigation), presence of native plants (selectivity) and optimum timing of application and optimum rate to achieve maximum weed control, with minimal non-target damage and lowest cost.

All the products listed in Table 1 are registered for terrestrial uses, and have been reviewed by regulatory authorities. The carcinogenicity, fish/invertebrate toxicity, effects of metabolites, degradation products are all known to EPA and much of these data are available from herbicide profiles, Weed Science Society of America handbooks, MSDS sheets and from information requested of the product manufacturer.

Unfortunately, hydrilla, the most serious aquatic weed in Osceola County waters, and in the state as well, has exhibited resistance to the herbicide fluridone. Fluridone has been the most widely used herbicide for large-scale hydrilla control since the early 1990’s. While fluridone applications of < 15 ppb have historically controlled hydrilla for up to a year or more, in the past few years fluridone resistant hydrilla requires application rates of > 25 ppb at which point economics and damage to native plants becomes an issue. Thus, the discovery and use of new herbicides and more importantly, modes of action, are important to discover to prevent resistance from developing to new herbicides. Unfortunately, three of the herbicides listed in Table 1 for whole lake hydrilla treatments (penoxulam, imazamox, and bispyribac- sodium) are all in the same herbicide family. Resistance development to one of these would likely result in resistance to the remaining two. Therefore, care needs to be taken to rotate the use of herbicides in the future and greenhouse/laboratory search for new hydrilla herbicides needs to be pursued.

The specific tasks outlined below will address these and related issues with regard to “new herbicides.”

 

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Element 1, Task 1: Determine field selectivity, efficacy and water residues of new aquatic herbicides.

Objectives

1) To evaluate the effectiveness of Experiment Use Permit (EUP) herbicides in the treatment of hydrilla and hygrophila.

2) To evaluate new technology processes or practices, or a new combination or uses of technologies, processes or practices for the control of hydrilla and hygrophila using small-scale field work;

Justification

To learn how to use, and determine water residues and impacts of new herbicides on target and non-target species in ponds and lakes.

Approach

Pending the results of regulatory actions, there appears to be four herbicides that can be tested in Spring/Summer of 2006, and the other chemicals from Table 1 should be approved for testing shortly. The first chemicals to become available for testing are the systemic ALS inhibitors imazamox, penoxulam and bispyribac-sodium and the Protox contact herbicide flumioxazin.

Products for testing will be in various stages of labeling approval (EUP) or may be labeled as 24c or Section 18. In order to protect drinking water wells that may be seated in a surficial aquifer, a survey will be conducted to identify these drinking water wells within a mile of the lake application site. Should any such wells be identified, no treatment shall occur until the EPA Project Manager is notified and provides approval.

To assure that detention stormwater pond test sites do not result in drinking water well contamination, prior to applying registered or experimental use herbicides, Osceola County will inspect stormwater ponds to verify that they are in good repair and meet the permitted design standards.

In addition or as an alternative, limno corrals will be set up in the littoral portions of Osceola County lakes in such a way that diverse plant communities can be treated and the impacts of these treatments on weeds and non-target plants monitored over time. Limno corrals are watertight Teflon coated cloth barriers similar to silt barriers, but sealed to prevent water exchange.

The first year of testing will focus on the above-mentioned four chemicals. In future years as more products become available for testing, more products will be rotated through this process of Element 1, Task1.

Data collection: Whether applied to stormwater detention ponds or 0.25 acre limno corrals in large lakes, the data collected on herbicide treatment will be similar.

a) Where desired, herbicide residues in water will be determined on water samples collected at pre-determined times depending upon the characteristics of the test herbicide. Residue analysis will be by approved methods either by contract labs or by the herbicide manufacturer.

b) Herbicidal effects on target weeds (hydrilla, hygrophila, etc.) and non-target native species will be determined by photographic documentation and by sampling point transects on a pre-determined schedule depending upon the rate of herbicidal control.

Table 2. Approximate rates and treatment protocols for herbicides in ponds and enclosed waters – first year testing.

Herbicide

Rate

Sampling/transects

penoxulam

5 - 25 ppb

possible split treatments

exposure period similar to fluridone

1/2 life = 25-50 days

imazamox

5 - 25 ppb

possible split treatments

exposure period similar to fluridone

1/2 life = 25-50 days

bispyribac-sodium

5 - 25 ppb

possible split treatments

exposure period similar to fluridone

1/2 life = unknown, but similar to above

flumioxazin

100-400 ppb

possible split treatments

exposure period = minutes

1/2 life = very short, minutes to hours depending upon water pH.

Field efficacy, selectivity and water residue studies will be conducted on potential aquatic herbicides as they become available (registered) for aquatic use. Currently there are 7 relatively new herbicides in which selectivity data have not been systemically collected nor published papers. We also expect additional herbicides to become available over time as a result of work completed under Element 1, Task 2.

 

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Element 1, Task 1 Milestones

Hiring/training of personnel will occur in Year 1 and 3 to 4 treatment sites will be located for herbicide treatment the first and second quarter of year 2007. An additional 3 to 4 sites containing different native aquatic plants will be treated annually (spring) of each year and plant communities monitored for up to 1 year following herbicide application.

Schedule of Activities for Element 1, Task 1:

 

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Element 1, Task 2: Laboratory/greenhouse screening and preliminary evaluation of potential new aquatic herbicides.

Objective

1) To evaluate the effectiveness of Experiment Use Permit (EUP) herbicides in the treatment of hydrilla and hygrophila.

Approach

To investigate the time: rate relationships, selectivity and phyto-toxicity of potential new aquatic herbicides to determine feasibility of further registration.

Three of the four new aquatic herbicides listed in Table 2 are ALS inhibitors, herbicides that inhibit formation of amino acids found only in plants, not animals. Resistance to this mode of action (group of herbicides) has occurred quite rapidly in terrestrial weed control. Thus, we must find and develop herbicides with alternative modes of action to manage resistance development. The herbicide manufacturers have to have preliminary results on which to base a decision to proceed with aquatic registration. Not all herbicides control aquatic weeds. The questions addressed under this task are as follows:

1. What other herbicides and/or modes of action have efficacy against hydrilla?

There are approximately 250 herbicide active ingredients sold commercially in the U.S., 10 products registered for aquatic use, and some 30 products used on the semi-aquatic rice plant. With consideration to toxicities to fish/zooplankton and possible residues in water, herbicides will be selected and screened for activity against hydrilla. Hydrilla sprigs will be planted in sand in 1.5L pots and 4 pots placed in 94.5L (25 gallons) tubs for evaluation. After establishment for 10-20 days, the water in the tubs will be treated once with a range of herbicide concentrations, e.g. 0, 50, 100, 200, 400 and 800 ppb, depending upon the herbicide being treated. Plants will be harvested after 8 weeks and dry weights determined to evaluate herbicide efficacy.

2. What concentration and exposure times are required for potential new herbicides to control hydrilla, hygrophila and other aquatic weeds?

Products that show activity in the initial screening under Item 1 above will be further evaluated in replicated 94.5L containers and with individual sprigs of hydrilla and other test species in growth chambers and larger replicated tank studies. Parameters to be measured to ascertain herbicide activity include plant dry weights, and ion leakage as measured by a conductivity meter. Plants will be exposed to various herbicide concentrations for varied time periods to determine how long the herbicide, at various concentrations, need to be in contact with the weeds to be phyto-toxic.

3. Does the potential new herbicide damage non-target native plants at rates required for hydrilla control?

Once the concentration/exposure times are determined in Item 2 above, they will then be applied either on the plant foliage or in the water to determine the concentrations that affect native emergent, floating and submersed species. These tests will be performed in the greenhouse or shadehouses at the University of Florida. Native species will be grown in 1.5L pots, replicated and harvested at appropriate times to determine effects of the herbicides on non-target species.

4. What irrigation concerns, irrigation restrictions or setbacks from homeowner or commercial irrigation systems are necessary to prevent damage to homeowner turf and ornamental species?

Commercially grown turf, such as bahia grass, St. Augustine and centipede grass will be grown in pots and irrigated with water from a simulated herbicide treated area. Annual ornamental species such as begonia, impatiens, etc. will be purchased and treated similarly. Depending upon the herbicide, treatments will be applied one, or several times to determine EC-10; values, the concentrations of herbicide in irrigation water that cause a 10% growth reduction. Wheat, tomato, beans and corn are also plants that are used as indicator species. Other species may be tested for phytotoxicity, as warranted.

Once these questions are addressed, these data are usually sufficient for the manufacturer to move forward and apply for Experimental Use Permits or other registration that would allow larger scale field-testing. Upon regulatory approval, these herbicides would move into Task 1 protocols.

These studies, initial screening for new aquatic herbicides for use against hydrilla and hygrophila, concentration exposure studies, initial selectivity and phyto-toxicity will be conducted throughout the duration of the project, but also depends upon the number of new modes of action that has potential for registration. Data collected from these studies are used to assist registrants to make decisions regarding possible full registration.

 

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Element 1, Task 2 Milestones

In the first two years, 5-10 compounds will be tested annually for activity against hydrilla and hygrophila. Concentration/exposure times (CET) will be conducted on these products with the greatest potential for future registration, as well as some of the older products (1-2 products per year). Greenhouse and shadehouse studies (step 3 above), and phytotoxicity studies will be conducted on the greatest potential for future registration, which may be two to three products annually.

Schedule of Activities for Element 1, Task 2:

Overall Timeline of Element 1:

 

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