Background
• Chlorothalonil is a broad-spectrum, non-systemic (contact) fungicide with multiple modes of action. It was first registered for turfgrass use in 1966.
.• The EPA has approved the use of chlorothalonil to meet the needs of growers and turfgrass mangers for controlling approximately 125 diseases on over 65 crops. It is widely used on cucurbits, peanuts, potatoes, sweet corn, stone fruit, tomatoes, ornamental plants and turfgrass.
• The Fungicide Resistance Action Committee (FRAC) lists chlorothalonil as a multi-site fungicide in the chloronitrile chemical group; FRAC Code M05. It is the only compound in this chemical group.
.• The risk of turfgrass pathogens developing resistance to multi-site fungicides, including chlorothalonil, is considered low. To date, there are no confirmed reports of turfgrass pathogens developing resistance to multi-site fungicides.
• Chlorothalonil is the backbone of many disease management programs in turfgrass and essential to manage fungicide resistance.
• Fungicide rotations with chlorothalonil are critical for control of the pathogens which cause dollar spot (Clarireedia spp.), anthracnose (Colletotrichum cereale), and gray leaf spot (Pyricularia oryzae) and to prevent these pathogens from developing resistance to single-site mode of action fungicides.
• Dollar spot is a major disease of turfgrass, consistently rated by golf course superintendents as the most problematic disease nationwide. To effectively manage dollar spot, strategic fungicide rotation is essential, which includes the use of chlorothalonil.
• Additionally, chlorothalonil is an essential component for managing snow mold pathogens and is one of the few active ingredients registered for use in turfgrass to control algae.
Registration Review
Chlorothalonil is undergoing registration review at the EPA. Following extensive review of currently available scientific data, the Agency is seeking public comment on its Proposed Interim Decision (PID). This is the next step in the registration review process, governed by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).
Key Developments
• On October 18, 2023, the EPA published its Proposed Interim Decision (PID) for chlorothalonil. Syngenta and others requested a deadline extension, and the comment period now ends January 17, 2024.
• While risk exceedance was identified due to consideration of additional groundwater metabolites and updated risk assessment methods, the toxicological properties of chlorothalonil and/or its degradates have not changed.
• The EPA identified a potential dietary risk to the health of infants (<1-year-old) from drinking water consumed in baby formula, and the general public and females of reproductive age from drinking water.
• Rate reductions proposed in the PID are to mitigate dietary risk and ecological risk estimates. Additionally, interim ecological mitigation language is proposed to mitigate potential impact to endangered species.
Proposed Interim Decision Overview
Positive Conclusions
- The EPA used best available science to update their groundwater modeling, reducing the estimated risk cup for drinking water.
- The EPA did not identify any residential handler risk of concern, risk to bystanders or occupational handler risks.
- The EPA concluded that there was no further need to assess chlorothalonil for endocrine disruption potential for human health.
- The EPA concluded non-pollinator terrestrial invertebrates are sensitive to chlorothalonil at levels higher than the current labeled maximum use rates.
- The EPA continues to follow the risk benefits assessment approach for the use of the chlorothalonil which includes the proposed mitigation measures.
Risks Identified
- The EPA reviewed the available toxicology data on a metabolite of chlorothalonil and determined that it poses a potential dietary risk to the health of females who are of reproductive age if consumed through their diet (drinking water).
- The EPA expanded the definition of residue for drinking water to include additional metabolites. This expansion led to a risk exceedance for long-term exposure to chlorothalonil and its metabolites for both the general public and infants. This expansion influenced the EPA’s proposed rate reduction for most uses, specifically in areas with a high potential for groundwater contamination.
- As part of the registration review process, the EPA has more recently identified the need for toxicity studies in honey bees and residue studies in pollen and nectar.
- The EPA has a mandate to harmonize pesticide tolerances with CODEX MRLs, where possible.
Summary of Proposed Chlorothalonil Use Rate Mitigations for Turfgrass Use:
Table 1 lists the current chlorothalonil use rates and proposed use rates as outlined by the chlorothalonil proposed interim decision posted on 18 October 2023.
- Proposed use rates represent a 3, 13, 13, 35, and 38% annual maximum rate reduction for sod, industrial turf and athletic fields, golf course fairways, golf course tees and golf course putting greens, respectively.
