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What is Thiodicarb?

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  • Written By: Karyn Maier
  • Edited By: Bronwyn Harris
  • Last Modified Date: 27 November 2016
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Thiodicarb is a carbamate insecticide and pesticide that consists of two methomyl groups linked by amino nitrogen through sulfur molecules. The physical characteristics of this crystalline powder include a color ranging from white to tan and a faint sulfurous odor. While this carbamate is relatively stable in light and ambient conditions, it does degrade relatively easily at temperatures over 100 degrees Celsius (212 degrees Fahrenheit) into several byproducts, including dimethyl disulfide and carbon dioxide. The main byproduct of thiodicarb decomposition, however, is methomyl, which is achieved through hydrolysis catalyzed by acidic or alkaline conditions.

The chemical name for thiodicarb is 3,7,9,13-tetramethyl-5,11-dioxa-2,8,14-trithia-4,7,9,12-tetraazapentadeca-3,12-diene-6,10-dione. However, thiodicarb is also known by several alternate common names, including bismethomyl thioether, carbamic acid and UC 51762, among others. It is also sold under the trade name of Larvin.

Thiodicarb is commonly used to protect agricultural crops from Lepidopterous pests, such as Beet armyworm, Corn earworm and Black cutworm. As an insecticide, thiodicarb is effective against eggs as well as larvae, although the latter must feed upon treated foliage in order to be controlled. Heavy infestations of larvae may require higher applications than the standard dose, but not to exceed 60 ounces (1.77 liters) per acre (4047 square meters) per season.

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Thiocarb is formulated to include several liquid products and one powdered product that must be mixed with water before using. Application to agricultural crops may take place on the ground or from the air. Which crops are treated with thiodicarb depends on how this agent is registered with each state. For instance, in Florida, thiodicarb is registered as one of the insecticides that may be applied to sweet corn. In California, thiodicarb may be used on head lettuce, leaf lettuce, spinach, corn, and celery, as well as on cotton.

Thiodicarb is considered moderately toxic. Animal-based studies indicate that the metabolic byproduct of thiodicarb, a potential carcinogen known as acetamide, is eventually formed by the breakdown of methomyl in the stomach. However, this substance is further metabolized and excreted as carbon dioxide through respiration and urination. Since toxicity tests have only been conducted on animals, the long-term impact of carbamate pesticides on human health is still largely unknown.

Carbamates such as thiodicarb are cholinesterase-inhibiting, meaning that they disrupt the action of certain enzymes involved in central nervous system functioning. Symptoms of thiodicarb toxicity include increased salivation, headache, muscle weakness, dizziness, nausea, vomiting, abdominal cramping, and profuse sweating.

In the environment, decomposition of thiodicarb is dependent on sufficient aeration, microbial activity, temperature, and soil density and pH. With a half-life of less than seven days, thiodicarb does is not expected to accumulate in the environment or contaminate groundwater.

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