Propanil: Characteristics and Uses of a Herbicide
1. As a Post-Emergent Herbicide in Rice
Propanil is used primarily as a post-emergent herbicide in rice fields.
Its main purpose is to control 'grassy weeds' that are not affected by broadleaf-effective herbicides.
2. Chemical Composition and Role
Propanil is an anilide formed by the condensation of the carboxy group of propanoic acid with the amino group of 3,4-dichloroaniline.
It is a herbicide used for treating various grasses and broad-leaved weeds in rice, potatoes, and wheat.
It functions as a herbicide and is an anilide and a dichlorobenzene that is functionally related to 3,4-dichloroaniline.
The following are the application areas of the products:
3. Degradation and Mobility
Propanil is rapidly metabolized under both anaerobic and aerobic conditions in a water and soil matrix.
The half-life of propanil in soil is 1 to 3 days.
It is relatively stable to photo- and chemical degradation but more susceptible to biodegradation.
Propanil is mobile and has the potential for transport via water.
It is not persistent and is readily transformed into degradates such as 3,4-dichloroaniline and 3,3′,4,4′-tetrachloroazobenzene, which are generally more toxic and more persistent.
Propanil is rarely detected in groundwater.
4. Toxicity
In plants, it is toxic due to the inhibition of photosynthesis at the level of photosystem II.
In animals, it induces methemoglobinemia, resulting in tissue hypoxia.
Propanil is toxic to aquatic vertebrates (e.g., crayfish, worms, snails) and fish.
It is moderately toxic to birds.
The use for rice protection may lead to acute adverse ecological effects on birds, small mammals, freshwater invertebrates, and aquatic plants.
Small mammals and freshwater fish/invertebrates may be sensitive to chronic effects from long-term use.
The following are the application areas of the products:
5. Widespread Use and Selectivity
Propanil is a widely used contact herbicide.
In the United States in 2001, it had an estimated use of about 8 million pounds and is said to be used in approximately 400,000 acres of rice production each year.
Rice is relatively immune to propanil because of a high level of the enzyme aryl acylamidase (AAA), which rapidly metabolizes propanil to relatively nontoxic 3,4-dichloroaniline.
Susceptible weeds lack the gene(s) coding for the AAA enzyme and are vulnerable to propanil. However, intensive use has caused some weeds to become resistant to propanil.
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