Naptalam is a selective preёmergent herbicide, first registered in the US in 1949, to control sundry annual broadleaf weeds and grasses. Naptalam is a phthalic acid, though it is commonly also in sodium salt form. It is also used in Australia and Canada. In 1974, the USA used in agriculture.
Naptalam is unstable at temperatures over 180 °C or pH over 9.5.
Naptalam's mode of action makes it a Group P or Group 19 herbicide under the HRAC classification.
Application.
Naptalam has been used on soybean, peanut, cucumber and melon crops, and ornamentals. Typical application rates are 2 to 6 lbs per acre (active ingredient), (2.25-6.75 kg/Ha). Formulations are usually water based liquids, or granular. While primarily preёmergent, naptalam may also be sprayed postemergently in some cases.
It has been sold under the tradename "Alanap-L" and "Rescue" in the US, and has been manufactured by Uniroyal, Chemtura and Vertac. "Alanap-3" is a 240 g/L formulation sold in Canada.
Environmental behaviour.
In soil, naptalam is absorbed through the roots and translocated to the leaves. Soil mobility is high in fine sand, sandy loam, and silt loam; soil retention is increased with CEC and organic matter content.
Naptalam's toxicity is low for birds, fish, and aquatic invertebrates, presenting minimal hazard.
Safety.
Naptalam is not carcinogenic, even at 5000 mg/kg, the highest dose tested on mice. It has some teratogenicity, so the EPA recommends a NOEL of 15 mg/kg/day. However, it causes irreversible eye damage, and is corrosive.