Pendimethalin

Pendimethalin protects crops like wheat, corn, soybeans, potatoes, cabbage, peas, carrots, and asparagus. It controls annual grasses and certain broadleaf weeds which interfere with growth, yield and quality of crops by competing for nutrients, water and light.

Where weed infestation is particularly bad, yield loss can render wheat production uneconomical. Many other crops are grown in Europe that make a fraction of total agriculture. Herbicide options are limited for these minor crops, particularly in the vegetable sector. Long-term field studies call pendimethalin efficient for controlling blackgrass.

The related herbicide profluralin is more effective against johnsongrass than pendimethalin.

In 2012, 6-12 million pounds (2,700-5,400 t) of pendimethalin was used in the US.

Pendimethalin acts pre-weed-emergence and early post-emergence. Pendimethalin is absorbed into roots and shoots, inhibits cell division and prevents growth, to prevent weeds from emerging.

The HRAC classifies by mode of action; pendimethalin is listed as Group K1, (global), AKA Group D (Australia) or Group 3 (numeric).

At least one study suggests pendimethalin exposure is associated with pancreatic cancer.

A French study found no association with lung cancer.

The mechanism behind this purported increased risk is unknown, but pendimethalin exposure appears to reduce apoptosis in cultured tumor cells.

Herbicide resistance harms efficacy. Until 2009 pendimethalin showed no resistance. It is not cross-resistant with other grass weed herbicides, so pendimethalin can be coäpplied with herbicides of other modes of action. Lolium rigidum has evolved resistance to pendimethalin, at least in part due to increased cytochrome P450 activity. This resistance mechanism in ryegrass (shared with other dinitroanilines like trifluralin, see for longer explanation) is by an opposing mutation to resistance to prosulfocarb, a thiocarbamate herbicide. By evolving resistance to one, the weed devolves its resistance to the other.

Pendimethalin is registered globally for a wide range of crops, by the European Commission, US-EPA, Canada-PMRA, Japan, Brazil-ANVISA and others.

Pendimethalin is not toxic to mammals, though interestingly the oral LD₅₀ for rats and mice is 1050-1620 mg/kg, yet for dogs and rabbits it is much less harmful, at over 5000 mg/kg. For comparison, table salt's LD₅₀ is 3000 mg/kg. There may be chronic effects however; repeated or prolonged skin exposure may cause allergic reactions such as eczema, hives or anaphylaxis. Prolonged exposure by other routes may affect changes to the liver.

Pendimethalin is highly persistent in soil and water. It has high potential for bioaccumulation, and it is moderately mobile in soil, despite it adsorbing strongly into soil.

Tradenames include Pendimethalin 440, Satellite, Halts, Prowl, PRE-M, Stomp, Stealth and Pendulum, Hilpendi etc.