Pendimethalin is a selective herbicide of the dinitroaniline class[2] used premergently and postemergently to control annual grasses and certain broadleaf weeds. It inhibits cell division and cell elongation. Pendimethalin is approved in Europe, North America, South America, Africa, Asia and Oceania for different crops including cereals (wheat, barley, rye, triticale), corn, soybeans, rice, potato, legumes, fruits, vegetables, and nuts, plus lawns and ornamental plants.
Use
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.[3] 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.[4] Long-term field studies call pendimethalin efficient for controlling blackgrass.[5][6][7]
In 2012, 6–12 million pounds (2,700–5,400 t) of pendimethalin was used in the US.[9]
Mode of action
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.[10]
The HRAC classifies by mode of action; pendimethalin is listed as Group K1, (global), AKA Group D (Australia) or Group 3 (numeric).[10]
Possible carcinogenic effects
At least one study suggests pendimethalin exposure is associated with pancreatic cancer.[11]
A French study found no association with lung cancer.[12]
The mechanism behind this purported increased risk is unknown, but pendimethalin exposure appears to reduce apoptosis in cultured tumor cells.[13]
Resistance
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.[14]Lolium rigidum has evolved resistance to pendimethalin, at least in part due to increased cytochrome P450 activity.[2] 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.[15]
Registrative status
Pendimethalin is registered globally for a wide range of crops, by the European Commission, US-EPA, Canada-PMRA, Japan, Brazil-ANVISA and others.
Toxicology
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.[16]
Soil behavior
Pendimethalin is highly persistent in soil and water. It has high potential for bioaccumulation, and it is moderately mobile in soil,[17] despite it adsorbing strongly into soil.[18]
Tradenames
Tradenames include Pendimethalin 440, Satellite, Halts, Prowl, PRE-M, Stomp, Stealth and Pendulum, Hilpendi etc.
^Clarke, Wynn, Twinning, Berry, Cook, Ellis and Gladders Pesticide availability for cereals and oilseeds following revision of Directive 91/414/EEC; effects of losses and new research priorities. In: HGCA Research Review. Nr. 70, 2009.
^Little J.: EU´s pesticide regulation must be challenged. In: FarmBusiness. 2009 S. 26–27.
^Gehring, K. and S. Thyssen: Unkrautmanagement im Getreidebau – Herbizid-Leistungszahl – eine mehrfaktorielle Bewertung von Herbizidbehandlungen. LFL Pflanzenschutz. Institut für Pflanzenschutz der Bayerischen Landesanstalt für Landwirtschaft. In: Freising-Weihestephan, Deutschland. 2004.
^Gehring, K. and S. Thyssen: Unkrautmanagement im Getreidebau – Herbizid-Leistungszahl – eine mehrfaktorielle Bewertung von Herbizidbehandlungen. LFL Pflanzenschutz. Institut für Pflanzenschutz der Bayerischen Landesanstalt für Landwirtschaft. In: Freising-Weihestephan, Deutschland. 2007.
^Gehring, K.: Ackerfuchschwanz und Windhalm – die zwei bedeutendsten Ungräser im Getreidebau. In: Getreide Magazin. Nr. 1, 2009, S. 20-25.
^Jordan, T. N.; Baker, R. S.; Barrentine, W. L. (1978). "Comparative Toxicity of Several Dinitroaniline Herbicides". Weed Science. 26 (1): 72–75. doi:10.1017/S0043174500032707.
^Boulanger, Mathilde; Tual, Séverine; Lemarchand, Clémentine; Baldi, Isabelle; Clin, Bénédicte; Lebailly, Pierre (August 2017). "0441 Exposure to dinitroanilines and risk of lung cancer (Lc) by subtypes: Results from the agrican cohort". Occupational & Environmental Medicine. 74 (Suppl 1): A140.1. doi:10.1136/oemed-2017-104636.365.
^Moss, S. R. and R. Hull: The value of pre-emergence herbicides for combating herbicide-resistant Alopecurus myosuroides (blackgrass). In: Aspects of Applied Biology. Nr. 91, 2009.
