Mefenpyr-diethyl

The compound is applied on soft and durum wheat, triticale and rye, together with the safener mefenpyr-diethyl (Fig. 2.2.2) as the straight products Atlantis OF , Silverado and Osprey or in combination with iodosulfuron-methyl-sodium ( Atlantis WG , Cossack , Padfica ), diflufenican and propoxycarbazone-sodium (Table 2.2.12). 

Mesosulfuron-based products Formu- lation type Mesosulfuron- methyl lodosulfuron- methyl sodium Diflu- fenican Propoxy- carbazone Mefenpyr- diethyl... 

The safener mefenpyr-diethyl, as with iodosulfuron-methyl-sodium, selectively accelerates the degradation of the active ingredient to non-phytotoxic compounds in cereals but not in weeds. 

W. Roesch, H. Koecher, R. Wolf, Mefenpyr-diethyl - A safener for fenoxaprop-P-ethyl and iodosulfuron in cereals, Z. PflKrankh. PfiSchutz, Sonderh. XVII, 493-500 (2000). 

Fig. 5.1. Post-emergence safening of wheat by mefenpyr-diethyl against mesosulfuron-methyl. (A) Untreated (B) mesosulfuron-methyl at 60 g-a.i. ha h and (C) mesosulfuron at 60 g-a.i. ha" plus mefenpyr-diethyl at 30 g-a.i. ha" .

As already pointed out, mefenpyr-diethyl is a versatile safener and it has been commercialized in combinations with several single or mixed herbicides, including fenoxaprop-P-ethyl (e.g.. Puma S ), iodosulfuron-methyl-sodium (e.g.. Hussar ) and mesosulfuron-methyl (Atlantis ). In general, the quantity of mefenpyr-diethyl required to provide adequate safening lies between 20 and 100 g-a.i. ha , and there is no set ratio between the rates of the herbicides and... 

Mefenpyr-diethyl has a highly favorable toxicological and ecotoxicological profile (Table 5.7). 

In the environment, mefenpyr-diethyl dissipates rapidly with a soil DT50 of <10 days. Complete mineralization occurs due to photolysis, hydrolysis and microbial degradation. There is no leaching risk, with the parent compound and soil metabolites not exceeding 0.1 ppb at 1 m soil depth in lysimeter trials. 

Mefenpyr-diethyl is most probably a pro-safener, a term introduced by Rubin in 1985 [15]. With mefenpyr-diethyl a decarboxylation occurs rapidly in plants and soil and it is likely that the safening activity comes from mefenpyr-ethyl. How-... 

When applied alone, safeners generally have Utde visible effects on crop or weed species. This was found, for example, for the safeners fenchlorazole-ethyl and mefenpyr-diethyl [20, 21]. In contrast, fenchlorazole-ethyl exerted an immediate protective effect on wheat and prevented even a transient inhibition of leaf growth by fenoxaprop-ethyl [22). The same was observed subsequently for combinations of mefenpyr-diethyl with fenoxaprop-P-ethyl. 

Uptake studies were also carried out with the recently developed combinations of the safener mefenpyr-diethyl with the sulfonylurea herbicides mesosulfuron-methyl and iodosulfuron-methyl-sodium, which are used for selective postemergence weed control in wheat crop. In both combinations the safener had no influence on herbicide uptake [29]. 

As already mentioned, it is a major advantage of mefenpyr-diethyl to act as a safener also in combination with sulfonylurea herbicides in cereal species. Combinations have been developed with the sulfonylureas iodosulfuron-methyl-sodium and mesosulfuron-methyl. 

Fig. 5.2. Examples of herbicide detoxification reactions stimulated by the safener mefenpyr-diethyl. (A) Conjugation reaction of fenoxaprop with glutathione (GSH). (B) Oxidative demethylation of mesosulfuron-methyl.

---