Cross enhancement

There is evidence from a relatively few field studies to indicate that repeated treatments of 2,4-D and MCPA result in enhanced herbicide degradation rates as a result of adaptation by soil microorganisms. There is also some evidence that cross-enhancement can occur under field conditions, whereby previous applications of either 2,4-D or MCPA, result in enhanced breakdown of both herbicides. 

The phenomenon of cross-enhancement, or the ability of soils pretreated with specific herbicides to degrade other structurally related herbicides more rapidly than in untreated control soils, has been known for nearly 40 years. Both enhanced degradation and cross-adaptation have been observed under field conditions for phenoxyalkanoic acid herbicides (3-5). ... 

EPTC and butylate sulfoxides are initial metabolites of EPTC and butylate degradation. EPTC and butylate sulfoxides induced enhanced degradation of their respective parent compounds (Figure 8) (19). Pretreatment of the soil with either EPTC sulfoxide or butylate sulfoxide caused cross-enhanced degradation of butylate or EPTC. 

Studies with Other Dicarboximides and the Possibility of Cross Enhancement... 

Examples of the data from the cross-enhancement experiment are shown in Table IV. These are the residues measured 14 and 28... 

Vinclozolin degradation was affected only slightly by pretreatment of the soil with iprodione, which agrees with previous observations (12), and also affected to some extent by prior treatment with myclozolin. There are, therefore, no simple relationships where cross-enhancement is concerned, and it is probable that the only way to gain a better understanding of such phenomena will be to isolate the specific organisms and enzyme systems responsible for degradation. 

Table IV. Cross Enhancement between Different Dicarboximide...

Table XIV. Cross Enhancement Factors for Carbamate Pesticides...

Cross enhancement was observed between carbofuran and all the aryl methylcarbamates examined except furathiocarb. The behaviour of the oximino methylcarbamates (aldicarb, methomyl, oxamyl) was more variable. Both aldicarb and cloethocarb enhanced soils showed cross enhancement to carbofuran and oxamyl. The chlorpropham enhanced soil was not cross enhanced to carbofuran. The carbamate enhanced soils were not cross enhanced to butylate, EPTC or phorate. 

No cross enhancement was observed between carbofuran enhanced soil and tefluthrin or any of the 11 organophosphorus insecticides listed in Table XV. Diazinon and DOWCO 429X showed mutual cross... 

The results of a study of carbofuran treatment intensity on the cross enhancement factors for carbaryl, cloethocarb and oxamyl are... 

Table XVI. Effect of Treatment Intensity on Cross Enhancement to Carbofuran...

The data on diphenamid showed cross enhancement only between diphenamid and its monodemethylated degradation product (diphen M-l). The degradation of the bidemethylated derivative (diphen M-2) was not enhanced when diphen M-2 was applied to the... 

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