from both ExpF-based treatments were almost identical.
Not all xylem-mobile molecules behave in the same way and this is illustrated by a comparison between ExpF and ¯uquinconazole when both were mixed with Adj1. Fluquinconazole was recovered only in very small quantities, the single greatest recovery being 0.17% over a 24 h period. These recoveries are considerably less than those already described for ExpF when mixed with the same adjuvant. That recovery in guttation ¯uid is not solely related to the level of uptake into the plant is supported by data from other experiments (Harris RI unpublished) where the uptakes of both ¯uquinconazole and ExpF were very similar when mixed with Adj1 (60 and 69%, respectively, 24 h after application).
Using ExpF as a model compound it should be possible to investigate the behaviour of other formulation systems on target crops. A speci®c example of the use of this system is the evaluation of encapsulated formulations. It is possible to prepare capsules with a range of properties, one of these being ease of capsule breakdown, resulting in the release of the encapsulated compound. This can be monitored using arti®cial surfaces, but there is now the possibility of doing studies in vivo using the model described above.
Information about the loss of fungicide, insecticide and herbicide molecules in guttation ¯uid can also help explain biological performance against target species. For example, the activity of ExpF against Erysiphe graminis DC f sp tritici Marchal, (the causal organism of powdery mildew of wheat) was enhanced when mixed with Adj2 but not Adj1 (Moss, N A pers. comm.). From the results discussed above it is possible that a biologically signi®cant proportion of the applied dose of ExpF, when mixed with Adj1, was lost through guttation, resulting in an inferior performance compared with the mixture with Adj2. Life-cycle studies showed ExpF to be more effective as a protectant than curative fungicide and that the early stages of pathogen development were most affected. A formulation optimising surface retention rather than foliar uptake would, therefore, be more appropriate.
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