The rainfastness of the residual fungicides maneb and mancozeb was assessed on pot-grown pea (Pisum sativum L) and potato (Solanum tuberosum) plants using a rain simulator. Suspension concentrate formulations were generally retained better than wettable powder formulations. The rainfastness of the fungicides was found to he inversely related to particle size and this partly explained the diferences observed between the formulations. Three mm rain applied at a high intensity ( 2 7 m m h-'1 washed-ofmore fungicide than 3 mm applied at a low intensity (3 mm h-' 1.Addition of various adjuvants sign$cantly improved the rainfastness of the fungicides on both plant species. Oil adjuvants, however, only increased the rainfastness on pea. Furthermore, addition of a latex-based adjuvant was found to reduce the redistribution of mancozeb on potato leaves.

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Deposition variability from a conventional field sprayer, and effects of wind and travel speed were measured by collecting on small artificial targets in the swath. Whilst deposition on 0.1-m2 plots varied by a factor of 3, deposition on single vertical targets typically varied by a factor of 10 and on horizontal targets by a factor of 6. Distinct transversal deposition patterns appeared according to wind direction. The quantity and structure of variability was compared with wind speed and turbulence intensity, but few significant trends were found. Deposition on vertical targets was enhanced by increasing wind speed or increasing travel speed, whilst effects on horizontal targets were inconsistent.

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