The effects of temperature, humidity and rainfall on captan decline on apple leaves and fruit in controlled environment conditions.
BACKGROUND
Captan is an important fungicide for controlling diseases in horticultural crops. Predicting its dissipation is important for estimating dietary risks and optimising pesticide application. Experiments were conducted to determine the relationship of captan loss on apple leaves with temperature, humidity and rainfall, and to investigate captan loss on fruit in dry conditions.


RESULTS
There was large unit-to-unit variability in captan residues in spite of the controlled application. Temperature and humidity had negligible effects on captan loss. Captan loss is predominately due to washoff by rain, although a certain proportion of captan may bind to the plant surface tightly and hence may not be readily removed by rain. About 50% of captan can be washed off by as little as 1 mm of rain after an application, and the loss appeared not to relate to the amount of rain. Under dry conditions, daily loss of captan is estimated to be around 1% on both fruit and leaves, giving a half-life of ca 70 days.


CONCLUSIONS
Captan loss on leaf and fruit surfaces is primarily due to rain washoff.
Xu
Xiang-Ming
XM
Plant Pathology, East Malling Research, New Road, East Malling, Kent ME19 6BJ, UK. Xiangming.Xu@emr.ac.uk
Murray
Roy A
RA
Salazar
Jose D
JD
Hyder
Kieran
K
D002215:Captan / Q000032:analysis* / Q000378:metabolism; D005506:Food Contamination / Q000032:analysis; D005638:Fruit / Q000737:chemistry; D005659:Fungicides, Industrial / Q000032:analysis*; D027845:Malus / Q000737:chemistry*; D010573:Pesticide Residues / Q000032:analysis* / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry; D013997:Time Factors; D014887:Weather
D005659:Fungicides, Industrial; D010573:Pesticide Residues; D002215:Captan