The degradation rates and residue levels of malathion as an insecticide
and its metabolite malaoxon were studied on field grown four varieties of mango trees
(Alfouns, Zebdia, Fajeri Klan, and Langra). The samples were collected after one hour, 1, 3,
5, and 7 days post insecticide application. The data showed that the recovery rates of
QUCHER method were satisfied for both malathion and malaoxon. The obtained rates of
recovery were 97 and 99% for malathion and malaoxon, respectively. The obtained residues
of both compounds under investigation (malathion and malaoxon) decreased gradually with
time, whereas, and there were no residues found 5 days later for malathion. Also, malaoxon
showed the same pattern of degradation thus it disappeared after 3 days from treatment. The
half-life time values of malathion (LT50) ranged from 0.96 to 2.8 days in these four mango
varieties while they were ranged between 0.43 to 0.9 days for malaoxon. The pre-harvest
interval (PHI) for each compound was determined according to their maximum residue limits
which were 3 and 2 days for malathion and malaoxon, respectively on all four varieties of
mango fruits.