Side-effects of pesticides on non-target organisms (part 2)
Dithiocarbamate fungicides (cont from last month)
Many decades ago the fungicides zineb and maneb were found to be effective in controlling different species of mites.
In 1975 it was reported that mancozeb was the most effective fungicide for control of citrus rust mites, followed by zineb and then maneb.
Field trials conducted between 1981 and 1988 showed that mancozeb was slightly better than zineb in the suppression of the citrus rust mite, but neither demonstrated sufficient activity to justify its use alone as an acaricide.
Dithiocarbamate compounds in combination with ethion, chlorpyrifos, dicofol or propargite were found to provide extended control compared to an acaricide applied alone.
Maneb and zineb were effective against pear rust mite
Researchers from the USA found that maneb and zineb were effective against pear rust mite (Epitrimerus pyri), and mancozeb and propineb against apple rust mite (A. schlechtendali).
Fungicides may stimulate mite populations
While dithiocarbamate fungicides are not effective against tetranychid and tenuipalpid species, they may stimulate their populations.
It has been found that two-spotted spider mite, Tetranychus urticae Koch, fed on leaves treated with mancozeb had slightly higher numbers than mites fed on untreated leaves.
Fungicides toxic to predatory mites
When controlling phytophagous mites, it is important to take into consideration the effect of chosen chemicals on predatory mites.
It has been found that dithiocarbamates are toxic to several species of predatory mites.
(cont next month)
See this article in Tree Fruit March 2018