Dithiocarbamate fungicides - Fungicides toxic to predatory mites
Fungicides toxic to predatory mites (cont from last month)
When controlling phytophagous mites, it is important to consider how the chosen chemicals will affect predatory mites.
It has been found that dithiocarbamates are toxic to several species of predatory mites.
For example, there are many reports on toxic efficacy of zineb to Anystis baccarum. In laboratory tests, maneb, mancozeb, propineb and zineb were highly toxic to Amblyseius deleoni; zineb was moderately toxic to Amblyseius gossipi.
Fungicides as foliar fertilisers
Besides the toxic efficacy on mites and other organisms, some fungicides can also act as a foliar fertiliser—their nutritional input can be positive or negative.
They can promote tree vigour (which can favour development of some pests such as mites, aphids, cicadae etc.) or they may cause retardation, depending on their chemical composition.
For example, the ziram molecule contains zinc. One kilogram of ziram has 130 grams of zinc. Therefore, application of ziram can promote vigour, especially when applied with pesticides that also promote vigour such as pyrethroids and strobilurines.
On the other hand, molecules of maneb and mancozeb have manganese in their structure (mancozeb has both, zinc and manganese).
Manganese-dithiocarbamates applied in high rates can cause retardation, russeting and other problems on apples, especially if applied with other fungicides with a similar effect (sterol inhibitors).
In some cases the effect of retardation of the above ground parts of the plant can have a positive effect (e.g. wheat overwintering, root development etc.).
In some countries including Australia, we can find fungicides such as mancozeb that are registered for both applications—as a fungicide and a miticide.
Growers should check their spray programs with their agronomists and consider the possibility of applying some products, or at least conduct a small trial.
See this article in Tree Fruit April 2018
