Phytotoxicity of mineral oil treatments
Under certain conditions of application, mineral oils – which are used for seed potato production to limit the spread of non-persistent viruses – can cause various types of damage on foliage (burns, brown necroses, shrivelling, hardening of the leaves with metallic reflections, etc.), especially on young leaves at the top of the plants.
These symptoms, which are accompanied by delayed growth, are exacerbated and clearly visible when the temperature is high and following the application of repeated high doses. However, they have no repercussions on the daughter tubers (photo 1).
Some late blight fungicides are incompatible with mineral oils (e.g. fluazinam) (photo 2).
Prevention involves following the general instructions for applying treatments with mineral oils (rates, concentration) and avoiding overdosing, especially in hot weather.
Phytoxicité de traitements de plant ou d’engrais
Losses on emergence, or delayed emergence of stunted plants causing yield loss and tuber burns, are sometimes observed as a result of seed treatment against black scurf (photo 1).
This phytotoxicity is mainly observed with liquid treatments followed by inadequate drying and too rapid cold storage.
Some fertilisers can cause similar damage.
Haulm destruction treatment
Under certain conditions of haulm destruction (dehydrated leaves, extreme heat or application of chemicals late in the day on wilted plants), rot at the heel-end and browning of the vascular ring may be observed (photos 1 to 3).
More rarely, burns caused by direct application of chemical haulm desiccants on the surface of tubers may be observed (photo 4).
Treatment against storage rot diseases
For seed potato production, some fungicides used at harvest time for treatment against storage diseases may cause damage to tubers: burns, depressions on the surface of the tubers and possibly rot.
This lack of selectivity is due to poor drying after treatment or due to the application of chemicals on immature or sprouting tubers (photo 1).
Treatment with sprouting inhibitors
Sprouting inhibitors can induce two types of symptoms:
- prominent brown areas on the surface of the tuber following the application of CIPC to wet and/or newly harvested tubers (photos 1 and 2);
- losses and anomalies on emergence when replanting tubers that have been in contact with equipment or buildings with treatment residues, especially with CIPC due to the long persistence of the product or with overdosing of sprout inhibitors (photo 3).