Le plant français de pomme de terre FNPPPT Semae

Chemical damage

Badly applied treatments can have more or less serious consequences on potato crops, sometimes leading to repercussions on the crop progeny. This damage should be taken it into consideration for crop inspection and assessment.

Herbicides damage

Damage caused by herbicides is generally seen on the foliage.

When damage is due to herbicides used on the potato crop, the symptoms are often characterised by yellowing of the tips of the first leaves just after emergence, then on the crop by staining of leaves at the stem-base (white veins).

Sensitivity to herbicides (SENCORAL in particular) is relatively high depending on the variety (photo 1). Herbicide damage is enhanced by applying herbicide just after the plants emerge and during cold and damp weather conditions.

Hormones can cause damage when applied to the crop itself, or may come from the treatment of a neighbouring crop. Sometimes, the symptoms are only seen on the crop the following year. The plants remain stunted/weak, and the foliage is deformed (photo 2). The leaves develop only slightly or not at all, with fairly typical symptoms such as bent stems. The symptoms may either appear on emergence or some weeks later (photo 3), in the case of herbicide residues in the soil (photo 4).

Even at low doses (treatment residues in poorly cleaned sprays), some herbicides (glyphosate, etc) may cause deformation of the plants at harvest (photo 5).

Mineral oils damage

Mineral oils cause various types of damage on the foliage (heat necroses, brown necroses, puckering, hardening of the foliage which takes on a metallic hue, etc.), particularly on the young top leaves. These symptoms are accompanied by delayed growth, being accentuated and clearly visible during very hot or cold spells, as well as at strong and repeated doses. However, they have no effect on progeny.

Certain anti-late blight fungicides are incompatible with mineral oils.

Heat necroses from tuber treatment (Chemical damages on tubers)

Any chemical treatment is liable to lead to problems but, in practice, the main difficulties are encountered in the following cases:

• Treatment with Fungaflor TZ:

Depressions on the surface of the tubers, possible rot, reduced yield, delayed emergence.

This lack of selectivity is due to poor drying after treatment, or treatment carried out on sprouted or immature tubers.

• Desiccating treatment:

Stem-end rot and browning of the vascular ring is favoured by sudden haulm desiccation on dehydrated foliage, during very hot weather or at the end of the day.

• Anti-sprouting treatment with CIPC:

Presence of protuberant brown areas on the surface.

These symptoms can be observed when CIPC is applied on damp tubers and/or newly harvested tubers (less than two weeks)

• Seed potato treatment:

Emergence delayed or absent, reduced yield, puny plants are sometimes weak after seed potatoes have been treated against black scurf in the spring.

This phytotoxicity is particularly well seen after treatment with liquids or following poor drying, and sometimes when placed too quickly in refrigerator.

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