In nurseries, young plants show moist canker lesions on the stem, starting either from the senescent cotyledons or the first colonized leaf, or at the crown. A light brown rot sets in thereafter, leading inexorably to the death of the seedlings. This is often covered with a dense white mycelium and black structures: sclerotia. Some lesions may develop after planting if they were not detected when the plants were picked and sorted.

On older plants, these two fungi also behave as colonizers of wounds and nutrient bases represented by senescent tissues (floral parts, leaflets, etc.). They also attack very easily parts of organs that come into contact with the ground. Thus, wet and cankerous lesions can be observed on the stems , at the neck (figure 1 to 3) or in height. In the latter case, they are often localized near disbudding and leaf stripping wounds on staked tomatoes, especially grown under shelter. These alterations evolve gradually and end up girdling the stem, which takes on a beigeish to whitish hue as it necroses (figures 4 to 6). This one may have been colonized after the installation of the fungus on a leftover flower piece that fell directly on it or on a leaflet nearby.

The mycelium more or less fluffy and white forms on the affected tissues. We observe, on the stem but also in the pith which is entirely decomposed and hollowed out, sclerotia which make it possible to differentiate these two Sclerotinia spp. :
- a few large black sclerotia, rather elongated, measuring 2-20 mm x 3-7 mm for S. sclerotiorum ;
- small black sclerotia, irregular, rather circular, 0.5-2 mm in diameter for S. minor .
Leaflets like fruits (figure 7) are also affected by a wet and soft rot which causes the disintegration of the former and the liquefaction of the latter. Thus, the young green fruits undergo large damp and dark alterations more or less scalloped.

The teleomorph of these fungi is sometimes visible on the soil surface, mainly in the case of S. sclerotiorum . Thus, small "trumpets", apothecia (figure 8), are formed on the larger sclerotia. They produce ascospores , the source of airborne contamination.