Main symptoms

The main symptoms caused by Ilyonectria liriodendri fall into 2 categories:

Aerial symptoms

Young vines affected by black root often bud break in a delayed fashion; bud break may not even take place. Otherwise, the young twigs have poor development and the plants appear rather stunted. Their foliage is more or less chlorotic (Figure 1), and it can suddenly wilt and dry out during the summer, especially on a generally hot and windy day.
In fact, these aerial symptoms are linked to a dysfunction of the underground part of the plants and young vines.

Underground symptoms

Two very specific symptoms can be observed on the underground organs of the vine:

• a very dark brown to black coloration of the base of the root taproot at the height of the first root plate (figure 2) (symptom behind the name of the disease) and the frequent presence of a second root plate close to the surface from the ground (figure 3). Note that this second root system allows young plants to survive for a short period;
• limited development and extension of the roots of the first plateau, often parallel to the soil surface indicating difficulty in exploring the soil in depth. Note that the roots are often more or less necrotic and present a grayish to black color (Figure 4). The bark crumbles easily and an area of ​​brown necrosis extends more or less from the heel to the point where the graft is welded.
• Cross sections made in the necrotic part of the rootstock show one or more brownish necrotic lesions in the wood evolving from the bark to the pith (Figures 5 to 8). Longitudinal sections allow us to observe that they have a variable length and that they follow the vessels of the wood. Tylosis phenomena can accompany these symptoms.

Note that the distribution of diseased stocks in a plot can be random, in foci (by zones) or in line.