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Main symptoms

Many cucurbits are affected by anthracnose. Colletotrichum orbiculare can attack both nursery seedlings and adult plants, causing symptoms on the aerial organs of plants: leaves, stems, and especially fruits. Note that these symptoms are rather identical between species of cucurbits. It is for this reason that we will not detail them for each of them, but that a fairly generic description is offered. Finally, let us add that they appear rather, initially, on a few plants located in foci.

In France, it is mainly the fruits of squash that are affected. Small greasy, canker and / or corky spots are first observed on the latter. Subsequently, they become round to oval, depressed, healing poorly at the periphery and taking a brown to black tint (Figures 1 to 4). Note that these lesions are often covered by black punctures (stromas) and salmon-pink gelatinous masses (acervuli producing many spores) at the origin of the name red nuile. These fruiting bodies are sometimes arranged in concentric circles (Figures 5 and 6) and a white mycelial felting is visible on the lesions. Note that the symptoms on the latter can appear both during cultivation and during their conservation and marketing.

On leaves , C. orbiculare first causes small oily spots, quickly turning brown to reddish brown, then necrotic. These sometimes extend onto the ribs or are initiated from them. Circular to somewhat angular in shape, their size can exceed 1 cm and they may be surrounded by a translucent to yellowish halo. Tissues in the center of the lesions eventually dry out and may detach from the limbus.
Note that leaf attacks occur more particularly in open field crops. They can be the cause of defoliations, sometimes rapid and important, and thus increase the damage on fruits linked to the effects of the sun.
Depending on the species affected, diagnostic confusion on leaves is possible with several other aerial diseases of cucurbits: cladosporiosis especially, but also alternaria and septoria.

On the stems and petioles , this fungus forms oily lesions more or less elongated and slightly depressed from which sometimes a brown exudate bead. If the climatic conditions are favorable, these lesions extend, merge and are also covered with small pink to orange masses. Note that they can develop anywhere on the stem and petioles, and weaken them. This is particularly the case when they have given rise to bursts.

Last change : 04/16/21
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