COLLETOTRICHUM (Gloeosporium) Seedlings - Older seedlings can be infected at the growing point (picture). This infection can easily be overlooked. This can be mistaken with plants without growing tips.
COLLETOTRICHUM Pricked out plants - The first perceptible symptom is mostly a young misshapen leaf. A part of a leaf blade is missing and at that point the leaf margin is dried out and black. Closer inspection also shows infection in the growing points. Sometimes, beside the growing point, the surrounding part of the tuber is infected. Because of this, a dry, brown/black sunken spot appears.
COLLETOTRICHUM Recovery after chemical treatment - Colletotrichum can be controlled easily. Recovery growth occurs immediately (picture). However the infection of the growing point can be so severe that the plant cannot be sold commercially.
FUSARIUM Seedlings and pricked out plants - The cotyledon of the seedlings turns yellow early. Do not mistake this symptom with the normal dying of the germination leaf.
FUSARIUM When cutting open the tubers a brown/red ring or, as in the picture, a brown vascular bundle is perceptible. The tuber may be constricted. The plants grow normally until the infection becomes visible. The roots of infected plants often remain remarkably white.
FUSARIUM Potted up plants - One or more leaves turn yellow at the point of attachment of the leaf blade and wither. The yellow colouring is more intensive than if the plant dries out. The leaf stem wilts. Sometimes it turns black if infected by other fungi. Normally growth is not affected before the infection becomes visible. If you suspect an infection, always cut open the tuber.
FUSARIUM Potted up plants - Just after the first symptoms become visible, many leaves wither. Sometimes the youngest leaves are retarded.
FUSARIUM Potted up plants- infection of the tuber - The vascular bundles in the tuber become infected. They often turn partially orange/brown. An older infection is coloured a darker brown. Fungi and bacteria can easily develop on the infected spots (see picture, uppermost part). This is easily confused with other infections. The infection can penetrate the tuber from the bottom or from the top.
FUSARIUM Mature plant - One part of the plant withers. The leaves normally turn yellow. An infected plant normally shows no growth inhibition. To properly diagnose this problem the tuber has to be cut open. It is however important not to confuse the yellowing of leaves caused by Fusarium, with the normal die back of leaves as plants go dormant in the summer.
COLLETOTRICHUM Infected flower bud - A half grown flower bud is infected. The calyx is dried out. The transition from dead to living material is sharp. Also on the stem an infection is perceptible in which a yellow/orange spore mass is visible. Normally the infected spot is oval. When this infection arises and the stem is not fully grown, it will become curved and show cracking. The symptoms on the flower stem can also occur on the leaf stems.
COLLETOTRICHUM Infected flower - A part of the flower crown turns brown or black, depending on the flower colour. At first one petal of a flower is infected. The transition from dead to living material is sharp. In some cases, the calyx is totally or partially infected. The change from infected to non-infected tissue goes through the crack in the flower stem. In the picture the transition is visible as a "V". With a dark coloured flower stem, it is difficult to see the infection.
WITHERING OF THE FLOWER Under very dry circumstances in summer, flower withering can occur. A part of the flower stem dries out, which leads to cracking of the flower stem. The stem dries out irregularly, the transition from dead to living material is not sharp. Pay attention to the crack in the flower stem just under the calyx: this is not dried out. Dried out flowers can show a similar symptom. The flower crown dries out from the outside but does not turn black/brown.
CYLINDROCARPON Seedlings - with seedlings, round sunken, corky spots appear on the tuber. Often on the infected spots other fungi grow. When the infection arises close to the growing point, it can rot totally. The infection could easily be confused with Fusarium and Colletotrichum.
CYLINDROCARPON Infection of the roots - Infected roots turn strikingly black. This can especially be seen on the main roots. Because the growing point is infected first, the root growth stops. The plant reacts by forming new roots (white in picture). This gives the bushy appearance of an infected root.
CYLINDROCARPON Infection of the tuber - Cracking of the tuber characterises the infection. First the cracks are brown colored, later they turn black. Often the upper skin of th whole tuber is rougher than a healthy tuber. Fungi and bacteria can easily develop in the cracks. An old Cylindrocarpon infection therefore, can easily be mistaken for another disease. The right side of the picture shows slime of a secondary bacterium infection. Control with sanitary conditions.
COLLETOTRICHUM Potted up plant - The first symptoms become visible on the developing leaves and buds. At first nothing is to be seen on the leaves. Between the leaf stems one can see the flower stems of which the bottom most parts appear healthy. The upper most part is dried out and black/brown coloured. The transition from dead to living material on the stem is strikingly sharp. Especially with plants with many growing points, only a part of the growing points or developing buds and leaves become infected.
COLLETOTRICHUM Older infection in pricked out plants - The main bud is almost totally infected. Note the coalescence of the stems due to stem infection. The heart, which is often open, is the first to show symptoms. By that time the disease has progressed so far that the infected plant should be destroyed.
COLLETOTRICHUM Infected leaf - This picture shows a leaf infected just before the elongation of the leaf has taken place. The leaf is almost dried out. The margin marking the transition form dead to living material crosses the stem and is strikingly sharp.

We are grateful to De Ruiter USA for providing the data on this page.