Scharf & Salz 2009 (Article) Pests

Ein für Bromeliensammlungen gefährlicher Pilz: Colletotrichum sp. (Fungi, Ascomycota)

Author(s):—U. Scharf & W. Salz

Publication:—Die Bromelie 2009(2-3): 106-115. (2009)

Abstract:—Colletotrichum sp. (Fungi, Ascomvcota), a dangcrous fungus for bromeliads. Colletotrichum sp. seems to be omnipresent in nature. There is no reliable information about the reasons for which bromeliads are attacked. The first infection may happen outdoors when the ascospores of the teleomorph Glomerella cingulata are released in spring and early summer. In addition, in the anamorphic stadium called Colletotrichtun, single celled spores, called conides, are produced by conidiogene cells after mitosis and are distributed by precipitation. Even if air distribution seems to be more reasonable, only transmission by rain or irrigation water is described.
The spores probably stick on or under the scales of grey tillandsias in a special way. Moisture remains longest on the epidermis under the scales: there the spores germinate, penetrate the cuticula and change into a resting form in which they remain for an indefinite period. This may be caused by suboptimal conditions such as low or variable temperature and/or moisture level. Alternatively, the spores may rest on the epidermis under these conditions. After the plants are put into the greenhouse in autumn. the conditions change dramatically: The temperature stays above 15cC, the air humidity is extremely high for many days or even weeks, it takes a very lang time for the plants to dry after watering, and there is low to no ventilation. Now the fungus resumes growth and colonises deeper tissue layers. Obviously, the increased temperature is of greater importance than the availability of water, since plants kept indoors also fall ilI.
A second peak of disease symptoms occurs at the end of winter in February and March, when the plants begin to grow and bloom. Conspicuously, new growth and young inforescences get ill first, which means that the whole shoot is lost. Reasons are surely the weakening of the plants by the winter conditions (low light intensity, lack of ventilation. absence of a diumal temperature course) and an increased sensibility caused by cultivation mistakes (too much water, tightly packed individuals, insufficient supervision). Even when all plants are effectively treated with fungicides in autumn before being put inside. the new emerging shoots and inflorescences are not protected and may be infected by rinsed-off spores and hyphae (conidospores, conidia) during irrigation. The only solution seems to be a calculated shift of the cultivation conditions and care towards healthier plants, and a gapless pesticidal treatment. Under several commercial names, Azoxystrobin, Myclobutanil and Metiram are sold in Germany as active substances. At the moment, no systemic fungicides are available for the average consumer to protect the plants„ from inside against attacks by the fungus. A close eye musl be kept on the use and the quality of irrigation water and the use of fungicides. not only for bromeliads, but also for plants of other familien which are kept together in the collection (Agave!, orchids!). From now on, we have to be closer to our plants, which means that we have to observe them more frequently and more carefully (inspection and supervision). Our determination and activity have to be sped up; i.e. there is an urgent need to act after discovering the first symptoms, in terms of hygiene, cleaning of the plants, removal of dead plants and treatment of infected plants. Whether we like it or not, we have to think seriously about the preventive use of pesticides to protect our plants from pathogens. Observations of our English-speaking readers aec highly welcome. for more information, please ask.