Diseases of the gladiolus III. Botrytis rot of conms and its control

Abstract

The probability that the three types of corm rot of gladioli, associated with Botrytis spp., described by Moore (1939) are phases of the same disease is discussed.Control measures were of five types: (1) Measures to reduce the amount of active or dormant infection of the corms when lifted. Avoidance of heavy wet soil, ground in which gladioli had previously grown and shaded sites reduced the subsequent loss in storage. Relatively early lifting (during the first half of October) was beneficial. Rogueing of diseased plants during the summer and dusting of foliage with pentachloronitrobenzene dust (p.c.n.) gave some improvement, but further experiments are‐desirable. (2) Measures to reduce the development of the disease between lifting and storage. Early removal of adhering soil, cormels, roots, parent corms and old shoot and leaf bases (husks) gave good control. Rapid drying in warm, dry conditions was also beneficial, but washing the corms to remove soil was ineffective. Dusting with p.c.n. immediately after lifting and before cleaning gave a slight reduction in losses in two small‐scale experiments. (3) Pre‐storage fungicidal treatment of corms. Dusting with p.c.n. before storage gave good control, but almost complete control was obtained by steeping in a 01 % solution of mercuric chloride for 20 min. to 3 hr. This treatment has the advantage that it also controls hard rot (Septoria gladioli Passer.), scab (Bacterium marginatum McCull) and to a lesser extent dry rot (Sclerotinia gladioli Drayt.), but is liable to damage the corms. The safety limits are being worked out. (4) Conditions of storage. Corms should be stored in shallow trays in a dry, well‐ventilated shed, protected from frost. (5) Fungicidal treatment at planting time to protect the corm from soil infection. Mercuric chloride as a corm steep at this time gave only partial control, probably owing to rapid removal of the fungicide by leaching. Dusting with p.c.n. gave good results, not only in the protection of the old corm but in preventing infection of the new ones and the beneficial effect extended into the subsequent storage period. Soil treatment was not effective.