Influence of climatic conditions on white tip disease (Phytophthora porri) in leek (Allium porrum).

Abstract

In leek, one of the major vegetable crops in Belgium, Phytophthora porri causes the so-called white tip disease. During the growing seasons of 1999, 2000 and 2001 the incidence of the white tip disease and the role of environmental conditions in the appearance were investigated on several non-treated leek fields in Flanders (Belgium). The first symptoms of white tip disease on leek where recorded in July and the disease progressed until March. Lesions appeared after an incubation period of 91 to 204 DD (degree days above -3 degrees C) (t0) and were diagnostic at 120 DD. The obtained data confirmed a disease increase corresponding with an amount of rainfall of more than 20 l/m2 in 4 days in the period t = t0-92 to t = t0-154 DD. A good correlation was found between the daily disease increase on one hand and the leaf wetness, relative humidity and temperature (negative correlation) on the other hand. Daily disease increase only weakly correlated with rainfall. Based on these results recommendations can be made (for further studies) to develop a model, combining several of the climatic factors, to predict infection periods with high risk on disease increase in the production of leek.