CONTROL OF THE BEGONIA LEAF-BLIGHT NEMATODE 



E. F. Guba, Research Professor of Botany, 

 and C. J. Gilgut, Research Assistant in Botany' 



\\ inter-flowering begonias as represented by such \arieties as Melior, Lady 

 Mac, and Marjorie Gibbs are an important floricultural crop in many greenhouses 

 in Massachusetts. The production of these begonias varies from about 500 

 finished pot plants among the smallest growers to 4,000 among the largest growers 

 and the demand is confined almost entirely to the Christmas holiday season. 

 Some growers also specialize in the production of propagating stock. These 

 begonias are propagated from leaf cuttings in December and January, potted 

 in 23^^-inch pots and then shifted to larger pots with successive periods of growth. 

 The last shift to 5- or 5H-inch pots is usually made in July. 



Melior t\pes of begonias are ver\' susceptible to a well-known leaf-blight 

 disease caused by the nematode Aphelenchoides fragariae (Ritzema-Bos 1891) 

 Christie 1932. Clinton (4) in 1916 published an excellent illustrated account of 

 this disease on the varieties Cincinnati and Gloire de Chatelaine and designated 

 the nematode as Aphelenchiis olesistus Ritzema-Bos. The presence of discolored, 

 diseased leaves in the composition of the plant or their repeated removal to 

 improve the appearance of the plant and also as a sanitary measure causes inferior 

 quality, lower sale value and, in bad cases of infestation, a total loss. (Figs. 1, 2.) 



HISTORICAL 



RECOMMENDED CONTROL MEASURES 



A review of the literature on the control of the leaf-blight nematode reveals 

 recommendations that may be grouped into three distinct categories; namely, 

 treatment of begonias with chemicals, cultural practices, and hot-water sub- 

 mersion of infested plants. 



The spraying or dusting of begonias with chemical materials is the least worthy 

 of commercial practice because of the danger of injury and, according to several 

 reports, the lack of control. The submersion of valuable plants for one hour each 

 day for a week in water at 64.4° to 68° F. and subsequent spraying, while they 

 are still moist, with a 0.5 to 1 percent solution of amonia has been sugrested, 

 but this treatment is not practical. The water-bath treatment causes the nemas 

 to wander from the leaves. The water treatment and subsequent rinsing in 

 fresh water has been recommended for leaf cuttings before they are placed in 

 the sand bench for rooting, but because these baths do not kill the nematode, 

 the practice would appear to be very unsanitary and an ideal method of dis- 

 semination. 



Many cultural practices have been suggested; notably, wider spacing to avoid 

 contact with leaves of adjoining plants, careful bottom watering, removal of 

 diseased leaves, and the isolation of infested plants. Propagating from healthy 

 stock is very important. The selection of leaves from healthy plants in stock 

 showing disease is inadequate and ineffective. Aside from the practice of prop- 

 agating from clean stock, none of the measures mentioned may be considered 

 reliably effective or encouragingly successful in commercial practice because they 

 fail to eradicate the causal organism. 



'The writers are gratefully indebted to Dr. J. R. Christie. Nematologist, United States Depart- 

 ment of Agriculture, for supplying published articles and literature references and for information 

 pertinent to these studies. 



