THE BOOK OF THE PEONY 



when the roots are frequently divided and reset. 

 The affected roots are short, stubby, and irregu- 

 larly knotted or swollen. The crown on which 

 the bud sets is often much swollen. The fine 

 rootlets are often covered with galls. The lower 

 ends of the galled roots seem to rot away. 



Cause. — The nematode worm, Heterodera 

 radicicola, is probably responsible for some galls 

 on peony roots. Bessey * reports it as very injui'i- 

 ous to the roots of the peony. This microscopic 

 worm affects the roots of no less than 480 differ- 

 ent species of plants. It is most common and 

 destructive in the South, but is frequent on green- 

 house plants in northern United States and on 

 the roots of certain perennials, like ginseng and 

 peony, easily survives the Winter outside. 



Control. — Until a fuller investigation of the 

 disease has been made, suggestions as to control 

 cannot be very definite. In general it will prob- 

 ably be most profitable to dig up and destroy all 

 diseased plants. The experience of some growers 

 indicates that with rare or expensive varieties it 

 may be profitable to help the plant " outgrow " 



^ Bessey, E. A. Root Knot and its Control. U. S. 

 Agr. Dept. Bur. PI. Ind. Bui. 217: 18, 43. 



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