APPENDIX B 



new crop of spores, in just the best position to 

 infect the new shoots when they come up. I have 

 not yet determined whether these pathogens ever 

 attack crowns and roots or not. 



Control. — The control of this disease is very 

 difficult for several reasons. It is destructive only 

 in wet seasons. One of the pathogens, the small 

 sclerotial form, is very common and widely dis- 

 tributed. The other, the large sclerotial form, 

 having a number of different hosts, may readily 

 pass from one of them to the peony if it be near 

 by. Spores are produced in great quantities and 

 carried both by wind and insects. Ants seem to 

 carry the spores from the base of diseased stalks 

 to the buds of healthy plants. Here in the exuded 

 sugary solution, so abundant upon unopened 

 peony buds, the spores find both food and moist- 

 ure and germinate much more promptly and 

 vigorously than in water. The peony is very sus- 

 ceptible, there being apparently little difference 

 in susceptibility of the different varieties. Spray- 

 ing is in the first place undesirable, as it discolors 

 foliage and buds, and in the second place our ex- 

 periments indicate that the sugary exudate of the 

 buds effectively neutralizes the copper in Bor- 



251 



