Enemies 191 



The ground may be infested with bacteria from 

 various crops, and they may be introduced with plants 

 from infested localities. They live over the winter in 

 the soil in direct communication with diseased rhi- 

 zomes; possibly they may be able to survive the winter 

 in soil where they are not associated with diseased 

 plant parts, but this does not seem to have been 

 ascertained to a certainty. No spores are known to 

 be formed. Insects (as, flies, ants), snails, splashing 

 rain and flowing water are the chief agents in inocu- 

 lation. 



Excessive moisture is favorable for their develop- 

 ment — as when the drainage is so poor that water 

 stands until it soaks away. Manure, also, is apt to 

 encourage growth of the bacteria. The use of fresh 

 barnyard manure, either as a fertilizer or mulch, is 

 sure to result in rot, and even well rotted manure 

 sometimes has the same effect, especially in connection 

 with much moisture. The same result may follow the 

 use of any mulch, depending perhaps upon its thick- 

 ness — the effect of a mulch being to keep the surface 

 moist. There are, undoubtedly, other conditions, not 

 yet understood, conducive to the disease. 



Prevention. — In view of the known conditions 

 favorable for rot, as a preventative Irises should be 

 planted only where the drainage is either naturally 

 good, or has been made good — as in one of the ways 

 suggested under Where to Plant, pages 157-162 — and, 

 if possible, only in ground which has not been recently 

 manured, and in which there has not recently been 

 grown a tuberous crop (as, carrots, parsnips, salsify, 



