598 STATE BOARD OF AGRICULTURE. 



(4) attacks are most severe in the spring and fall; (5) greatest injury comes 

 from attacks on small plants; (6) older plants are not so seriously affected; 

 (7) trash of the greenhouse and field are important sources of infectious 

 material. 



It is out of the question to rely on any of our common varieties to resist 

 the attacks of the fungus. The varieties of best quality seem to be most 

 susceptible to the disease, and some of the varieties of poorest quality seem 

 to be slightly resistant, but not enough difference has been found to justify 

 the grower in sacrificing quality for resistance. 



The possibility of the disease being seed borne leads to the question of 

 seed treatment and sources of contaminated seeds. Phoma root rot has 

 not been reported from any seed producing section of the United States. 

 If it is present in any of these districts it is evidently causing little damage 

 and chances of seed infection would be very small. European grown seeds 

 are more apt to carry infection and treatment of such seeds may prove to 

 be a good insurance measure against introduction of the disease into the 

 seed-bed. 



A low temperature, combined with a high moisture content in the soil, 

 is necessary if the disease is to become of economic importance. In seed- 

 beds where conditions can be controlled as in the greenhouse, we believe 

 that it would be possible to check the disease and in many cases prevent 

 infection by limiting the water supplj^ and keeping the temperature relative- 

 ly high; but, since the seedling stage is the critical one for infection, it is 

 dangerous to rely on this treatment. If seedlings of the first crop are kept 

 free from infection until they are transplanted to the field, it is believed 

 that in an average year the disease, caused by infection from field sources, 

 is not capable of producing a great amount of destruction before its progress 

 is arrested by the warm weather of summer. It is far safer to keep watch 

 of the seed bed and if the disease appears, to change or to sterilize the soil 

 before another crop of plants is grown. 



In the greenhouse it is possible that the fungus may persist for a consid- 

 erable time in the partially rotted wood of benches and in other decaying 

 material. For this reason all parts which have been in contact with infested 

 soil should be drenched with some good disinfectant before disease-free 

 soil is brought from the outside. A solution of formaldehyde diluted to 

 one part formaldehyde to forty of water has been found to be very effec- 

 tive in killing spores and mycelium of the causal organism when this fungus 

 has been grown in sterile muck. Drenching infested soil with the same 

 strength of solution would no doubt prove effective in destroying the fungus 

 in seed beds under natural conditions. 



In the case of the fall crop, field infection may be a source of considerable 

 loss. In dealing with this, it may be necessary to practice rotation and to 

 remove all diseased trash from the crops of celery which are grown in the 

 rotation. Under field conditions it is not known how long the causal organ- 

 ism may persist in the soil and trash, but the removal of diseased parts from 

 the field should decrease considerably the amount of infection. Crop ro- 

 tation would seem to be a very effective method of control in sections where 

 land is available and celery can be replaced by crops equally valuable. In 

 districts where rotation is not practiced it is believed that the removal of 

 diseased trash and the use of disease-free plants as mentioned above, will 

 hold the disease in check and insure the grower a crop comparatively free 

 from this t3rpe of root rot. 



