THE CULTURE OF SET ONIONS U 



Soil 



Bacterial soft rot and Fusarium bottom rot, the two most important bulb 

 diseases of set onions, are both caused by organisms commonly found in cultivated 

 soils. It is only reasonable to expect that the soil itself might be an important 

 source of inoculum while the bulbs are in contact with it, both during growth 

 and after pulling, especially' those soils on which onions have been grown con- 

 tinually for many years. Careful studies by Munn (2) in New York State, on 

 the neck rot disease of onions, have shown that the soil is the source of the fungus 

 causing this disease. Although such detailed studies have not yet been carried 

 out on the organisms causing soft rot and bottom rot, convincing evidence from 

 experiments conducted in the Connecticut Valley indicates that, under certain 

 conditions, the soil is an important, if not the principal, source of inoculum for 

 these diseases. 



Some of the results obtained in 1941 are presented in Table 7. 



Table 7. — Yields and Shrinkage Losses of Seven Lots of Set 

 Onions Grown on Dry and on Moist Soils. 



Lot and Type Yield — 50 lb. Bags per A. Percentage Loss by Nov. 1 



Dry Soil 



1 Jap - 840 



2 Jap.. 840 



3 Jap ... 820 



10 Jap 870 



11 Globe 880 



12 Globe 760 



13 Globe 860 



Trials conducted in 1940 gave similar results. All plots were handled alike 

 and in such a way, in the growing, harvesting and storing of the crop, as to in- 

 sure the most favorable conditions for keeping in storage. In both years, seasonal 

 weather conditions were good for growing onions. Onions grown on the drier, 

 well-drained sections of the experimental area kept much better in storage than 

 those grown where the soil was more moist. This was true for all lots of seed sets 

 grown in both locations and indicates that the trouble began in the field long 

 before the onions were put into storage. 



These results show the importance of the relationship of soil moisture to bulb 

 infection by disease organisms. They may show why in wet seasons, when the 

 moisture content of most soils is high, the keeping quality of most onion crops 

 is usually poor. They help explain why, in favorable years, some crops of onions 

 keep poorly in storage even though the quality of the seed sets is excellent and 

 storage facilities are good. Although onion soils as a whole are fairly uniform, 

 minor differences in topography and soil texture exist, even within the same field, 

 which result in some sections being much more moist than others. These moister 

 sections would not necessarily be considered as poorly drained but onions from 

 them would probably develop more rot in storage than those from the drier sec- 

 tions, even though weather conditions and other factors affecting keeping quality 

 were favorable. 



In these experiments yields were always greater from moist soils than from dry 

 ones. Since the same number of sets was planted in each plot, the increased 



