A Stem Beight of Field and Garden Peas 41 
METHOD OF INFECTION 
Both our laboratory experiments and our field observations 
indicate that the causal organism enters the plants either thru the 
stomata or thru wounds produced by mechanical injuries. 
In looking into the history of the trouble last spring we found 
one striking case where the outbreak unquestionably followed culti¬ 
vation with a spike-toothed harrow at a time when the wind was 
carrying quantities of soil. The custom of harrowing tO' break the 
crust and to conserve moisture is a dangerous practice, because it 
wounds the tender plants and opens the way for soil infection. This 
was brought to our attention in a very graphic manner in a field 
where a large number of varieties had been planted for experimental 
purposes. A spike-toothed harrow had been dragged across the 
lower part of one of these rows and the upper end left untouched; 
all of the varieties blighted more or less in that portion of the row 
that was harrowed, while in the unharrowed part several of the 
same varieties exhibited miarked resistance. 
Two other instances were noted where infection followed 
closely upon a severe sand-storm which bruised the vines and liter¬ 
ally injected the tissue with germ-laden soil particles. In fact, soil- 
laden wind alone, where it blows as violently and persistently as 
it does in Colorado in the springtime, is adequate explanation for 
all the infection that might ever occur in our vState. 
CONTROL MEASURES 
1. Resistant varieties offer the only satisfactory remedy for 
the blight, and in the next two years we shall endeavor tO' obtain 
strains that are disease-resistant and, at the same time, desirable 
types both for forage and canning purposes. 
2. In the meantime, when practicable, we would suggest 
planting from ten days to twO' weeks later than is the local custom. 
3. So far as possible, avoid mechanical injury to the plants by 
harrowing or by other similar practices. 
4. Avoid planting peas on the same land that was in peas the 
previous year, or where the disease has been present. 
5. While we have had no opportunity as yet of determining 
whether the blight organism can pass thru the digestive tract of 
animals, fed with diseased vines, unharmed, and thus infect the 
manure, it may not be out of place to suggest the possibility of 
this at this time, and if we should have occasion to use any such 
manure on our gardens or in our fields, to remember that we may 
be sowing the seed of endless woe. Until we know definitely that 
