Feb. 15,1925 Root Rot of Peas Caused by Aphanomyces Euteiches 325 
temperature for development of the 
disease is approximately between 15° 
and 30°. Differences in soil moisture 
gave little difference in infection under 
the conditions of these experiments, 
whereas observation in the field seems 
to show that the disease is more severe 
on soil with high moisture-holding 
capacity or on soil in which water is 
held by impervious subsoil or by sub¬ 
irrigation. 
9. The fungus appears to occur 
widely in cultivated soils and may be 
conveyed from infested fields to others 
by any agency that carries soil. There 
is no evidence indicating that it is 
carried with seed. 
10. The disease can be prevented 
and controlled most effectively by crop 
rotation. The length of rotation re¬ 
quired appears to vary greatly with local 
conditions. On certain irrigated soils 
which appear to have such low mois¬ 
ture-holding capacity that they pro¬ 
vide unfavorable conditions for the 
development of the fungus, the disease 
has not appeared or has not become 
destructive even after peas have been 
grown nearly every year for 10 years. 
The disease has become destructive on 
similar soil when it is subirrigated. 
On some soils in humid territory the 
third successive crop of peas is often 
badly damaged by this root rot, and a 
comparatively long rotation appears to 
be necessary to prevent it from ac¬ 
cumulating in the soil. In some soils 
which have become heavily infested 
the fungus appears to have persisted 
in sufficient amount to produce con¬ 
spicuous injury to peas after a six- 
year rotation. 
11. Although all varieties of field 
and garden peas are subject to this 
disease, there is considerable difference 
in the amount of injury which they 
incur from it, especially in situations 
where the disease does not develop 
great severity. Study of the nature 
and commercial value of this resistance 
is in progress. 
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