Alfalfa 
Bacterial wilt, and in some cases the fungus diseases of alfalfa, 
have been most destructive through early stand losses, which have 
reduced the productive life of fields in the humid and irrigated 
areas of the country from 6 or more to only 2 or 3 years. Since 
unproductive fields are generally plowed and planted to other crops, 
the loss caused by bacterial wilt is not truly reflected by the 
loss in yield and quality of the short-lived crop. Wilt-resistant 
varieties have been made available in sufficient quantities to 
overcome about a third of this loss. Ranger and Buffalo have filled 
the need for adapted wilt-resistant varieties in most areas. Where 
winter hardiness coupled with wilt resistance is required, the new 
variety Vernal soon will be available. The fungus diseases attack- 
ing the leaves and stems of alfalfa also limit the productive life 
of the stand, but are more important in reducing the annual harvest 
in both amount and quality. The development of disease-resistant 
varieties offers promise in bringing these pests under control. 
The stem nematode of alfalfa was first recognized as an important 
pest in some of the valleys of California and western Nevada. It 
is spread rapidly across fields by irrigation water. Where the pest 
exists the loss is heavy. Damage may be noted at any time during 
the growing season, but appears to be most severe in the spring and 
early sumer. Infected plants are dwarfed and have fewer stems, 
Susceptible varieties are completely eliminated in 2 to 3 years. 
The pest is now controlled most effectively by the growing of 
resistant varieties. The damage may be reduced, but is likely to 
continue because the nematode is spreading into areas where adapted 
resistant varieties are not yet available. 
The virus that causes Pierce's disease of grape also affects alfalfa, 
in which the resultant disease is called alfalfa dwarf. It is confined 
principally to the southern two-thirds of California and the western 
third of Arizona. The incidence of dwarf disease depends upon the 
proximity of alfalfa fields to fields of diseased grapes and upon the 
population of insect vectors. Alfalfa plants infected by the virus 
become dark green and dwarfed. They gradually decline in vigor and 
eventually die prematurely. 
Clovers 
More than a dozen diseases attack the true clovers and sweetclover, 
causing severe losses of stand, yield, and often final destruction 
of the crop. Leaf and stem diseases also reduce the quality of the 
hay or pasture produced. The estimated losses do not take into 
account the reduced value in pastures or grazed hay fields from which 
no hay or seed is removed. Since white clover and crimson clover 
are used primarily for pasture and the total feed production from all 
pasture and range land is about twice that harvested as hay, it is 
reasonable to assume that disease loss of the clovers in pastures 
alone may well exceed the losses from all diseases causing injury to 
all hay crops. 
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