42 
Colorado Experiment Station 
Leaf-Spot (Cercospora beti- 
cola) (40) — This leaf-spot affects 
both garden beets and sugar beets 
although it is much more injurious 
on the latter. It is common where 
ever beets are grown and is often 
the cause of much loss in the yield 
of sugar beets in Colorado. 
The spots first appear on the 
outer leaves as small brown dots 
often with a purple margin. As 
the spots increase in size usually 
reaching one-eighth to one-fourth 
inch in diameter, the centers be- 
come ashen gray due to the forma- 
tion of thousands of spores of the 
fungus. As soon as the spores are 
formed they may be scattered 
about by wind and rain and irriga- 
tion water to healthy leaves 
causing new spots to form where 
ever they fall. The spots may be- 
come very numerous affecting the 
leaf stalk as well as the blade. 
Badly affected leaves become brown and dry. The destruction 
of outer leaves and the formation of new ones in the center often 
causes the crown to become considerably elongated. 
Spraying with Bordeaux (4-5-50) is said to be effective though 
somewhat impracticable. It has recently been shown that the first 
infection in spring may come from infected seed and that plants 
raised from seed treated with a formaldehyde solution (15 parts to 
1,000 for seven minutes) attain a better development and are more 
productive than those grown from untreated seed. 
The most common source of infection however is the old beet 
top material left on the ground after the preceding harvest. Re- 
moval of infected beet tops or deep plowing to cover up all such 
refuse will greatly reduce the amount of the disease. 
Beets should not be planted on the same soil oftener than once 
in three years and such rotated fields should be separated from 
unrotated fields by at least one hundred yards. 
Leaf-Spot (Phoma betae) — A leaf spot differing from the one 
described above is common on sugar beets throughout the state 
