New York AGRICULTURAL EXPERIMENT STATION. 173 
fested fields may be accomplished without the reappearance of dod- 
der in the new seeding provided dodder-free seed is used. 
Yellow trefoil closely resembles alfalfa, but it has a yellow blos- 
som whereas alfalfa has a purple one. Another striking difference 
is found in the root-systems of the two plants. Alfalfa has a 
strong tap-root with few side roots, while the tap-root of yellow tre- 
foil is smaller and has numerous side roots. Yellow trefoil is not 
a troublesome weed; it is merely a worthless plant. In New York, 
yellow trefoil is regularly a biennial in alfalfa fields and lawns. It 
becomes conspicuous in the first cutting of the second season, then 
disappears. The adulteration of alfalfa seed with yellow trefoil is 
much less frequent than it was a few years ago. 
In newly-seeded alfalfa fields weeds are a serious menace. Be- 
fore seeding with alfalfa the land should be cleaned thoroughly. 
It is folly to sow alfalfa on foul land. Practically all of the trouble 
with weeds comes during the first season. In established alfalfa 
fields few weeds are able to maintain themselves. When weeds 
threaten to smother young alfalfa the field should be promptly 
clipped, but not mown closely. Close mowing may ruin young 
alfalfa. 
The only really important fungus disease of alfalfa in New York 
is the leaf spot caused by Pseudopeziza medicaginis. 
Other diseases sometimes found are wilt (Sclerotinia liber- 
ttana), anthracnose (Colletotrichum trifolit), downy 
mildew (Peronospora trifoliorum), Ascochyta leaf spot 
(Ascochytasp.), Stagonospora leaf spot (Stagonospora 
mrrpariircda (7)-), and Cercospora leaf spot (Cercospora 
medtcagints). In germination tests, dead, brown seeds com- 
monly become overgrown with a species of Alternaria, but whether 
the fungus is parasitic or saprophytic is not clear. 
- Frost blisters occur on the under surface of alfalfa leaves after 
every frost. A root-knot disease caused by nematodes is common 
but probably not important. There appear to be no very important 
insect enemies of alfalfa in New York. 
There were found four diseases the cause of which could not be 
determined, viz.: White spot, an unimportant disease of alfalfa 
leaves ; yellow top, which causes the plants to stop growing and turn 
yellow; pitting of the tap-root, due to the gnawing of some un- 
known animal, and a blackening of the fibro-vascular bundles in the 
tap-root. There was found, also, a freak alfalfa plant having 
unifoliate leaves throughout. 
