820 
at the present time. White and alsike 
clover, on account of their small size, can- 
not be entirely freed from dodder. Red 
clover, by thorough re-cleaning, can be 
entirely freed of clover and small-seeded 
alfalfa dodder. The size of the screen is 
important, but sufficient space is not avail- 
able here for thorough discussion of the 
processes of separation. 
The most logical precaution to take is 
never to plant seed infested with dodder. 
This can be accomplished by bwying only 
the best of re-cleaned seed and having it 
previously tested by an expert for the 
presence of dodder. 
When dodder becomes introduced into 
a field, the method of eradication is fre- 
quently difficult, depending upon the lo- 
cation of the field and the species of dod- 
der. Space will not permit a detailed dis- 
cussion here of the methods of eradication, 
and interested growers should apply for 
information to the Experiment Station, 
giving a full statement of conditions, or 
should procure a copy of the farmers’ bul- 
letin above mentioned, in which the meth- 
ods of eradication are fully discussed. 
Downy Mildew 
Peronospora trifohorum D’By. 
The downy mildew fungus has occurred 
in Colorado, and is very liable to occur 
in other states. No suggestions can yet 
be made as to its prevention. 
A. D. S. 
Leaf Spot 
Pseudopeziza medicaginis 
H. S. Jackson 
The common disease of the alfalfa 
known as leaf spot is prevalent in most 
sections of the country where alfalfa is 
grown. It is also the most common fun- 
gous disease on this crop in Oregon, but 
under the ordinary conditions is not re- 
sponsible for large losses. 
Symptoms 
The disease is characterized by the for- 
mation of brown or black irregular spots 
on either side of the leaf. The spots are 
most conspicuous, however, on the upper 
surfaces. They are small, seldom over 
one-eighth of an inch in diameter, and 
are scattered irregularly but frequently 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
very thickly over the surfaces of the 
leaves. 
Cause 
In many of the spots the presence of 
little shining amber-colored structures 
with black margins may be observed by 
the aid of a good pocket lens. These are 
the fruiting bodies of the fungus causing 
the disease which is known technically as 
Pseudopeziza medicaginis. These struc- 
tures are the apothecia or fruiting bodies 
of the fungus and contain, in a layer on 
the upper surface, many cylindrical sacs, 
called asci. Hight spores are formed in 
each of these asci. 
The general effect of these spots on the 
leaves is to cause them gradually to turn 
yellow and fall, so that the plants, where 
severely affected, may be almost entirely 
stripped of foliage. This brings about re- 
duction in forage, and, on account of hin- 
dering the normal development of foliage, 
results in interference with root growth 
which may cause reduction in subsequent 
crops. 
In Western Oregon the fungus is most 
abundant in the fruiting condition in the 
fall, when mature spores are produced in 
large numbers from September to Decem- 
ber. It is possible that the fungus, under 
Oregon conditions, spreads all winter. It 
is probable that the fungus is dissemin- 
ated locally most frequently by the wind, 
but there is evidence to show that it may 
be carried to new localities through the 
seed. 
A. similar disease, which is considered 
by some authorities as identical with the 
alfalfa leaf spot, but which is usually 
referred to by scientists as Pseudopeziza 
trifolorum, occurs in Oregon on red 
clover. 
Remedy 
On account of the nature of the host 
crop, no very satisfactory remedy for this 
trouble suggests itself. When the disease 
appears to be serious in the spring so that 
the leaves drop abundantly and the forage 
value is likely to be much reduced in the 
first crop, it might be advisable to mow 
the plants early, as this would cause a 
tendency to throw out new sprouts which 
would grow vigorously and might escape 
