348 OHIO EXPERIMENT STATION: BULLETIN 214 
Foliage diseases, moreover, are liable to recur each year and 
- tnis is an added reason for anticipatory treatments to ward them off. 
- Foliage diseases may not be neglected with impunity since the leaf ts the 
plant's vital working organ and the plant must suffer from its im- 
pairment. 
BITING AND SUCKING INSECTS AND LEAF DISEASES 
The part played by insects which wound the leaf epidermis, in 
the spread of leaf diseases, is often very important. Such wounding 
Fig. 22. Showing sections of blades of oats attacked by green 
lice (aphides), The right hand specimen shows type of injury re- 
sulting from the sucking of the aphis. In case these lice are carry- 
ing the organisms of oat blade blight, this sucking will lead to 
infection by the disease. (From a photograph by T. F. Manns), 
of the leaf or green 
stem whether by 
insects such as flea 
beetles, foliage eat- 
ing worms, or by 
sucking insects such 
as mites, leaf hopp- 
ers and plant lice, 
opens the way for 
the spores of para- 
sitic fungi or of bac- 
teria or mere molds, 
any one of which 
may be injurious to 
the leaf. The eariy 
blight disease of 
’ potatoes is a good 
example. In seasons 
when there aremany 
of these little black 
flea-beetles to punc- 
ture the leaves, the 
thorough control of 
both these insects 
and the early blight, 
Alternaria fungus, 
is called for. ' Many 
fungi of doubtful 
penetrating powers 
are truly injurious 
when they follow in- 
sect puncturesof the 
leaves. Fortunately 
both these are se- 
cured by Bordeaux sprays. The reasons for such applications are 
of double character since they are to combat both the insect and the 
fungus to follow it. 
