6 
Journal of Agricultural Research 
VoL XIV, No. t 
CIRCUMSTANTIAL EVIDENCE OF THE NATURE OF THE DISEASE 
For some years past growers have observed that spinach-blight fol¬ 
lowed within a reasonably short time after serious outbreaks of aphids. 
These observations pointed toward the possibility that aphids were the 
direct cause of blight. Recent experiments disprove this theory, and 
at the same time explain the indirect relation between the outbreaks of 
aphids and the subsequent epidemics of spinach-blight. 
INOCULATION OF FIELD PLANTS WITH THE JUICE FROM BLIGHTED PLANTS 
IN THE WINTER OF 1915-16 
In Bulletin 4 of the Virginia Truck Experiment Station, 1 Harter called 
attention to the fact that spinach-blight resembled the mosaic disease of 
tobacco, and plants in certain stages of spinach-blight have decidedly 
mottled leaves, quite characteristic of mosaic diseases. These observa¬ 
tions, together with the indication that no microscopic organism appeared 
to be the cause of spinach-blight, led to the inoculation of healthy field 
plants with the juice of blighted plants. A bed of plants about one- 
half the size of marketable spinach was selected for this experiment. 
A quantity of blighted plants were collected on an adjoining farm, and 
the juice was obtained by mashing the tissues and straining through 
cloth. To serve as controls two rows of plants in the above-mentioned 
bed were pricked with a flamed needle, care being taken to wound both 
young and old leaves. The other rows of plants were inoculated by 
placing drops of juice from the diseased plants on leaves of various ages 
and pricking the juice into them with a flamed needle. These were kept 
under observation until they were large enough to harvest. No attempt 
was made to cover any of these plants, or to keep insects from them; but 
up to the time of inoculation no signs of blight had appeared in this bed 
or in any of the adjoining beds. Not long after the inoculations had been 
made, an outbreak of aphids occurred throughout the entire section. 
The plants on many farms became so badly infested that it injured their 
value for market purposes. Data collected from time to time showed 
that spinach-blight had developed on the inoculated plants. Blight also 
occurred to a limited extent on the control plants. This experiment 
gave merely an indication that spinach-blight is a communicable disease, 
and is spread in some manner, possibly by aphids, possibly by needle 
pricks when the juice is thus artificially carried, or possibly by some 
unknown agent. 
RELATION OF DRAINAGE TO SPINACH-BLIGHT 
It was the opinion of some growers that spinach-blight was directly 
associated with poor soil drainage; therefore the assistance of Dr. J. A. 
Bonsteel, of the Bureau of Soils of the United States Department of 
Agriculture, was obtained, and the relation of this factor to spinach- 
1 Harter, I,. U op. err., 1910. 
