Dec. 3, 1917 
Podblight of Lima Bean 
475 
DESCRIPTION OF PODBLIGHT 
Although the ascogenous stage of this fungus has been connected by the 
writer with the pycnidial stage, the latter is alone concerned in the injury 
to the crop in the field. A macroscopic description of this disease there¬ 
fore will be confined to the pycnidial or imperfect stage. In the field 
under suitable conditions the disease first appears on the leaves of plants 
from 1 to 2 feet high. Wet weather is conducive to the spread and warm 
weather promotes the development of this as well as many other dis¬ 
eases of this type. Serious outbreaks have often occurred immediately 
following a few days of rainy, warm weather in fields where previously 
the disease was scarcely noticeable. In such a case the loss is often se¬ 
rious; but if dry weather follows new growth of leaves and fruit will be 
produced comparatively free of the disease. If, however, the weather 
continues wet, a new outbreak is liable to occur. 
The leaves function as host for the fungus during the earlier part of the 
season, from which it spreads later to the pods. Large, subcircular, 
brown, often bordered patches are produced on the leaves (PI. 42, A). 
These patches, varying in size naturally with age, often attain a diameter 
of 1 to 3 cm. Infection is not restricted to any portion of the leaflets 
but the regions bordering the midrib are most frequently attacked. The 
fungus spreads more or less in all directions from the point of infection, 
but may often be delimited by a large vein or midrib. In this moribund 
tissue, or in tissue soon after it is killed, the fruiting bodies (pycnidia) of 
the fungus break through the epidermis. They are arranged more or 
less concentrically, and appear first as gray or grayish raised pimples, 
which later darken and become nearly black. They therefore may be 
seen as conspicuous, minute black specks on the upper surface of the 
leaves standing apart, sometimes confluent, on a brown background. 
The dead tissues finally become dry and fall out, leaving a ragged hole. 
This disease must not be confused with a leafspot of Lima beans and 
other varieties of beans, as well as of cowpeas, caused by Phyllostida 
phaseolina Sacc., the spots of which are smaller, more nearly round, and 
the pycnidia smaller and fewer in number. 
The disease appears on the pods usually the latter part of July or early 
in August, at a time when the vines have nearly reached their full devel¬ 
opment. Under field conditions it is not certain at what stage in the de¬ 
velopment of the pod infection takes place. Young pods are rarely 
found diseased, and inoculation experiments have shown that they are 
infected less easily than ones nearly matured. The disease progresses 
rather slowly, requiring a week or 10 days after inoculation to produce a 
spot of any size or for the production of pycnidia. The growth of a bean 
pod is comparatively rapid, and it is likely that infection may take place 
when the pods are young, the fungus becoming visible as the pod ap¬ 
proaches maturity. Infection occurs at any point on the surface of the 
