Mar. 3,1923 
Gray Mold of Castor Bean 
685 
The influence of temperature was not so definitely traced, though the 
indications are that it has its effect as well. As will be seen elsewhere in 
the paper, the optimum temperature for the development of the fungus 
in pure culture is approximately 25 0 C. (77 0 F.). Where temperature 
much below this prevailed in a locality otherwise favorable to infection it 
might be assumed that its failure to appear was due to too low tempera¬ 
ture. Such a condition existed at Little Rock, Ark. After October 17, 
the moisture was favorable but the maximum temperature was above 
72 0 F. on only two days, October 19 and 20, and it was 70° F. or lower 
practically all the rest of the month. The minimum fell below 6o° F. 
several days. Likewise in Florida, with the cooler weather in the fall, the 
fungus definitely ceased to progress. It is likely that the fungus would 
not be nearly so active in a climate a few degrees cooler than Florida, even 
though moisture conditions were equally favorable. 
DESCRIPTION OF THE DISEASE 
Professor Stevens has given a very good description of the gray-mold dis- 
easeinhis Florida publications (16,17). A more complete description might 
well be given, however, especially of the earlier stages. Infection first 
becomes evident on leaves, panicles, or stems, in the form of small bluish 
spots, from which yellowish drops of liquid exude. Shortly after—in the 
course of only a few hours if weather conditions remain favorable— 
strands of hyphae may be seen extending from original infected spots 
along the surface of the host like a spider's web. These strands produce 
new points of infection. Development is rapid. The fungus infects 
constantly increasing areas on the host, meanwhile sending forth its fruit¬ 
ing hyphae. The inflorescence or (to use the common, though botanically 
incorrect terminology) “spike" becomes covered with this at first gray, 
then olive-drab mold. Plate 1 shows a typical young spike in an early 
stage of infection. Plate 3 shows three spikes with the mold farther ad¬ 
vanced. At this stage the slightest jar will release a veritable cloud of 
conidia, which spread further destruction to the rest of the field. As an 
affected inflorescence becomes older, the mass becomes darker in color 
and more compact, and the stem droops and gradually loses its imma¬ 
ture pods or blossoms. (PI. 4, A, B.) Close examination of an infected 
spike will always disclose the presence of the mold itself, or some other 
characteristic feature of the disease to distinguish it from the natural 
drying of the male blossoms with which it is sometimes confused. The 
disease is sometimes still further complicated by the presence of the pink 
com worm (Pyroderces rileyi Wals.), which is said to do injury at this 
stage. 5 The two conditions are often found together. In fact, specimens 
sent to Washington for examination were at first misleading because of 
the constant presence of this worm. 
On the leaves, the disease is usually traceable to a small bit of an 
inflorescence that has fallen from above. From this central point the 
fungus spreads, producing a dead spot on the leaf, accompanied by the 
gray mold. Infection may also occur at the margin of a leaf, causing its 
death in characteristic Botrytis fashion. However, leaf infections are 
comparatively rare. Infections on the stalk and branches do not readily 
occur, the tissues here being more mature and consequently more 
• KISUUK, Max, Jr. op. cit. 
