Gray Leaf Spot [Cercospora cruenfa Saee.) — This leaf spot was 

 found on one of the native edible seeded varieties, causing a serious 

 weakening of the plants and partial defoliation. The diseased areas 

 were angular to indefinite, three to eight millimeters in diameter 

 at first, but rapidly coalescing, a dirty gray in color below, due to 

 the copious production of conidia and conidiophores and yello^nsh 

 or chlorotic above, becoming dull rust red. Would doubtless be con- 

 trolled l\v Bordeaux or other fungicide. 



On the iron cowpea a powdery mildew (Erysiphe polygoni DC?) 

 was noted in several instances. ])ut causing little harm. The OicHum, 

 stage only of the fungus was present. 



Cucumber {Gucumis sativus). 



Attempts to grow cucumbers in Porto Rico have been particularly 

 disastrous. In some instances a splendid first crop has been obtained, 

 but the second almost invariably fell prey to disease. A similar state 

 of affairs occurred in the Station trials. The cause was largely the 

 disease known as do"\\Tiy mildew and described below. Successful 

 cucumber culture will depend upon its control. 



Downy ]\Iildew {Pseudopcronospora cubensis [B & C] Clinton.) — 

 This disease was characterized by indefinite yellow spots on the leaves, 

 which under the luunid conditions existing here were so numerous 

 or so rapidly coalesced that the death of the leaves quickly resulted 

 The superficial growth of the fungus itself could be seen as a delicate 

 grayish purple layer on the under side of the leaves. The older 

 leaves were attacked first and the disease progressed with the growth 

 of the vines, usually three to four leaves behind the grooving point. 

 In wet weather, however, the leaves were attacked before they were 

 completely unfolded, and in the second planting the cotyledons (seed- 

 leaves) were attacked and destroyed before the second leaf had com- 

 pletely unfolded. 



The mildew appeared on the first planting when the viiies were 

 about a foot long and had developed from four to seven leaves. 

 Bordeaux mixture at a strength of 3-3-50 was immediately applied 

 and additional applications made at weekly intervals until March 2, 

 or eleven sprayings in all. As far as it was possible to observe 

 spraying was without practicable results, except that aphids devel- 

 oped unchecked by fungus (Acrosfalagmus albus ?). The disease 

 progressed in the same degree upon sprayed plants and checks. Mar- 

 ketable cucumbers were secured for a time, hut tlip disease finally 

 gained the upper hand and the few fruit set after that time Avere 

 small and misshapen. 



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