EXPERIMENT STATION BULLETINS. 



385 



These little cups give off spores at maturity as in the case of the apple rust fungus. 

 By some this early rust stage is believed to be connected with a later one repre- 

 sented by Puccinia ribis D. C, which corresponds to a similar spore stage of other 

 rust fungi. 



Few suggestions for treating this disease are given. While sprayed plants 

 are less apt to show the disease in its worst form yet it has been found by the 

 writer on plants thus treated. To be at all effectual spraying should be made 

 early, as the fungus when once established in the tissues of its host cannot 

 be reached by external applications. Picking and burning diseased parts has 

 been suggested as likely to reduce the attacks for the succeeding season. The 

 copper sulphate solution should be tried just before the buds open in spring to 

 be followed by one of the clear fungicides after the fruit has formed. 



POWDERY MILDEW. 



(Sphaerotheca mors-uvae (Schw.) B. & C.) 



The powdery mildew of the gooseberry and currant is widely distributed and is 

 capable of causing considerable damage to foliage, young shoots and fruit. It may 

 appear quite early in the season and continue for some time. Affected parts at 

 first appear to be coated with a whitish cobweb-like growth of minute threads. 

 These soon give rise to spore bearing stalks in abundance each minute stalk 

 breaking up into a chain of colorless spores thus giving a powdery appearance to 



Fig. 35. — Powdery mildew gooseberry, a, A resting spore case (perithecium), discharging its 

 single spore sac (ascus), which contains eight winter or resting spores; c, the summer spore 

 stage of the disease, showing a spore stalk (conidiaphore), which divides, thus forming spores 

 which soon fall apart. Magnified. (Original.) 



the disease portions. While the fungus is confined to the surface of the host 

 plant it obtains nourishment by means of minute sucker-like branches (haustoria) 

 which enter the epidermis of affected parts. Later in the season the fungus 

 threads darken in color and if examined with a lens will be found to have 

 small dai'k bodies imbedded among them. These little specks are the resting 

 or winter spore cases (Perithecia) of the fungus and are destined to carry the 

 disease over to the next season. The gooseberry mildew thrives best in the warmer 

 portions of the United States and during the hottest seasons. It has been found 

 to be especially bad also on the foreign varieties of the gooseberry while the 

 native sorts are less subject to its attacks. 



Treatment. — As powdery mildew is an external parasite it yields quite readily 

 to treatment. Spraying should be begun as soon as the leaves are unfolding; 

 the first application may be of Bordeaux mixture but the potassium sulphide 



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