1911.] PUBLIC DOCUMENT — No. 31. 169 



l*Li'.\i I'ocMvKrs [I'J.codscLi.s J'nnii, Uiickd). 



The organism causing the disease known as " plum pockets " 

 is closely related to that causing peach leaf curl, although not 

 occurring on the peach. It Avas previously thought that tlie 

 source of infection was only through the hibernating mycelium 

 in the twigs and branches, but from what can be learned in re- 

 gard to this more investigation seems to be needed on this point. 

 A short time after the young fruit forms, it becomes yellowish, 

 much swollen and stoneless. 



These hollow, dropsical-like plums are often streaked with 

 red at first, but after a time they take on a moldy, grayish ap- 

 pearance, similar to the peach leaf curl, and soon fall to the 

 ground. This moldy covering is composed of sacs (asci) which 

 contain the spores. 



The attacks of this parasite are generally local, possibly only 

 one tree in a large orchard being affected, and the treatment 

 given for peach leaf curl would probably suffice here. 



Black Knot (Plowrightia morhosa (Schw.) Sacc). 



One often notices in small family orchards containing a va- 

 riety of trees, where little care is given them, that some of the 

 plum trees show signs of a disease kno^vu as black knot. The 

 knots often extend entirely around the limbs, and as a conse- 

 quence the more distal parts of the limbs receive but little nour- 

 ishment, and finally die. 



Black knot, if given no treatment, usually destroys the value 

 of the tree Avithin a year or two, even if it does not kill the tree 

 in that time. Almost all varieties of plums are subject to this 

 disease. The first noticeable indication of the disease in the 

 spring is the enlargement of limbs and branches afl"ected. The 

 bark then breaks open, and this new surface soon becomes cov- 

 ered with a moldy, green-like substance which contains the 

 spores. This is followed by black knots containing s]X)res 

 which become mature before the next spring. The spores evi- 

 dently ol)tain a foothold on their host through cracks or injuries 

 caused by various agencies. It is therefore essential in the care 



