TUE PLUM. 



101 



spores escape from the knots during the late winter or early spring 

 months. 



Eemedy.—Upon their first appear- 

 ance these swellings should be removed 

 and burned, if they are on the smaller 

 branches where it is practicable to cut 

 them off; if on the trunk or larger 

 branches where they cannot be cut out 

 they should be painted with a paste 

 made of yellow ochre and linseed oil, 

 using care to keep the oil away from 

 the healthy bark ; where trees are very 

 badly infested they should be removed 

 entirely. This same disease also grows 

 in the wild black and choke cherries, 

 and if abundant on them their removal 

 will make the extermination of the dis- 

 ease more easy. 



Other Diseases.— There are sev- 

 eral other fungus diseases which occa- 

 sionally injure the plum. One of them 

 (iWonilia friictigena) causes the fruit to 

 rot, while another produces round, dry, 

 scabby spots on the skin. Probably the 

 best treatment where these are abun- 

 dant is to spray the fruit with Bordeaux 

 mixture as soon as it is well formed, 

 and again when about half grown. For 

 recipe for making Bordeaux mixture 

 see chapter on the strawberry. 



Insects.— Plum Curculio.— This is 

 the insect which causes the plums to 

 prematurely ripen and drop to the 

 ground. It is not nearly so destructive 

 to our native plums as to those of the 

 Prutius domestica tribe. The latter are 

 often so badly infested that none of the 

 fruit comes to full maturity. While our 

 native plums are stung just as much by 

 the curculio as the others, but few of the eggs of the curculio de- 

 velop into the grub. This insect is a small, rough, greyish or 

 blackish beetle, about one-fifth of an inch long with a black, shin- 

 ing lump on the middle of each wing, and behind this a more or 

 less distinct band of a dull yellow color, with some whitish marks 

 about the middle (see Fig. 76). The snout is rather short. The 

 female lays her eggs in the young green fruit shortly after it is 

 formed. After laying the egg she cuts a circle round it to prevent 

 the part in which the egg is laid from growing (see Fig. 77). The 

 3gg hatches in a few days and the larva works around the outside 



Fig. 75.— Black knot, or ivart 

 on J) turn wood. 



