166 INJURIOUS INSECTS OF 1909 AND IQIO. 
Onion. 
BiigHt—Downy MitpEw: Warm, moist weather is especially 
favorable to the spread of the disease. The tips are first attacked, 
presenting a water-soaked appearance, which is followed by a fuzzy 
outgrowth. Later the plants may collapse entirely, thus preventing 
the formation of normal bulbs. 
Crop rotation, clean culture and spraying will prevent the disease. 
If it has never appeared before, it may not be necessary to spray 
before the disease appears, but upon the first indication of its ap- 
pearance 5-5-50 bordeaux should be applied. One spraying may 
or may not be sufficient, depending on weather conditions. 
Smut: The smut persists in the soil, so is particularly liable 
to attack seedlings upon which it causes the formation of black, 
dusty patches of spores. Rotation is beneficial as is soil treatment 
with lime used at the rate of about 100 bushels per acre. Treating 
seed with formalin at the rate of 1 pound to 30 gallons of water is 
also beneficial. 
Pea. 
See Bean. 
Plum. 
1. PrLum Curcutio: (See plum curculio under Apple). 
2. SCALES: (Same as under scale on Apple): 
Biack Knot: This disease is prevalent on both wild and cu! 
tivated plums and cherries. The first indication of its presence is 
usually the development on young twigs of velvety, greenish or 
olive colored swellings. These later in the season become black and 
brittle. Not only young twigs, but also larger branches may be- 
come affected. The branches may be killed on account of the inter- 
ference with the transportation of nourishment, or their vitality 
may be lessened. Infection probably takes place largely through 
wounds and abrasions, so all of these should be carefully avoided. 
Further, the disease spreads most rapidly while the knots are still 
young, so that careful pruning before they have had time to de- 
velop is necessary. If any have been missed, they should be re- 
moved later. Pruning alone, however, is not sufficieat to control 
the disease, since it occurs also on wild plums and cherries. Spray- 
ing should also be practiced. The first application should be made 
in the late winter or early spring while the trees are still dormant, 
another should be made when the buds begin to swell. while the 
others may be made as necessity demands. For the first spraying a 
