BLACK KNOT 49 



efficient remedy for it was to cut oft' and burn the knots, but 

 from experiments at several stations, it seems probable that the 

 disease may be controlled by spraying with a fungicide. In 

 order that the spraying may be effective, it is necessary to 

 know something of its life history. Black knot is caused by 

 a fungous plant which grows in the inner bark of the tree, 

 causing it to swell and crack open. The fungous plant repro- 

 duces itself b}' means of spores, of which there are two princi- 

 pal kinds. One kind is known as the summer spore, and the 

 other as the winter spore. 



The summer spores are formed soon after the bark cracks 

 open in the spring, in May or June, and serve to spread the 

 disease at that time. After this form of spore has disappeared, 

 a change takes place in the young knot, in which it assumes 

 its well-known appearance of a black swelling on the twigs or 

 branches. The surface of the black swelling is now thickly 

 studded with minute pimple-like projections, in the interior of 

 which are produced the winter spores. This form of spore is 

 mature and capable of germination in February or March 

 and serves to spread the disease early in the spring, when the 

 leaves and young shoots are making their appearance. 



The spraying against this disease should be done at such a 

 time as will bring the fungicide in contact with the spores be- 

 fore they have time to germinate and infect the t'ees. Hence 

 it is recommended that the trees be sprayed early, before 

 growth begins, and again when the buds are ready to burst. 

 These sprayings are to destroy the winter spores. To destroy 

 the summer spores, the trees should be sprayed about the last 

 of May, and again about the middle of June. The best fungi- 

 cide for this purpose is the Bordeaux mixture. If this treat- 

 ment is faithfully followed, it is probable that the disease will, 

 to a large extent, be prevented. If spraying is not done, the 

 trees should be carefully examined in the spring and fall, when 

 the leaves are ofi', for knots or swellings ; these, when found, 

 should be removed and burned. Where large wounds are 

 made by this pruning, they should be covered with paint of 

 some kind. 



It would be well if there were a law in New Hampshire, 

 properly enforced, compelling each fruit grower to keep his 



