8 BULLETIN 316, U. S. DEPARTMENT OF AGRICULTURE. 



recommended, therefore, that specimens of the insects, fresh evi- 

 dence of then work, and a description of the character and extent 

 of their injury be sent to the Forest Entomologist of the Bureau 

 of Entomology for information and advice with regard to control 



measures. 



FUNGI. 



The injury caused by the various fungi, principally defoliation 

 and decay in the wood, is probably less than that occasioned by 

 insects. Willows with a sufficient ornamental value to warrant 

 the expense can be kept free from leaf diseases by spraying. Where 

 this is done, a relatively large amount of lime, rosin, or fish-oil soap 

 is necessary to make the spray adhere to the leaves, especially those 

 of the smooth-leaved species, such as the laurelleaf willow. The 

 fungi that attack the wood are of the common type, known as bracket 

 or shelf fungi, which gain admission to the tree through injuries 

 caused by wind, insects, and the like. Some of these grow in the 

 living tissue and destroy sound wood, but often they simply disin- 

 tegrate portions that have been deadened by other agencies. The 

 heartwood of the willow is particularly susceptible to such attacks. 

 The dark-red heartwood of most of the willows does not show the 

 ravages of decay until it has far advanced, often not until the fruiting 

 bodies appear on the surface. In the black willow stands of the 

 South the principal fungous troubles are large "burls," commonly 

 known as "sap knots," and heart rot. The heart rot does not 

 necessarily occur at the base of the tree and may extend for only a 

 short distance, the wood being sound in either direction. 



WIND AND GRAZING. 



Probably the greatest enemy of the willow plantation is wind. 

 The wide use of willows in exposed situations and the weakness of 

 the green wood has been known to result in the almost complete 

 demolition of individual trees and even rows of trees within 25 years 

 after their establishment. In Iowa two rows were observed on 

 apparently the same soil and extending in the same direction, one 

 row exposed to the full sweep of the wind and the other protected 

 by a cottonwood grove. Both rows were planted the same year 

 and in the same manner. The protected row averaged 60 feet in 

 height and only 3 per cent of the tops had been broken by the wind. 

 In the other row 28 per cent of the trees averaged 55 feet high, and 

 of these practically none of the tops were broken; so this height 

 represented the normal. The other 72 per cent, however, were on 

 an average only 40 feet high. All of these trees were more or less 

 broken and cracked and could be saved from being completely 

 wasted only by prompt utilization. At the age of 27 years the ex- 



