278 TJte Spraying of Plants. 



either when mixed with water or when dry. The latter method 

 is preferred by cotton planters, the undiluted poison being placed 

 in osnaburg bags which are held over the plants. Machines 

 which use the poisons diluted about ten times with flour or 

 plaster are also made. 



COTTOXWOOD. 

 FUNGOUS DISEASES. 



Leaf Rust (Melampsora populina, Lev.). Description. Poplar 

 and cotton wood trees are frequently attacked by a fungus 

 which produces an orange-colored powder on the under side 

 of the leaves. Such leaves may fall quite early in the year, and 

 if the attack is severe, the trees will be partially or entirely 

 defoliated. The winter stage of the fungus is found upon the 

 under side of the leaves also ; waxy pustules of a brown color 

 mark its presence. 



Treatment. This leaf rust may be checked by applications of 

 the Bordeaux mixture made early in the season when the first 

 leaves have unfolded ; the treatments should be continued at 

 intervals of two or three weeks until about the middle of 

 July. 



INSECT ENEMIES. 



Leaf-beetle (Lina scrlpta, Riley). Description. This beetle 

 is nearly three-eighths of an inch in length, of a deep, blue-black 

 color, more or less freely marked with yellow, or the ground 

 color may be yellow and the markings black. The adults 

 hibernate during the winter, and lay their eggs upon the young- 

 foliage. The eggs soon hatch, and the young black grubs 

 begin to feed voraciously, at the same time growing rapidly. 

 As the larvae grow older this color becomes of a lighter shade. 

 They have the power of emitting from the spines found upon 

 their bodies a milky liquid possessing a strong odor. There 

 are several broods each year. 



Treatment. The arsenites should be freely used for the 

 destruction of the first broods, and if the insects appear again 

 during the summer, the applications should be repeated. 



Willow-worm. See under WILLOW. 



