52 



MISC. PUBLICATION 62 6, U. S. DEPT.'OF AGRICULTURE 



Figure 84. — Eggs of angular-winged 

 katydid on rose. Twice natural 

 size. 



HYDRANGEA 



Several pests occasionally cause in- 

 jury to hydrangea. These have been 

 discussed elsewhere, as indicated below: 



Page 



Aphids 9 



Tarnished plant bug 35 



Red spiders 11 



Rose chafer - 66,75 



IRIS 



Iris Borer 



The iris borer (Macronoctua onusta 

 Grote) injures the roots (fig. 85) and 

 crowns of iris, including the Japanese 

 and the Siberian types. Decay and 

 blackening (or a tear-stain effect) of the 

 leaves of infested plants are usually 

 good, indications of its presence. The 

 injury becomes more evident during 

 July and August. In heavy infesta- 

 tions entire plants are killed. The full- 

 grown worm is usually pinkish, with a 

 brown head, and about 1% to 2 inches 

 long. Pupation takes place in the soil 

 near the base of the plant. The adults 

 are brownish moths which appear in the 

 fall and lay the overwintering eggs, 

 preferably on dead or dry leaves. The 

 young caterpillars, on hatching in the 

 spring, gnaw their way into the leaves 

 and then work down to the roots, which 

 they hollow out completely. 



Treatment . — D uring the active 

 growing season all plants should be 

 carefully watched, and when injury is 

 observed the appropriate treatment 

 should be applied. The young cater- 

 pillars, if detected by the tear-stained 

 appearance of the leaf while they are 

 still mining in the foliage, can be mashed 

 by pressing the infested parts between 

 the thumb and forefinger. Spraying 

 new growth early in the season with 

 lead arsenate or nicotine sulfate at the 

 time the first injury is observed may 

 be of some value. Recent tests have 

 shown that a derris-pyrethrum spray 

 kills the young borers if it is applied 

 as they are eating their way into the 

 leaves or stems and before they have 

 reached the roots. Such a spray may 

 be prepared by mixing 2\i ounces of 

 derris powder (containing 4 percent of 

 rotenone), 4 ounces of an alcoholic 

 extract of pyrethrum, and 2% teaspoon- 

 fuls of a commercial spreader (p. 103) 

 in 3 gallons of water. The method of 

 mixing is discussed on page 99. 



If an infestation is not detected until 

 the borers have reached the roots, the 

 plants should be lifted after they have 

 flowered and all infested parts removed 

 and destroyed. If the rhizomes have 



Figure 85. — Caterpillar of the iris 

 borer tunneling in a root. About 

 half natural size. 



