58 



MISC. PUBLICATION 6 2 6, U. S. DEPT. OF AGRICULTURE 



limited to a few of the Eastern States. 

 The hornet is about an inch long, black- 

 ish with yellowish-orange markings, 

 and somewhat hairy. It is often active 

 until late in the evening. The large, 

 dark, papery nest of this hornet is 

 usually built in such protected places 

 as tree cavities, between the rafters of 

 buildings, or occasionally in holes in 

 the ground. 





Figure 93. — Lilac branch girdled by 

 the giant hornet. 



Treatment. — No satisfactory meth- 

 od of stopping the bark gnawing has 

 been discovered. Probably the best 

 method of control would be to trace the 

 hornets to their nest and then destroy 

 the colony. This might be done by 

 soaking the nest with kerosene, by 

 plugging the opening with cotton soaked 

 in chloroform and then destroying the 

 nest, or by injecting about a tablespoon- 

 ful of carbon disulfide into the nest and 

 closing the opening. Blowing or throw- 

 ing about a handful of derris powder 

 (containing 4 or 5 percent of rotenone) 

 into the nest should be effective, since 

 this material has proved effective against 

 certain wasps and bees when dusted 

 into their nests or placed where the 

 insects must walk through it. Heavily 

 dusting the portions of the branches 

 upon which the hornet feeds with derris 

 powder would also be worth trying. 

 The treating of the nests preferably 

 should be done during the night while 



the hornets are inside. It would be 

 advisable to wear heavy gloves and 

 clothing and a veil to avoid being stung. 



Lilac Leaf Miner 



The young caterpillars of the lilac 

 leaf miner (Gracilaria syringella (F.)) 

 feed for a time inside the leaves, caus- 

 ing blotchlike mines which can be seen 

 on the surface. After several weeks 

 they abandon these mines, roll the 

 leaves or web them together in masses, 

 and feed on the inner surface of the 

 curled foliage. This insect attacks 

 ash, deutzia, euonymus, lilac, and 

 privet. In the Northeastern States 

 there are usually two generations of 

 caterpillars, the first starting to mine 

 the leaves about June and the second 

 late in July or in August. The full- 



grown caterpillars are about 



inch 



long and yellowish. The adults are 

 tiny moths. They lay their eggs in 

 small groups on the leaves. 



Treatment. — Spray with a nicotine 

 sulfate and soap solution when the leaf 

 mining starts, thoroughly wetting both 

 surfaces of the foliage. If necessary, 

 make a second application about 2 

 weeks later, using twice the ordinary 

 amount of nicotine. Lead arsenate 

 spray is useful if applied before many 

 of the leaves have been rolled. Spray- 

 ing or dusting with pyrethrum, as 

 recommended for the greenhouse leaf 

 tier (p. 5), might also be tried against 

 the caterpillars in the rolled leaves. 

 Where only a few leaves are infested, 

 these can be picked off and destroyed, 

 thus preventing a more serious infesta- 

 tion later. 



Other Pests of Lilac 



Page 



Oblique-banded leaf roller 83 



Hornworms 4 



Citrus whitefly 43 



Melon aphid 90 



Cottony maple scale 47 



Scurfy scale 48 



White peach scale 72 



Euonymus scale 41 



MARIGOLD 



Potato Leafhopper 



The potato leafhopper (Empoasca 

 fabae (Harr.)) is often the cause of a 

 peculiar diseaselike injury on the African 

 marigold. Plants attacked by this 

 insect show a curling and reddening of 

 the leaflets and a stunting and killing 

 of the young tips. Another phase of 

 the injury is the complete wilting (fig. 

 94) of the tips and the young leaflets on 

 some branches. These leaves become 



