HANDBOOK OX INSECT ENEMIES OF FLOWER.- AND SHRUBS 11 



in the case of the rose leafhopper (p. 

 80 . The potato leafhopper (p. 35) 

 causes a dying of the edges of dahlia 

 and other leaves which is called hopper- 

 burn (fig. 19. Some species transmit 

 certain plant diseases: for example, the 

 aster leafhopper (p. 20) transmits the 

 virus of aster yellows from diseased to 

 healthy plants. 



§ 





v 



Figure 19. — Hopperburn injury on 

 leaves caused by leaf hoppers. Inset, 

 adult and nymphs of the potato leaf- 

 hopper, about 6 times natural size. 



Leafhoppers are slender, delicate 

 insects, usually H inch or less in length. 

 They vary in color from brown to pale 

 green. They are very active and have 

 the habit of hopping a considerable 

 distance when disturbed. The eass 

 are laid in the leaf tissue or stalks, and 

 two or more broods may occur annually. 

 Aster, calendula, dahlia, gladiolus, holly- 

 hock, marigold, rose, and zinnia are 

 among the many plants that are com- 

 monly attacked. 



Treatment. — Dusting once a week 

 with a mixture of 9 parts of dusting 

 sulfur and 1 part of pyrethrum powder 

 (containing at least * 0.9 percent of 

 pyrethrins) by weight is one of the most 

 effective measures, especially on aster 

 leafhopper. Pyrethrum applied as a 

 spray is also useful. Nicotine sulfate 

 as a spray or dust may also be used. 

 Bordeaux mixture applied at frequent 

 intervals serves as a repellent. 



Prevention. — Burn over all weed 

 patches in early spring before the insects 

 can reach the garden plants, wherever 

 such measures are practical and the 

 burning can be done without danger of 

 the fire spreading. 



RED SPIDERS, OR SPIDER MITES 



Among the most persistent of the 

 general plant-feeding pests are the spider 

 mites, especially the two-spotted spider 

 mite {Tetranychus bimacukUus Harvey 

 'fig. 20j. These minute animals are not 



Figure 20. — Stages of the two-spotted 

 spider mite: .4. Egg: B. newly hatched 

 nymph, having three pairs of legs: 

 C. adult, having four pairs of legs. 

 About 25 times natural size. 



really insects, but are relatives of the 

 spiders. Their injury to plants, how- 

 ever, is similar to that caused by sucking 

 insects. Spider mites feed by sucking 

 juices from the leaves and other tender 

 plant tissue. Their attack causes pal- 

 ing or browning of the foliage, which on 

 close examination resembles stippling. 

 Sometimes the infested parts of the 

 plant are covered with fine webbing 

 (fig. 21). and in heavy infestations the 

 mites can be found gathering in swarms 

 on the under sides of leaves or running 

 over the webbing which they spin. If 

 the infestation is light there may be little 

 or no webbing, and some species do not 

 spin a web. The individual mites are 

 so small that they can scarcely be seen 

 with the naked eye. Although the liv- 

 ing mites are not always found on in- 

 jured plant specimens, their whitish 

 shed skins and globular eggs or eggshells 

 are usually present and visible under a 

 lens. If these are numerous, this evi- 

 dence is usually sufficient to identify the 

 cause of the poor health of the plants. 

 The red spider spends the winter in 

 protected places, as among the buds or 



