HANDBOOK OX INSECT ENEMIES OF FLOWERS AXD SHRUBS 53 



considerable rot, the diseased parts 

 should also be cut out and the cleaned 

 divisions soaked in mercuric chloride 

 solution (1 to 1,000) (p. 102) for 10 

 minutes. The plants should then be 

 reset in a new location if possible. 



Prevention. — Winter burning of de- 

 bris and weeds reduces the possibility 

 of reinfestation the succeeding season, 

 since it destroys the overwintering eggs. 



Iris Thrips 



The iris thrips (Bregjtiatothrips iridis 

 Watson), |a recently introduced in- 

 sect, is primarily a pest of iris, although 

 it has been found on pokerplant. It 

 feeds on the inner surface of leaf sheaths 

 and on young leaves of many types of 

 iris from May until November, and 

 causes a rusty or sootlike blackening 

 (fig. 86). A varying amount of stunt- 

 ing of the growth may also result. 

 On Japanese iris the flower bracts and 

 petals may be injured and in some cases 

 the flowers become bloated. These 

 insects are very tiny, like the gladiolus 

 and other thrips (fig. 74, p. 45). The 

 eggs are laid in the plant tissue, and the 

 milky-white larvae and pupae are found 

 together with the glistening dark-brown 

 adults. The adult female thrips over- 

 winter in the crown of the iris. Most 

 adults are wingless, but winged ones 



Figure 86. — A, Uninjured leaf sheath 

 of Iris pseudacorus; B, leaf sheath in- 

 jured by iris thrips. 



appear with the first generation and are 

 present during the summer and early 

 fall. Migration to other plants occurs 

 in June when the winged forms are 

 abundant. 



Treatment. — For complete elimina- 

 tion of the thrips, immerse the plants 

 for 30 minutes in water at a temperature 

 of 110° F., when the plants are lifted 

 and freed of soil. This can be done at 

 the time of dividing and resetting the 

 plants. Growing plants in beds may 

 be treated by flooding them with water 

 maintained at the desired temperature 

 and confined in a cylinder pressed into 

 the ground around the plant. Jap- 

 anese iris should be treated preferably 

 in the spring, but may also be treated 

 in late summer or fall, provided the 

 newly set plants are regularly watered. 

 Bearded irises and southern types of 

 iris should be treated only late in the 

 summer or in the fall. 



Satisfactory control may be obtained 

 by spraying with a nicotine sulfate and 

 soap solution, using 2 teaspoonfuls of 

 nicotine sulfate in each gallon of soapy 

 water. Spray eight times at weekly 

 intervals, four times before and four 

 times after the blooming period. The 

 foliage should be thoroughly sprayed, 

 with particular attention to the base of 

 the fan of leaves, where the thrips occur; 

 they are rarely found elsewhere on the 

 plants. The gladiolus thrips (p. 45) 

 also causes serious injury to iris at times. 

 It differs from the iris thrips in that it 

 prefers to feed on the flowers. 



Iris Weevil 



The iris weevil (Mononychus vul- 

 peculus (F.)), while known to breed com- 

 monly in the seed pods of blueflag iris 

 (Ins versicolor), occasionally attack- the 

 flowers of Japanese, European, and 

 native iris, making numerous small 

 punctures in the seed pods. This 

 causes much disfigurement by the 

 formation of rough, corky, irregular 

 scars. The eggs are laid in the iris 

 ovary. The young fat grubs feed on the 

 seeds and develop and pupate within the 

 seed pods. The adults emerge when 

 the pods burst open. They are about 

 l 5 -inch long, black above, and covered 

 below with yellowish and whitish scale-. 

 There is apparently only one generation 

 annually, and the adults, which over- 

 winter, appear in May or early in June. 

 This weevil occurs in Canada, and in this 

 country as far south as Georgia. 



Treatment. — If seeds are not de- 

 sired, remove and destroy all flower 

 heads as soon as they are past their 

 prime, to prevent the beetles from com- 



