626 INSECTS AFFECTING VEGETATION 



circles, as do the spots made by parasitic fungi, such as Septoria 

 (spot disease) and Heterosporium (fairy ring). 



Very badly diseased plants, especially when much crowded 

 and growing in damp atmosphere, have more yellowish green leaves 

 than normal, of a more transparent appearance, and usually 

 smaller. The lower leaves of diseased plants in any atmosphere or 

 soil die prematurely and the vitality of the plant is so lowered as to 

 check the growth and decrease the size and number of the flowers. 

 (Purdue E. S. B. 69.) 



That aphides and not bacteria are responsible for the trouble is 

 shown by the fact that the injuries produced are not accompanied 

 in the earlier stages by fungi or bacteria. The aphides therefore 

 can not be looked upon as simply carriers of some fungus or bac- 

 terium, as they produced the disease on plants growing under per' 

 fectly antiseptic conditions as quickly as upon those not protected 

 by antiseptics. 



Injuries similar in many respects to those produced by aphides 

 also result from the attacks of thrips insects which are often 

 present on carnations growing under glass, althoughj sometimes 

 overlooked by growers. Another form of the disease is produced by 

 red spiders. 



No matter how badly diseased plants may be, if otherwise vigor- 

 ous they will grow out of the disease entirely and the young leaves 

 and shoots will remain free from spots if kept completely free from 

 aphides, thrips, and red spiders. 



Treatment. The grower can successfully combat this disease 

 by the proper selection of cuttings; careful propagation of stock; 

 good soil ; the proper amount of moisture, light, and air ; and by the 

 reduction of aphides, thrips, and red spiders to a minimum. (U. S. 

 Div. Veg. Path. B. 19.) 



Bud-Rot. The bud-rot of carnations produces effects which 

 show externally, the character depending upon the extent and sever- 

 ity of the infection. The most striking external symptom is the 

 failure of the affected buds to expand into perfect flowers. Carna- 

 tion benches in which the bud-rot is prevalent generally show a con- 

 siderable number of flowers that will never open completely. Some- 

 times the affected flowers deviate only slightly from the normal. 

 Flowers which have a split calyx may resemble these superficially 

 in the unfolding of the petals. In buds in which the infection is 

 more severe or begins at an earlier date, the petals become only 

 slightly expanded and the buds die without ever developing into 

 perfect flowers. If such affected flowers are not picked off, the pro- 

 jecting portions of the petals wither and turn brown and the calyx 

 soon dies also, and assumes a brown coloration. In a few cases the 

 buds are apparently infected at a very early stage, for the calyx 

 does not open sufficiently to allow any projection of the petals, but 

 turns brown and dries up. (Nebraska E. S. B. 103.) 



All affected buds show upon closer examination that all or part 

 of the flower parts included within the calyx are affected with a rot 

 which has caused a brown coloration and a softening of the tissues. 



