632 INSECTS AFFECTING VEGETATION 



case, one side of a leaf will 'be diseased and the other remain com- 

 paratively healthy. Again, the tissues of the stem at the point of 

 attachment of diseased leaves often collapse and turn brown in much 

 the same way as do the tissues of the leaf. (B. Veg. Path. B. 14.) 



When the flowers become spotted, the plants are unsalable, no 

 matter whether the leaves are badly diseased or not, and are there- 

 fore a complete loss to the grower. When the flowers and a few of 

 the upper whorls of leaves escape, the plants are usually disposed 

 of for decorative purposes where only the flowers are required. The 

 popular demand, however, is for perfect flowers and perfect leaves, 

 as even a slight disfigurement will cut down the market value of the 

 plant. 



Many theories have been advanced as to the cause of the lily 

 disease and in our investigations these have all been studied as far 

 as possible. The writer was, how r ever, unable to obtain bulbs from 

 which flower stems had been cut or which were known to be im- 

 mature, hence our conclusions relative to these points are only gen- 

 eral, having been based on the second growth of bulbs which were 

 developed by forced plants. 



Some growers attribute the trouble to exhaustion of food in the 

 soil in which the bulbs are grown. That this is not the case, how- 

 ever, is at once apparent from the fact that it often appears on new 

 land never before planted to lilies and on lands highly fertilized, 

 and from the further fact that healthy plants are frequently grown 

 on old soils which have been cropped to lilies for several years. 

 Another argument against this theory is the sporadic distribution 

 of the diseased plants in a field. 



When the secondary bulbs from susceptible plants start to grow, 

 the young growth is usually infected. The explanation for this is 

 that the plants are not only favorable to the insects, but the latter 

 are present in the bulb between the scales ready to attack the new 

 growth as it appears. The writer has found that the insects pass the 

 winter in this way in bulbs planted out of doors. 



Preventive Measures. From what has been said, it is evident 

 that preventive measures against the lily disease must begin with 

 careful attention to the culture of the bulb in the field and with 

 rigid selection of bulbs for use or sale. Every plant which shows 

 the disease should be dug up and destroyed. Only bulbs of strong, 

 healthy plants should be used for propagating purposes. Scales 

 which are spotted should not be used. A second selection should be 

 made when the plants from the scales are transferred to the field, and 

 all those showing spotted leaves or mite-infested roots or bulbs should 

 be destroyed. A third selection should 'be made in marketing, all 

 badly spotted bulbs and those having decayed bases being destroyed 

 If this rigid selection were practiced by the growers in Bermuda, the 

 quality of the bulbs received in this country would be far superior 

 to what it is at present and the difficulties encountered in forcing 

 would be greatly lessened. 



As yet no treatment has been found which will effectually free 

 infested bulbs without injuring them. In our experiments bulbs 



