136 MASSACHUSETTS HORTICULTURAL SOCIETY 



the meantime, too, the transplanted seedlings are now beginning to 

 show definite symptoms of mosaic, and the trouble is now spread 

 about by the new broods of these plant lice. It becomes therefore 

 obvious that if instead of allowing the potted plants to remain 

 outdoors until they are ready to be taken indoors, they be kept 

 from the very beginning inside in a protected cold house, they will 

 remain free and non-infected. In bringing in clean plants there 

 will be no mosaic to bother us. This is indeed very simple and is 

 the only way as far as is known to control mosaic on indoor sweet 

 peas. 



Mosaic is readily distinguished by a yellow mottling on the 

 leaves, presenting in some instances, a beautiful mosaic structure, 

 hence the name of the disease. This, however, is not the only 

 symptom. Diseased plants exhibit a curling of the leaves, re- 

 sembling the curling induced by the green aphids, but in this case, 

 the plant lice do not curl the sweet pea leaves. Mosaic makes its 

 appearance when the seedlings are from three to four weeks old. 

 Often the trouble is so bad and the curling so pronounced that the 

 plants thus affected cannot make any headway but remain dwarfed 

 and wrinkled and twisted. Occasionally, however, diseased plants 

 grow with the disease keeping pace. In this case, too, the affected 

 host is useless, as far as commercial purposes are concerned, since 

 the blossoms, too, are twisted and they are borne on short crooked 

 peduncles. 



Powdery Mildew, Micros phera aim (Wallr.) Salm. 



The sweet pea mildew was first described by Massee ^ as being 

 prevalent in England. Erysiphc poJygoni was attributed as the 

 cause, both of sweet pea mildew and that of the edible garden pea. 

 In this country, the disease is very prevalent on greenhouse sweet 

 peas, and outdoors during wet seasons. Ordinarily, however, in 

 small garden lots, and especially where the plants do not receive 

 anj^ water, the disease is practically unimportant since the attack 

 is usually very mild during the active season, but becomes some- 



1 Massee, G. Fungoid diseases of the sweet pea. Sweet Pea Annual: 20-21, 190G, 

 England. 



