92 



MISC. PUBLICATION 62 6, U. S. DEPT. OF AGRICULTURE 



WATERLILY 

 Watcrlily Aphid 



The waterlily aphid (Rhopalosiphum 

 nymphaeae (L.)), which feeds by suck- 

 ing the plant juices, causes much dam- 

 age to waterlilies. It disfigures and 

 causes decay of the leaves, distorts the 

 flower stems, and discolors the flowers. 

 Other aquatic plants which it attacks 

 are waterplantain, cattail, pondweed, 

 and knotweed. This aphid is brownish, 

 the winged form having a black head 

 and body. It is also known as the red- 

 dish-brown plum aphid, because it is 

 often found feeding in the early spring on 

 the under sides of the leaves or on tender 

 twigs of plum. In June the aphids 

 leave the plum and infest waterlilies and 

 other aquatic plants, on which they live 

 and reproduce during the summer 

 months. In the fall they return to the 

 plum to deposit the overwintering eggs. 



Treatment. — In pools or ponds that 

 contain fish it is safest first to remove 

 the fish and lower the water level to 

 expose as much of the foliage as possi- 

 ble. Then spray the infested plants 

 with either pyrethrum (p. 98) or nico- 

 tine (p. 97). Before returning the fish, 

 allow the water to run for some time so 

 that there will be a complete change of 

 water. 



Where it is not practical to remove 

 the fish, the overflow should be plugged 

 and the pool filled to overflowing. 

 When the water begins to flow over the 

 sides a forcible stream from the garden 

 hose should be played on the infested 

 flowers and foliage. The dislodged 

 aphids will float on the surface and can 

 be washed over the side of the pool to 

 the lawn, where they can be killed by 

 spraying with nicotine sulfate or pyre- 

 thrum. It may be necessary to repeat 

 this treatment once or twice during the 

 summer. Weighting down and com- 

 pletely submerging the plants for some 

 time with a hoop or frame will permit 

 the fish to feed on the aphids. 



Prevention. — Since these insects mi- 

 grate from plum to water plants, infesta- 

 tion on lilies can be prevented by con- 

 trolling them on the plum trees, as soon 

 as their presence is observed in the 

 spring, by spraying with nicotine sulfate 

 or pyrethrum. 



Waterlily or Pondlily Beetle 



Both adults and larvae of the water 

 lily or pondlily beetle (Galerucella nym- 

 phaeae (L.)), feed on the leaves and 

 flowers of the yellow and white pond- 

 lilies and other water plants. Their 



feeding imparts a ragged appearance, 

 and later the leaves turn brown. They 

 are often serious pests in aquatic nur- 

 series and private pools. The beetles 

 (fig. 156) are dark brown, with a dull- 

 yellow thorax, or waist, and are a little 

 over y 4 inch long. The larvae, or grubs, 

 are dark brown or blackish above and 

 yellow underneath. At first the young 

 larvae feed in groups on the upper sur- 

 face of the leaves and flowers. Later 

 they may feed on both surfaces of leaves 

 above water. Two generations occur 

 annually. The second-generation adults 

 overwinter in the dead stems of water 

 plants and other nearby plants as well as 

 under the loose bark of trees and in sim- 

 ilar hiding places. They appear in the 

 spring to lay their yellowish egg clusters 

 on the leaves. 



Figure 156. — Waterlily or pondlily 

 beetle. About 4 times natural size. 



Several species of leaf beetles belong- 

 ing to the genus Donacia also feed on 

 the leaves of waterlilies. These beetles 

 are usually metallic-bluish or brownish 

 and about % inch long. 



Treatment. — No entirely satisfac- 

 tory remedy is known. The plants may 

 be dusted or sprayed with lead arsenate, 

 the spray being applied as a fine mist 

 so as not to submerge the foliage and 

 wash off the poison. If fish are kept in 

 the pool, they should be removed while 

 the treatments are applied, and the 

 water should be changed before the fish 

 are returned. If spraying is impracti- 

 cal, attempt to wash off the insects oc- 

 casionally with a strong stream of water, 

 or submerge the plants for a number of 

 days by weighing them with a hoop. If 

 fish are present, this will enable them to 

 feed on the insects. 



Prevention. — In late fall collect and 

 burn all dead plant stems and debris 

 in and adjacent to the pool, thus de- 

 stroying all beetles that might be hiber- 

 nating in such material. 



