﻿STRAWBEKBY ROOTWORM ON" GRJIENHOUSE ROSES 45 



Observations have shown that plants retained in beds for three 

 years or longer are usually the more heavily infested. By removing 

 the plants and soil at the end of three years at the latest, the chances 

 of severe infestation are very much reduced. A rotation should be 

 planned and followed whereby the plants in no section will remain 

 in the beds longer than three years. For example : If a range of sev- 

 eral houses is divided into three separate sections — A, B, and C — all 

 of the plants in section A should be completely torn out and re- 

 planted the first season, all those in section B the next season, and 

 those in section C the third season. In this way the 3-year-old plants 

 in section A would be replaced the fourth season, and so on. Several 

 florists are now of the opinion that forcing their plants as much as 

 possible for three years, instead of retaining them for a longer 

 period, increases their production and more than compensates for 

 any extra expense due to the more frequent replanting. 



SUMMARY 



Within the last seven years two varieties of the strawberry root- 

 worm, Paria cam,ella — quadrinotata and gilvipes — ^have appeared in 

 greenhouses in the commercial rose-growing districts east of the 

 Rocky Mountains and have done great injury to the rose plants. 

 Although normally an outdoor pest on strawberry, raspberry, and a 

 number of miscellaneous plants, this insect has become one of the 

 serious enemies of roses grown under glass. 



The plants are injured by the larvae and adults. The larvae feed 

 on the roots and the adults eat foliage, stems, buds, and flowers. 



The overwintering adults appear in February and lay eggs during 

 a period of two or three months. The larvae from these eggs feed on 

 the roots for a period of from 33 to 74 days, after which they trans- 

 form to pupae. The adult beetles emerge from 8 to 17 days later. 

 Because of the long period of egg-laying, the emergence of the adults 

 during June and July is almost continuous. From the eggs which 

 are laid by these beetles a second brood of adults develops and 

 emerges during September and October. The two generations over- 

 lap to ^uch an extent that oftentimes no distinctions can be noted. 



Natural enemies of the strawberry leaf beetle are apparently few 

 in the greenhouse, as no parasites have been observed attacking any 

 of the stages. Among the predators may be mentioned carabid 

 beetles, spiders, and toads. IJropod mites frequently attach them- 

 selves to adults. 



Early experiments established the fact that the usual measures 

 recommended for leaf-eating insects were practially useless in con- 

 trolling the strawberry rootworm. Spraying with the arsenicals 

 did not prove practical under ordinary conditions, but was found to 

 be successful in protecting the swelling and breaking buds at 

 the time the plants were cut back. Under similar conditions a 

 Bordeaux-arsenate of lead mixture served as a repellent. In exten- 

 sive trials the use of a 10 or 1.5 per cent dry mixture of arsenate of 

 lead or calcium arsenate and superfine sulphur showed that dusting 

 with these materials was a satisfactory and effective method of keep- 

 ing the foliage coated with an arsenical to repel the beetles. Experi- 

 ments with Paris green gave unsatisfactory results. In 21 commer- 

 cial houses fumigation with hydrocyanic-acid gas during the resting 



