DISEASES AND PESTS OF PLANTS. 



01 



Fig. 21. The onion-maggot, (a) Adult; (6) larva ; 

 (c) puparium ; (d) anal spiracles, enlarged. (From 

 i. nt. lii-pi., 1909, N.J.) 



THE ONION-MAGGOT (Phorbia ceparum). 



The presence of the onion-maggot 

 is first shown by the plants changing 

 to a yellowish colour and finally 

 wilting. On examination one or 

 more maggots may be found feed- 

 ing in the interior of a plant. This 

 maggot is the larva of a two-winged 

 fly bearing a close resemblance to 

 the house-fly. This insect passes 

 the winter in the pupal stage in the 

 ground. There are several broods 

 each season. 



Control. It is recommended to 

 remove all infested plants found 

 while thinning and burn immedi- 

 ately. Change of land is also recom- 

 mended. 



THE SMALL WHITE CABBAGE-BUTTER- 

 FLY (Pontia rapcc). 

 This insect was imported from 

 Europe and first became conspicu- 

 ous on the North American Conti- 

 nent in 1865. It is now one of our 



most common pests and is responsible for extensive losses to vegetable-growers every 

 year. This insect passes the winter in the chrysalis stage on rubbish in the field, 

 on fence-rails, under the eaves or buildings, or any other convenient place. There 

 are several broods each year which overlap each other, so that all stages of the 

 insect may be found throughout the summer months. These butterflies are familiar 

 objects and are readily recognized by the growers. The caterpillar is the destruc- 

 tive stage and is generally referred to as the green cabbage-worm. 



Control. When the caterpillars are present, dust the plants with a mixture of 

 pyrethrum powder, 1 part to 10 to 15 parts of cheap flour. See that the pyrethrum 

 powder is fresh when purchasing and store in air-tight canisters. 



THE DIAMOND-BACK MOTH (Plutella maculipennis) . 



This insect is an impor- 

 tation from Europe. It 

 attacks the under-side 

 of the leaves of many 

 plants. It has been ob- 

 served during the past 

 two years in unusually 

 large numbers in certain 

 localities in British Colum- 

 bia. The adult is a very 

 small moth, which may 

 be readily noticed when 

 flying in large numbers 

 in a cabbage or turnip 

 field. They remain in 

 close proximity to the 

 plants they attack, and 

 do not apparently in- 

 dulge in extensive flight. 



C 



Fig. 22. Tho diamond-back moth, (a) Larva; (&) segment 

 of same -greatly enlarged; (d) pupa; (e) pupa in cocoon; 

 (f) adult moth; (g) wings of dark variety; (h) moth with 

 wings folded. (After Riley, U.S. Dcpt. Agr.) 



There are several broods each year. 



