INJURIOUS TO MINOR VEGETABLE CROPS 257 



Potato aphis : 150 

 Common stalk-borer : 157 

 Garden flea-hopper : 77 

 Army-worm : 288 

 Semi-tropical army-worm : 297 

 Potato flea-beetle : 314 

 Western potato flea-beetle : 318 

 Root-knot nematode : 338 

 Red-spider : 351 



Water-Cress 



Owing to its semi-aquatic habit water-cress is comparatively 

 free from insect attack. In certain localities its most serious 

 enemy is a small crustacean, the water-cress sowbug. 



The water-cress soivbug, Mancasellus brachyurus Harger 



In the eastern United States water-cress is often seriously 

 injured by an aquatic species of sowbug that attacks the sub- 

 merged portions of the plant, cuts off the roots and stems and 

 causes large masses of the cress to float on top of the water. 

 This form differs from the species found in greenhouses by hav- 

 ing longer legs and antennae and being shrimp-like in form 

 when viewed from the side. It is about ^ inch in length and 

 gray in color. It often occurs in immense numbers so as to 

 destroy practically the whole crop. 



Where cress is grown in natural streams or ponds, no prac- 

 tical method of controlling the sowbugs has been devised. 

 Some growers, however, have been able to overcome the dif- 

 ficulty by growing the plants in broad shallow beds sloping to- 

 wards the center, where a trough ten inches square lined with 

 boards extends the whole length of the bed. When the sow- 

 bugs become abundant, the water is shut off for twelve to 

 twenty-four hours allowing the beds to drain. Water is re- 

 tained in the trough, in which the sowbugs soon accumulate in 

 great numbers. They may be destroyed by the addition of 



