210 Diseases of Greenhouse Crops 



trouble is a Fusarium fungus, of which little is now 

 known. 



Control. Since the Fusarium fungus is a soil in- 

 habiting organism, steam sterilization of the soil at 

 once suggests itself. The seed should always be 

 started on a sterilized soil, and this trouble will be 

 entirely eliminated. Diseased plants should be 

 pulled out and burned, and by no means allowed to 

 find their way into the manure pile. Spraying in 

 this case will be of no value, since the seat of the 

 trouble is confined to the interior of the roots and 

 stems. 



Other Troubles Mistaken for Wilt. An injury in- 

 flicted by the common white grub (Lachnostema) 

 is often mistaken for wilt. The latter feeds on the 

 roots, and the result is a general wilting. When the 

 aflEected plant is pulled up, the grubs will be foimd 

 in the act of feeding. By careful watching, they 

 may be destroyed before serious damage results to 

 the plants. 



Another cause of apparent wilt and stimted 

 growth may be due to the sucking of the root lice. 

 The latter are of a bluish color, and are usually 

 foimd in large number on a single plant. This pest 

 usually is harbored in the soil, especially where as- 

 ters are continually grown in the same beds. Chang- 

 ing the soil or sterilizing it with steam will eflFect a 

 cure. 



In Europe, Fusarium incamatum (Desm.) Sacc. 

 is believed to be the cause of an aster wilt there. 



