200 Diseases of Greenhouse Crops 



as P. amaranthi^ which attacks the pigweed, Amaran- 

 thus retroflexus. 



Control. It is probable that spraying with a 

 standard fungicide will control the trouble. 



Root Rot 



Caused by Rhizoctonia solani Kuhn. 



This form of injury is commonly met with in 

 propagating benches of Alternanthera. The young 

 cuttings often rot off before setting roots. On well 

 established plants, the Rhizoctonia fungus is found 

 as strands on the sides of the branches which touch 

 the ground. In this case there is apparently no in- 

 jury. It seems that the reddish varieties of Alter- 

 nanthera is covered with more Rhizoctonia strands 

 than are the green or the variegated varieties. For 

 a description of the causal organism and methods 

 of control, see p. 20. 



Antirrhinum {Antirrhinum Majus), 



Cultural Co7 iderations. Antirrhinums have be- 

 come important plants, forced primarily as cut 

 flowers. The plants require a light sandy loam com- 

 post. In filling the benches, we must avoid fresh 

 and undecomposed manure. It is necessary also to 

 avoid the excessive use of nitrogen. Where this is 

 overlooked, the flowers will have a tendency to 

 "sport" and possess too much yellow color, which is 

 objectionable to the trade. Some growers prefer to 



