i82 Diseases of Greenhouse Crops 



Such plants when examined are found to have hol- 

 low stems and seem too weak to stand up. 



Cause. There are several causes, any one or all 

 of which may lead up to hollow stem. ( i ) A highly 

 nitrogenous fertilizer applied to the seed bed to force 

 the seedlings. (2) An abundance of water supply 

 to make the fertilizer quickly available. (3) Sow- 

 ing seeds of a rapid growing variety. (4) Trans- 

 planting without hardening off. (5) Transplanting 

 into a dry soil. 



Control, It is evident from what has been said 

 that the fertilizer in the seed bed should be well 

 balanced. Care should be taken to prevent the seed- 

 lings from becoming leggy, and to see that they are 

 properly hardened before transplanting. The Stone 

 and its related varieties seem to be more resistant 

 to hollow stem. On the other hand, the Dwarf 

 Champion seems to be especially susceptible to hol- 

 low stem. 



Winter Blight 

 Cause, unknown. 



Symptoms, This disease seems to be very preva- 

 lent on forced tomatoes in the United States and 

 Canada. Howitt and Stone,"^ who have recently 

 studied this disease, describe it as follows: The 

 leaves show distinct brown or blackened, angular, 

 diamond-shaped spots scattered between the larger 

 veins. When the spots are numerous and close to- 

 gether they appear as a distinct pattern. In a more 



♦Howitt, J. E., and Stone, R. E., Phytopath. 6: 161-166, 1916, 



