134 Diseases of Greenhouse Crops 



Leaf Curl 



Cause, physiological. 



Symptoms. The trouble is often manifested as a 

 wilting of the edges of the leaves which curl into a 

 spherical fonn. The wilted area soon dies, thus 

 preventing any further development of the affected 

 leaf. As the inner part of the leaf continues to grow 

 and as it is restricted by its outer dead area, it as- 

 sumes a convex form and a contorted margin, so 

 that it curls up and assumes the shape of a ball. 

 In advanced cases the stems, too, curl. The disease 

 was studied by Stone * who believes that the cause 

 of the trouble is overmanuring. Abnormal modifi- 

 cations in the light, soil texture, and moisture condi- 

 tions may frequently induce the same trouble. To 

 prevent this disease the use of excessive manures 

 should be avoided. As far as possible, conditions 

 which favor weak soft growth should be eliminated. 



Malnutrition of Cucumbers 



Cause, physiological. 



Malnutrition generally results fr{Mn an overfer- 

 tilization of the soil. This trouble has been care- 

 fully studied by Haskins t who found it very preva- 

 lent on indoor cucumbers. 



* Stone, G. E., Mass. (Hatch) Agr. Expt Sta., Bui. 87: 3-43, 

 1903. 



t Haskins, H. D^ Mass. Agr. Expt. Sta. Twenty-fifth Ann. Rept.: 

 71-76, 1913. 



