548 INSECTS AFFECTING VEGETATION 



of wilt, sometimes met with in greenhouses, which is due to over- 

 fertilizing. (S. C. E. S. B. 116.) 



GOURD DISEASES. 



Anthracnose, Downy Mildew, Etc. Gourds are susceptible to 

 the same fungous diseases as the cucumber. The two most conspicu- 

 ous are anthracnose and downy mildew. The anthracnose, espe- 

 cially, causes spotting and discoloration on the gourds. This may 

 be arrested if, when the gourds are gathered, they are subjected to 

 treatment with scalding water; otherwise the development of the 

 fungus continues while the disfiguring increases. Meld treatment 

 in this case is the same as recommended for like diseases of the cu- 

 cumber. (Col. E. S. B. 218.) 



LETTUCE DISEASES. 



Anthracnose or Leaf Perforation. It shows upon the lettuce 

 plants as dying of spots in the leaves which break free and drop out. 

 The fungus also produces lesions in the midrib of the leaf. In cases 

 of young leaves the attacks of the fungus causes distortion of the 

 leaf, especially toward the top. Apparently very few plants recover 

 after being once attacked, although one may reasonably keep down 

 this disease in the seed beds and young plants by the use of Bor- 

 deaux mixture. For houses once seriously infested, thorough fumi- 

 gation and soil treatment would probably be profitable. It is not 

 generally distributed. 



Downy Mildew. This is the w r ork of another fungus which be- 

 longs to the same class as the downy mildew of the cucumber. It 

 forms yellow spots in the upper leaf surface which appear below as 

 whitened, downy covered areas. Like the downy mildew of cucum- 

 bers this one may spread very rapidly under favorable conditions, 

 such as warmth and surface watering in the greenhouse. Keeping 

 water from the foliage by sub-irrigation of the beds has been found 

 very beneficial. Gathering and burning the diseased leaves or plants 

 will usually repay the labor. Particular attention to heat and mois- 

 ture will usually render spraying unnecessary and it is certainly in- 

 advisable except to eliminate the fungus from the house. Avoid too 

 high temperature or too much moisture on plants. 



Rosette or Rhizoctonia. This is a very troublesome disease of 

 greenhouse lettuce which arises from the accumulation of the sterile 

 fungus (Rhizoctonia sp.) in heavily manured soils used for continu- 

 ous greenhouse culture. Upon the young seedlings the Rosette fun- 

 gus produces stem lesions and rotting off or damping off of the plants 

 or with larger plants which are later attacked upon the branch roots 

 or. rootlets, the restricted root development prevents growth of the 

 plant axis and gives a basal development of normal leaves with a 

 rosette-shortened center of leaves. Where serious, the crop is short- 

 ened very much and the loss of stand on smaller plants is frequently 

 very heavy. Good results in prevention have been obtained, both 

 from steaming and from formalin drench as per directions in seed 

 and soil treatments. The fungus also attacks the succeeding crops 

 of tomatoes, cucumbers, etc. Attention must in all cases first be given 



