546 INSECTS AFFECTING VEGETATION 



carried by the wind and other usual agents. No perfect stage has 

 been discovered, but it is probable that the fungus lives over winter 

 in the fields, and the experience of farmers indicates that it is worse 

 on fields repeatedly planted in melons. Rotation of crops is there- 

 fore advisable to lessen its ravages. This disease does not, as a rule, 

 develop in the field as rapidly as the downy mildew, but in warm, 

 humid weather it spreads quickly and does great harm. The ripen- 

 ing of the melons is hastened, their quality greatly injured, and the 

 total crop diminished. 



Anthracnose. This occurs on the leaves and stems of cucum- 

 bers and muskmelons, and on the leaves, stems, and fruits of water- 

 melons. It also attacks other cucurbits. It is common and some- 

 times injurious, but is relatively of less importance than the downy 

 mildew or the leaf-blight. 



Circular dead spots from one-fourth to one-half inch in diame- 

 ter are formed on the leaves. They are distinguishable from the 

 angular spots of the downy mildew, except when the latter have 

 grown very slowly. On the stems anthracnose causes elongated, dis- 

 colored, and shrunken areas, which finally lead to the death of the 

 branch. Watermelon fruits are often badly spotted by this disease, 

 and much injury is done to the vines. 



Anthracnose is due to the fungus Colletotrichum lagenarium, 

 which is related to the fungi causing anthracnose in grapes, rasp- 

 berries, cotton, and beans, and the bitter rot of the apple. It is 

 spread freely by the conidiospores which are produced in abundance 

 in the spots on the leaves and fruit. A perfect form is not known, 

 but the field evidence indicates that the disease persists in the dead 

 vines or elsewhere in old fields, and the destruction of such vines, 

 together with rotation of crops, is recommended as a means of pre- 

 vention. 



Other Leaf-Spot Diseases. The three fungi previously men- 

 tioned are the most common and injurious cucurbit pests, but sev- 

 eral minor troubles occur and cause slight losses, which could be 

 prevented by spraying. They hardly require separate mention in a 

 publication of this character, as it would be difficult for the practical 

 grower to distinguish them. The fungi causing them are Phyllostica 

 cucurbitacearum, Cladosporium cucumerinum, Acremonium sp., and 

 Cercospora citrullina. The powdery mildew of the cucumber, Ery- 

 siphe polygoni, is common in greenhouses, but infrequent outdoors. 

 It forms a powdery white coating on the leaves without causing a 

 spot, and is thus easily distinguished from the downy mildew. 



Other troubles encountered in the field and greenhouse are stig- 

 monose. due to an attack of aphides ; wilt and leaf-curl, due to over- 

 fertilizing, etc., and root-knot, caused by nem-atodes. 



Wilt. There is a form of wilt sometimes met with in green- 

 houses which is due to overfertilizing. Another distinct cucurbit 

 disease is prevalent in the North and West, and is mentioned to avoid 

 confusion with the leaf-blights already described. When a melon, 

 cucumber, or squash vine suddenly wilts throughout its length and 

 dies without appreciable spotting of the leaves the trouble is usually 



