1910.] PUBLIC DOCUMENT — No. 31. 163 



CALICO OR MOSAIC DISEASE OF CUCUMBER 



AND MELON. 



BY G. E, STONE. 



For a number of years our atteutiou has been called to mot- 

 tled cucumber leaves occasionally found in greenhouses. This 

 trouble has the same characteristics as the so-called " calico " on 

 tobacco, or " mosaic disease," as it is often termed. It also oc- 

 casionally occurs on other plants. 



A case of calico was noticed on melon plants grown under 

 glass in the department's conservatory the past summer. Only 

 four plants were aifected, and there was no evidence of contagion 

 or infection. This disease, so far as is known, is not associated 

 with pathogenic organisms, and little is known concerning it. 



The trouble is characterized by a mottled or spotted appearance 

 of the foliage, and the' whole plant appears abnormal. The 

 plants were growing in soil well enriched with horse manure, and 

 in all cases the laterals were kept pruned, and the affected 

 plants topped. A similar spotting and mottling occurred on 

 pruned tomato plants, and was more abundant when the plants 

 were topped than when the laterals were pruned. 



A study of this peculiar and little known trouble is now being 

 made by Mr. G. H. Chapman of this department. 



