36 BULLETIN 727, U. S. DEPARTMENT OF AGRICULTURE. 



To further test the possibility of leaf infection from soil, a large 

 sample of soil was collected from anthracnose centers in field 2 on 

 August 14, 1916, four days after a rain. Under healthy runners 

 in each of eight locations in four plats in field 1, 4 tablespoonfuls of 

 this soil were sprinkled. In an examination of these runners on 

 August 31 infection was found in one case consisting of lesions on six 

 leaves, abundant on three. In this instance the soil inoculum had 

 been sprinkled upon the leaves and then shaken off, while in all 

 the other tests an effort was made not to sprinkle the soil on the 

 leaves. 



These tests prove that the spores of this fungus are abundant 

 in the soil under diseased plants immediately after a rain and are 

 viable even four days later. The common occurrence of anthracnose 

 lesions on the lower side of a watermelon fruit in the field indicates 

 infection from spores in the soil or in drainage water. 



With regard to the spattering of spores upon healthy leaves, two 

 tests were made. Within two hours after a heavy rain, September 5, 

 1916, an undiseased leaf was taken from field 2 near diseased leaves 

 and the blade washed in 200 c. c. of sterile water. From the five 

 dilution plates poured from this wash water, one colony of anthrac- 

 nose was isolated. This indicated, according to the quantity of 

 wash water represented, that there were 96 spores on the leaf lamina. 

 A similar test made with an undiseased seedling within 1 foot of 

 diseased leaves yielded negative results. The isolation of the fungus 

 from an undiseased leaf proves that the spores were present on the 

 leaf surface after a rain. 



During both seasons of 1915 and 1916 anthracnose occurred 

 on plants under cheesecloth cages which eliminated both insects 

 and pickers as agents of dissemination. Since these plants were 

 very evidently not original centers of infection, the entrance of the 

 fungus can be attributed only to water splashing through the cloth 

 or, more likely, washing under the cages. 



Among watermelons in the field, cases have been noted in which 

 the fruit lesions were arranged in vertical rows in such a way as to 

 indicate beyond a doubt drip infection from overhanging diseased 

 leaves. 



ARTIFICIAL WATERING. 



Another line of evidence relative to the local spread of the disease 

 by the spattering of water is furnished by the severity of anthrac- 

 nose as noted among certain of the fields of cucumbers in coldframes 

 at Norfolk, Va., in 1917. Here, daily watering by an overhead sys- 

 tem was practiced, and this may explain in part the advanced 

 development of the disease in these fields as compared with its 

 relative obscurity in other fields of the region. 



