BACTERIAL WILT OF CUCURBITS. I 



counted. These figures were in each case multiplied by 10 to give 

 the assumed actual number of beetles in the whole field at each date, 

 and these totals were used in plotting the curves. Obviously it 

 would be impossible to make these figures absolutely accurate, but 

 the counts were carefully made, always by the same person, and were 

 checked up by general observations over the field; and there is no 

 doubt that the figures are comparable for purposes of plotting the 

 curve. 



In the case of the wilt records, each plant showing wilt was marked 

 by a stake dated when the disease was first observed, and careful 

 records were- kept by row, hill, and plant, so that a wilted plant was 

 counted once and only once. These records were as accurate as it 

 was possible to make them. 



During the summer of 1917, similar careful records were kept in the 

 experimental field near Tuxedo, Md. The cucumber and cantaloupe 

 spray blocks and the cucurbit variety block were all contained in one 

 rectangular field of 1^- acres, and the beetle and wilt records cover this 

 field as a whole. In the graphs (fig. 4) made from these figures the 

 wilt is expressed in actual number of new cases at each date of obser- 

 vation, and the beetle prevalence is given in percentages, 100 per cent 

 representing the maximum number of beetles for each brood. 



Similar records also were kept (1916) of beetle and wilt prevalence 

 in two experimental fields at Giesboro Point, D. C. (fig. 5; XI, XVI), 

 with records over a part of the season in several other fields in the same 

 locality; and records for two other fields at East Marion, Long Island, 

 were made. 



A detailed discussion of the beetle and wilt records follows: 



In Fields I and II (figs. 1 and 2), East Marion, 1915, the striped-beetle curve snows 

 that the maximum covers several days during the last of June and first of July, while 

 the maxima of the corresponding wilt curves cover the last few days of July, almost 

 one month later. In Field III , though planted only three days after Field I, the striped 

 beetles were much later in appearing. Here the maximum of the beetle curve is about 

 the first of August and the maximum of the wilt curve the last few days of August, 

 almost a month later. Fields I and III were less than a quarter of a mile apart; in 

 fact, both were a portion of one larger field, so that the meteorological conditions were 

 similar, yet the wilt curves in the two cases were approximately a month apart. In 

 Fields I and II the maxima of the wilt curves came just before the greatest rainfall of 

 the season, while in Field III the reverse was true. No definite relation between the 

 wilt and the temperature or rainfall could be detected in any case. Thus in these 

 three fields wilt prevalence bore a clear and definite relation to striped-beetle preva- 

 lence rather than to weather or to time of planting. 



At East Marion (L. I.), N. Y., in 1916 (figs. 1 and 3) the maximum of the striped- 

 beetle curve for the first brood occurred about June 26, while for the corresponding 

 Fields, II and Ila, the wilt-curve maximum occurred, respectively, around July 27 

 and 29, about one month later. As shown in the graph, downy mildew (Pseudo- 

 peronospora cubensis) appeared early in August and during the rest of the month, 

 while the summer brood of striped beetles was making its appearance, gradually 

 destroyed the vines in our experimental fields. No evidence of another brood was 



