64 a EXPERBIEXT STATION. [Jan. 



reported. In the spring of 1921 a general epidemic of the 

 disease occurred in the seed-beds of the Connecticut valley, 

 causing widespread concern among tobacco growers. From 

 the seed-beds the disease was carried to the field, where in 

 many instances it spread with alarming rapidity. Xo attempt 

 has been made to estimate the loss from this disease, but 

 fields in which infection of the plants was practically total 

 were not uncommon. X'aturally, the value of such a crop is 

 very greatly reduced, if indeed the grower is able to find a 

 market for it. Although there has been no thorough study of 

 the relation of weather conditions to occurrence and spread of 

 wildfire, it is known that moisture favors its development, and 

 that rain contributes to its dissemination in the field. It 

 therefore seems probable that the abnormally wet weather of 

 April and May was of major importance in the outbreak and 

 development of the disease in seed-beds, and that the frequent 

 showers and high humidity were to a large degree responsible 

 for its spread and development in the field. 



The third disease to appear in epidemic form was the downy 

 mildew of cucumber and melon caused by Pscudoycronospora 

 cubcnsis. This disease is favored by warm, humid and rainy 

 weather occurring after the first of June. It causes no ap- 

 preciable injury in dry summers. The earliest recorded seasonal 

 date of its appearance in Massachusetts is May 1, 1915. In 

 1921 it was first noted early in June, when it appeared on 

 cucumbers both in greenhouses and out of doors. From that 

 time, favored by weather conditions of late June and July, it 

 spread and developed rapidly. The resultant damage to the 

 cucumber crop was very heavy, for following the initial out- 

 break vines were killed and new growth was very generally 

 checked, thus eft'ectively preventing setting and development of 

 new fruit. In a few houses, where Bordeaux mixture was 

 applied under the direction of the department, the disease 

 was held in check and paying crops were harvested. Judging 

 from this year's results it is probable that spraying for cu- 

 cumber mildew under glass will prove profitable in years when 

 the disease appears. As the spraying was in no instance 

 started until after the mildew appeared on the vines, it seems 

 likely that a preventive spray, that is, one applied prior to 



