276 MASS. EXPERIMENT STATION BULLETIN 245 



mixture 4-1-50 or dusting with a standard copper-lime dust, by the schedule 

 of applications used in the previous years, did not result in any increases in 

 yield over the yield on plots not sprayed or dusted. 



According to Chupp (2), some of the growers on Long Island have prac- 

 ticed spraying carrots with Bordeaux mixture for the control of l)light, evi- 

 dently with satisfactory results. 



On the basis of the results of the exjieriments and observations of tlie 

 writers, however, spraying carrots with Bordeaux mixture is not likely to he 

 profitable in Massachusetts except in tlie very worst years of blight. Since 

 they cannot be predicted, and since tiie loss cau.sed l)y l)light and leaf-sj)ot 

 in the average season is not suflicientl}^ gre;it here to warrant nmch extra 

 expense for control measures, the writers do not recommend that carrots he 

 sprayed every year. 



In a rainy season when the indications are that blight and leaf-spot will 

 he severe, the use of a fungicide should be })rofi table. Since only the older 

 leaves of carrot are susceptible to blight, fungicidal protection of the new 

 growth is less important than in the case of most crops which are sprayed. 

 The application of Bordeaux mixture, on the nuiin crop sown early in June, 

 need not begin before the first week in August in Massachusetts, and later 

 applications need be made only often enough to replace the copper which is 

 lost by weathering, which means usually at intervals of ten days or two weeks. 

 For carrots sown early in May, treatments should begin early in July. 



A horse-drawn sprayer naturally cannot be used in such a closely planted 

 crop as carrots. A small compressed-air spraj-er lacks in both capacity and 

 pressure. There have recently become available several tyjies of power spray- 

 ers designed for or adapted to use on closely planted crops such as carrots. 

 In the absence of such equipment, a hand duster seems to be the onlj"^ feasible 

 alternative, although the effectiveness of a copper-lime dust for the protection 

 of carrots against l)]ight in years when the disease is severe has not lieen 

 determined. 



Effect of Time of Planting 



Because of the relation which was discovered between the age of carrot 

 leaves and their susceptibility to l)light, a field experiment was conducted in 

 1925 with the object of determining the relation of date of planting to the 

 time of the first appearance of blight. This happened to be a season of Init 

 little blight. 



Carrots were sowed April 17, May 5, May 22, and June 11. All were 

 harvested October 15 and 16. 



During August, the blight was more conspicuous on the early sowed carrots, 

 those sowed April 17 and May 5, then on those sowed later. The develop- 

 ment of the disease was clearly associated with the approaching maturity of 

 the carrots. A few weeks before harvest, however, blight, although mild, was 

 uniformly present in all plots. Delay in planting postponed the date of the 

 first appearance of blight, but, when measured by the stage of growth of 

 the carrots, the time of onset of the disease was practically the same in ad 

 plots. 



The disease appeared relatively late in the growth of each plot of carrots, 

 when the roots were already well grown, and no measurable reduction in 

 yield resulted from blight. 



At harvest time, the average weight per root of the carrots sown on each 



