BLIGHT AND LEAF-SPOT OF CARROT 277 



of the several dates was obtained. In the absence of a severe infection oi 

 blight, the weiglits of the roots were affected more by the length of the grow- 

 ing period. The best carrots, considering both size and quality, were those 

 planted May 22. When both the optimum length of the growing period and 

 the relation of age of leaves to susceptibility to blight are taken into consid- 

 eration, it is probable that, for the late crop, carrots sowed about the last of 

 Ma^■ or first of June in Massachusetts will do best. 



Relation of Fertilizers to Blight 



This experiment was undertaken with the object of learnmg whether or not 

 increasing the amount of nitrogenous or other fertilizer results in an increasvj 

 in yield of carrots by stimulating blighting plants to the growth of new, and 

 consequently resistant, foliage. 



A complete fertilizer, of a 5-8-7 formula, was applied to all plots (0.01 acre 

 in area and in duplicate) at the rate of 1000 pounds per acre before seed 

 was sowed. Other fertilizers, in the amounts per acre named below, were 

 applied as side dressings when the tops were about five inches higji. 



Blight was only mild and there were no visible differences in growth of 

 tops or in degree of blight infection in the several plots. 



The carrots were harvested and weighed at the end of the season. Tlie 

 yields per unit area, expressed as relative numliers, with 100 as an index of 

 the yield on plots which received no side dressings of additional fertilizer, 

 were as follows: with 275 pounds nitrate of soda, yield 106; with 500 pounds 

 acid phosphate, yield 102; with 140 pounds sulfate of potash, yield, 96. 



The differences in yields are too small to be significant. In the absence of 

 sufficient blight for the original purpose of the experiment, the effect of the 

 disease on yield was not influenced by the fertilizers. 



Control Measures 



Since these fungi pass the winter in and on the soil in the refuse of the 

 preceding crop, the possibility of partial control by crop rotation and by 

 deeply plowing under or destroying the blighted tops after harvest is sug- 

 gested. 



Wild carrots should not l)e allowed to l)ec()nie conimoii near fields wlu-re 

 carrots are to be grown, for the fungi wliicli cause lilight and leaf-spot are 

 ])resent on these weeds. 



Tliere is no reason to disinfect carrot seeds to i)revent these diseases. 



Carrots planted as late as will permit them to reach marketal)le nuiturity 

 are not likely to be affected by blight as se^ erely as carrots j)lanted earlier. 



These diseases have not often been se\ere euougii in Massachusetts to make 

 the use of fungicides profitable. It is not recommended that carrot growers 

 here make a general practice of spraying or dusting carrots. If there is con- 

 tinued rainy weather and the grower desires to spray for the protection of 

 carrots, he should use Bordeaux mixtures of the usual fornmla or dust witli 

 a standard copper-lime dust such as is used on celery, beginning about Aug- 

 ust 15 and making applications at such intervals as are necessarj- to replace 

 the material which has been washed off tlie older leaves. 



