20 



The Cucumber Leaf . Blotch. 



[APRIL, 



Leaves and stems of the treated plant showed no copper 

 on examination in the laboratory. 



The second crop was watered with copper sulphate solution 

 as before, and early in September, when the growth was about 

 five feet high, the leaves on half the plants in each house 

 were also sprayed with cupram (see Joiirnal of the Board of 

 Agriculture, Vol. XI., 1904, p. 287), 1 oz. of copper carbonate 

 dissolved in ammonia and diluted to 10 gallons of water. 



The leaves showed in a few days some signs of injury, and 

 were more attacked by Cercospora than the un sprayed leaves, 

 so that the other plants in each house were treated with the 

 same mixture at half the strength, a few plants in each case 

 being left as checks. Although the treatment was renewed 

 twice a week until the fruit began to form, and although the 

 copper sulphate solution was being applied to the root at 

 the same time, there was little gain from the treatment ; 

 as before, one cutting of cucumbers was marketed and then 

 the whole plant collapsed. 



. There seems but little hope from copper treatment in any 

 form ; in this case it had a very careful and thorough trial upon 

 a large scale, yet the disease ran its usual course. The houses 

 under experiment are six in number, of the ordinary type, 

 about 180 ft. long, lying side by side on a gentle slope in the 

 Lea Valley. As usual, the spots were first seen on the foliage 

 near the ventilators ; they were always more numerous on the 

 sunny side of the houses ; and the disease was at its worst in 

 the upper houses, which are also the warmest, since they are 

 all connected under the gutters. 



The eradication of this disease offers an exceedingly difficult 

 problem ; the cucumbers are grown in a very forcing soil, 

 consisting of nearly half farmyard manure ; the temperature 

 is high and the humidity great. In consequence, the leaves are 

 soft in the extreme and nearly always have the damp surface 

 which affords an excellent germinating ground for fungus spores. 

 There seems little doubt but that the spores blow in from outside, 

 arising from the aebris of previous crops and material returned 

 from market, &c. Some places are still free from disease, but 

 it also occurs in ranges of glass houses that are isolated and 

 not within two or three miles of any other cucumber grower ; in 



