BLACK SPOT IN FRUIT.

Press, Volume LXI, Issue 18408, 15 June 1925, Page 13

BLACK SPOT IN FRUIT.

TO THX EDITOR OP ."HI MXSB.™ Sir, —I think the worst disease the fruitgrower has to contend against in this part of the Dominion is ' black spot. The writer has collected a large amount of information on the subject of apple scab (or black spot), as _wo call it. Dr. Curtis, of Cawthron, Nelson, states that the infection in' the spring is due to the disease being carried over during the winter by■ the fallen leaves: Professor WhetnalL. of Xcw York State College of Agriculture, says rmich the same. But these two authorities disagree about it oh many points. I have just received sectional volume No. 1. 1924, from the Minister of Agriculture, No. 10 Whitehall, London.- The following; is copied from the volume: "On the wood—for many years the manner iu which the scab futigus lived through the winter in this country was not fully understood. The matter has, however, been carefully investigated at Wye College, and it" has been clearly established that the fungus passes the winter in a dormant condition ou the young wood of many varieties of apples and pears. These diseased shoots are perhaps the main source of the initial infections the following season. Affected wood is readily distinguished by its rough, blistered appearance, due to the formation of numerous small eushion-liko growths of myoelium just beneath the bark. These cushions,, remain dormant during the winter. As soon as the spring arrives they Tecomrconce growth, and finally liberate thousands of spores which infect the young leaves and thus start afresh the' life cycle of tho fungus." The infected wood varies considerably •in appearance with the variety of apple 3 or pears, the blister being large or small, scattered as. iu Cox's Orange Pippin, or crowded together as is the caso with Lord Suffield. So far as is possible this scabinfected wood should be cut out when pruning the trees in winter. Quite recently, however, the fructifications have been rediscovered and identified Uy the plant'pathologist of Wye College. They . were found in large numbers on ialleh leaves of applo and pear which had not decayed during the winter. If the development of these winter fructifications should prove to be no uncommon thing in this country, it is clear that if is an important source of early spring infection, in addition to .that connectod with the disease described above. . Measures of control.—These consist of cutting out infected wood and spraying. The pruning should be.'finished before, spring, and.':if' done carofully this source of infection will be, reduced to a. minimum. The sprays used aro much the same as tlioso used horc— Bordeaux and lime-sulphur. The writer discovered the' disease on the. pear trees about nino years ago. For two years previously I'had cleared'every leaf from under the pear. trees, and kept the ground absolutely clean, but the fruit was infected with black spot, as bad'as ever. I-then examined the young, shoots with- a good glass, and found the wood infected. I then cut every shoot off and with the ordinary spraying recommended- f or. pears, the crop was clean.- Every year I cut off all diseased shoots,- but I'leave the leaves where'they fall, and I have very little spot on the fruit. If the readers vof these notes will examine their. Delicious apple trees, I-have no doubt they, will find the .diseased wood, not only on the last year's shoots,.-but on old" wood. The same thing applies to other .apple 'trees that are subject to' black spot.—Yours, etc.. ' " ' GEOKGE. LEE. June 11th,. 1925... -