BLIGHTS AND DISEASES 



487 



autumn spraying is imperative to protect the dormant twigs. In 

 spraying for apple and pear scab, the addition of five pounds of 

 lead arsenate to each one hundred gallons of Bordeaux mixture 

 makes the application answer also for the codlin moth, as described 

 in the preceding chapter. 



The lime, salt and sulphur mixture, as already prescribed for 

 scale insects in the preceding chapter, is an active fungicide for 

 winter use. It is a satisfactory curl-leaf preventive when used just 

 before the buds open. 



Toadstool Destruction. Trees are often destroyed through in- 

 vasion by toadstool fungi from the decaying roots or wood with 

 which their roots come in contact. Prof. W. T. Home, who has 

 made a special study of the trouble for several years, provides the 

 following summary : 



The Armillaria root-rot or "oak fungus" is caused by a native fungus which 

 lives in roots of woody plants. Trees and bushes are killed in spots, which 

 enlarge year after year. Affected trees fail gradually from the diseased side 

 or die suddenly in summer. Under the affected bark of roots there is a yel- 

 lowish white fan-shaped mycelium which progresses into live bark. Black 

 shining root-like strings (rhizomorphs) grow out from old rotting roots. 

 The wood decays with a uniform white rot. Large tan-brown toadstools 

 (edible when cooked) arise from old infections in October to February. 

 Surgery as in Crown Gall ("root knot") or Pear Blight can sometimes be 

 practised on roots and crowns of trees not too far gone. Black walnut, 

 French pear, and fig roots are practically immune. Annual fibrous rooted 

 plants are rarely injured. Affected areas in orchard may be isolated by open- 

 ing a trench 3 to 4 feet deep around them. This may be filled immediately 

 if reopened every two years to keep the roots cut off. Nursery should not 

 be planted in infected soil. 



Moss, Lichens, etc., on the Bark. All trees should be assisted 

 to maintain clean, healthy bark. This is accomplished by the use 

 of the lime, salt and sulphur mixture already prescribed for scale 

 insects. It can also be done by winter spraying with caustic soda 

 or potash, one pound to ten gallons of water. Hard hitting with 

 power sprayer is necessary. 



Blights and Decays. There are several blights which are trace- 

 able to bacteria, parasitic growths which are not discernible as 

 are the fungi, and not usually amenable to spray treatment, be- 

 cause they exist wholly within the tissues of the plant and are not 

 reached by applications. The blights of the pear, the black heart 

 of the apricot, the olive tuberculosis, etc., are instances. Cutting 

 back to healthy wood (with tools dipped after each cut in corro- 

 sive sublimate, one part to one thousand parts of water), and burn- 

 ing all removed parts, is the best treatment which can at present 

 be prescribed. 



The walnut blight is caused by a bacterium, and has so far re- 

 sisted treatment. The disease appears on the nuts, generally worst 

 at the blossom end and usually first seen there early in the season ; 

 later the spots run together and encompass considerable areas of 

 the surface, and the nut is transformed into a hateful black mass 

 and is utterly destroyed. The disease also affects the leaves and 



