1026 DISEASES AND INSECTS 



DISEASES AND INSECTS 



1286. Grapes ruined by black-rot. 



1. Exclusion measures are directed toward keeping 

 disease organisms, usually insects, fungi and bacteria, 

 out of areas, regions or countries in which they do not 

 occur. This is commonly attempted by the passing of 

 laws forbidding the importation of plants affected with 



such parasites. As 

 means of enfor- 

 cing such regula- 

 tions, some sort of 

 inspection, either 

 at port of entry or 

 at point of destina- 

 tion, is provided. 

 Inspection in the 

 country from 

 which they are 

 exported is also 

 often required. 

 Absolute quaran- 

 tine against all 

 importation of 

 certain plants 

 from those coun- 

 tries in which dan- 

 gerous diseases 

 are known to 

 occur is also being 

 practised in some 

 countries, as, for 

 example, prohibit- 

 ing the importation of potatoes into the United States 

 from those countries in which the black-scab is now 

 known to occur. Exclusion measures, often undertaken 

 when it is too late, are at best under present conditions 

 of doubtful efficiency. Those interested in these methods 

 of control should consult the various pest and disease 

 acts of the different countries of the world. See In- 

 spection, in Vol. III. 



2. Eradication. On the principle of eradication are 

 based those measures which are 



directed to the elimination of patho- 

 gens already established. While 

 absolute eradication is seldom to 

 be effected, the pathogen may often 

 be eliminated to such an extent as 

 to reduce losses therefrom to a prof- 

 itable minimum. In Denmark, the 

 destruction of all barberry bushes, 

 the alternate host of the grain-rust 

 fungus, Puccinia graminis, has 

 decidedly reduced the severity of 

 this disease in recent years. The 

 careful eradication of all diseased 

 plants is often quite effective even 

 in a small area, like a raspberry or 

 blackberry plantation suffering 

 from the red rust. Here the myce- 

 lium of the pathogen lives from 

 year to year in the roots of diseased 

 plants, which each spring send up 

 diseased shoots. On the under side % lAIJfc 1,'H 

 of the leaves of these shoots, the 

 orange-red spores are produced in 

 great abundance, and serve to 

 spread the pathogen to healthy 

 plants. As diseased plants are 

 readily detected in early spring by 

 the pale clustered shoots, they may 

 be removed before spores appear 

 and the pathogen thus eradicated. 

 The black-knot of plums and cher- 

 ries is most readily and profitably 

 controlled in a similar manner, the 

 knot-affected limbs and twigs being 

 cut out and burned early in the 

 spring before spores appear. The 1287. Smut of oats. 



fire-blight of pears is to be controlled only by system- 

 atic eradication, first of all cankers in autumn or early 

 spring, then of all blossom blight as fast as it appears 

 and later of the affected twigs when twig-blight comes 

 on. To be effective, the trees must be inspected two 

 or three times each week throughout the growing 

 season and all diseased parts removed at once as soon 

 as discovered. 



Another method of eradication especially applicable 

 to seeds, tubers or bulbs, on which spores of the patho- 

 gen pass the dormant period, is disinfection. This is 

 accomplished by the application of chemical poisons, 

 either in solution, as powder or as gas, at a strength 

 and for a period of time sufficient to destroy the 

 pathogen without injury to the host. When the patho- 

 gen lives over as mycelium in the seed or tuber, the 

 application of heat is sometimes effective. Formalde- 

 hyde, as a gas or in solution in water, is now generally 

 employed for the eradication of the smut of oats, the 

 stinking smut of wheat and the potato-scab. (For details 

 of method, see Formaldehyde, p. 1028). The spraying 

 of peach trees with 

 copp er-sulf ate 

 solution, lime-sul- 

 fur solution or 

 bordeaux, just be- 

 fore the buds start 

 in the spring, dis- 

 infects the trees by 

 destroying the 

 spores of the leaf- 

 curl fungus which 

 pass the winter on 

 the buds. 



Pathogens which 

 attack the under- 

 ground parts of 

 plants may some- 

 times be eradicated 

 by disinfection of 

 the soil before 

 planting. Drench- 

 ing the soil with a 

 formaldehyde solu- 

 tion of a strength 

 sufficient to distrib- 

 ute one gallon of 

 the strong 40 per 

 cent solution to 

 each 100 square feet 

 of surface, wetting 

 the soil to a depth 

 of 6 to 8 inches, has 

 been found to be 1288 ' Loose smut of barley " 



very effective against damping-off, root-rot and simi- 

 lar diseases in forest tree seed-beds, ginseng seed-beds 

 and in the benches in greenhouses. It is also often 

 effective in the eradication of nematodes in green- 

 houses. Steaming of the soil is also very effective, 

 destroying insects and weed seeds as well as pathogenic 

 fungi. It is not always conveniently applied. 



3. Protection measures are to be employed in those 

 regions in which the pathogen is very generally and 

 very thoroughly established, or in which for one reason 

 or another eradication is impossible or unprofitable. 

 They aim to protect the crop against attacks of the 

 parasite by means of some external barrier. Spraying is 

 the most commonly employed protective measure. In 

 spraying, the susceptible surfaces of the plant are coated 

 with some slowly soluble poison, known as a fungicide. 

 Fungicides are of various types. They are applied in 

 suspension in water, in solution or dry, i.e., in the form 

 of a fine impalpable powder. The fungicide most 

 generally applied in liquid spraying is bordeaux, a 

 colloidal compound formed by the union of lime-milk 

 and copper-sulfate solution. Minute blue gelatinous 



