SPOT DISEASE OF THE VIOLET. 



491 



SPOT DISEASE OF THE VIOLET. 



Condensed by Dr. Cooke from a Memoir by P. H. Dorsett, U.S. Depart- 

 ment of Agricitlture, Bulletin No. 23, Washington, November 1900, 

 with 7 plates. 



This memoir declares this disease to be one of the most widespread 

 and destructive maladies known to attack the Violet. The cultivation 

 has been abandoned in many districts of the country on account of its 

 ravages. Five or six years ago 50,000 to 75,000 square feet of glass near 

 Alexandria, Va., were devoted to the cultivation of the Violet, and now 

 on account of the disease the industry has been practically abandoned. 



This spot disease {Alternaria Violce, G. Sz D.) will attack the plants 

 at any stage of growth. Plants making a vigorous but soft and succu- 

 lent growth are most subject to this disease. It may occur on any 

 portion of the plant aboveground, but causes most damage on the leaves. 

 Its first appearance is made by small circular, yellowish-white spots on 

 the leaves, from a size scarcely perceptible to the naked eye to T^'^nd of 

 an inch diameter, surrounded by a narrow rim of discoloured tissue. 

 Sometimes these spots spread until they occupy the entire leaf. More 

 frequently the leaf is attacked at a number of different points, which 

 may coalesce. The majority of the spots are usually free from fungus 

 spores, but spores are produced in abundance after the leaves have been 

 kept in a saturated atmosphere for from twenty-four to forty-eight hours. 

 The spores are borne in chains, on darkish brown threads, which rise 

 from the diseased surface. They break away from their attachment and 

 separate easily, so that they can be carried by currents of air and trans- 

 ported to healthy leaves. These spores, or conidia, are club-shaped or 

 Hask-shaped, divided by transverse, as well as vertical septa, so as to be 

 muriform, 40 to 60 mm. by 10 to 17 mm., somewhat olive in colour. 



Details are given of a number of experiments made by inoculating 

 healthy plants with these fungus spores, and thereby producing the 

 disease. 



It is declared that at present no eftective remedy for this disease 

 has been found, when it has gained a foothold. The usual sprayings 

 with fungicides have produced little or no effect. The only suggestions 

 made are in favour of prevention rather than cure by giving careful 

 attention to the production of vigorous, healthy plants, in preference to 

 any attempt to check the trouble after it has once gained a hold. 



Endeavour to secure plants of ideal development. Grow the plants 

 under conditions necessary for producing vigorous, healthy growth, and 

 protected from conditions likely to induce disease. Keep the houses or 

 frames clean, sweet, and devoid of all rubbish likely to harbour vermin 

 or disease. Propagate only from healthy, vigorous stock at the most 

 favourable season. Select each spring none but perfectly healthy, 

 vigorous plants, from the rooted cuttings, for planting in the houses or 

 frames. Old plants are sometimes carried over, but they are not so 

 reliable as the young plants, and much more liable to all kinds of 



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