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FIG. 38—TUBERS WITH AND WITHOUT SCAB Centre one free from disease. The one on the left shows second growth also. (See pages 85, 118.) to tue disease. Scabby seed will inoculate clean land. Scabby potatoes cannot be sold. If used as fertilizer, even after steaming for twenty minutes' or being exposed to the weather all winter, they will inoculate the land they are spread on.
Exposing tubers to sunlight for four weeks before planting reduces the percentage of scab and hastens growth.
Scab can live in the soil at least six years without a known host. Beets, mangolds, turnips, and rutabagas are subject to the same disease; hence in the rotation these crops should be avoided, if possible.
Varieties vary in their susceptibility to scab,' the thicker skinned varieties being reported as most resistant.
It seems to be useless to treat scabby seed if they are to be planted on scab-infested land.”
Plowing under green rye does not diminish scab, as has been stated."
Applying sulphur in the rows at the rate of 300 pounds per acre and more has been tried extensively, but is not recommended as a practice, as it is of little use on infested land.
Diseases in Storage.-WET ROT has several causes.
1. Blight or Rot (Phytophthora infestans). The tissues of the tuber become soft either partially or wholly, the skin shrinks, and the layer under it becomes pasty. Potatoes from light soils appear to be
IN. J. Report, 1899, pp. 344-345. ? N. J. Report, 1899, p. 329; 1900, p. 417. * (N. Y.) Geneva Bul. 138, p. 631. • (N. Y.) Geneva Bul, 138, p. 629. N. J. Report, 1900, p. 417.
less subject to it than those from heavy soils, and the disease spreads most rapidly in a damp, warm, and close cellar.
2. Due to bacteria.' The tubers may be wholly or partially soft, and exhale a disagreeable odor. Butyric acid may be liberated and the destruction of the tubers is slow. Contact with other potatoes should be avoided.
If to be used for seed, in some cases depending on the cause, soaking, the tubers in formalin before planting is beneficial.
Dry Rot may be the evidence of the presence of one or more of several troubles."
1. Stem rot,» bundle blackening, dry end rot, is believed to be due to a fungus (Fusarium oxysporum); the leaves curl, and the foliage wilts and dies. The tubers show brown or blackened bundles at the stem end under an apparently sound skin. The disease spreads rapidly in storage, especially if the rooms are warm. Some investigators advise that diseased tubers should not be fed to stock, thrown on the manure-pile, or planted, and that all such potatoes should be destroyed at harvest-time or as soon as discovered. No remedy is known.
2. Due to bacteria. The tubers may be free from odor, moderately firm, but more or less soft in spots, showing in places a loose skin, which yields to the finger, and under which are white, gray, or brownish blotches. Soaking unaffected tubers in formalin before planting is suggested.
1 Ill. Bul. 40, p. 140.
2 111. Bul. 40, p. 139. Tex. Bul. 42, p. 926. 3 U. S. D. A. Bureau of Plant Industry Bul. 55. (N. Y.) Geneva Bul. 101, pp. 83, 84; Bul. 138, pp. 632, 634.
4. Insects.—THE FLEA-BEETLE (Crepidodera (Epitrix) cucumeris) (Fig. 39).—These small insects often
cause more loss than the potato beetles. They perforate the leaves (Fig. 40) during a critical
FIG. 39 — THE CUCUMBER FLEA-BEETLE (Crepidodera (Epitrix) cucumeris)
(After Chittenden) Highly magnified. The insect. is barely one-eighth inch long.. The damage done by this in- . sect is considerably under
period of the plant's
FIG. 40-LEAFLET OF POTATO, SHOW. spores of both early ing OVER A HUNDRED HOLES MADE and late blight for
BY FLEA-BEETLES entrance into the leaf. The ease with which this damage might be
overlooked is evident. These holes make Arsenical poisoning is suitable avenues for the entrance of spores usually first noticed of disease, and pave the way for the rapid
destruction of the plant. on the margins of these holes. At no time in their life history can these insects be readily destroyed. They dislike Bordeaux mixture; hence, the only known means of reducing their ravages is to spray the plants with this material.
NUMBER OF FLEA-BEETLE PUNCTURES IN 50 LEAFLETS FROM
12 ADJACENT rows 1
Punctures Row 1.-Sprayed with very weak Bordeaux mixture : 1,794 Row 2.-Sprayed with very weak Bordeaux mixture and soap . . . . . . . . .
1,071 Row 3. —Not Sprayed . . . . . . . . . . . . 2,511 Row 4.-Sprayed with strong Bordeaux mixture . . 1,194 Row 5.-Sprayed with strong Bordeaux mixture and
soap . . . . . . . . . . . . . . . . . 1,090 Row 6.-Sprayed with weak Bordeaux mixture . . . 1,29 Row 7.-Sprayed with weak Bordeaux mixture and soap 901 Row 8.-Not sprayed . . . . . . . . . . . . 2,287
The grubs of the flea-beetle infest the tubers and roots of potatoes, doing some damage and causing the trouble known as “pimply potatoes."
In the Pacific Coast the flea-beetles (Epitrix subcrinita, Lec., and E. hirtipennis, Mels.) sometimes reduce the yield 50 per cent. by their ravages. As they are leaf-eaters, the foliage should be sprayed or dusted with an arsenical poison. One pound of Paris green to 150 gallons of water per acre is suggested, but it is better to apply the Paris green in Bordeaux mixture.
THE POTATO BEETLE, COLORADO POTATO BEETLE, OR POTATO BUG (Doryphora decemlineata).--Until 1850 this insect was confined to Mexico and the Rockies. In 1859 its eastward movement was noted, and it is now well distributed. A related species (D. juncta)
2 (N. Y.) Geneva Bul. 113, pp. 312–317.
1 Vt. Bul. 72, pp. 6-9. * Cal. Bul. 135, p. 29.