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retreated before its advance, and is now more common in the South. In New Mexico' a parasite lives on the eggs and larvæ. The eggs are laid on the potato leaves, on which the young “bugs” live, chewing holes in or eating the whole of the leaf. The insects are most active about blossoming-time, and do considerable damage if left alone.
Modes of Combatting.—The leaf should be thoroughly coated with a poison, generally an arsenical compound being used. The poison should be applied as soon as the “bugs” hatch, because the younger the “bugs” the more easily they are destroyed. Various arsenical compounds are used—as, Paris green, arsenate of lead, and others. “Bugs" object to Bordeaux mixture, hence in applying the poison it is found to be good practice to apply Bordeaux mixture at the same time. The whole of the plant should be covered, because if badly sprayed the bugs live on the unsprayed foliage. The standard application is 14 to 1/2 pound of Paris green to 50 gallons of mixture. Generally 1 pound of Paris green is sufficient per acre, and if it is desired to apply more than 100 gallons, the proportion of Paris green should be varied accordingly. If desired, Paris green may be applied in the dry form by means of a powder gun, the Paris green being mixed with flour, land plaster, etc., as desired. About 50 cents per acre should cover the cost of one application.
THE POTATO WORM, also known in the South as the tobacco-leaf miner (Gelechia operculella, Zell.), is estimated to destroy 25 per cent. of the potato crop on the Pacific Coast. Great losses often occur in storage as well as in the field. The moths fly at night, and lay eggs on the stalks and tubers. Destruction of the moths by trap lanterns, the destruction of infested stems, careful hilling of potatoes, getting them under cover as soon as dug, cleaning up the refuse of the field, and a rotation of crops is recommended. In storage, fumigation with 12 pounds of carbon bisulphide per thousand cubic feet of air-space will destroy all the larvæ if repeated five times at intervals of two weeks. This gas is inflammable, and no lights must be taken near. It is a heavy gas, and sinks from the top of the building.
| American Naturalist, 1899, pp. 927–29. New Mexico Bul. 33, pp. 47-51, 2 Cal. Bul. 135, pp. 5-29.
POTATO STALK WEEVIL' (Trichobaris trinotata). — This beetle attacks the stalks, causing them to wilt. It is found from Canada to Texas and Florida. The vines should be destroyed as soon as attacked, and weeds belonging to the potato family kept down.
Another insect has caused similar trouble in Maine.? GRASSHOPPERS (Melanoplus sp.) do much damage during some seasons, especially after the hay crop is cut, by severing parts of the leaves. Bordeaux mixture containing an arsenical poison is the best deterrent, being better than the arsenical compound alone.
THE JUNE BUG (Lachnosterna sp.).—The big white larvæ of these beetles often eat the tubers. They are most prevalent on land which has been in grass, although if land is in clover but one or two years less trouble may be expected.
i Consult U. S. D. A. Div. of Entomology, Bul. 33, 6. Ind. Report, 1895. Kan. Bul. 82. Pa. D. A. Report, 1896. N. J. Bul. 109, pp. 25-32.
* Me. Report, 1897, p. 173.
Wireworms injure potatoes by boring through them. They are more prevalent on land which has been in grass a few years. Frequent rotation and fall plowing are advised for both of these pests.
Other insects injurious to potatoes include: Striped Blister Beetle, or “ Old-fashioned Potato Bug” (Epicauta vittata). This insect should be combatted in the same way as the Colorado potato beetle-by applications of arsenical poisons to the foliage. The Tomato Worm and Cutworms are injurious. The latter are very destructive at times, and the best remedy seems to be to place bait, made of moist bran and sugar, poisoned with Paris green in the fields.
Arsenical Poisoning.–Paris green, London purple, and other arsenical compounds usually carry their arsenic in an insoluble form, but some may be soluble. This soluble arsenious oxide may burn the leaves, especially the tips where the mixture flows, and the edges of mutilated leaves, causing death of the spot and a "target-like" appearance of the leaf.
Remedy.—Do not use more than 1 pound of Paris green per acre, dissolved in 100 to 200 gallons of Bordeaux mixture. The trouble is most prevalent where people half spray and use Paris green alone, or I pound of Paris green in one barrel (50 gallons) of water and lime or Bordeaux mixture.
iN. J. Bul. 109; Report, 1895, p. 366.
SPRAYS AND SPRAYING FUNGICIDES are materials used to combat fungi, or small plants which are usually parasitic.
Bordeaux mixture is the leading fungicide for potatoes. The ingredients for making this mixture are freshly slaked lime and copper sulphate. The fungicidal value lies in the copper compound. The lime is added to prevent the copper sulphate burning the foliage, and to make the mixture more adhesive and more readily seen when applied. The amount of lime and copper sulphate used vary considerably. Not less than 2 pounds of lime can be used to 3 pounds of copper sulphate. Excess of lime is disadvantageous in some ways, as it renders the mixture less efficient by making it thicker, and in this way more liable to settle' and more difficult to apply, causing nozzles to clog, but in a wet season an excess of lime is desirable. A thin mixture can, however, be more uniformly applied.
Use freshly burnt, clean, firm lime; slake it by pouring water, preferably hot, over it in small amounts at a time, until the lime has fallen to a fine powder ; then add enough water to make a thin paste. A large quantity of lime may be slaked at one time and kept covered with water. This is a “stock solution.”
To dissolve copper sulphate, it should be placed in a coarse sack and suspended in the top of the water in a wood, brass, or porcelain vessel-usually a wooden barrel, as it corrodes iron. The copper sulphate sinks in the water as it dissolves, and a gallon of water will dissolve 3 pounds of copper sulphate. This is a saturated solution. If 6 pounds of copper sulphate are required to a barrel of water, 2 gallons of this stock solution should be used.
1 (N. Y.) Geneva Bul. 243, p. 320.
Mixing.-It is economical to have an elevated stage, under or alongside of which the spray-cart may be drawn. Place four 50-gallon barrels on this stage, two of which are for the stock solutions of lime and copper sulphate, and two for making the mixture. To make 50 gallons of Bordeaux mixture, pour 2 gallons of copper sulphate saturated solution into one barrel and fill it up to the 25-gallon mark with water. Stir up the stock solution of lime and dip out as much as is required; if 5 pounds, then the solution equivalent to this amount; strain it, to exclude particles which might clog nozzles, into the lime-mixing barrel, and fill up to the 25-gallon mark and stir. The mixingbarrels should be provided with 2-inch or 3-inch rubber hose, one end of which is attached in an opening near the bottom of the barrel, the other free. When ready, put the hose from each barrel into the spray-tank, and let them empty and mix together. The rubber hose should be long enough so that the free end can be turned over into its barrel when not in use. If desired, the stock-solution barrels may be placed above and over the mixing-barrels, so that dipping out solution is avoided; it may be run out through a faucet. Convenience to a water-supply expedites the work.