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. 1 N. J. Bul. 109; Report, 1895, p. 366. CHAPTER XI 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 1 (N. Y.) Geneva Bul. 243, p. 320. 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. 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. Testing Bordeaux Mixture.-In practice little attention is paid to the quantity of lime, except that sufficient is added to combine with all of the copper sulphate. To determine when this has taken place the potassium ferrocyanide test is made. Purchase ten cents' worth of potassium ferrocyanide, or yellow prussiate of potash, and dissolve it in water. Label it "Poison." Stir the Bordeaux mixture in the spraytank and take out a sample in a small vessel, to which add a drop of potassium ferrocyanide. If no change in color is noted where it dropped there is sufficient lime, but it is better to add lime solution equivalent to a pound of lime more. If the drop changed the color of the solution reddish brown it shows that there is not enough lime. Strength of Solution. -For potatoes, I pound of copper sulphate to 7 or 8 gallons of water is commonly used; that is: Copper sulphate (blue vitriol), 6 pounds. Quicklime (not slaked), 4 to 6 pounds. Bordeaux Dust,' or Dry Bordeaux Mixture, can be made in two ways: 1. Slaking the lime by pouring a strong solution of copper sulphate over it. 2. Mixing the strong copper sulphate solution with freshly slaked lime which has been made into a paste, then placing the mixture in a bag and drying and pulverizing it. The two ingredients must be well mixed and passed through a fine sieve. Dry Bordeaux is offered for sale under various names. Adler's Bor 1 For details, see Missouri Bul. 60. (N. Y.) Geneva Bul. 243, P. 325. deaux is reported to be as efficient as newly mixed,' but generally these preparations are much inferior to the newly prepared, and, when applied drv, are less effective than in the wet form. Washing Soda and Copper Sulphate Mixture. -This mixture is being used with success in parts of Europe. It does not clog nozzles, spreads evenly over the leaf, and is easily and cheaply prepared. The washing soda is dissolved in water, poured into the barrel of water and stirred, and the copper sulphate added and stirred. Various strengths are in use, but the most satisfactory one for American conditions has yet to be determined. We are trying 4 pounds of copper sulphate, 6 pounds of washing soda, and 50 gallons of water, adding 1 pound of lime if Paris green is used. A little over 1 pound of washing soda might be sufficient to neutralize the 4 pounds of copper sulphate, but it is safer to use more. In Ireland 5 pounds are used and for three successive years in extended trials this mixture has given better results than Bordeaux mixture. At (N. Y.) Geneva Station, in 1904, it was not so good as ordinary Bordeaux mixture. Spraying with Bordeaux Mixture.-Benefits.Spraying with Bordeaux mixture influences the potato crop in the following ways: 1. The structure of the leaf shows a slight increase in thickness and in strength, and so offers more resistance to the growth of disease spores. 2. The chlorophyll,' or green coloring matter of the leaf and stem, is increased. 1 Me. Bul. 73, P. 55. 2 Department of Agric. for Ireland Leaflet, 14. Frank & Krüger. E. S. R., VI., p. 306. |