During the summer and early autumn months attention should be given to the spraying of plants for blight and for injurious insects. The potato is commonly affected by a fungous disease which causes the stalks to blacken and die before the tubers have matured. This disease may be prevented in large measure by the use of a fungicide known as Bordeaux mixture. This may be prepared as follows:
Take one pound of copper sulphate (blue vitriol); make it fine by pounding it in a bag or cloth and then dissolve it in water, using a wooden pail. It dissolves rapidly if put in a little cheese-cloth sack, which is suspended near the top of the pail by putting a stick across the pail and tying the sack of copper sulphate to it. Dilute this solution to five gallons. Take also a pound of unslaked or quick-lime and add a cupful of water to it. When it begins to swell up and get hot, add more water slowly, and, when the action ceases, dilute to five gallons. Mix these two solutions together in a tub or barrel, and churn them up, or stir them together vigorously. They give a deep robin's-egg-blue mixture, which is slightly alkaline and should be used at once. The solutions can be kept separate as stock solutions throughout the summer and then diluted and mixed whenever needed. Care should be observed in not mixing the solutions before each has been diluted to the strength, one pound to five gallons. A piece of blue litmus paper will be convenient to prove that the mixture is alkaline. If alkaline, as it should be, the paper remains blue when dipped in it. If the mixture turns the litmus paper red, it must have more lime-water added to make it alkaline. The potato tops should be thoroughly sprayed with this mixture when about ten inches high and then once every two weeks, until they have been treated three or four times. This is to prevent blight and not to kill bugs. If the potato-beetle is troubling the potatoes, add paris-green to the Bordeaux mixture—a teaspoonful to every two gallons. To prove the value of this treatment have a trial plot of potatoes which receive all attention save spraying with Bordeaux mixture. If a heavy rain should follow the spraying, it should be repeated.
Potato-scab may be prevented to a large degree by soaking the tubers before cutting for planting in a solution of formalin (a 40-per cent. solution of formaldehyde) one-half pint to fifteen gallons of water. Seed grain is frequently treated this way before sowing, to destroy smut spores. A pound of formalin is put in forty gallons of water in a large barrel. A bag full of the grain to be treated is set in the barrel of formalin mixture for about two hours and then taken and dried on a floor that has been previously washed with water containing formalin. A solution of copper sulphate (bluestone), one pound in twenty gallons of water is sometimes used. The grain is left in this solution for twelve hours and then dried for sowing. All bags and utensils should also be disinfected with this formalin solution.
TREATMENT OF INSECTS
In order to poison insects successfully, it is necessary to determine how the insect feeds. If it is a biting insect, that is one that eats the leaf, such as the potato beetle, paris-green should be used. Paris-green sometimes burns the tender leaves. This may be prevented by adding a tablespoonful of lime to each pail of water used. It may also be used dry with flour or dust.
If the insect feeds by sucking the juices from the leaf, as is the case with plant-lice, then a solution that kills by contact must be used, such as whale-oil soap, one ounce to a quart of water. Tobacco-water is sometimes mixed with the soap solution as follows:
Four pounds of tobacco-waste is steeped in nine gallons of hot water for five hours; this is then strained, and to the tobacco-water one pound of whale-oil soap dissolved in one gallon of hot water is added and mixed thoroughly.
Kerosene emulsion, which is made as follows, is very destructive to plant-lice and scale insects:
Dissolve a quarter of a pound of common laundry soap in half a gallon of rain-water and, while hot, mix with one gallon of coal-oil and churn vigorously for five minutes to get a smooth, creamy mixture. On cooling, it thickens and is diluted before using by adding nine quarts of warm water to one quart of the emulsion. Use smaller quantities in correct proportions when only a few plants are to be treated.