Material. Copper sulphate, stone lime, hydrated lime.

Apparatus. Quart fruit jar, granite kettle, glass stirring-rod.

Fungicides are chemicals that are used for the prevention or the killing of plant diseases. In some cases, where the fungus, or parasitic growth, is on the outside of the host, the external application of the fungicide will kill the disease. In other cases, where the disease is on the inside of the plant tissue, the host is covered with a fungicide, so that the spores, or reproductive bodies of the disease, are killed before they have a chance to enter the host plant.

There are several important fungicides. Bordeaux mixture is probably the best-known one, and it is made in different strengths for different purposes. It is a mixture of copper sulphate and lime, and the different strengths depend upon the amount of the chemicals used. The regular standard formulas for commercial spraying are as follows:

No. 1, Standard Bordeaux Mixture

4 lb. copper sulphate 4 lb. stone lime 50 gal. water

No. 2, Half-strength Bordeaux Mixture

2 lb. copper sulphate 2 lb. stone lime 50 gal. water

Laboratory formula for standard Bordeaux mixture. Dissolve one ounce of copper sulphate in two pints of water. Place one ounce of stone lime in a vessel, and slake in two pints of water and stir while slaking. Describe fully what takes place. Use these as stock solutions.

1. Now take one fourth of the copper sulphate solution and dilute it with the same quantity of cold water. Also take one fourth of the lime solution and dilute it with the same quantity of cold water. Pour the two diluted solutions together, fill a quart jar, and label. Describe what takes place and give the color of the solution.

2. Now repeat the same operation as in 1, but use hot water to dilute each of the stock solutions. Place in a second glass jar, and label. Describe, and give your results.

3. Take one ounce of each of the stock solutions and pour into a glass jar. Dilute the mixture to eight ounces with cold water, and label.

4. Shake all three samples of Bordeaux and allow them to settle. After half an hour examine each sample carefully, note the differences, and record all data. Now permit the solutions to remain for three or four days and again agitate them and describe fully what takes place.

5. Make a second set of solutions as in Laboratory Formula 1, but instead of using stone lime use one and one-third ounces of hydrated lime. What is the difference between the hydrated lime and the stone lime? Describe. What result do you get from pouring water on the hydrated lime? Does this differ any from Laboratory Formula 1? If so, how and why? Describe the Bordeaux made from the hydrated lime. Does this differ any from that made from the stone lime? Describe.

Describe Bordeaux mixture. What, in your opinion, is the best sample? Why? After Bordeaux has stood for some time is it as good as when it is first made? Discuss. Is it advisable to keep a stock solution of Bordeaux? Why? Tell which is the most important chemical in the mixture and give the reason for your answer. Why is it necessary to make Bordeaux in either glass or wooden vessels? Tell the differences between the combined solutions and the separate ingredients. Why is it important that the diluted solutions be mixed rather than the concentrated? Discuss.

Laboratory formula for half-strength Bordeaux mixture. Now take one pint of the standard Bordeaux mixture and add one pint of water. What does this dilution of the mixture make? Describe the difference between the half-strength Bordeaux and the standard Bordeaux. When and on what plants is half-strength Bordeaux mixture used?

Now take one pint of the standard Bordeaux made from hydrated lime, and add one pint of water. Does this differ from that made from the stone lime? If so, describe.

Problem 1. If it takes seven and one-half gallons of standard Bordeaux mixture to spray a fair-sized apple tree once, how much will be required to spray fifty trees three times? If copper sulphate costs five and one-half cents a pound and lime a cent a pound, what will be the cost of the material?

Problem 2. I have a ten-acre apple orchard. There are forty-nine trees to the acre. I wish to spray this orchard four times. How much Bordeaux mixture will be required, and what will be the cost of the chemicals?

References

Bulletin No. 135, Illinois Agricultural Experiment Station.

Farmers' Bulletin No. 243, United States Department of Agriculture, pp. 5-14. Lodeman, "The Spraying of Plants," pp. 19-45.