The annual loss in the United States to vegetable crops from the depredations of insects and diseases amounts to millions of dollars. Practical growers, economic entomologists and plant pathologists believe that most of the losses could be forestalled by taking the proper preventive measures. In too many instances, however, the grower makes no preparation for control and when the pests appear it is impossible to secure a spraying outfit and materials before great damage has been done.
In the control of fungous diseases and insect pests of the garden, preventive measures are of prime importance. Spraying is often necessary, but it is expensive and should not be employed ordinarily until all other practical means of prevention have failed. Single cropping or the want of proper rotation frequently causes trouble. When a crop pays unusually well, the temptation is to continue its cultivation upon the same ground for years - a practice which harbors insects and diseases.
Diseased or infested seed or stock often introduce enemies. This is a strong argument in favor of the home production of seeds and plants. When plants are kept in a thrifty condition there is reduced danger of serious loss from both insects and diseases. Judicious fertilizing, cultivating and watering may be worth far more in warding off attacks than any amount of spraying. Infested soils when used in starting plants become a source of contamination. Too much care cannot be exercised in the selection of soil known to be free from disease germs.
The use of contaminated manure may also introduce diseases. Plowing and cultivating at just the right time often prove effective preventive measures; and clean tillage and the destruction of refuse after harvesting crops may be the means of avoiding serious losses.
Notwithstanding all general preventive measures, spraying is often necessary to avoid heavy damages. The fundamental principle involved is that of protection. If the operator uses an insecticide it serves as a poison or a repellent and should be applied before the enemy has made a serious attack; and if injury is expected from fungous diseases, by the application of a fungicide the parts in danger of infection are armored with material which will prevent the entrance of the parasites.
Five things are important in successful spraying: (1) Know your enemy; (2) select the most effective poison for its control; (3) spray thoroughly; (4) spray as often as may be necessary under existing conditions; (5) spray at the proper time.
Inexpensive pumps are seldom satisfactory. The best materials should be used in the construction of spray pumps; all metal parts which come in contact with the solutions should be made of brass or copper to prevent serious corrosion. A large air chamber is an advantage in securing an even and continuous discharge. Over 100 pounds pressure is essential to the best work in orchard spraying, but less than this is effective in garden operations.
Various types of pumps are available. The bucket pumps, which may be bought for a few dollars, answer the purpose in small home gardens. Knapsack sprayers are very convenient on small areas where the crops are planted close together, and in large plantations when growth is so far advanced as to prevent the use of barrel or power sprayers. It is not an easy task to carry and operate a knapsack sprayer, but it is unquestionably the best pump under certain conditions. For example, aphides sometimes infest cabbage after the plants are too large to permit the use of barrel or power sprayers, and in addition, they colonize on the under sides of the leaves as well as on the upper. These conditions make the knapsack sprayer the most desirable pump for this work, especially if used with a crooked extension rod.
Barrel pumps are more satisfactory and less laborious to operate than knapsack sprayers, and are most popular with commercial growers. Chain and sprocket power machines are frequently employed. By their use large areas may be covered in a day. With a good pump and efficient nozzles properly placed and adjusted, the work is satisfactory. Gas, compressed air and gasoline engine pumps are not used extensively in commercial gardening. Various powder guns on. the market are effective in the application of powders.
For its value in spraying vegetables a nozzle depends upon its ability to break up solutions and mixtures into the finest particles. In orchard spraying and sometimes in garden treatment, an additional factor is important; namely, the ability of a nozzle to project the spray with the greatest possible force. The best known and most popular nozzles used by commercial vegetable growers are the "Vermorel" and the "Friend."
Insecticides may be divided into three classes, namely: Stomach poisons, contact poisons and repellents. Stomach poisons are used in destroying insects with biting mouth parts; for example, the potato beetle and the asparagus beetle. Contact poisons are used in killing sucking insects, as aphides and the stink squash bug. Repellents, as lime and tobacco, may not kill insect foes, but they may be effective as deterrents.
Arsenate Of Lead is the most valuable of the arsenical poisons. It is a stomach poison and has three distinct advantages over other arsenical mixtures, which are: (i) It is harmless to the foliage, (2) it adheres better to the foliage; (3) it remains longer in suspension. The usual strength is 3 pounds of lead arsenate to 50 gallons of water. Weaker mixtures are often effective, while 5 pounds to 50 gallons may be an advantage in killing insects difficult to poison. The commercial preparation which comes in the form of a paste should be mixed thoroughly with a small quantity of water before diluting in the sprayer. It may be used with bordeaux mixture without diminishing the value of either.