Imágenes de páginas
PDF

(2) Blue stone or copper sulphate: Immerse for ten minutes in a solution of copper sulphate at the rate of one pound to five gallons of water. Allow to stand for ten minutes in bag or basket to drain; then spread and dry. Or the seed may be sprinkled at the rate of one gallon of the solution to four bushels of the grain, sprinkling and stirring until thoroughly wet. At the end of an hour dry.

(3) Formalin: Treat seed by sprinkling or immersion for thirty minutes with a solution of one pound of formalin (forty per cent solution of formaldehyde) to fifty gallons of water.

In all treatments it is desirable first to stir seed into a tub of cold water and skim off the smut balls which rise to the surface. After treatment, the drying may be hastened by using slaked lime, but the lime is not essential.

[graphic]

150. Insect Enemies of Growing Wheat.—More than one hundred species of insects are known to feed upon the growing wheat plant, but very few are sufficiently injurious to be of economic importance. These few, however, do enormous damage, stinking .mut. single grain The chinch bug has been estimated

much enlarged on the right.

(After Keiierman.) to cause a loss of over a hundred

million dollars to wheat alone in the United States in a single year.1

The five most important insect enemies of wheat are as follows:

(1) The chinch bug (Blissus leucoptems Say.)

(2) The Hessian fly (Cecidomyia destructor Say.)

(3) The wheat bulb-worm (Meromyza americana Fitch.)

(4) The wheat midge (Diplosis tritici Kirby.)

(5) The wheat plant-louse (Nectarophora cerealis Kalt.) Of the above, the chinch bug and the Hessian fly are by far

the most destructive, although the others frequently do considerable damage. Among the wheat insects of secondary importance

1C. L. Marlatt: The Principal Insect Enemies of Growing Wheat. U.S. Dept. of Agr., Farmers' Bui. 132, p. 6.

are the wheat straw worms, army worms, wheat sawflies. In the past, grasshoppers, especially the migratory species, have done enormous damage to wheat, but at present this class of insects usually do their greatest injury to meadows and pastures.

There are two general causes for the great damage done to wheat and other grain crops by insects. The long hot summers and the present practice of growing somewhat continuously large areas of wheat on the same land produce favorable conditions for their rapid multiplication. The rotation of crops and a more thorough and more intensive system of agriculture will tend to hold these insects in check.

151. The Chinch Bug.—The appearance of the six different stages from the egg to the adult chinch bug is shown in this paragraph. The newly hatched larva is of a pale reddish color with a yellow band across the first two abdominal segments. As the insect changes from one stage to another it changes somewhat in appearance by becoming increasingly darker in color and finally in the, adult form by thewhite The chinch bug: Adult on the left; eggs upon the right; four wings So that while larval stages between. (Adapted from Riley and Webster.) in the first larval stage

the color was principally red and yellow, in the adult form it is black and white. There is also an adult form with short wings.

The chinch bug passes the winter in the adult form under any object which may offer protection from wet and cold. The grass stools of pastures and meadows, stalks of maize, straw, rubbish in fence and hedgerows furnish them a winter home. The eggs for the spring brood are deposited on the plants beneath the soil not far from May 1st. These eggs reach the adult stage during July; while the second brood reaches its maximum damage in August and its adult stage in September and October. It is the first brood that does the most damage to the wheat, rye or barley, and less frequently to oats, during the last few weeks of the growth of the crop. In the early part of July this brood migrates to maize fields, thereby injuring this crop also.

Preventive measures aside from those already mentioned (150) are the cleaning up or burning of all rubbish or vegetation in fields and fence rows under which the chinch bugs may hibernate. There is no remedy for them while in the wheat crop, but they may be trapped while migrating to maize fields by means of barriers of various sorts. Millet or Hungarian grass is probably the most effective. After the chinch bugs have congregated in the millet, they should be plowed under deeply,—preferably after spraying with pure kerosene oil. Usually, however, the chinch bug has migrated to the maize fields before protective measures have been inaugurated. The best remedy then is to spray with pure kerosene in the early morning when the chinch bugs will be congregated at the base of the maize plants. The kerosene will do some injury to the maize but not nearly so much as the chinch bugs.

[graphic]

The chinch bug is attacked by two parasitic fungi which tend to hold It In check. A number of experiment stations have propagated and distributed these fungi to farmers for the purpose of spreading them among healthy insects. It has been found, however, that this method is practically effective only during the moist cool weather when the insects are destroyed without the introduction of the disease germs. While the insects are young, even after they have wings, they are migratory in habit, but when the time for the union of sexes comes they take to wing and are no longer noticed by the casual observer. It happens that this occurs from one to three weeks after they migrate to maize fields. Frequently remedies have been reported effective, when in fact the disappearance of the chinch bugs was due to their midsummer flight .

152. The Hessian FLY^The Hessian fly is a small, two-winged, dusky-col

The Hessian fly is usually two-brooded, although it may be one-brooded in the northern spring wheat districts, or in the more southerly section of the United States may be three-brooded, the third brood living upon voluntary wheat in the summer months. When two-brooded, the fall brood reaches the adult stage during the latter part of August, during September and the first days of October, depending upon latitude and other seasonal conditions. The adults probably disappear with the first sharp frost. At any rate, the condition which is most favorable to the

[graphic][ocr errors][merged small]

* Cornell Bui. 194, p. 255.

insect is mild weather for four to six weeks after the wheat is planted. The spring brood reaches the adult stage during the latter part of April, during May and the first part of June.

The adult lays an oval-shaped egg, reddish in color, one-fiftieth of an inch long, on the inner side of the leaf blade. The egg hatches in a few days into a pinkish larva, soon changing to greenish, which finds its way down to the base of the leaf sheath. As the eggs in the fall are usually laid upon the youngest plants, the larvae are to be found somewhat under the ground, where they kill the diminutive culm. In this case the plant will be killed unless it has tillered, and some of the tillered culms escape. In the spring the eggs are laid on leaves somewhat higher up and the larvae will be found at the base of the first two or three leaves above the ground, where the injury causes many of the culms to fall before the grain is ripe. The puparium of the insect resembles in form and color a flaxseed. The pupal stage is therefore called the "flaxseed stage." When two-brooded, this insect passes the winter and the summer in the flaxseed stage.

Preventive measures are (i) late sowing, preferably delayed until after sharp frosts; (2) rotation of crops; (3) burning stubble; (4) sowing strips of wheat early as baits to be plowed under as soon as eggs have been laid. Of these the first two are to be especially recommended. The Hessian fly has many parasitic insects, otherwise it would probably make the raising of wheat impossible. Burning the stubble will destroy the parasites as well as the Hessian fly, which may not always be advisable. The destruction of organic matter also usually will not be desirable. In order to get the best results from late sowing it is advisable for farmers to act together, else the spring brood from the early sown wheat may attack the field which has escaped the fall brood.

There are no Hessian fly proof varieties of wheat, although those varieties which tiller most freely and have the stiffest and hardest culms will doubtless resist their attacks the best.

153. The Wheat Bulb-worm.—The wheat bulb-worm is a two-winged fly with essentially the same habits as the Hessian fly, except that it lives upon oats as well as several grasses, including timothy. The injury from the fall brood is almost identical with that of the Hessian fly; while the spring brood lays its eggs usually upon the upper leaf, thus causing the culm to wither and die above the upper node. While the Hessian fly therefore usually remains in the stubble after harvest, the wheat bulb-worm is carried from the field with the straw. The damage done by this insect is much less than that of the Hessian fly, for which it is doubtless frequently mistaken.

154. The Wheat Midge.—The wheat midge is also a two-winged insect. About the time the wheat is in the flower, the adult lays its eggs singly or in clusters to the number of ten upon the glumes of the wheat spike. The larvae suck the milky juice from the young grains, causing them to shrivel. They impart their orange-yellow color to the blighted spike. The insect is probably third in the injury to the wheat plant, but unlike the chinch bug and the Hessian fly, it thrives best in moist weather. The larvae enter the ground after about three weeks and pass the winter in the pupal stage. Many, however, are still in the spikes when harvested, and are believed to survive in the straw for months without food or moisture.

[graphic]

Preventive measures are (i) the burning of chaff and screenings as soon as the wheat is threshed, and (2) deep plowing of stubble field to bury the larvae and pupae.

155. The Wheat Plant-louse.—This insect appears on winter wheat in September, going through several generations in the early fall but doing little damage. If the spring is cool and moist, its natural enemies may fail to hold it in check and it may then cause considerable damage. Extensive damage has occurred only at rare intervals, as in 1861 and 1S99.I No effective remedy has yet been suggested.

156. Insects Injurious To Stored Grain.—While upwards of forty different species of insects occur in granaries, the following four species are the most injurious: 2

(1) The granary weevil (Calandra granaria L.)

(2) The rice weevil (Calandra oryza L.)

(3) The Angoumois grain moth (Sitotroga cerealella Oliv.)

(4) The wolf moth (Linea granella L.) The first two are beetles and the last two moths. The larvae of the first three

live within the grains, as do the adults of both weevils. This adds very much to their injurious effects, to the ease with which they may be distributed, and the difficulty of eradication. All breed more rapidly in warm than in cold weather and consequently do their greatest damage in the southern sections of the country, where they cause enormous losses.

The simplest and best remedy is the use of bisulphide of carbon at the rate of one pound to one ton of grain or in empty rooms for every 1,000 cubic feet.

There are a number of insects injurious to flour. The Mediterranean flour moth [Ephestia kmhniella Zell.) has recently become a most serious pest, requiring the adoption of extensive precautions in flouring mills to guard against its ravages.

Beetle and larva of the granary weevil. (After Chittenden.)

Adult and larva of the
Angoumois grain moth.
(After Chittenden.)

II. HARVESTING AND PRESERVATION.

157. Date of Harvesting.—The wheat harvest of the United States begins in Texas in May and ends in the Dakotas in August. In California the harvest begins about June ist and

1 U. S. Dept. of Agr., Farmers' Bui. 132, p. 24.

2 For a description and life history of these insects see U. S. Dept. of Agr, Farmers' Bui. 45.

« AnteriorContinuar »