Imágenes de páginas

larvæ, is passed in the stubble in the flaxseed stage. In Michigan the fall brood appears about the last of August, while in Georgia it appears about 3 months later. The eggs are now deposited on the young fall wheat, and the life cycle begins over again. In regions far north there may be only one brood, and in the south there may be supplemental broods, both in the spring and fall, this being dependent on the weather. Drought prolongs the flaxseed stage.

In the spring wheat regions the insects winter in the flaxseed stage, chiefly in stubble, but also in volunteer wheat. Egg laying begins late in May and continues to October 1st. Eggs are often deposited on grass and weeds, but the larvæ are not known to survive except on wheat, barley and rye. The fly





is now known to flourish even where spring crops are exclusively grown.

EFFECT OF LARVAE ON WHEAT.—At first the plant seems to be stimulated, and turns a dark green color. Later the infested tillers turn a brownish and then a yellowish color. If the attack comes early, and the plant fails to tiller, death results. If the plant has tillered, some stalks may escape and form the basis for a crop. The larvæ are usually found just above the first joint, but may be found from above the third joint to below the soil. The stalk is usually so weakened that it breaks to the ground, when the wheat is said to be "straw


LOSSES.—The Hessian fly is the worst insect enemy of growing wheat. It is never entirely absent. The minimum

annual damage to wheat is thought to average 10 per cent of the crop, that is, over 50,000,000 bushels. In some localities an injury varying from 50 per cent to total failure is not infrequent. In 1901 the loss in New York was about $3,000,000, and the loss in Ontario was nearly as great. In 1900 it was $16,800,000 in Ohio, and nearly two-thirds of the Indiana wheat was not harvested on account of the fly. The outbreak of the Hessian fly in 1900 was the most notable of recent years. The total loss for the United States was estimated at $100,000,000, and milling operations were seriously hampered in the worst affected region. The damage which the fly does is often laid to rust, drought or other causes. In 1904 there was little complaint of damage from the insect, yet many fields in the Ohio valley were injured to the extent of over 50 per cent.

REMEDIES.—There are a number of natural enemies which attack the Hessian fly in the larval and pupal stages. Some are native, and others are being artifically introduced. While they limit the damage, they are useful mainly where other preventives are neglected. The best remedy for a field of wheat severely attacked is to plow deeply, and plant a spring crop. In case of mild infection, the prompt use of fertilizer may increase the tillering of the wheat so as to produce a partial crop. If the crop has a good growth pasturing or cutting in the fall may be beneficial. When injuries from the fly may be anticipated, moderately late planting of winter wheat is perhaps the best preventive. Seeding for this purpose should be about the middle of September in the northern districts, during the first half of October in Kentucky, and during the first half of November in the extreme south. The rotation of crops should be practiced. Burning or plowing under the stubble is of great advantage. The fly can be starved out almost completely over a district of any size by abandoning for one year the culture of wheat, rye and barley. Volunteer grains should also be destroyed. Early plantings of trap or decoy crops will attract the flies, and, after ovipositing, these crops may be plowed under deeply. While no varieties of wheat are absolutely “fly proof,” some tiller more and are less injured than others, such as Underhill, Mediterranean, Red Cap, Red May and Clawson. Preventive measures reduce the annual loss from the Hessian fly by an amount estimated

from $100,000,000 to $200,000,000 for the wheat crop alone. The insect shifts so rapidly from place to place that remedies are practically of no avail unless there is concerted action in an infected region.'

Chinch Bug (Blissus leucopterus Say).—This is a native insect. Its ravages were first noticed toward the close of the eighteenth century, and since that time notable outbreaks and serious losses have been quite constant. It is now found from Nova Scotia and Manitoba southward to the Gulf of Mexico, as well as on the Pacific coast, in Mexico -and Central America, and on several of the West Indian Islands. The genus Blissus is widely distributed over the Old World. It is a gregarious


[ocr errors]



pest, and its destructiveness is due to this fact rather than to its enormous numbers.,

LIFE HISTORY.-Hibernating in grass stools, straw, rubbish or other shelters, the chinch bug begins its life cycle by a spring flight to the wheat fields. The mating occurs at the wheat roots. The eggs are deposited about May 1st, from 100 to 500 by each female, and the egg period is of 2 or 3 weeks' duration. The young hatch in about 2 weeks, and at maturity in July they make a second flight to late corn, millet or other crops. In this country, except in northern regions, a second brood appears after this flight. The second brood is most injurious in August and matures in September and October. It is the first brood that injures wheat, while both broods attack other crops. A short-winged form incapable of flight frequently occurs, especially in maritime districts. There are a number of species of Hemiptera that are often mistaken for chinch bugs.

1 Marlett, Principal Insect Enemies of Growing Wheat; Osborn, Hessian Fly in the United States.

THE CHIEF LOSSES are occasioned in the Ohio and upper Mississippi valleys, and on the Atlantic coast highland. It does more damage to wheat than to any other crop, and the average annual loss is about 5 per cent of the crop. In years when the chinch bugs were unusually severe, the damage to wheat in single states has been estimated to be from ten to twenty million dollars. The losses are great because of the wide distribution of the pest, its prevalence to some extent every year, and its enormous multiplication in favorable sea


REMEDIES.—(1) Burning over the land; especially should this be done on waste and grass lands, and all rubbish should be burned. Grass is not injured by being burned over after the ground is frozen. It has been thought that the chinch bug was kept in check by the annual prairie fires in the early years of our country, the hibernating bugs being thus killed. Chinch bugs and other insects injurious to growing grain are practically unknown on the Pacific coast, where the large wheat fields are regularly burned over every year by burning the straw. (2) Trap or decoy crops, such as millet or Hungarian grass; these should be plowed under. When the young insects hatch, they easily reach the surface, but will perish if no crops are near. (3) Rotation; this involves a system disassociating small grains from corn. (4) Plowing; deeply plowing under the bugs collected on the edge of a field is helpful. (5) Spraying; the edge of the field infested may be sprayed with a very strong oily insecticide, even if the crop is killed with the bugs. (6) Protecting furrows. (7) Coal-tar barriers. (8) Artificial spreading of parasitic fungi; considerable work has been done in this line, with the conclusion that it is of little value. The bug is practically exterminated for the season, however, by wet weather and various fungous diseases which this causes. (9) Many bugs are also destroyed by: birds, especially quails.”

The Wheat Midge (Diplosis tritici Kirby) belongs to the same order of insects as the Hessian fly, but in appearance and habit it is entirely distinct. It is believed to be identical with the notorious wheat midge of Europe, and it may also have been in

1 Yearbook U. S. Dept. Ag”, 1904, p. 466.
2 Webster, The Chinch Bug; Howard, The Chinch Bug.

troduced into America in straw. It probably appeared first in Quebec, and has now spread throughout the Mississippi valley. The injury is inflicted by its orange-yellow larvæ which extract the milky juice from the embryos forming in the wheat heads, thus causing the grain to shrivel and the heads to Llight. In cases of unusual outbreaks the average losses of whole states have been from two-thirds to three-fourths of the entire yield. The wheat midge oviposits directly in the wheat head. The eggs hatch in about a week, and the larvæ enter the kernel at once. They have extraordinary vitality, thrive best in moist weather, and winter in the ground, which they enter about three weeks after hatching. Plowing old wheat




fields deeply, burning the chaff and screenings of wheat from infested fields, and rotating crops are preventives.

The Wheat Plant Lice cause injury by sucking their food from the soft, forming kernels. The yield may be reduced by as much as one-half, but extensive damage rarely occurs. The annual loss is thought to be at least 2 per cent.

Locusts or Grasshoppers.--The locust, formerly present in some years in such overwhelming numbers that large swarms devastated extensive areas of all vegetation, has during the last decade ceased to be of such great economic importance. Locust plagues seem to occur occasionally on all of the continents, and do not seem to be limited to comparatively newly settled

« AnteriorContinuar »