| OCR Text |
Show ALFALFA-SEED PEST RESEMBLES THE GNAT Alfalfa-Seed, or Clover-Seed Chalcis-Fly A, Adult; B, Larvae; C, Pupa-Much Pupa-Much Enlarged. (Prepared by the United States Department Depart-ment of Agriculture). The alfalfa-seed destroyer, known as the chalcis-fly, does its destructive work in clover or alfalfa seeds, from the Gulf coast to the northern limits of the United States, according to the United States department of agriculture's agricul-ture's specialist who has personally seen the widespread devastation of this pest. By harvesting severely infested in-fested crops, by cleaning fence lines and ditch banks, and by winter cultivation culti-vation the grower of alfalfa seed may help to control this insect. A new Farmers' Bulletin, (No. C3C) entitled "The Chalcis-Fly in Alfalfa Seed," gives the details of these methods of control, and may be had free of charge on application to the department. depart-ment. The chalcis-fly under the microscope is a formidable-looking insect but when seen in the field it is frequently confused with the gnat. These pests may be seen iu great numbers flying over alfalfa-seed shocks and swarming swarm-ing over the sickle bar when the alfalfa al-falfa is being cut. The eggs are so small as to be invisible to the naked eye and are deposited through the soft, green seed pods directly into the soft seeds when the pods are about half-grown. Immediately upon becoming becom-ing a fly, the insect eats its way out through the shells of the infested seeds, then through the green pods. Large portions of the seeds are hollowed hol-lowed out in this manner, when they are still green and growing. The infected seeds which still contain con-tain the living larvae of the insect may be recognized by their abnormal shape and usually by the dull brown color. Some of the infested seeds, however, retain their natural color, but they always lack the glossy appearance ap-pearance of normal seeds. The extent ex-tent to which alfalfa seed is damaged by the fly is not generally apparent, owing to the minuteness of the insect and because its destructive work is accornplished within the growing" seeds. The alfalfa-seed grower can only estimate the. percentage of his crop destroyed by opening a large number of the seed pods and observing observ-ing the infested seeds. Harvesting Infested Crops. An alfalfa field is frequently found with such a severe infestation by chalcis-flies that the grower considers it of insufficient value to be harvested and simply drives In a herd of cows to pasture the crop. With regard to the control of the chalcis-fly for the protection of future seed productio.n, this is a costly mistake. Obervations show that many of the pods burst open, while others are trampled to the ground. Here great numbers of Infested seeds offer favorable conditions condi-tions for the hibernation of the chalcis-fly larvae. Thflse, as mature flies, will infest the seed crops the follow- ing spring. Under such circumstances the crop should be mowed, removed from the field, and staked. It may then be used as rough fodder; and if the remaining straw is burned in early spring the hibernating larvae will be destroyed. Cleaning Fence Lines and Ditch Banks. The following facts emphasize the importance of cutting the alfalfa along ditch banks and fence lines, as well as in the fields: 1. The earliest seed pods are found to develop on the isolated and vigorous vigor-ous growing plants found in such places. 2. The earliest pods have an especially espec-ially large percentage of the seeds infested with chalcis-fly larvae. 3. The chalcis-fly larvae are able to pass completely through the first generation in the earliest pods before the regular seed fields are sufficiently advanced for oviposition. This cutting should be done with the harvesting of each hay crop, before be-fore the seed crop is grown. It is sometimes necessary to have two or more irrigation ditches running run-ning parallel, making it impracticable to cut the alfalfa between them. In such cases it is economy to fence the ditches and use this land as a small summer pasture, thus preventing prevent-ing the development of alfalfa seed pods and the chalcis-flies. Winter Cultivation. In the process of harvesting the seed crop many pods containing infested in-fested seeds fall to the ground. Here they remain until the following spring when the hibernating insects emerge, although cultivation with an alfalfa cultivator, at some time late in the fall or in early winter, will sufficiently cover such pods and will prevent the emergence of most of the adults when the warm weather arrives. Destroying the Screenings. After the alfalfa is thrashed the great mass of screenings which is left frequently contains large numbers of seeds infested with hibernating larvae. If the chaff, together with the screenings, screen-ings, is placed in a compost pile for three or four months, so that it will become heated and decay, most of the Insect life will be destroyed. Unless It is possible to treat the screenings in this manner they should be burned before the growing season opens In the spring. Many of the alfalfa seed pods along check ridges and fence lines may be destroyed by burning off the weeds and alfalfa. This should be done either in the fall or early spring. In purchasing alfalfa seed, farmers should insist upon having seed which has been well cleaned after thrashing thrash-ing and should never plant the uncleared un-cleared product in new fields. |
