While the behavior of the insect in radish plantings has not heretofore been carefully considered, the life history of the pest was worked out by Schoene1 in his study of the insect in cabbage seedling beds. From his study the activities of the first brood in radish plantings are approximately as shown in Chart 1.

STUDIES ON BEHAVIOR OF INSECT IN RADISH BEDS.

Under this heading there are presented the results of a series of experiments which were designed to obtain more specific data than heretofore available as to the period of injuries to radishes by maggots and the relative susceptibility of early and late sowings to attack. As one-half of each sowing was covered with cheesecloth, the tests also furnished opportunities to determine the influence of screening in preventing damages by maggots and flea beetles as well as on the growth and quality of the roots. The details of the experimental operations for each year are considered separately, and then the principal results are summarized and discussed in regard to their bearing on radish culture.

EXPERIMENTS DURING 1914.

For this season's work, two plats, each one hundred feet long and twelve feet wide, were laid out and top-dressed with a liberal application of a mixed fertilizer composed of sodium nitrate, 25 parts; acid phosphate, 871⁄2 parts; and muriate of potash, 25 parts. The soil was harrowed and reduced to a fine state of tilth. On May 9 the seed was sown with a garden drill at the rate of three seeds to each two inches in rows six inches apart. As seedlings were making their appearance on May 15 one of the beds was screened with a cheesecloth sheet. Flea beetles (Phyllotreta vittata Fab.) were very abundant on May 23 in the unscreened bed and soon caused marked injury to the seedlings. At this date a few adults of the radish maggot were observed but the species was apparently not very numerous. On May 22 and 23 both beds were weeded and thinned, leaving the plants about two inches apart. Thruout the remainder of the month of May the uncovered planting was constantly subject to attacks by large numbers of flea beetles and there were also evidences of a small amount of injury to the plants in the screened bed. The Cabbage Maggot: Its Biology and Control. N. Y. Agr. 1916.

1 Schoene, W. J. Exp, Sta. Bul, 419.

On June 5, when the radishes in the protected plat were of suitable size for marketing and the unscreened planting showed abundant infestation from maggots, the roots were pulled. The yields and weights of the two plats are given in Table I.

TABLE I.— YIELDS OF SCREENED AND OPEN RADISH BEDS DURING 1914.
(Counts and weighings based on rows of 100 feet in length.)

The methods of preparing the plats and sowing the seed were the same as practised in the preceding test. The dates for the different sowings were Plat I, March 15; Plat II, March 22; Plat III, April 1; Plat IV, April 5; Plat V, April 13; and Plat VI, April 14.

With each plat one-half the bed was screened immediately after the planting of the seed, while the unprotected portion of the bed served as a check. A record was kept of the daily temperatures during the growing period of the radishes, which is as follows:

TABLE II.— RECORD OF TEMPERATURES DURING EXPERIMENTS OF 1915.

During the latter portion of April flea beetles became very numerous, causing considerable damage to the leaves of the unscreened plants. They were also quite abundant in the screened beds but the evidences of their attacks were much less conspicuous since the

SUMMARY.

Total

Roots

weight.

marketable.

Lbs.

No.

plants were growing rapidly. In the open beds lack of moisture and incrustation of soil, in addition to the attacks of flea beetles, greatly retarded the growth of the plants. Until about May 18 the differences in the screened and unscreened plats were largely due to the effects of the cheesecloth in modifying their physical environment, principally as regards temperature and the moisture content of soil. Thereafter flea beetles and maggots exerted an important influence in the unscreened plats, killing many plants or so injuring them as to greatly retard their growth. Radishes pulled after June 1 were so maggoty that they were unfit to market.

The yields and weights of radishes in the screened and unscreened plats are given in Table III.

EXPERIMENTS DURING 1916.

During this year radish seed was sowed on the following dates: Plat 1, April 4; Plat 2, April 11; Plat 3, April 18; Plat 4, April 25; and Plat 5, May 6. After a cold, wet period, followed by very hot weather, flea beetles appeared in great numbers about May 20 and were very injurious to radishes, especially in the unscreened frames until the roots were harvested. On May 24 eggs of the radish maggot flies were noticed about unprotected plants in goodly numbers and, commencing with June 1, radishes became increasingly infested with maggots as the season advanced. The yields of the different plats are given in Table IV.

EXPERIMENTS DURING 1917.

For 1917 nine sowings of radish seed were made as follows: Plat I, Mar. 23; Plat II, Mar. 30; Plat III, April 6; Plat IV, April 12; Plat V, April 19; Plat VI, April 27; Plat VII, May 4; Plat VIII, May 10; and Plat IX, May 18. On May 9 feeding by flea beetles was first noticed, and on May 15 seedlings showed plainly evidences of injury, although the insects were not nearly as numerous or as destructive as in preceding years. Likewise maggots were not very abundant and, while the first adult of this species was observed on May 9, eggs and larvæ were not detected until the first week of June. Low temperatures and rains prevailed during the growing period of the radishes so that the season was very backward, at least