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TABLE VI.— SHOWING YIELDS OF SCREENED AND OPEN RADISH BEDS

DURING 1917.

(Counts and weighings based on rows of 100 feet in length.)

SCREENED PLATS.

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Roots marketable.

No.

Average per 100 feet screened ...
Average per 100 feet unscreened.

1,089
1,063

16.4
13.1

596
568

6.5
5.8

GENERAL CONSIDERATIONS AND SUMMARY.

TIME OF OCCURRENCE OF INJURY.

The activities of the radish maggot in the different plats of the experiments, as described, are indicated in Table VII.

TABLE VII.-CONDITIONS OF PLATS WITH REFERENCE TO MAGGOT INJURY

FROM 1914 To 1917.

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As will be observed in the foregoing table, the radish maggot has varied greatly in importance during the four years mentioned, causing considerable damage to the late plantings during 1914, 1915 and 1916, while in 1917 the extent of injury to roots was relatively insignificant. The injury was caused by the first brood of maggots as previously demonstrated by Schoene* in his study of the insect in cabbage plantings, and in the main chief losses of radish roots occurred during the latter part of May and during early June. Plantings that were ready to be pulled by the beginning of the last week in May escaped with little or no injury.

* Schoene, W. J., N. Y. Agr. Exp. Sta., Bul. 419, p. 125. 1916.

EFFECT OF SCREENING ON GROWTH AND QUALITY OF ROOTS,

With the exception of 1917 when cold wet weather prevailed during the growing period most of the sowings in the screened beds showed a higher rate of germination of radish seed, which was largely due to the better physical condition of the soil. In the uncovered plats the surface soil was frequently dry and hard so that germination of seed was retarded, if not entirely checked, and young seedlings often failed to establish themselves. As a rule the seedlings in the open beds were one or more days behind the screened plants in the time of their appearance above ground. (See Table V.) Besides a larger and more even stand on the average the screened radishes also grew more rapidly and presented throughout the growing season a more vigorous appearance.

The period of growth of radishes in the covered frames from time of sowing to the harvesting of the roots was variable, being largely governed by the date of planting and seasonal conditions. An examination of Table VII shows that the time required for the production of marketable roots was as follows:

For sowings during March, 58 to 69 days.
For sowings during April, 41 to 57 days.
For sowings during May, 27 to 46 days.

The total average yields of the screened and open plats are tabulated in Table VIII.

Besides larger yields the roots grown in the screened frames were for the most part more succulent and tender and therefore a more satisfactory product for the market. In addition to smaller yields of roots the leaves of the unscreened plants have usually been small, leathery and prickly to the touch. The explanation for these differences is that, with the meteorological conditions that normally prevail during the months covered by these tests, screening modified the physical environment of the plants, principally as regards temperature and moisture conditions of the soil, which, as a rule, proved very congenial to them. On clay soils, such as used in these experiments, incrustation of the surface of the soil, accompanied by hot weather and slight precipitation, have proven, as shown by the behavior of the check plats, severe handicaps to the production of roots of good size and desirable quality.

TABLE VIII. - SUMMARIZED YIELDS OF SCREENED AND UNSCREENED RADISH

PLATS FROM 1914 to 1917.
(Counts and weighings are based on rows of one hundred feet in length.)

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The differences between screened and unscreened beds with respect to attacks by flea-beetles and maggots have usually been very marked. With the exception of 1917 each year that the tests have been conducted both pests have been sufficiently abundant to cause appreciable damage. The flea-beetles were usually first to appear and they attacked the cotyledons of the radish seedlings, 'eating small round holes which resulted in damage of varying intensity. Young seedlings frequently succumbed to the first onslaughts of the beetles and many other plants were so stunted by the repeated attacks of the insects that they never produced roots of marketable size. Another form of injury that escapes the attention of the average grower is the work of the larvæ on the roots, which is unquestionably of sufficient importance during some seasons to exert a retarding influence on the growth of the plants. While screening has not completely protected radishes from flea beetles there has been, on the whole, considerably less evidence of the work of these insects in screened beds than in the open beds; and in all attacks by the creatures in screened beds the amount of damage by them has been considered negligible.

With respects to maggots the contrasts between screened and unscreened beds have been uniformly more conspicuous than those produced by the flea beetles. By means of tight frames and proper attachment of cloth injuries by maggots have been completely avoided. As shown by reports of the experiments during the different years, maggots began to appear during the latter part of May and radishes in open beds maturing during early June have frequently been too much infested with maggots to be marketable. Besides rendering roots less desirable for purposes of consumption there have also been losses due to actual destruction of seedlings. by maggots and retardation of growth and dwarfing of plants.

INFLUENCE OF SCREENING ON OTHER PESTS.

As grown under screening radishes possess tender foliage and roots. The plants are thickly massed, and the large leaves cause considerable shading of both plants and the ground about them. Cheesecloth restricts air circulation and reduces the intensity of light. There is, as a rule, more moisture in the soil, as probably of the air also, and temperatures range higher than in open beds. As compared with the latter method of growing radishes, it would appear that conditions under screening are more favorable for the development and growth of damping-off and downy mildew (Peronospora parasitica Pers.). While the latter disease has in occasional years, especially during 1917, caused quite a little damage to cabbage seedlings in screened frames, no noticeable injury has so far been observed with radishes.

Of more importance to date than the foregoing diseases are certain species of slugs and millipedes which, during seasons when there are prolonged spells of cold, wet weather, have proven capable of causing quite a little damage.

Three species of slugs have been collected about radish beds which, through the courtesy of Dr. F. C. Baker of the N. Y. College of Forestry, were identified as Agriolimax agrestis Linné, Agriolimax campestris Binney and Limax maximus Linné. All are known to obtain subsistence from various plants, including vegetables, but A.

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