Florida Agricultural Experiment Station


depletion of the organic matter in the soil. The further pre-
caution of removing the tobacco roots from the field gave slightly
poorer results, but the difference was within the limit of experi-
mental error.
 A cover crop of Crotalaria spectabilis, planted in 27-inch rows
and cultivated several times, followed in November by fallow,
gave somewhat poorer results than clean fallow followed by
a cover crop of oats.
 A cover crop of native vegetation, mostly grasses, plowed
under in January, gave variable results, with slightly to greatly
reduced yields, but average quality or better. The tobacco root
systems were abnormally coarse and deficient in fibrous roots.
 The nematode control obtained with clean fallow treatments
is explainable by the operation of 4 factors: (1) Aeration to
promote hatching of nematode eggs; (2) starvation of larvae
in the absence of host plants; (3) heat and (4) drying in a
surface layer of soil, which was changed at each listing.

 LITERATURE CITED
 1. CHAMBERLIN, F. S., and A. H. MADDEN. Insect pests of cigar-type
 tobaccos in the southern districts. U. S. D. A. Circ. 639. 54 pp. 1942.
2. GEORGIA COASTAL PLAIN EXP. STA. Root-knot control by cultural prac-
 tices. In its 19th Ann. Rpt. 1938-1939; 126-127. 1939.
 3. HOSHINO, HELENE MORITA, and G. H. GODFREY. Thermal death point of
 Heterodera radicicola in relation to time. Phytopath. 23: 260-270.
 1933.
 4. LE Roux, J. C., and F. J. STOFBERG. Control of the root-knot nematode
 by cultural practices. Union So. Africa Dept. Agr. and Forestry,
 Science Bul. 188. 29 pp. 1939.
 5. LINFORD, M. B., FRANCIS YAP and J. M. OLIVEIRA. Reduction of soil
 populations of the root-knot nematode during decomposition of organic
 matter. Soil Science 45: 127-142. 1938.
 6. TYLER, JOCELYN. The root-knot nematode. Calif. Agr. Exp. Sta. Cir.
 330. 35 pp. 1933. Reprinted, 1937.
 7. WATSON, J. R., and C. C. GOFF. Control of root-knot in Florida. Fla.
 Agr. Exp. Sta. Bul. 311. 22 pp. 1937.