PLANT NEMATODES THE GROWER SHOULD KNOW 7

lower fertility level in a soil or take more advantage of one that has been
artificially increased by fertilizer applications, than will one that is af-
fected by disease.


 Figure 1.-Roots of a tobacco plant grown in South Carolina and disfigured
through a heavy infection by root-knot nematodes. Note the stunted, blinded and
swollen roots and compare with type of root disfiguration and galling shown in
Figure 2. Such variations in character of root galling and disfiguration may be
related to different root-knot nematode species, but may also be the result of different
reactions by the hosts.1
 How are the growers to recognize the presence of these microscopic
nematode pests on their crops, and how are they to know the kinds in-
volved? Are there specific symptoms which indicate that a disease or
abnormal behavior is caused by a nematode, or an association of nema-
todes, or a combination of nematodes and fungi or bacteria, or a combi-
nation of all three of them, or a combination of still some other factor or
group of factors with nematodes? There exists one sure way to determine
this, namely the location and identification of the nematodes themselves.
May we therefore emphasize that it is not possible to recognize and
properly diagnose nematode diseases of plants by symptoms alone; in
 1 Most of the photographs used to illustrate the booklet were taken by Mr.
Marcel L. F. Faubert of the office of Plant and Operations; others by Mr. Wilfred
T. Mead of the Agricultural Research Service. The author wishes to express to
both of them his appreciation for the excellent service.