DEPARTMENT OF AGRICULTURE


tode. (A. fragariae Ritzema Bos) causing spring dwarf in strawberry!
plants, Bessey's strawberry nematode (A. besseyi Christie) causing sum-
mer dwarf, the chrysanthemum nematode (A. ritzemna-bosi); the needlE
nematodes (Genus Xiphinema Cobb); and certain spear nematodes of
the Genera Dorylaimus Bastian, Pungentus Thorne and others. Therq
are known today several hundred different species of nematodes that
attack plants and at least a dozen must be considered major pests whilq
others will undoubtedly be considered as such after they are better
known. In general, however, their significance as pests is certainly under
estimated. There are several reasons for this. One is the soil-bornt
character of all plant nematodes; a second, their small microscopic size
a third, their hidden mode of life either in the soil or inside the plant
tissues; a fourth, that their study is technically very difficult; a fifth, thaj
they are considered a border subject not properly belonging to the
field of the entomologist or that of the plant pathologist or the parasite
ologist. In addition plant nematology and its related subject soil, fresh-
water, and marine nematology are not given as courses in our college
and universities and are considered only a side line of research by mosf
agricultural institutions.
 Then, too, there is the tendency on the part of growers and investi-
gators to judge the health and growth conditions of plants mainly orl
the basis of the appearance of the above-ground parts. This generally
leads to an underestimation of the significance of nematodes in theil
role as plant pathogens and their influence on plant growth. Since the
roots and other underground parts of plants are the principal portionI
attacked by nematodes, a full evaluation of their damage naturally
necessitates the uprooting of a sufficient number of plants for inspection
of the root system. This, of course, often means the loss of many plants.
In the case of shrubs and trees this may involve a considerable loss,
without the gain of more than a chance result. The evaluation of the'
significance of other underground pests and diseases of crops, as in
the case of plant nematodes, is also more difficult than that of those
found above ground.
 I
 Growers frequently are also inclined to blame reduced yields on a
lack of soil fertility, on deficiencies of certain elements, on drought and!
other seasonal conditions, on winter kill, sunburn, lightning, and other
factors, when actually nematodes may be the cause of these conditions.,
Growers also sometimes tell of the wonderful crops they or their parents
used to grow and that the production of such crops is no longer possible,,
even with heavy applications of fertilizers. We are convinced that many
such instances not infrequently would prove upon examination to be
the result of root destruction by nematodes. In other countries the
term "sick soil" is sometimes used to express failure of a given soil to
continue to produce, notwithstanding fertilizer applications or the use
of other means to induce increased production. Nematodes were repeat-
edly found to cause such conditions, often more specifically termed by