Download Natural Enemies of Nematod

Natural Enemies of Nematod
studies of complex soil environment aimed at favoring fungi
and other organisms that limit plant nematode populations
R. Mankau
nematodes are obligate parasites belong- relativcly large mouths with rasping
ing mostly to the Zoopaguceue, a family toothlike structures which tear into the
and other nematodes. There are indica- of Mucomles. These fungi operate mainly bodies of their victims, but they have not
tions that some bacteria may cause re- by the production of sticky spores which been found to be very effective in reductions in nematode populations and, adhere to the nematodes, although some ducing populations of the plant parasitic
although no virus diseases of nematodes species also have sticky hyphae. There nematodes.
A few species of predaceous styletare known at present, some conceivably are also several species of Chytrids and
other lower Phycornycetes which are bearing nematodes, having hollow spears
exist.
obligate parasites of nematodes. They with which they pierce the cuticle of their
produce tiny zoospores which attach prey and suck out the body contents,
Fungi
themselves to the surface of a neniatode, have been isolated from California soils
Many species of fungi-mainly hypho- penetrate its cuticle and develop within and can be reared artificially in the
capture its body, eventually producing more laboratory and increased to fairly large
mycetous Monilides -which
nematodes in unusual ways are widely zoospores which attack more nematodes. numbers. Relatively little is known about
of the ~
~ butotests~are p
distributed in California, both in agriunder way which will indicate whether
cultural soils and in virgin areas. They
enmesh the nematodes in a mycelium of ward free-living soil forms and do not or not they can provide a practical coninterwoven threadlike filaments, either greatly affect populations of plant-para- trol method for plant parasitic nematodes.
by sticky knobs or by the general sticki- sitic nematodes.
It has been believed for some time that
ness of the individual threads-hyphac
-or through snares or loops which, when decaying vegetable matter, manure, and
triggered as a nematode passes through similar soil amendments call restrict Toxic Plants
them, hold and constrict the prey very some nematode populations in the soil.
Another phase of biological control of
tightly. In all cases, the cuticle of the Such materials may favor the develop- plant parasitic nematodes was recently
nematode is penetrated by an outgrowth ment of fungi and other organisms that discovered in the Netherlands, where
of the fungus, which ramifies through the attack nematodes. Trials with mulches certain plants were found to possess
body of the captured prey and absorbs of olive pomace, pine shavings, redwood nematocidal substances in their roots.
its contents. Such fungi can be grown shavings, or shredded fir bark in citrus Species of Tagetes, the common Afrion artificial media and, under laboratory groves, where one to several species can marigolds, can reduce populations
fungi occurred of root-lesion nematodes--PratyZenchs
conditions at least, are capable of de- of nematode-ca~ur~ng
naturally, have failed to control popula- spp.-in the soil, but not all plant parastroying large numbers of nematodes.
Trapping fungi evidently vary in their tions of the citrus nematode. Whether sitic nematodes are affected by the same
ability to reduce nematode populations similar practices have any practical value plants. Trials now under way in some
in the soil. Their dectiveness has not with other crops remains to be deter- southern California rose nurseries may
yet been adequately investigated. Re- mined.
indicate whether marigolds can be used
Predaceous and parasitic fungi are to reduce root-lesion nematode populasearch workers in Hawaii, about twenty
years ago, demonstrated that one of the obviously beneficial mmbers of the soil tions in infested soil. Other plants may
five species of nematode-trapp~ngfungi flora, and should be considered in shap- exist which possess similar properties
used in an experiment was able to reduce ing general agricultural practices. An and are effective on a wider range of
a poulation of root-knot nematodes sig- attempt is being made to determine nematode pests.
nificantly. The fact that many fungus whether efficient and practical methods
species occur in the soil in association for utilizing such fungi can be developed.
with large populations of nematodes Much remains to be learned about basic Eradication Untikely
parasitic on some California crops would soil biology. However, where these organThe utilization of natural enemies of
indicate that in the natural biological
ba€ance of the soil these fungi are not
CornpIeteEy effective in controlling such
parasites, The possibility exists that
about this subject. Complete eradication
species of fungi discovered in other
of a plant parasitic nematode species by
regions of the world may prove more
its natural enemies will be unlikely. Howeffective in reducing the important plant Predaceous Nematodes
ever, contrived biological control holds
Several types of nematodes which ap- out a possibility of keeping nematode
nematodes in California. Areas to which
nematode species are native may yield parently feed mainly on other nematodes pests in check to a point where their
natural enemies not occurring elsewhere, are widely distributed in all soils, al- attacks on crops are economically unbut almost nothing is known about geo- though generally not in large numbers. noticed.
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graphic origins of important plant para- They are abundant in California soils ~
and are under investigation as possible
R. Mankau is Assistant Nernatologkt, Unisitic nematodes.
Fungi of another group that attacks agents in biological control. Some have versity of California, Riverside.
Nematodes are attacked by a variety
of organisms including protozoa, fungi,
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C A L I F 0R N I A A G R I C U L T U R E , S E P T E M B E R , 1959
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