Antagonistic Plants for Nematode Management

Cultural Strategies for Nematode Management

Nematode Management With Plants

- No plants – fallow

- Nonhosts – crop rotation

- Green manure cover crops

- Antagonistic plants

- Trap crops

- Resistant cultivars

- Timing of planting and harvest to avoid damage

= “escaping in time”

A number of plants are antagonistic to nematodes.

Mechanism of “antagonism” is not always clear.

Need more study as potential sources of suppression.

Used as a rotation crop, cover crop, or an intercrop.

Some are simply “nonhosts” due to some

biochemical or physical incompatibility between the

nematode and the plant.

ANTAGONISTIC PLANTS

However, others appear to produce some kind of

chemical exudate that acts nematicidal.

In other cases, the growing plant is not particularly

nematicidal, but the decomposing plant, when

incorporated as a green manure, displays nematicidal

properties.

Rapeseed is a host for Pratylenchus penetrans but a

green manure amendment of rapeseed tops can reduce

P. penetrans populations.

It may also be possible that the growing or

decomposing plant encourages microbial antagonists.

ANTAGONISTIC PLANTS

“Antagonistic plants” have not been studied

extensively in developed countries but are commonly

studied in developing countries.

Interest has increased as nematicides are lost.

Information often comes from anecdotal observations.

Literature often hard to retrieve since most research is

done and published in undeveloped countries.

Will go through the more prominent examples.

ANTAGONISTIC PLANTS

Marigolds - Tagetes

Few nematodes reproduce well on marigolds.

Apparently does not affect the eggs of cyst nematodes.

French marigolds - growth period of 3-4 months (16

varieties tested) necessary to reduce Pp populations.

African marigolds reduced Pratylenchus penetrans;

yield of the following crop of Daffodil was doubled.

Population decline is due to nematicidal action of

root-diffusates (terthienyl and bithienyl compounds)

Minimum lethal dose = 0.2-5 ppm! Kill in soil?

Have to be careful! Sap and diffusates can burn skin,

can also be phytotoxic.

EFFECTS OF GREEN MANURE COVER CROPS

ON PRATYLENCHUS PENETRANS

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D-ESSEX TRUDAN STEPTOE SAIA TANGIA

Unclipped

Clipped

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Population Densities 16 weeks after Planting

**

Plants were clipped to 10 cm at 8

and 12 weeks to simulate mowing

Initial Density

Marigold

Sinapsis alba = white mustard

Brassica hirta = white mustard, called yellow mustard

Brassica nigra = black mustard

Lepidium sativum = cress

All inhibited emergence of Globodera rostochiensis J2,

Suppress Meloidogyne chitwoodi, Stubby-root?

Attributed to isothiocyanate (remember MIT?) from

glucosinolates in root diffusate.

Cruciferae

Produces glycoside “aspargic acid”

Inhibits juvenile emergence from cyst eggs and is

toxic to several nematodes.

Reduced numbers of Paratrichodorus minor and had

systemic nematicidal properties when sprayed on

tomato roots.

Asparagus

Crotalaria juncea – Sunn Hemp

Being used as a cover crop in tropical and subtropics

Crotalaria spectabilis (Rattlebox) = suppress nematodes

when used in various cropping sequences.

May be due to the alkaloid monocrotaline =

pyrrolizidine ester

- Inhibited mobility of Meloidogyne incognita.

However, other plants with this compound are

susceptible.

Crotalaria

= many medicinal properties = “Nature’s Drugstore”

Parts of the plant as well as seed-cakes (seed remnants

after oil is removed) are highly nematicidal. .

Neem

Intercropped seedlings suppress Meloidogyne

incognita and Rotylenchulus reniformis on tomato as

well as Tylenchorhynchus brassicae on cabbage and

cauliflower but free-living nematodes remained high.

Root exudates seem to be toxic to many nematodes.

Inhibit hatching of M. incognita.

Neem

Mixed cropping with neem is often impractical.

An organic amendment with neem seed-cakes is a

little more practical.

Neem may serve as a model for developing new

control strategies and new nematicidal compounds

that could be commercially produced.

This stresses the importance of plant diversity and

looking for naturally occurring compounds.

Often nematode control with an antagonistic plant can

be enhanced by incorporating it as a green manure.

Neem







- Trap crops




Trap Crops

Plants which are good hosts for sedentary parasites.

Nematodes are allowed to infect the plants, and then

the plants are killed, trapping the nematodes inside

where they die before they can lay eggs.

Particularly effective for species that require a host

exudate to hatch (i.e. cyst nematodes)

Does not work for ectoparasites or migratory

endoparasites that are not “trapped” in roots.

Initial concept was to use susceptible commercial

cultivars, which could result in population increase

if the plants were not killed before females laid eggs.

Trap Crops

Recently, cultivars have been developed specifically

as trap crops (radish for sugar beet cyst nematode).

These cultivars may be attractive to the nematode

for invasion but may lack nutritional requirements

for females to develop and lay eggs.

This allows the plant to be grown longer and

provide some of the other benefits from cover crop

such as building organic matter, weed suppression

and increasing beneficial microbial populations.

Practiced more in developing countries.

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Susceptible Tobacco as a Trap Crop

to Reduce Tobacco Cyst Nematode %

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LaMondia, 1996

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Tobacco as a Trap Crop

to Reduce Tobacco Cyst Nematode

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Resistant

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P Period of Growth Before Plant Destruction

LaMondia, 1996







- Trap crops




Nematode Management by

Early Planting and Harvest

Nematodes are limited by cool soil temperatures.

For crops that tolerate cool temperatures

planting early can give the crop a “head start” before

temperatures allow nematode activity to cause

substantial damage.

Once the crop develops a sufficient root system it can

tolerate a moderate density of nematodes when they

do become active.

Earlier planting can also result in an earlier harvest

and crops can be removed before damage can occur.

Examples

Sugarbeet seed germinates at cool spring

temperatures before sugar beet cyst nematode

(Heterodera schachtii) becomes active.

Planting early when it is cool allows the plant to

develop a robust root system that can tolerate a larger

nematode population when soils warm later.

Examples

Cereal cyst nematode (Heterodera avenae) hatch and

infect roots in the spring.

Fall-planted cereals are larger than spring-planted

cereals when nematodes begin infecting roots so

plants tolerate nematodes better, are not as stressed,

and yield reduction is less.

Examples

The first generation J2 of Northern root-knot

nematode (Meloidogyne hapla) infect roots of potato

when soil temperature is warm enough.

Second and later generations infect tubers as well as

roots. If potato is planted and harvested early, you

can avoid most or all nematode infection of tubers.

Any nematodes in tubers will not develop in storage

because temperatures are too cool, symptoms will not

be expressed.

Examples

This will not work for Columbia root-knot nematode

which becomes active at cooler temperatures and

infects potato roots much earlier.

Therefore, second generation J2 emerge earlier and

infect tubers before they are large enough to harvest.

Columbia root-knot nematode also can continue to

develop under some storage temperatures so

symptoms can be expressed in storage.

Antagonistic Plants for Nematode Management

Education

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