Nematodes

Background

Plant-parasitic nematodes are microscopic, soil-dwelling worms measuring approximately 0.1-5 mm in length. At a certain threshold density, which is dependent on the type of nematode and the affected plant, nematode populations can cause considerable damage to a wide range of high-value vegetable crops and horticultural species. For example, 10-490 stubby-root nematodes per 500 cm3 of soil should not affect the growth of crucifer crops (e.g. broccoli, cabbage and turnips), but the application of a nematode treatment would be recommended for populations of greater than 500 per 500 cm3 of soil. The most severely affected plants include intensively-grown crops such as potatoes, tomatoes, carrots, grapevines and many perennial fruits that are grown under monoculture conditions, plus sugar beet and golf course turf. The financial cost of nematode damage for farmers, gardeners and owners of golf courses and sports fields is substantial. At present, effective nematode control requires an integrated approach including cultural, physical and chemical methods.

Plant parasitic nematodes (stained red) feeding on a
plant root and the root hairs.

An infective juvenile nematode as seen through
a microscope lens

There are different types of plant-parasitic nematodes with characteristic patterns of plant infestation:

Ectoparasites feed on the outside of plant roots causing severe moisture stress and a dramatic reduction in yield, e.g. sting, awl and stubby-root nematodes
Endoparasites enter the plant roots and root hairs resulting in malformation and yield reduction, e.g. reniform, cyst and root-knot nematodes

Plant-parasitic nematodes have a spear-like feeding structure known as a stylet, located at the forward end of the worm, and this is used to inject digestive enzymes into root cells, as well as for sucking out the digested cell contents. The resulting damage causes surrounding root cells to swell up or die, depending on the attacking species.

Signs of nematode damage:
Healthy potato foliage (left) and
nematode-infested potato plants
(right).

Nematode infestation has negative effects on plant emergence, vigour and response to fertilisers, and if left untreated, nematodes can cause a reduction in crop yield. The root damage caused by nematodes makes plants susceptible to drought stress and mineral deficiency, and can also lead to detrimental bacterial or viral infections. Furthermore, some nematodes carry harmful viruses that can be transmitted directly into the infested plant.

Potato tuber with spraing, a disorder
caused by the tobacco rattle virus (TRV)
that can be transmitted by nematodes

Effective management of nematode infestations requires an integrated policy of nematode identification and population density analysis, together with cultural, physical and chemical approaches to lessen the impact of nematode feeding damage.

Chemical management of nematode infestations includes the use of fumigants and non-fumigants. Fumigants are not only expensive, but they are also phytotoxic and must therefore be applied weeks or months prior to planting. Non-fumigants are not phytotoxic, but they act by paralysing, rather than killing nematodes. Eden Research products have several potential benefits over current nematicide and nematistatic treatments:

Terpene products are not phytotoxic
They are not environmentally toxic
Products can be used as a late pre-harvest treatment
Most notably, soil drenching with Eden products has resulted in dramatic reductions in the number of nematodes present, indicating that Eden products are highly potent against these microscopic pests

Eden Research and Development - Nematode trials

Initial laboratory tests against plant-parasitic nematodes suggested that Eden Research products are an excellent prospect for nematode control. Over the last 3 years, internationally-respected nematode experts have conducted pot and field trials, and the efficacy of Eden products has been assessed on several relevant agricultural crops.

The first field trial was performed on grapevines in South Africa and the results showed very encouraging reductions in the level of nematode soil infestation.
Small-plot efficacy testing against free-living nematodes, which cause severe problems in root crops such as carrots and sugar beet, were completed by independent contractors in 2007 and indicated that Eden Research products were more successful than a standard commercial nematode treatment in terms of both reducing nematode numbers and maintaining crop yield.

The results from Eden product efficacy trials include data on the control (expressed as the reduction in nematode numbers present in the soil) of stubby-root, stunt and northern root-lesion nematode populations (Figures 1, 2 and 3, respectively), the crop yield (measured in grams of mean individual carrot weight) from carrot plants grown in soil containing all three nematode species (mixed natural field population from Lincolnshire, UK) (Figure 4) and plant growth following treatment with Eden products.

Figure 1. Efficacy testing of Eden products against stubby-root nematodes

Efficacy testing conducted by Eurofins/Agrisearch, 2007

Stubby root nematode control

Six different Eden products (at 500 ppm) were tested against stubby-root nematodes (Trichodorus species), a pest that causes sparse, thickened roots, transmits tobacco rattle virus (TRV) causing ‘spraing’ disease in potatoes. Carrot, sugar beet and cereal crops are also often attacked.

Eden products were more successful against stubby-root nematodes than the commercial nematode product Vydate® (Dupont, 18 kg/hectare).

Figure 2. Efficacy testing of Eden products against stunt nematodes

Efficacy testing conducted by Eurofins/Agrisearch, 2007

Migratory stunt nematode control

Six different Eden products (at 500 ppm) were tested against the stunt nematode (Tylenchorhynchus species), a migratory pest that attacks almost any plant, but prefers the sandy soils associated with the turf grass of links golf courses.

All the Eden products were more effective than Vydate. The most successful stunt nematode control was observed with products B2Y31 and H2Y31.

Figure 3. Efficacy testing of Eden products against Northern root lesion nematodes

Efficacy testing conducted by Eurofins/Agrisearch, 2007

Northern root lesion nematode control

Six different Eden products (at 500 ppm) were tested against root lesion nematodes (Pratylenchus penetrans), a type of nematode that penetrates the roots and root hairs. P. penetrans particularly affects strawberry and raspberry plants at population densities as low as 50 worms per litre of soil.

Eden products B2Y13, H2Y11 and H2Y31 were effective against this species of root lesion nematode.

Figure 4. Yield from carrot plants following treatment with Eden products

Efficacy testing conducted by Eurofins/Agrisearch, 2007

Carrot crop yield

All Eden product treatments resulted in a greater yield of carrots (by weight) compared with the commercial Vydate® treatment.

Further nematode trials include:

A long-term pot and field trial was established to assess product efficacy against nematodes that attack young stone-fruit orchards in Colorado. These nematode infestations are known to transmit damaging plant-pathogenic viruses that cause major economic losses.
Pot trials on Papaya plants were conducted in Florida with favourable results for 3 different Eden products when used as a soil drench.

Conclusions

Trial data indicate that in particular two of Eden products are successful in terms of reducing populations of plant-parasitic nematodes, thereby increasing crop yield. Product application can potentially be achieved through irrigation systems, and it is hoped that this will help to extend the life of vineyards and orchards and enhance the viability of production units.

We therefore propose that Eden Research products are strong candidates for use in the battle against nematodes, and the development of these products as efficient nematode control agents will be one of the main targets for 2009 and beyond.

Future Directions

In conjunction with research and development specialists Battelle, it is our aim to produce a granular formulation of the Eden products in order to optimise the delivery of a soil treatment.
We wish to expand the database of nematode species that can be effectively controlled using Eden products.
Trials will establish the optimal timing of Eden product treatments for maximum efficacy, and explore the potential benefits of multiple treatment applications in one crop cycle.
It is not currently known how Eden products exert their observed effect on nematodes (i.e., nematicidal or nematistatic mode of action) and investigations to determine the mechanism of terpene product action against nematodes are scheduled for 2009.

For further detailed information on Eden's products, please contact Eden at info@edenresearch.com