One or more of the features that are needed to show you the maps functionality are not available in the web browser that you are using.
Please consider upgrading your browser to the latest version or installing a new browser.
More information about modern web browsers can be found at http://browsehappy.com/
Potato cyst nematodes, in common with other cyst nematodes, do not cause specific symptoms of infection. Initially, crops display patches of poor growth and affected plants may show chlorosis and wilting, with poor top growth. Good top growth is essential for photosynthesis and production of sufficient nutrients for the health of the plant and production of new tubers. Affected plants suffer yield loss and tubers are smaller. To be confident that these symptoms are caused by potato cyst nematode and to give an indication of population density, soil samples must be taken or the females or cysts must be observed directly on the host roots.
Legislation provides a definitive set of rules (MAFF, 2000) designed to prevent the spread of potato cyst nematodes. The movement of soil is a common factor in the spread of potato cyst nematode, whether this is between countries, between farms or between sites in one field. Potato cyst nematodes probably spread to Europe through trade and the movement of potato tubers and soil adhering to them from other continents. Most countries have quarantine organizations that inspect potato shipments to protect their own countries from inadvertent importation of pests and diseases.
Physical barriers also tend to isolate pests in local areas, for example, deserts and rivers may isolate pests. Trade is the most common probable simple cause of new infestations of plant parasitic nematodes (Parker, 2000). Farmers are made are made aware of the risk of moving contaminated matter from one site to another on machinery, and of the need for preventive measures such as not sharing machinery between farms without thorough washing, cleaning and disinfestation first. Some natural movement cannot be controlled, for instance topsoil blown by strong winds from field to field, or infected topsoil moved by flood water onto clean sites. Animal manure has also been shown to contain viable cysts; the ingestion of the cyst appears not to impair its reproductive ability so can provide the means for new infestations to arise.
The following prevention methods can be used:
1. Check that machinery is thoroughly clean and free from plant debris.
2. Do not return soil that may contain potato cyst nematode to fields.
3. Clean the soil from potato tubers and have the soil tested to be sure that potato cyst nematodes are not transferred.
4. Make sure that the agency that tests the soil is competent and tests 500 g of soil per sample.
5. Grow susceptible and resistant potato cultivars alternately, thus reducing the possibility of selecting a highly virulent or new pathotype.
Crop rotation is frequently used to reduce population densities of potato cyst nematode. The major commercial hosts of the two potato cyst nematode species are in the plant family Solanaceae, namely potato, tomato and aubergine, all important cash crops. Where these crops are grown in monoculture for several seasons in infested soil, nematode densities increase to extremely high levels and crop yields become uneconomic. To reduce nematode population densities, non-host crops such as barley are grown between host crops (Whitehead, 1995). The length of the rotation and the crops used can have variable effects on the yield and the potato cyst nematode density. In South American countries, slightly different regimes are used and may include fallow, with intervening crops of lima beans, maize, barley or wheat. The annual decline rate in soil of G. pallida is, in general, slower than that of Globodera rostochiensis. When the reduction of potato cyst nematode is too slow by rotation alone, other additional methods can be used; for example, trap cropping can hasten the reduction of population densities.
Trap cropping is a simple method that has been used successfully for the reduction of cyst nematode populations (Halford et al., 1999). Sufficient crop growth time is allowed for the nematodes to penetrate the roots and develop into young adults (5-6 weeks), but not enough time for them to form new eggs. Potato cyst nematode populations can be reduced very quickly as long as the grower removes and destroys the crop, including the nematodes in the roots. If left too late, the nematode density will increase but, if the crop is removed in time, the nematode density is reduced and there will be a significant yield benefit for any subsequent potato crop. G. pallida can be reduced by as much as 80% per annum and even greater reductions were found when ethopropos was used in the soil before the first of two potato trap crops; almost 100% control was achieved (Mugniery and Balandras, 1984). The use of other non-tuberous solanaceous plant species to stimulate hatching has proved very efficient in Dutch studies. Non-hosts that are well adapted to temperate conditions, in this case Solanum sisymbrifolium, proved capable of inducing large hatches of potato cyst nematode juveniles. Solanum sisymbrifolium is fully resistant to potato cyst nematode, therefore eliminating the risk of increasing potato cyst nematode density (Scholte, 2000).
The use of 10 potato clones as trap crops has been tested in field trials in Northern Ireland (Turner et al., 2006) and their potential for the organic market has also been shown. Non-hosts that are well adapted to temperate conditions, in this case S. sisymbriifolium, proved capable of inducing large hatches of potato cyst nematode juveniles. S. sisymbriifolium is fully resistant to potato cyst nematodes, thus eliminating the risk of increasing potato cyst nematode density (Scholte, 2000). A note of caution: it is important to use the correct seed accession number as Stelter (1987) recorded lines no.72 and 121 as poor hosts, although producing fewer than 5 cysts per pot.
Solarization is a good method of killing nematodes in hot climates. The soil is covered with two layers of polyethylene sheeting, allowing the soil underneath to heat up to temperatures of 60°C or more. In cooler climates solarization is much less effective.
Certain European cultivars of potato have resistance (often only partial) to European pathotypes of potato cyst nematode but some South American populations are more virulent than European populations and are able to overcome the resistance in European cultivars (Kort and Jaspers, 1973; Turner et al., 1995). Thus, strict quarantine measures remain essential. Studies at the International Potato Centre (CIP) in Lima, Peru, on 3000 accessions of potato, have focused on the two locally predominant pathotypes of G. pallida: P4A and P5A. A more virulent pathotype (P6A) has emerged and been selected in some areas. Variety of cultivars (tolerant, resistant and partially resistant) has an important part to play in maintaining an acceptable balance of pathotypes. For example, Maris Piper is a popular potato cultivar in the UK and has full resistance to UK populations of G. rostochiensis but no resistance to G. pallida. Its widespread cultivation has selected G. pallida and it is now recognized that other types of cultivars (e.g. tolerant ones) should be included in the rotation to avoid this problem. Some potato cultivars with high resistance to G. pallida are grown in Europe and others are currently being developed. For example, Karaka (Anderson et al., 1993) and Gladiator (Genet et al., 1995) both have high resistance to both species of potato cyst nematode. Other cultivars with desirable qualities are listed in Whitehead (1998). UK populations of G. pallida are genetically more diverse than UK populations of G. rostochiensis. Resistance to G. pallida is usually polygenic and only partial, as in the cultivars Santé and Morag. Another problem in introducing new cultivars of potato is persuading retailers and consumers of the value and desirability of those cultivars.
Biological control agents active against potato cyst nematode are currently the subject of intense study. Although several parasites of eggs and females have been identified, none has given consistent control (Crump, 1987). Soils suppressive to potato cyst nematode have been identified (Roessner, 1986; Crump, 1998) and the fungal causal agents isolated. Selected isolates of Verticillium chlamydosporium, Paecilomyces lilacinus and Acremonium sp. show considerable potential and methods for their production, formulation and application are being evaluated. Natural parasites and biological control are being studied in order to identify natural agents for potato cyst nematode control, without needing to use the toxic chemicals currently in use. These methods will integrate with a variety of strategies such as trap cropping and rotation in sustainable management systems. This work began in the late 1930s (Linford et al., 1938) and still continues (Crump and Flynn, 1995; Segers et al., 1996).
The majority of studies in the late 1990s have concentrated on the fungal control agents Verticillium, Hirsutella and Arthrobotrys, and the bacterium Pasteuria. Several workers (e.g. Roessner, 1986) have studied biological control of G. rostochiensis in pots and in vitro. This work is difficult to transfer to the field for several reasons. For example, the form and volume in which to apply the control agent must be decided, and how the inoculum reacts to the microbial population already present in the field must be determined. Verticillium chlamydosporium will infect young females in pots but is less effective when potatoes are grown in the presence of low nematode population densities.
Very few data are available on the effectiveness of biological control in the field. This is due in part to the logistics of such operations, such as producing sufficent inoculum. It is also known that some tests do not produce the expected results for reasons as yet undefined, but they are probably related in some way to the physiology and ecology of the host parasite relationship. Progress in the area of biological control requires a better understanding of the population dynamics of potato cyst nematode and their parasites (Davies, 1998; Davies et al., 1991). A number of factors interact, such as plant host, the action of root exudates, soil type and the mode of parasitism of the control micro-organism at any one point in time. Also, potato cyst nematode may be more susceptible to infection by any one fungus at different points in its life- cycle. For example, the three major fungal parasites V. chlamydosporium, Fusarium oxysporum and Cylindrocarpon destructans, have all been detected at different times in the nematode life cycle but the most active of the three depends on the life-stage present (Crump, 1987).
The fungi, Paecilomyces lilacinis, Pochonia chlamydosporia and Monographella cucumerina may be used to aid control in PCN infested areas, but not used as the only method of control as field data suggests that the reduction in PCN populations is only around 60%. M. cucumaria is available commercially (MeloCon WG and BioAct WG - approved in the USA).
Some isolates of the bacteria Pasteuria penetrans can reduce populations of PCN. Applications are made during rotation of non-potato crops or before sowing potato to trigger a reduction in population density. Pasteuria penetrans is commercially available for root-knot nematodes. (Nematech Ltd., Tokyo).
Integrated pest management schemes benefit from the inclusion of a biocontrol agent, but, to date, no biocontrol agent can offer full protection on its own. Mutualistic bacteria and fungal endophytes are probably common in the agroecosystem (Sikora, 2007) but, to exploit potential candidates, a necessary objective for the future, is to understand the complicated manner in which they interact. The need to identify the mechanisms of control, how they function and then to scale up the technology for use commercial use in the field will take time.
A novel biological nematicide DiTera®, produced by Valent Biosciences Corp., USA, which has already been shown to control other plant parasitic nematodes in the field such as Xiphinema spp. and Radopholus spp., seems to have the capability to prevent hatching of potato cyst nematode in a specific manner. The specificity is linked to the permeability of the eggshell membrane. After testing DiTera® in solutions of 1 to 10 %, all were found to inhibit the hatching of the eggs. Meloidogyne incognita was used as a control and hatching of its eggs was not inhibited by DiTera® (Twomey et al., 2000).
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources: