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A Technical Guide for Wine Producers
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Nematodes In Vine Nurseries
Practical Guidelines For The Short- And Long-Term Control Of Nematodes
Compiled for the Deciduous Fruit Industry by Sheila Storey of Nemlab. Tel 021 - 9752350, Fax 021 - 9765006 or e-mail sheila@nemlab.co.za www.nemlab.co.za
INTRODUCTION
Nematodes are microsopic worm-like organisms that attack the roots of plants. Damaged roots result in a reduced uptake of nutrients and water.
Vines are attacked by various nematodes, of which the root-knot nematode is the most important. Due to the large-scale use of root-knot nematode resistant rootstocks, the characteristic galls of root-knot nematode are absent. The damage caused by other nematodes is not detectable, both above and below ground. Dagger and ring nematodes are becoming an increasing problem in vines, and control of the latter is problematic.
There are several reasons for the increase in nematode problems over the last number of years. The first reason is the greater awareness of nematode damage. A second reason is the increasing pressure to re-use soils. Certain practices which are carried out give rise to these problems. The fact that establishment takes place on the same soils is the main reason. Associated herewith is the fact that few nurseries consider fumigating the soil, or realise how important it sometimes is.
Different nematodes attack different fruit types (see Table 1).
Nematodes are divided into two groups, depending on their feeding habits, viz. endo- and ectoparasites (Table II).
INFESTATION SOURCES
There are three possible infestation sources, viz. water, plant material and soil.
Water
Water originating from fast-flowing rivers with significant agricultural activity (particularly vegetable production) can act as a nematode infestation source. Such water is however a minor source of infestation in comparison to the other two sources. The percentage of nematodes that originate from water is minimal. The build-up of nematodes in the soil is thus slow. In the case of nurseries where establishment often takes place on the same soil, the build-up can take place more rapidly.
Plant material
Only rooted plant material can be a possible source of infestation. Such infestation is particularly true of the migrating endoparasite, root-lesion nematode and the sedentary endoparasite, root-knot nematode. Both nematode types live in the roots. It has also been found that ring and dagger nematodes, with their long stylets, are inclined to cling onto roots and can thus be transported together with plant roots.
The current certification scheme requires that plant material must be visibly free of nematode infestation. The scheme does not require a compulsory test for nematodes. The test for Xiphinema index, the carrier of grapevine fanleaf virus, is very specific and does not include the other nematodes. Symptoms of only one nematode, i.e. the root-knot nematode, are visible. No provision is therefore made for the other nematodes within the grapevine certification scheme, not even for low populations of root-knot nematode where the symptoms are not yet visible.
Soil
The soil is the most important infestation source. Infestation in the soil is determined by previous crops, cover crops, weeds or natural vegetation (fynbos) that were present in the soil. Should any of these plants have been a host for the range of nematodes that occur on vines, then the population will increase very quickly in the presence of vines and subsequently cause damage. The new plant material can thus be infected and this infestation is subsequently carried over to the producer.
Monoculture remains a risky practice, and will allow the various nematodes to increase rapidly. The populations later reach a level which is impossible to manage or control, and then fumigation is the only control option. The lack of knowledge of the host status of the previous crop often leads to problems.
MONITORING AND CONTROL
PREVENTION IS BETTER THAN CONTROL!
Water
Water cannot be treated chemically, it can however be filtered. Any filter, including sandfilters, will give a measure of control. Filters with 5 æm openings are required to totally exclude nematodes from water, but this is impractical in the orchard situation. In the nursery, where water possibly holds a large risk, filters should seriously be considered.
Infestation from rivers can also be drastically reduced by pumping water into dams. The water should preferably stand for 48 hours to give the nematodes time to settle, and then water must be drawn from the surface.
The monitoring of water is impractical and is not recommended.
Plant material
As mentioned previously, only rooted material is a source of infestation. Should rooted material be brought in from outside, it is of critical importance that it is free of nematodes.
The use of a warm water treatment to remove nematodes from plant material is very effective. The plant material is placed in warm water at 50 øC for 15 minutes. This method has been proved and is 100% effective against root-knot nematode. The method is probably also effective against most other nematodes but must still be tested to establish its effectiveness.
Chemical treatment of plant material (root dip) can be problematic and is less effective than the warm water treatment.
There are certain vine rootstocks which provide varying degrees of resistance towards root-knot nematodes (Table III). The plants are however still sensitive to other nematodes that attack them. In the literature there are references to possible sensitivity of certain rootstocks to some of the other nematodes.
Soil
Prior to establishment
It is of critical importance to limit the nematodes in the soil to a minimum before new plantings are established.
a. Identify at least one (or more) year(s) in advance (the summer before planting) on which soils new plantings are going to be established. It is particularly old stone fruit and vine soils that cause problems because the same range of nematodes attack these crops (Table 1). Other crops that hold possible risks include most vegetables, cucurbits, most weeds, Port Jackson, Acacia, Black Wattle and rye. Except for rye, most of these plants are excellent hosts for root-knot nematodes. Rye and onions are good hosts for root-lesion nematodes.
b. Establish the risk of the soil in relation to nematode infestation by taking both soil and root samples. The samples should be taken while a crop is still present, i.e. before trees, vines, or other previous crops are removed from the soil. When the host plants are removed, the nematodes revert to an egg stage, which then makes it impossible to determine populations at a commercial level.
c. Remove as many of the old roots of the previous crop as possible. It is particularly the endoparasitic root-lesion and root-knot nematodes which find shelter within the roots.
d. The result of the nematode analysis and the time period before the next planting determine what control measures should be applied. Non-chemical measures include a rest/fallow period or the establishment of non- or weak hosts. Other possibilities include solarisation, biofumigation or the use of fumigants.
A fallow period can be considered but it is very important that all weeds and volunteer plants are kept to a minimum. The longer the fallow period for the soil, the more effective the rest period will be for nematode control. It is preferable to rather establish a weak host such as oats than leaving the soil fallow. In the absense of a host, eggs survive for long periods in the soil, and hatch later in the presence of a host. In the case of a weak host the eggs hatch but the nematode cannot complete its life cycle. It is important to again determine the nematode infestation just before the cover crop dies or is ploughed in.
The establishment of non-hosts (particularly for root-knot nematode) such as Tagetes and Crotalaria spp for a period of at least one year, but preferably longer (3 years), should be considered. The long-term establishment (3 years) of Eragrostis spp as a non-host is also a good control measure. It is again important to determine the nematode infestation just before the cover crop dies or is ploughed in.
The establishment of weak hosts in a rotation system can be considered. Crops that are considered weak hosts include oats, triticale and wheat. Rye must be avoided where root-lesion nematode occurs. The effectiveness of the rotation system in terms of nematode control will depend upon the infestation at the beginning of the rotation as well as the time period of the rotation. A period of at least three years is required if the infestation is initially relatively high. Much research still needs to be done to determine the extent of susceptibility of these crops to various nematodes. This is one of the large gaps in our knowledge base. It is important to conduct an analysis of the nematode infestation again just before the crop dies or is ploughed in.
If the population is exceptionally high, and no fallow period is planned, it is sometimes essential to fumigate the soil before the new vines are established. The result of the nematode analysis will give an indication if fumigation is required or not. Some producers believe that chemical treatment after establishment gives the same results as fumigation. This is however not true.
Fumigation can only be carried out prior to establishment. The following fumigants can be considered: methyl bromide; 1,3-D (Telone II); ethylene dibromide (EDB); furfural (Protect) and metham sodium (Herbifume). Each of these fumigants has very specific requirements to guarantee successful treatment. The requirements include, amongst others, temperature, soil type, moisture, organic material content, etc. Establish thus timeously what the requirements of each product are. The requirements are available from Nemlab or the agricultural chemical companies.
Solarisation is a method to control soil-borne organisms and pathogens through the use of raised soil temperatures. The temperature is increased by placing a thin, transparent poly-ethylene plastic over a moist soil surface. Solarisation reduces the nematode population drastically, but will not totally eradicate it.
Biofumigation or biological fumigation is a technique that uses certain plants' own protection functions to control a range of organisms and pathogens, including fungi, bacteria, nematodes, insects and certain weeds. The plants produce special volatile compounds, of which glucosinolates are the most important. Plant types particularly suitable for biofumigation include the family Brassicaceae (cabbage, cauliflower, broccoli, kale, canola and mustard), and the family Moringaceae (horseradish and certain types of radishes). The plants are harvested immature, chopped fine, and worked into the soil. The land then lies fallow for 10 - 14 days before the next crop is planted.
After establishment
It is extremely important that populations are limited to the minimum during this stage. Roots that are damaged in this young stage do not recover easily and will never reach their full potential. The last analysis which was conducted on the site will indicate if chemical treatment after establishment must take place or not.
a Nursery vines
Should the result of the nematode analysis recommend chemical treatment after establishment, then the first treatment can be applied when the white roots are 8 - 10 cm long.
b During the season
Since most nematodes only hatch in the presence of root exudates, it takes approximately six weeks from establishment for the soil to reach an equilibrium. Sampling should thus commence at this stage. Take soil and root samples throughout the growing season. Populations are highest in the summer months and decline as the soil becomes colder. Recommendations based on the results are adjusted according to the time of sampling.
The results will indicate whether a treatment is necessary or not. Thereafter, sites can be monitored on a regular basis (ñ every 2 months) and the necessary treatments applied according to the results. Regular monitoring should take place where the infestation is high. Establish the last nematode status from February to March in order that treatments can be carried out timeously.
c Vines standing over to following season
Sampling should begin in the early spring. Take soil and root samples throughout the growing season. Populations are highest in the summer months and decline as the soil becomes colder. Recommendations based on the results are adjusted according to the time of sampling.
The result of the first sampling will indicate whether a treatment is necessary or not. Thereafter, sites can be monitored on a regular basis (ñ every 2 months) and the necessary treatments applied according to the results. Regular monitoring should take place where the infestation is high. Establish the last nematode status from February to March in the previous season in order that treatments can be carried out timeously.
d Foundation blocks and mother blocks
Always first determine the level of infestation before any action is taken against nematodes. The result of the nematode analysis will indicate the number of treatments. The treatments must commence just before root growth peaks in the spring and autumn. The optimum stage for treatment is within 30 days after harvest, followed by the period just before and after bud-burst. Treatments can be applied throughout the year, but the above-mentioned times give the best results.
It is important that the periods between treatments are limited to 6 months. The year-on-year treatments are not successful. The ring nematode is more difficult to control and it thus takes longer to achieve a reduction in its numbers. It is unnecessary to eradicate nematodes. Try to reduce nematode numbers to acceptable levels.
Currently (August 2006) aldicarb (Temik), cadusafos (Rugby) and fenamiphos (Nemacur, Fenamiphos) are registered on vines. The recommended dosages prescribed on the label must be used. It is important to wash the nematicide in with sufficient water (10 - 20 mm). It is also important that the planting row or ridge is free of cover crops or weeds at the time of application. Due to the possibility of accelerated microbial degradation, it is important to alternate the nematicides.
e Heeling in soils
Heeling in soil of both nurseries AND producers should be monitored and, if necessary, appropriate action must be taken. The same rules, as for all soils where planting will take place, apply here.
Choice and use of nematicides
Nematodes are pathogens which must be well managed to reduce the risks. It is incorrect to believe that the problem can be solved by chemical control.
Currently (August 2006) aldicarb (Temik), cadusafos (Rugby) and fenamiphos (Nemacur, Fenamiphos) are registered on vines. The standard dosage for established vines is not sufficient. Due to the close plantings in nurseries the dosage should be determined in conjunction with a chemical company and a nematologist.
The chemicals can possibly be phytotoxic to young vines and should not be applied too early. It is suggested that the first applications take place when the white roots are 8 - 10 cm long. The chemicals must be applied by knapsack sprayers. Application by overhead sprinklers is discouraged.
It is important to wash the nematicide in with sufficient water (10 - 20 mm). Since the soil is already moist, and because irrigation is applied every second day, less water than recommended above is sometimes necessary to wash in the nematicide. It is important that all personnel wear protective clothing, i.e. gloves and gumboots, for one week after the application. It is also important that the soil surface is free of cover crops or weeds at the time of application. Due to the possibility of accelerated microbial degradation, it is important to alternate the nematicides.
The ring nematode is more difficult to control and it thus takes longer to achieve a reduction in its numbers. It is unnecessary to eradicate nematodes. Try to reduce nematode numbers to acceptable levels.
GENERAL ROOT HEALTH AND NURSERY SANITATION
It is advisable to promote root growth with the use of a root stimulant. A mulch on top of the soil or the addition of any organic material will be of great benefit. None of these additions will control high nematode numbers, but will encourage root growth and natural enemies (beneficial soil organisms), thereby reducing damage by nematodes. Nematode numbers will then decline over the long-term.
General nursery hygiene must be maintained at all times. Soil implements that have been used in infected sites must be cleaned before they are moved to new, clean sites. Infected plant material must be removed and burned.
The guidelines as set out above are largely based on experience. Due to the lack of sufficient scientific knowledge, it is not possible to confirm these guidelines with scientific evidence.
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