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
ANTAGONISTIC PLANTS 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.
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 Narcissus 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 Population Densities 16 weeks after Planting NEMATODES/POT 4500 4000 3500 3000 2500 2000 1500 1000 500 0 Plants were clipped to 10 cm at 8 and 12 weeks to simulate mowing ** Unclipped Clipped Initial Density D-ESSEX TRUDAN STEPTOE SAIA TANGIA Marigold
Cruciferae 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.
Asparagus 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.
Crotalaria 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.
Neem = 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.
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
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.
Susceptible Tobacco as a Trap Crop to Reduce Tobacco Cyst Nematode 140 % of Starting Density 120 100 80 60 40 20 0 3 WKS 4 WKS 5 WKS 6 WKS 13 WKS Period of Growth Before Plant Destruction P LaMondia, 1996
Tobacco as a Trap Crop to Reduce Tobacco Cyst Nematode % of Starting Density 140 120 100 80 60 40 20 0 Susceptible Resistant 3 WKS 4 WKS 5 WKS 6 WKS 13 WKS Period of Growth Before Plant Destruction P LaMondia, 1996
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
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 large 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 of Northern root-knot nematode (Meloidogyne hapla) infects roots of potato before tubers are present. Second and later generations infect tubers. 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 and symptoms will not be expressed. This will not work for Columbia root-knot nematode which becomes active at cool temperatures and infects potato roots as soon as they emerge.