Reduced Nematode Populations Research Articles

Root-lesion nematodes (Pratylenchus thorneiandP. neglectus): a review of recent progress in managing a significant pest of grain crops in northern Australia

Two species of root-lesion nematode (predominantly Pratylenchus thornei but also P. neglectus) are widespread pathogens of wheat and other crops in Australia's northern grain belt, a subtropical region with deep, fertile clay soils and a summer-dominant rainfall pattern. Losses in grain yield from P. thornei can be as high as 70% for intolerant wheat cultivars. This review focuses on research which has led to the development of effective integrated management programs for these nematodes. It highlights the importance of correct identification in managing Pratylenchus species, reviews the plant breeding work done in developing tolerant and resistant cultivars, outlines the methods used to screen for tolerance and resistance, and discusses how planned crop sequencing with tolerant and partially resistant wheat cultivars, together with crops such as sorghum, sunflower, millets and canaryseed, can be used to reduce nematode populations and limit crop damage. The declining levels of soil organic matter in cropped soils are also discussed with reference to their effect on soil health and biological suppression of root-lesion nematodes.

Incidence and control of the citrus nematode, Tylenchulus semipenetrans Cobb, in the north of Iran

Abstract A survey of citrus orchards of northern Iran revealed that the citrus nematode, Tylenchulus semipenetrans, was present in 89% of soil and root samples collected. The number of juveniles and females averaged 6490/250 ml soil and 214/g root, respectively, in infested samples, and the mean numbers of juveniles and females in soil and root samples of sweet orange and sour orange rootstocks were greater than the damage threshold level in most regions. Population patterns of citrus nematode on sour orange Citrus aurantium and Poncirus, Poncirus trifoliata, rootstocks were monitored for 2 successive years. Nematode population densities peaked once a year during July-August and declined to lower levels during autumn and winter on both rootstocks. The duration of the life cycle of T. semipenetrans was 8 and 9 weeks on sour orange C. aurantium and Troyer citrange, C. sinensis × P. trifoliata, seedlings, respectively, at 24 ± 2°C. In glasshouse experiments, T. semipenetrans was controlled on sour orange seedlings by the granular nematicides, fenamiphos and cadusafos, the doses 4 and 8 ppm having the greatest effect when applied simultaneously with nematodes, whereas the nematicides Vydate and fenamiphos at 8 ppm showed greatest effects on nematodes in roots when applied 6 weeks after nematodes had been added to the soil. The effects of granular fenamiphos and cadusafos (10G) on T. semipenetrans population densities were also investigated in infested citrus orchard with rates 1.0 and 2.0 g a. s. of nematicides/m2 for 1 year. Although the nematicide treatments reduced nematode population densities in soil and roots, fruit weight and size was not affected by these treatments.

Nematicidal activity of culture filtrate of Beauveria bassiana against Meloidogyne hapla

Culture filtrates of Beauveria bassiana at different concentrations were evaluated for nematicidal activity against the northern root knot nematode (Meloidogyne hapla); bioassays included egg hatching, mortality and infectivity on tomato plants in pots under glasshouse conditions. The percentage mortality and inhibition of hatching of root-knot nematode were directly proportional to the concentration of culture filtrates of B. bassiana. Soil drenching with culture filtrate of B. bassiana significantly reduced nematode population densities in soil and in the roots and subsequent gall formation and egg-mass production by M. hapla under glasshouse conditions.

Control of root-knot nematodes in organic farming systems by organic amendments and soil solarization

The efficacy of organic amendments, with or without soil solarization, for the control of the root-knot nematodes Meloidogyne incognita and M. javanica in organic farming systems was tested in pot, container and greenhouse experiments. Broiler litter, cottonseed meal, feather meal or soybean oilcake, which had been effective in reduction of galling caused by M. javanica on tomato plants in pot experiments, were applied to a field at 0.75–2.0 kg m −2. In three experiments, soil solarization alone reduced nematode populations in the soil and galling indices on tomato and pepper plants, whereas the amendments alone were not effective. Combinations of the amendments with soil solarization were more effective than the amendments or soil solarization alone in reducing nematode populations and galling indices in most cases. High soil temperatures and accumulation of ammonium/ammonia in these treatments seemed to be involved in controlling root-knot nematodes. Nematode control efficacy on the edges of solarized beds, with or without amendments, was lower than that in the middle of beds. Soil solarization in combination with organic amendments could be used for root-knot nematode control in organic farms.

Potensi Bakteri Endofit Pengendali Nematoda Peluka Akar (Pratylenchus brachyurus) pada Nilam

Root lesion nematode ( Pratylenchus brachyurus ) is one of the most important pathogens of patchouli that caused significant losses. Studies on the potential of endophytic bacterial to control P. brachyurus on patchouli had been conducted. To evaluate the effectiveness of endophytic bacterial against to P. brachyurus on patchouli, nine isolates of bacteria (NJ2, NJ25, NJ41, NJ46, NJ57, NA22, ERB21, ES32, and E26) were applied by deeping root seedling into bacterial suspension. A study of the physiological characteristics of nine isolates was conducted by using specific medium. The results showed that endophytic bacterial was significantly reduced the population of P. brachyurus and all isolates bacterial promoted growth of patchouli (shoot weight, root weight, and root length). Four isolates, i.e. Bacillus NJ46, Bacillus Na22, Bacillus NJ2, and Bacillus NJ57 were among the potential control agents that reduced nematode populations as much as 68.1–73.9%. Almost all of the isolated bacteria from patchouli roots were able to solubilizing phosphate, while some of them had the ability to produce chitinase, cellulase, protease, HCN, and fluorescency.

Potential of Endophytic Bacterial to Control Lesion Nematode Pratylenchus brachyurus) on Patchouli

Root lesion nematode (Pratylenchus brachyurus) is one of the most important pathogens of patchouli that caused significant losses. Studies on the potential of endophytic bacterial to control P. brachyurus on patchouli had been conducted. To evaluate the effectiveness of endophytic bacterial against to P. brachyurus on patchouli, nine isolates of bacteria ( NJ2, NJ25, NJ41, NJ46, NJ57, NA22, ERB21, ES32, and E26) were applied by deeping root seedling into bacterial suspension. A study of the physiological characteristics of nine isolates was conducted by using specific medium. The results showed that endophytic bacterial was significantly reduced the population of P. brachyurus and all isolates bacterial promoted growth of patchouli (shoot weight, root weight, and root length). Four isolates, i.e. Bacillus NJ46, Bacillus Na22, Bacillus NJ2, and Bacillus NJ57 were among the potential control agents that reduced nematode populations as much as 68.1-73.9%. Almost all of the isolated bacteria from patchouli roots were able to solubilizing phosphate, while some of them had the ability to produce chitinase, cellulase, protease, HCN, and fluorescency. Key words: endophytic bacterial, Pratylenchus brachyurus, Pogostemon cablin, patchouli, nematode, biological control

Evaluating Brassica species as an alternative control measure for root-knot nematode ( M. incognita) in Georgia vegetable plasticulture

Multiple Brassica species commonly grown in Georgia were evaluated as a potential alternative to methyl bromide for management of root-knot nematode in vegetables. Brassica species produce general biocides called glucosinolates and were grown as cover crops and incorporated as green manures prior to transplanting of vegetable crop. Nematicidal activity of the Brassica species was based on net changes in nematode population and root damage caused by root-knot infection and feeding. Plant growth and crop yield was also evaluated to determine the response of the subsequent vegetable crop to the incorporated Brassica species. Incorporation of select Brassica species reduced root-knot populations and root damage caused by root-knot infection comparable to non- Brassica species cover crops with metam sodium in most years; however, the level and consistency of the nematicidal activity varied between and within Brassica species. Variations in plant growth and yield were also observed among and with Brassica and non- Brassica species. Generally, increased growth and yield corresponded with cover crop treatments that had the lowest levels of root-knot nematode populations at planting of the subsequent crop. Several cover crop treatments had a negative affect on the growth and yield potential of the vegetable crops. Therefore, a producer will need to choose a Brassica species cover crop that can significantly reduce nematode populations without adversely affecting the growth/yield of the subsequent vegetable crop.

Nematicidal effects of Leucaena leucocephala and Gliricidia sepium extracts on Meloidogyne incognita infecting okra

Two separate but identical greenhouse trials were conducted to investigate the effects of extracts of leaves and roots of Leucaena leucocephala and Gliricidia sepium each at 80,000 mg / kg and 40,000 mg / kg on Meloidogyne incognita on okra. Each potted nine-day old okra seedling was inoculated with 3,000 fresh eggs of M. incognita and 5ml of each of the extracts was added simultaneously around the roots of the seedling. Treatment of okra plant with L. leucocephala and G. sepium extracts resulted in reduced nematode population, reduced galling, reduced nematode reproduction rate and enhanced fruit weight. Chemical analysis revealed that G. sepium leaves contained phenolic compound and carboxylic acid, while the roots showed the presence of aromatic amide, phenolic compound and carboxylic acid. L. leucocephala leaves showed the presence of phenolic compound, aromatic amide and carboxylic acid, while the roots showed the presence of phenolic compound and carboxylic acid. The results of this study suggest that leaf and root extracts of L. leucocephala and G. sepium at the rate of 40,000 mg / kg could be useful in root knot nematode management in vegetable beds.

Determination of appropriate decomposition period of two organic materials for effective control of root-knot nematodes on okra

The efficacy of fruit peelings and cow dung used as soil amendments each at the rates of 0, 4, 8, and 16t ha-1 in the control of root-knot nematodes on' okra was tested in two field trials at the National Horticultural Research Institute, Ibadan. The organic wastes were each ploughed 0,20m into the soil and were subjected to three decomposition periods of two, four and six weeks before okra seeds were sown. The plots that were not amended served as the control treatment. The layout was a 2 x 4 x 3 factorial experiment in a randomized complete block design with four replications. The results showed a consistent decline in nematode population and increase in yield of okra with increasing rate of each soil amendment. Regardless of each type of organic waste, six week­ decomposed wastes reduced nematode populations and improved yield more than two­-week decomposed manure. While the plants in fruit peelings amended soil recorded a higher level of nematode population reduction by 68.1% and resulted in a yield increase of 89.2% over the control, cow dung reduced nematode population by 64.6% with resultant yield increase of 30.9%. While the effect of year of study (Y) was not significant for the assessed parameters, the interaction between manure rate (M) at 16t ha-1 and decomposition period of six weeks recorded the best significant suppressive effect on nematode population and enhanced the yield of okra. The overall results thus suggest that the efficacy of fruit peelings was significantly better in nematode control, enhanced plant growth and yield response over the corresponding effect of cow dung on the measured parameters. Keywords: decomposition period, cow dung, fruit peelings, root-knot nematodes Moor Journal of Agricultural Research Vol. 5(1) 2004: 19-25

Rotation Crop Evaluation for Management of the Soybean Cyst Nematode in Minnesota

Crop rotation is an effective tactic for soybean cyst nematode (SCN) management. In the North Central region of the USA, corn is almost exclusively used as a nonhost rotation crop with soybean. This study was conducted to determine the effectiveness of crops common to or having potential use in the North Central region as rotation crops for managing SCN. Sixteen potential rotation crops and SCN‐resistant and susceptible soybeans were grown along with six fallow controls in three commercial field sites near Waseca, Lamberton, and Morris, MN, in 2001, and SCN‐susceptible soybean was grown on all plots in 2002. Nematode populations at planting, midseason, and harvest were measured both years; soybean yield was measured in 2002. There was large variability in SCN populations and soybean yields at the three sites. Nevertheless, significant treatment effects were detected at all sites. While all of the rotation crops lowered SCN populations compared with SCN‐susceptible soybean, there were only subtle differences among the individual rotation crops and among different groups of the crops. Leguminous nonhosts or poor hosts were best in reducing SCN population density. Corn, the most common rotation crop in Minnesota, was among the least effective in reducing nematode populations. There was an undetectable yield benefit from SCN management, although differences in yield were observed among the rotation crop treatments—probably due to agronomic factors. The data suggest that a single year of rotation of soybean with any of these crops before planting a susceptible soybean may not be sufficient in managing SCN.

Root-Knot and Root-Lesion Nematode Suppression by Cover Crops, Poultry Litter, and Poultry Litter Compost.

Experiments using soil-incorporated cover crops and amendments of poultry litter (PL) and PL compost to suppress root-knot (RKN) and root-lesion nematodes were conducted in response to increasing nematode populations in Maryland's potato production areas. Identical experiments were established in microplots infested with Meloidogyne incognita or Pratylenchus penetrans. Treatments consisted of 12 3-year rotational sequences comprising potato (year 1) and cucumber (year 2) followed by a moderately RKN-resistant or susceptible soybean cultivar, castor bean, grain sorghum, or sorghum sudangrass; PL or PL compost were amended to some of the RKN-susceptible soybean and sorghum sudangrass plots. In the third year of the rotation, potato followed by soybean was planted in all 12 treatments. The RKN-resistant soybean, castor bean, sorghum sudangrass, and fallow or tillage decreased the populations of M. incognita compared with microplots where RKN-susceptible soybean had been grown. However, RKN populations quickly recovered. Root-lesion nematode was reduced in the spring of 2001 following application of high rates of PL and PL compost in 2000. In the fall of 2001, sorghum sudangrass alone or in combination with PL or PL compost, grain sorghum, or fallow or tillage reduced root-lesion nematodes compared with either soybean cultivar. No treatment affected root-lesion nematode the following year. The use of cover crops and PL compost is an effective method to reduce nematode populations only if successively incorporated into rotational cropping sequences.

Solarização do solo e biofumigação no cultivo protegido de tomate

The effect of solarization and biofumigation on tomatoes under protected cultivation A greenhouse experiment was carried out to test the effects of solarization and biofumigation on the population of the plant parasitic nematode Meloidogyne sp., on the incidence of weeds and on soil chemical properties in protected areas for the cultivation of tomatoes. Brassica residues (broccoli and cauliflower) and chicken litter amendments (2% v/v), methyl bromide and no amendment were evaluated with or without solarization. The tomato hybrids 'Alambra', Meloidogyne incognita resistant (gene Mi), and 'Duradoro' (susceptible), were planted after two months soil solarization. Weed seed bank and weed survival were evaluated by soil sampling and germination of viable seeds and by sampling the emerged plants 30 days after transplanting of the tomato seedlings. Soil samples were analyzed for their chemical properties after solarization and biofumigation. Soil solarization, chicken litter amendment and methyl bromide treatments reduced nematode populations and the number of egg masses on both tomato hybrids. However, 'Alambra' presented significantly higher total fresh and dry weight, plant height and fruit weight in comparison to 'Duradoro'. 'Alambra' was more responsive to treatments than 'Duradoro'. Methyl bromide fumigation and solarization reduced the number and survival of weed seeds in the soil. Solarization increased levels of P and Cu, and reduced levels of Zn in the soil.

Root-Knot Nematode Resistance in Pearl Millet From West and East Africa.

Resistance to Meloidogyne incognita is important to provide stability to pearl millet production and to reduce nematode populations that can damage crops grown in rotation with pearl millet. The objectives of this study were to determine whether resistance to M. incognita exists in pearl millet from West and East Africa, and to determine if heterogeneity for resistance exists within selected cultivars. Resistance was assessed as nematode egg production per gram of root in greenhouse trials. Seventeen pearl millet cultivars of diverse origin were evaluated as bulk (S0) populations. All African cultivars expressed some level of resistance. P3Kollo was among the least resistant of the African cultivars, Zongo and Gwagwa were intermediate, and SoSat-C88 was among the most resistant. Thirty selfed (S1) progeny selections from SoSat-C88, Gwagwa, Zongo, and P3Kollo were evaluated for heterogeneity of resistance within cultivar. Reactions were verified in 13 S2 progeny of each of the four cultivars. In S1 evaluations, each of these cultivars was heterogeneous for resistance. Progeny reaction varied from highly resistant to highly susceptible. Patterns of apparent segregation of resistance varied among the four cultivars. Discreet resistant and susceptible phenotypes were identified in Zongo progeny, and it was estimated that two dominant genes for resistance segregated in this cultivar. Averaged across progenies, egg production on the four cultivars was less (P ≤ 0.001) than on the susceptible hybrid HGM-100, but was not different from resistant hybrid TifGrain 102. Reproduction of M. incognita on the S2 progeny tended to confirm the results from inoculations of S1 progeny. Heritability of nematode reproduction (standardized as the ratio of the value to HGM-100) determined by parent-offspring regression was 0.54. Realized heritability determined by divergent selection was 0.87.

Evaluation of fallow and cover crops for nematode suppression in three agroecologies of south western Nigeria

A study was conducted in three agroecological zones of south-western Nigeria to evaluate the effect of siam weed (Chromolaena odorata) and mucuna (Mucuna utilis) cover/fallow crops on plant-parasitic nematode population. The natural bush regrowth was used as control. Plant-parasitic nematodes were identified and counted during the fallow periods. Eleven genera of nematodes were identified and three (Meloidogyne, Pratylenchus, and Helicotylenchus) species were predominant across the trial locations. Other important genera present were Scutellonema, Tylenchorhynchus and Rotylenchus species. Nematode population densities of pre-crop were lowest in Alagba soil (Rhodic lixisols) at Ikenne in the wet forest zone of Nigeria. The populations in Iwo soil (Rhodic haplustalf) at Ibadan, a dry forest zone was lower than in the Temidire soil (Plinthic luvisol) at Ilora in the derived savannah of south-western Nigeria. There was significant suppression of nematode population densities under the different crops as the fallow period increased. The population reduction in the different locations depended on the nematode species and the cover crops. The natural bush re-growth had the least effect on the nematode suppression at the end of the fallow period. On the average, siam weed fallow reduced nematode population densities by 67-79%, mucuna by 64-72% and the natural bush by 30-49% across the trial locations. For effective nematode suppression with fallow cropping, proper determination of the principal nematode species predominant in an environment is essential.

Factors affecting the efficacy of non‐fumigant nematicides for controlling root‐knot nematodes

Second-stage juveniles (J2) and egg masses of root-knot nematodes as well as root debris heavily infected by the latter were exposed for different periods of time to six different doses of the nematicides cadusafos and fenamiphos. The efficacy of the nematicides increased significantly with increasing exposure time. Both nematicides were more effective against J2, although they could not provide acceptable control of J2 inside egg masses or heavily galled root debris. The effect of different application strategies on the efficacy and persistence of certain nematicides was also assessed in a field study. Cadusafos, fenamiphos, fosthiazate and oxamyl were applied in field micro-plots either as a single full dose at the time of crop establishment or as multiple reduced-rate applications at 14-day intervals throughout the cropping period, and their efficacy and persistence were determined using bioassays and analytical studies. Fosthiazate was the most efficient nematicide studied, and this was mainly attributed to its long soil persistence. Oxamyl also provided adequate nematode control for the first 48-56 days after its application, regardless of the application method used and its relatively rapid field dissipation. Fenamiphos and cadusafos failed to provide adequate nematode control, although cadusafos was the most persistent of the nematicides tested. The failure of fenamiphos to provide adequate nematode control was mainly attributed to its rapid degradation by soil micro-organisms, which were stimulated after its repeated low-rate application at 14-day intervals. In contrast cadusafos failure was attributed to the inability of the nematicide to reduce nematode populations even at relatively high concentrations in soil.

Yield of ‘Superior’ potatoes (Solanum tuberosum) and dynamics of root-lesion nematode (Pratylenchus penetrans) populations following “nematode suppressive” cover crops and fumigation

Studies were conducted at Simcoe, Ontario from 1992 to 1996 to evaluate various cover crop species as possible alternatives to fumigation prior to potatoes (Solanum tuberosum). Cereal rye (Secale cereale), a common overwinter cover crop in vegetable production systems, is an excellent host for the root-lesion nematode (Pratylenchus penetrans) and provides a suitable overwintering host on coarse sandy soils. Vorlex Plus CP and Telone IIB fumigants were compared to 'Domo' mustard (Brassica juncea) for the 1993 and 1994 potato crop years. Rye plus red clover (Trifolium pratense) was included as a known host cover crop system. Cyanogenic plants including 'Domo' mustard (1994) or 'Cutlass' mustard (1995, 1996), 'Forge' canola (Brassica rapa), 'Sordan 79' and 'Trudan 8' sorghum-sudangrass hybrids (Sorghum bicolor), and flax (Linum usitatissimum) were compared to Vorlex Plus CP fumigant and 'NK557' sorghum (Sorghum vulgare) for effects on potato yield and nematodes. Shallow (15 cm) and deep (45 cm) fumigation with Vorlex Plus CP were also compared prior to potatoes for the 1994 to 1996 crop years. There was little detectable difference in percent or days to 50% emergence of potatoes following any treatment. Highest total and marketable yields resulted from Telone IIB fumigation, then Vorlex Plus CP fumigation and 'Domo' mustard, followed by control and rye plus red clover cover. Populations of nematodes surpassed the threshold of 1000 kg-1 soil in all treatments and were highest in potatoes following rye plus red clover. Yield and nematode control following sorghum-sudangrass hybrids and mustards appeared to be intermediate between fumigated and not fumigated. All of the cover crops appeared to be root-lesion nematode hosts in the field, and reduction of population levels appeared to result after incorporation or nematode winterkill. Nematode mortality was excellent with fumigation and next best from kill over the winter after 'Sordan 79' incorporation. 'Sordan 79' grown over at least part of the summer followed by incorporation was an alternative to fumigation prior to potatoes. Deep chiselling appears to reduce nematode population, possibly by physical action. Where nematode populations warrant, deep fumigation prior to potatoes appears to be of merit.

The influence of fungicides on Arthrobotrys oligospora in simulated putting green soil

Summary Plant-parasitic nematodes are destructive pests in bentgrass putting greens. Few chemical or nonchemical approaches for nematode management exist. Studies were conducted to determine: the in vitro tolerance of the nematophagous fungus Arthrobotrys oligospora, to the fungicides chlorothalonil and myclobutanil used to manage diseases on putting greens; the concentration of fungicides obtained from simulated putting green soil; and the ability of the fungus to reduce populations of the ring nematode, Criconemella ornata. Both fungicides reduced in vitro hyphal growth and germination of conidia above 10 mg kg –1 . Soil concentrations of chlorothalonil were less than 5 mg kg –1 and concentrations of myclobutanil were below detection limits. Nematode populations were not affected by A. oligospora in simulated greens but nematode populations were lowest in pots inoculated with A. oligospora and receiving fungicide treatments. Results of these studies indicate that applications of chlorothalonil and myclobutanil used to manage fungal diseases of bentgrass may not adversely affect A. oligospora; however, the fungus may not reduce nematode populations below desired thresholds.

Suppression of root knot nematode (Meloidogyne javanica) after incorporation of Indian mustard cv. Nemfix as green manure and seed meal in vineyards

Suppression of root-knot nematode (Meloidogyne javanica) in soil within the vine row was assessed between 14–36 weeks after incorporation of Indian mustard (Brassica juncea) cv. Nemfix as green manure and as seed meal in a 3-year-old and a 15-year-old vineyard. Application of mustard green manure and seed meal either to the inter-row or the vine row soil reduced nematode population densities significantly in the vine row soil in both vineyards. However, the reduction of M. javanica J2 population densities was greater when the vine row soil was treated with mustard green manure (9.0–11.51 DM/ha) and seed meal (2 t/ha treated area) compared with inter-row treatments. At 36 weeks after treatment, there was 13-to 14-fold reduction of nematode population densities in plots having green manure or seed meal to the vine row soil in the 3-year-old vineyard compared with 4-fold reduction in the 15-year-old vineyard.

Efficacy of hot water drenches of Anthurium andraeanum plants against the burrowing nematode Radopholus similis and plant thermotolerance

SummaryHot‐water drench treatments were evaluated for disinfesting roots of potted anthurium Anthurium andraeanum of the burrowing nematode Radopholus similis. A continuous drench of roots and media in pots with 50°C water for 5 to 20 min eliminated or reduced nematode populations to < 1 g−1 of dry root. A second hot water drench, 2 months after the first drenching, tended to increase the efficacy of the heat treatment. A few survivors persisted in the roots and/or stems of a few plants 2 to 4 months after heat treatment. Non‐treatment of the shoots and possible migration from stem to root tissues are probable causes of nematode survival. Drenching potting media and roots in pot were as effective against R. similis in the roots as hot water dipping bare‐rooted plants. Plant response to hot‐water drenching varied among cultivars, but most exhibited tolerance to the heat treatments. Visual inspection of the plants showed little difference between treated and untreated plants in the heat tolerant cultivars. However, all heat‐treated ‘Marian Seefurth’ plants, especially hot water‐dipped bare‐rooted plants, appeared to suffer some degree of growth reduction as measured by lower root and stem dry weights when compared to untreated plants 3 months after treatment. Conditioning anthurium plants with hot water or hot air prior to hot water drenching did not benefit plant quality when compared to unconditioned, heat‐treated plants.

Effect of Biofumigation with Solarization and Larrea tridentata Extract on Soil-Borne Pathogens of Pepper Plants

ABSTRACT The effect of Larrea tridentata leaf resin extract applied to solarized and nonsolarized plots was evaluated on disease severity of soilborne pathogens, nematode natural populations and total yield of pepper cv. Anaheim. Solarization caused a significant reduction of disease severity and the inhibitory effect of nematode populations, since the control treatment showed a 7.8 fold increase in nematode population and 2 fold increase in root damage of pepper plants compared with solarized plots. L. tridentata resin reduced nematode populations, but did not have a reliable nematicidal effect. Solarization treatment amended with 20 kg ha−1 of leaf extract presented no noticeable root damage by soil root pathogens; by comparison, solarization without L. tridentata extract showed a 134% increase in root damage severity. Solarization alone or in combination with L. tridentata resin effectively reduced the incidence and disease severity of soilborne pathogens and provided partial protection against nematodes. Most importantly, these treatments had a positive effect on yield, resulting in a significant increase over that obtained in the control plots. Combination of solarization and L. tridentata extract deserves further study as an alternative method for fungi and nematode control under field conditions.