Effect of Winter Cover Crops on Nematode Population Levels in North Florida

Two experiments were conducted in north-central Florida to examine the effects of various winter cover crops on plant-parasitic nematode populations through time. In the first experiment, six winter cover crops were rotated with summer corn (Zea mays), arranged in a randomized complete block design. The cover crops evaluated were wheat (Triticum aestivum), rye (Secale cereale), oat (Avena sativa), lupine (Lupinus angustifolius), hairy vetch (Vicia villosa), and crimson clover (Trifolium incarnatum). At the end of the corn crop in year 1, population densities of Meloidogyne incognita were lowest on corn following rye or oat (P ≤ 0.05), but no treatment differences were observed in year 2. Wheat was a good host to Paratrichodorus minor, whereas vetch was a poor host, but numbers of P. minor were not lower in vetch-planted plots after corn was grown. The second experiment used a split-plot design in which rye or lupine was planted into field plots with histories of five tropical cover crops: soybean (Glycine max), cowpea (Vigna unguiculata), sorghum-sudangrass (Sorghum bicolor × S. sudanense), sunn hemp (Crotalaria juncea), and corn. Population densities of M. incognita and Helicotylenchus dihystera were affected by previous tropical cover crops (P ≤ 0.05) but not by the winter cover crops present at the time of sampling. Plots planted to sunn hemp in the fall maintained the lowest M. incognita and H. dihystera numbers. Results suggest that winter cover crops tested did not suppress plant-parasitic nematodes effectively. Planting tropical cover crops such as sunn hemp after corn in a triple-cropping system with winter cover crops may provide more versatile nematode management strategies in northern Florida.     

Effect of a Terminated Cover Crop and Aldicarb on Cotton Yield and Meloidogyne incognita Population Density

Terminated small grain cover crops are valuable in light textured soils to reduce wind and rain erosion and for protection of young cotton seedlings. A three-year study was conducted to determine the impact of terminated small grain winter cover crops, which are hosts for Meloidogyne incognita, on cotton yield, root galling and nematode midseason population density. The small plot test consisted of the cover treatment as the main plots (winter fallow, oats, rye and wheat) and rate of aldicarb applied in-furrow at-plant (0, 0.59 and 0.84 kg a.i./ha) as subplots in a split-plot design with eight replications, arranged in a randomized complete block design. Roots of 10 cotton plants per plot were examined at approximately 35 days after planting. Root galling was affected by aldicarb rate (9.1, 3.8 and 3.4 galls/root system for 0, 0.59 and 0.84 kg aldicarb/ha), but not by cover crop. Soil samples were collected in mid-July and assayed for nematodes. The winter fallow plots had a lower density of M. incognita second-stage juveniles (J2) (transformed to Log₁₀ (J2 + 1)/500 cm³ soil) than any of the cover crops (0.88, 1.58, 1.67 and 1.75 Log₁₀(J2 + 1)/500 cm³ soil for winter fallow, oats, rye and wheat, respectively). There were also fewer M. incognita eggs at midseason in the winter fallow (3,512, 7,953, 8,262 and 11,392 eggs/500 cm³ soil for winter fallow, oats, rye and wheat, respectively). Yield (kg lint per ha) was increased by application of aldicarb (1,544, 1,710 and 1,697 for 0, 0.59 and 0.84 kg aldicarb/ha), but not by any cover crop treatments. These results were consistent over three years. The soil temperature at 15 cm depth, from when soils reached 18°C to termination of the grass cover crop, averaged 9,588, 7,274 and 1,639 centigrade hours (with a minimum threshold of 10°C), in 2005, 2006 and 2007, respectively. Under these conditions, potential reproduction of M. incognita on the cover crop did not result in a yield penalty.     

Effects of Tropical Rotation Crops on Meloidogyne arenaria Population Densities and Vegetable Yields in Microplots

The effects of 12 summer crop rotation treatments on population densities of Meloidogyne arenaria race 1 and on yields of subsequent spring vegetable crops were determined in microplots. The crop sequence was: (i) rotation crops during summer 1991 ; (ii) cover crop of rye (Secale cereale) during winter 1991-92; (iii) squash (Cucurbita pepo) during spring 1992; (iv) rotation crops during summer 1992; (v) rye during winter 1992-93; (vi) eggplant (Solanum melongena) during spring 1993. The 12 rotation treatments were castor (Ricinus communis), cotton (Gossypium hirsutum), velvetbean (Mucuna deeringiana), crotalaria (Crotalaria spectabilis), fallow, hairy indigo (Indigofera hirsuta), American jointvetch (Aeschynomene americana), sorghum-sudangrass (Sorghum bicolor x S. sudanense), soybean (Glycine max), horsebean (Canavalia ensiformis), sesame (Sesamum indicum), and peanut (Arachis hypogaea). Compared to peanut, the first eight rotation treatments resulted in lower (P ≤ 0.05) numbers of M. arenaria juveniles on most sampling dates. Soybean, horsebean, and sesame rotations were less effective in suppressing nematodes. Yield of squash was greater (P ≤ 0.05) following castor, cotton, velvetbean, and crotalaria than following peanut. Compared to the peanut rotation, yield of eggplant was enhanced (P ≤ 0.10) following castor, crotalaria, hairy indigo, American jointvetch, and sorghum-sudangrass. Several of these rotation crops may provide a means for depressing M. arenaria population densities on a short-term basis to enhance yields in a subsequent susceptible vegetable crop.     

Effects of Planting Date,Small Grain Crop Destruction,Fallow, and Soil Temperature on the Management of Meloidogyne incognita

The effects of planting date, rye (Secale cereale cv. Wren Abruzzi) and wheat (Triticura aestivum cv. Coker 797), crop destruction, fallow, and soil temperature on managing Meloidogyne incognita race 1 were determined in a 2-year study. More M. incognita juveniles (J2) and egg-producing adults were found in roots of rye planted 1 October than in roots of rye planted 1 November and wheat planted 1 November and 1 December. Numbers of M. incognita adults with and without egg masses were near or below detectable levels in roots of rye planted 1 November and wheat planted 1 November and 1 December. Meloidogyne incognita survived the mild winters in southern Georgia as J2 and eggs. The destruction of rye and wheat as a trap crop 1 March suppressed numbers of J2 in the soil temporarily but did not provide long-term benefits for susceptible crops that followed. In warmer areas where rye and wheat are grown in winter, reproduction of M. incognita may be avoided by delaying planting dates until soil temperature declines below the nematode penetration threshold (18 C), but no long-term benefits should be expected. The temperature threshold may be an important consideration in managing M. incognita population densities in areas having lower winter soil temperatures than southern Georgia.     

Influence of cover crops on insect pests and predators in conservation tillage cotton

In fall 2000, an on-farm sustainable agricultural research project was established for cotton, Gossypium hirsutum L., in Tift County, Georgia. The objective of our 2-yr research project was to determine the impact of several cover crops on pest and predator insects in cotton. The five cover crop treatments included 1) cereal rye, Secale cereale L., a standard grass cover crop; 2) crimson clover, Trifolium incarnatum L., a standard legume cover crop; 3) a legume mixture of balansa clover, Trifolium michelianum Savi; crimson clover; and hairy vetch, Vicia villosa Roth; 4) a legume mixture + rye combination; and 5) no cover crop in conventionally tilled fields. Three main groups or species of pests were collected in cover crops and cotton: 1) the heliothines Heliothis virescens (F.) and Helicoverpa zea (Boddie); 2) the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois); and 3) stink bugs. The main stink bugs collected were the southern green stink bug, Nezara viridula (L.); the brown stink bug, Euschistus servus (Say); and the green stink bug, Acrosternum hilare (Say). Cotton aphids, Aphis gossypii Glover, were collected only on cotton. For both years of the study, the heliothines were the only pests that exceeded their economic threshold in cotton, and the number of times this threshold was exceeded in cotton was higher in control cotton than in crimson clover and rye cotton. Heliothine predators and aphidophagous lady beetles occurred in cover crops and cotton during both years of the experiment. Geocoris punctipes (Say), Orius insidiosus (Say), and red imported fire ant, Solenopsis invicta Buren were relatively the most abundant heliothine predators observed. Lady beetles included the convergent lady beetle, Hippodamia convergens Guérin-Méneville; the sevenspotted lady beetle, Coccinella septempunctata L.; spotted lady beetle, Coleomegilla maculata (DeGeer); and the multicolored Asian lady beetle, Harmonia axyridis (Pallas). Density of G. punctipes was higher in cotton fields previously planted in crimson clover compared with control cotton fields for all combined sampling dates in 2001. Intercropping cotton in live strips of cover crop was probably responsible for the relay of G. punctipes onto cotton in these crimson clover fields. Density of O. insidiosus was not significantly different between cover crop and control cotton fields. Lady beetles seemed to relay from cover crops into cotton. Conservation of the habitat of fire ants during planting probably was responsible for the higher density of red imported fire ants observed in all conservation tillage cotton fields relative to control cotton fields. Reduction in the number of times in which economic thresholds for heliothines were exceeded in crimson clover and rye compared with control fields indicated that the buildup of predaceous fire ants and G. punctipes in these cover crops subsequently resulted in reduction in the level of heliothines in conservation tillage cotton with these cover crops compared with conventional tillage cotton without cover crops.     

Effects of Rapeseed and Vetch as Green Manure Crops and Fallow on Nematodes and Soil-borne Pathogens

In a rapeseed-squash cropping system, Meloidogyne incognita race 1 and M. javanica did not enter, feed, or reproduce in roots of seven rapeseed cultivars. Both nematode species reproduced at low levels on roots of the third crop of rapeseed. Reproduction of M. incognita and M. javanica was high on squash following rapeseed, hairy vetch, and fallow. The application of fenamiphos suppressed (P = 0.05) root-gall indices on squash following rapeseed, hairy vetch, and fallow; and on Dwarf Essex and Cascade rapeseed, but not Bridger and Humus rapeseed in 1987. The incorporation of 30-61 mt/ha green biomass of rapeseed into the soil 6 months after planting did not affect the population densities of Criconemella ornata, M. incognita, M. javanica, Pythium spp., Rhizoctonia solani AG-4; nor did it consistently increase yield of squash. Hairy vetch supported larger numbers of M. incognita and M. javanica than rapeseed cultivars or fallow. Meloidogyne incognita and M. javanica survived in fallow plots in the absence of a host from October to May each year at a level sufficient to warrant the use of a nematicide to manage nematodes on the following susceptible crop.     

Effects of Management Practices on Meloidogyne incognita and Snap Bean Yield

Phenamiphos applied at 6.7 kg ai/ha through a solid set or a center pivot irrigation system with 28 mm of water effectively controlled root-knot nematodes, Meloidogyne incognita, and resulted in greater snap bean growth and yields irrespective of growing season, tillage method, or cover crop system. The percentage yield increases attributed to this method of M. incognita control over nontreated controls were 45% in the spring crop, and 90% and 409% in the fall crops following winter rye and fallow, respectively. Root galling was not affected by tillage systems or cover crop, but disk tillage resulted in over 50% reduction in bean yield compared with yields from the subsoil-bed tillage system.     

Effects of the Mi-1, N and Tabasco Genes on Infection and Reproduction of Meloidogyne mayaguensis on Tomato and Pepper Genotypes

Meloidogyne mayaguensis is a damaging root-knot nematode able to reproduce on root-knot nematode-resistant tomato and other economically important crops. In a growth chamber experiment conducted at 22 and 33°C, isolate 1 of M. mayaguensis reproduced at both temperatures on the Mi-1-carrying tomato lines BHN 543 and BHN 585, whereas M. incognita race 4 failed to reproduce at 22°C, but reproduced well at 33°C. These results were confirmed in another experiment at 26 ± 1.8°C, where minimal or no reproduction of M. incognita race 4 was observed on the Mi-1-carrying tomato genotypes BHN 543, BHN 585, BHN 586 and ‘Sanibel’, whereas heavy infection and reproduction of M. mayaguensis isolate 1 occurred on these four genotypes. Seven additional Florida M. mayaguensis isolates also reproduced on resistant ‘Sanibel’ tomato at 26 ± 1.8°C. Isolate 3 was the most virulent, with reproduction factor (Rf) equal to 8.4, and isolate 8 was the least virulent (Rf = 2.1). At 24°C, isolate 1 of M. mayaguensis also reproduced well (Rf ≥ 1) and induced numerous small galls and large egg masses on the roots of root-knot nematode-resistant bell pepper ‘Charleston Belle’ carrying the N gene and on three root-knot nematode-resistant sweet pepper lines (9913/2, SAIS 97.9001 and SAIS 97.9008) carrying the Tabasco gene. In contrast, M. incognita race 4 failed to reproduce or reproduced poorly on these resistant pepper genotypes. The ability of M. mayaguensis isolates to overcome the resistance of tomato and pepper genotypes carrying the Mi-1, N and Tabasco genes limits the use of resistant cultivars to manage this nematode species in infested tomato and pepper fields in Florida.     

Tropical Rotation Crops Influence Nematode Densities and Vegetable Yields

The effects of eight summer rotation crops on nematode densities and yields of subsequent spring vegetable crops were determined in field studies conducted in north Florida from 1991 to 1993. The crop sequence was as follows: (i) rotation crops during summer 1991; (ii) cover crop of rye (Secale cereale) during winter 1991-92; (iii) ''Lemondrop L'' squash (Cucurbita pepo) during spring 1992; (iv) rotation crops during summer 1992; (v) rye during winter 1992-93; (vi) ''Classic'' eggplant (Solanum melongena) during spring 1993. The eight summer crop rotation treatments were as follows: ''Hale'' castor (Ricinus communis), velvetbean (Mucuna deeringiana), sesame (Sesamum indicum), American jointvetch (Aeschynomene americana), weed fallow, ''SX- 17'' sorghum-sudangrass (Sorghum bicolor x S. sudanense), ''Kirby'' soybean (Glycine max), and ''Clemson Spineless'' okra (Hibiscus esculentus) as a control. Rotations with castor, velvetbean, American jointvetch, and sorghum-sudangrass were most effective in maintaining the lowest population densities of Meloidogyne spp. (a mixture of M. incognita race 1 and M. arenaria race 1), but Paratrichodorus minor built up in the sorghum-sudangrass rotation. Yield of squash was lower (P ≤ 0.05) following sorghum-sudangrass than after any of the other treatments except fallow. Yield of eggplant was greater (P ≤ 0.05) following castor, sesame, or American jointvetch than following okra or fallow. Several of the rotation crops evaluated here may be useful for managing nematodes in the field and for improving yields of subsequent vegetable crops.     

Population Development of Pasteuria penetrans on Meloidogyne arenaria

A microplot study on the influence of cropping sequences with peanut in summer and bare fallowed or cover crops of rye or vetch in winter on the population development of Pasteuria penetrans was initiated in the spring of 1987. The number of spores of P. penetrans attached per second-stage juvenile of Meloidogyne arenaria race 1 increased from 0.11 in the fall of 1987 to 7.6, 8.6, and 3.6 in the fall of 1989 in the rye, vetch, and fallowed plots, respectively. Higher (P ≤ 0.05) levels of P. penetrans occurred in the rye and vetch plots than in fallowed plots. No influence of P. penetrans on peanut, rye, or vetch yield was observed in 1987 and 1988, but in 1989 peanut yield was 64% higher (P ≤ 0.05) in plots infested with P. penetrans than in plots without P. penetrans. Numbers of M. arenaria in plots without P. penetrans were influenced by the cropping sequences in the spring of 1988 and 1989 but not in the fall following the peanut crop. In the spring the plots with rye had the lowest nematode numbers in either year (P ≤ 0.05). Nematode numbers were lower (P ≤ 0.05) in plots with P. penetrans than in plots without P. penetrans in the spring of 1989 (vetch) and the fall of 1989 (rye, vetch, and fallowed).     

Influence of Selected Plant Species on Hatching of Eggs and Development of Juveniles of Heterodera glycines

The influence of selected plant species on egg hatch and subsequent development of Heterodera glycines race 3 was investigated. Plants tested included four soybean cultivars, red clover, alfalfa, hairy vetch, field corn, sweet corn, cabbage, tobacco, cotton, and wheat. Soybean stimulated egg hatching more than any of the other plant species, with H. glycines-resistant cultivars being more stimulating than susceptible ones. Hairy vetch also increased hatch. Roots of cabbage, red clover, alfalfa, and hairy vetch were readily penetrated by juveniles of H. glycines. Maturation to adult occurred only on soybean and hairy vetch.     

Management of Lesion Nematodes and Potato Early Dying with Rotation Crops

Soil-incorporated rotation/green manure crops were evaluated for management of potato early dying caused by Verticillium dahliae and Pratylenchus penetrans. After two years of rotation/green manure and a subsequent potato crop, P. penetrans numbers were less after ‘Saia’ oat/‘Polynema’ marigold, ‘Triple S’ sorghum-sudangrass, or ‘Garry’ oat than ‘Superior’ potato or ‘Humus’ rapeseed. The area under the disease progress curve (AUDPC) for early dying was lowest after Saia oat/marigold, and tuber yields were greater than continuous potato after all crops except sorghum-sudangrass. Saia oat/marigold crops resulted in the greatest tuber yields. After one year of rotation/green manure, a marigold crop increased tuber yields and reduced AUDPC and P. penetrans. In the second potato crop after a single year of rotation, plots previously planted to marigolds had reduced P. penetrans densities and AUDPC and increased tuber yield. Rapeseed supported more P. penetrans than potato, but had greater yields. After two years of rotation/green manure crops and a subsequent potato crop, continuous potato had the highest AUDPC and lowest tuber weight. Rotation with Saia oats (2 yr) and Rudbeckia hirta (1 yr) reduced P. penetrans and increased tuber yields. AUDPC was lowest after R. hirta. Two years of sorghum-sudangrass did not affect P. penetrans, tuber yield or AUDPC. These results demonstrate that P. penetrans may be reduced by one or two years of rotation to non-host or antagonistic plants such as Saia oat, Polynema marigold, or R. hirta and that nematode control may reduce the severity of potato early dying.     

Root-knot Nematode Management and Yield of Soybean as Affected by Winter Cover Crops,Tillage Systems,and Nematicides

Management of Meloidogyne incognita on soybean as affected by winter small grain crops or fallow, two tillage systems, and nematicides was studied. Numbers of M. incognita did not differ in plots planted to wheat and rye. Yields of soybean planted after these crops also did not differ. Numbers of M. incognita were greater in fallow than in rye plots, but soybean yield was not affected by the two treatments. Soybean yields were greater in subsoil-plant than in moldboard plowed plots. Ethylene dibromide reduced nematode population densities more consistently than aldicarb and phenamiphos. Also, ethylene dibromide increased yields the most and phenamiphos the least. There was a positive correlation (P = 0.001) of seed size (weight of 100 seeds) with yield (r = 0.79), indicating that factors affecting yield also affected seed size.     

Influence of Seeding Ratio,Planting Date,and Termination Date on Rye-Hairy Vetch Cover Crop Mixture Performance under Organic Management

Cover crop benefits include nitrogen accumulation and retention, weed suppression, organic matter maintenance, and reduced erosion. Organic farmers need region-specific information on winter cover crop performance to effectively integrate cover crops into their crop rotations. Our research objective was to compare cover crop seeding mixtures, planting dates, and termination dates on performance of rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) monocultures and mixtures in the maritime Pacific Northwest USA. The study included four seed mixtures (100% hairy vetch, 25% rye-75% hairy vetch, 50% rye-50% hairy vetch, and 100% rye by seed weight), two planting dates, and two termination dates, using a split-split plot design with four replications over six years. Measurements included winter ground cover; stand composition; cover crop biomass, N concentration, and N uptake; and June soil NO₃ ^--N. Rye planted in mid-September and terminated in late April averaged 5.1 Mg ha^-1 biomass, whereas mixtures averaged 4.1 Mg ha^-1 and hairy vetch 2.3 Mg ha^-1. Delaying planting by 2.5 weeks reduced average winter ground cover by 65%, biomass by 50%, and cover crop N accumulation by 40%. Similar reductions in biomass and N accumulation occurred for late March termination, compared with late April termination. Mixtures had less annual biomass variability than rye. Mixtures accumulated 103 kg ha^-1 N and had mean C:N ratio <17:1 when planted in mid-September and terminated in late April. June soil NO₃ ^--N (0 to 30 cm depth) averaged 62 kg ha^-1 for rye, 97 kg ha^-1 for the mixtures, and 119 kg ha^-1 for hairy vetch. Weeds comprised less of the mixtures biomass (20% weeds by weight at termination) compared with the monocultures (29%). Cover crop mixtures provided a balance between biomass accumulation and N concentration, more consistent biomass over the six-year study, and were more effective at reducing winter weeds compared with monocultures.     

Cover crop, rye residue and in-furrow treatment effects on thrips

Abstract:  Thrips and thrips damage to cotton and peanut plants were compared in plots with in-furrow treatments of aldicarb, phorate and diammonium phosphate (DAP) fertilizer under two tillage regimes with a winter cover of crimson clover and under different levels of rye residue ground cover. Adult and larval thrips numbers were significantly lower in cotton plots following winter crimson clover cultivation compared with no-cover plots in all 3 years. Thrips numbers did not differ with respect to the in-furrow treatments in the clover plots, but in the no-cover plots, they were significantly higher in the untreated control and DAP treatments compared with the aldicarb treatment. Thrips damage was higher in the no-cover than the clover plots except in the aldicarb treatments. Within the cover crop plots, thrips damage was highest in the control and phorate treatments and similar in the DAP and aldicarb treatments. There was an inverse relationship between the amount of rye residue ground cover and thrips density and thrips damage in cotton and peanuts. There was also an inverse relationship between the density of rye residue and damage to peanuts from Bunyaviridae tospovirus. Cotton yield was reduced in the cover crop plots and was not measured in the rye residue and peanut plots. These results suggest that ground cover alone decreases thrips numbers and thrips damage in both cotton and peanuts and that a winter crimson clover cover and an in-furrow treatment of DAP enhanced plant protection from thrips in cotton.     

Population Dynamics of Meloidogyne incognita,M. arenaria,and Other Nematodes and Crop Yields in Rotations of Cotton,Peanut, and Wheat Under Minimum Tillage

Wheat, cotton, and peanut were arranged in three cropping sequences to determine the effects of fenamiphos (6.7 kg a.i./ha) and cropping sequence on nematode population densities and crop yields under conservation tillage and irrigation for 6 years. The cropping sequences included a wheat winter cover crop each year and summer crops of cotton every year, peanut every year, or cotton rotated every other year with peanut. The population densities of Meloidogyne spp. and Helicotylenchus dihystera were determined monthly during the experiment. Numbers of M. incognita increased on cotton and decreased on peanut, whereas M. arenaria increased on peanut, and decreased on cotton; both nematode species remained in moderate to high numbers in plots of wheat. Root damage was more severe on cotton than peanut and was not affected by fenamiphos treatment. The H. dihystera population densities were highest in plots with cotton every summer, intermediate in the cotton-peanut rotation, and lowest in plots with peanut every summer. Over all years and cropping sequences, yield increases in fenamiphos treatment over untreated control were 9% for wheat, 8% for cotton, and 0% for peanut. Peanut yields following cotton were generally higher than yields following peanut. These results show that nematode problems may be manageable in cotton and peanut production under conservation tillage and irrigation in the southeastern United States.     

Population Dynamics of Plant Nematodes in Cultivated Soil: Length of Rotation in Newly Cleared and Old Agricultural Land

During a 6-year study of 1-, 2-, and 3-year crop rotations, population densities of Pratylenchus brachyurus, Trichodorus christiei, and Meloidogyne incognita were significantly affected by the choice of crops but not by length of crop rotation. The density of P. brachyurus and T. christiei increased rapidly on milo (Sorghum vulgate). In addition, populations of P. brachyurus increased significantly in cropping systems that involved crotalaria (C. rnucronata), millet (Setaria italica), and sudangrass (Sorghum sudanense). Lowest numbers of P. brachyurus occurred where okra (Hibiscus esculentus) was grown or where land was fallow. The largest increase in populations of T. christiei occurred in cropping systems that involved millet, sudangrass, and okra whereas the smallest increase occurred in cropping systems that involved crotalaria or fallow. A winter cover of rye (Secale cereale) had no distinguishable effect on population densities of P. brachyurus or T. christiei. Meloidogyne incognita was detected during the fourth year in both newly cleared and old agricultural land when okra was included in the cropping system. Detectable populations of M. incognita did not develop in any of the other cropping systems. Yields of tomato transplants were higher on the newly cleared land than on the old land. Highest yields were obtained when crotalaria was included in the cropping system. Lowest yields were obtained when milo, or fallow were included in the cropping system. Length of rotation had no distinguishable effect on yields of tomato transplants.     

Evaluation of 31 Potential Biofumigant Brassicaceous Plants as Hosts for Three Meloiodogyne Species

Brassicaceous cover crops can be used for biofumigation after soil incorporation of the mowed crop. This strategy can be used to manage root-knot nematodes (Meloidogyne spp.), but the fact that many of these crops are host to root-knot nematodes can result in an undesired nematode population increase during the cultivation of the cover crop. To avoid this, cover crop cultivars that are poor or nonhosts should be selected. In this study, the host status of 31 plants in the family Brassicaceae for the three root-knot nematode species M. incognita, M. javanica, and M. hapla were evaluated, and compared with a susceptible tomato host in repeated greenhouse pot trials. The results showed that M. incognita and M. javanica responded in a similar fashion to the different cover cultivars. Indian mustard (Brassica juncea) and turnip (B. rapa) were generally good hosts, whereas most oil radish cultivars (Raphanus. sativus ssp. oleiferus) were poor hosts. However, some oil radish cultivars were among the best hosts for M. hapla. The arugula (Eruca sativa) cultivar Nemat was a poor host for all three nematode species tested. This study provides important information for chosing a cover crop with the purpose of managing root-knot nematodes.     

Reproduction of Belonolaimus longicaudatus,Meloidogyne javanica,Paratrichodorus minor,and Pratylenchus brachyurus on Pearl Millet (Pennisetum glaucum)

Pearl millet (Pennisetum glaucum) has potential as a grain crop for dryland crop production in the southeastern United States. Whether or not pearl millet will be compatible in rotation with cotton (Gossypium hirsutum), corn (Zea mays), and peanut (Arachis hypogaea) will depend, in part, on its host status for important plant-parasitic nematodes of these crops. The pearl millet hybrid ''TifGrain 102'' is resistant to both Meloidogyne incognita race 3 and M. arenaria race 1; however, its host status for other plant-parasitic nematodes was unknown. In this study, the reproduction of Belonolaimus longicaudatus, Paratrichodorus minor, Pratylenchus brachyurus, and Meloidogyne javanica race 3 on pearl millet (''HGM-100'' and TifGrain 102) was compared relative to cotton, corn, and peanut. Separate greenhouse experiments were conducted for each nematode species. Reproduction of B. longicaudatus was lower on peanut and the two millet hybrids than on cotton and corn. Reproduction of P. minor was lower on peanut and TifGrain 102 than on cotton, corn, and HGM-100. Reproduction of P. brachyurus was lower on both millet hybrids than on cotton, corn, and peanut. Reproduction of M. javanica race 3 was greater on peanut than on the two millet hybrids and corn. Cotton was a nonhost. TifGrain 102 was more resistant than HGM-100 to reproduction of B. longicaudatus, P. minor, and M. javanica. Our results demonstrated that TifGrain 102 was a poor host for B. longicaudatus and P. brachyurus (Rf < 1) and, relative to other crops tested, was less likely to increase densities of P. minor and M. javanica.     

Mi-1-Mediated Nematode Resistance in Tomatoes is Broken by Short-Term Heat Stress but Recovers Over Time

Tomato (Solanum lycopersicum L.) is among the most valuable agricultural products, but Meloidogyne spp. (root-knot nematode) infestations result in serious crop losses. In tomato, resistance to root-knot nematodes is controlled by the gene Mi-1, but heat stress interferes with Mi-1-associated resistance. Inconsistent results in published field and greenhouse experiments led us to test the effect of short-term midday heat stress on tomato susceptibility to Meloidogyne incognita race 1. Under controlled day/night temperatures of 25°C/21°C, ‘Amelia’, which was verified as possessing the Mi-1 gene, was deemed resistant (4.1 ± 0.4 galls/plant) and Rutgers, which does not possess the Mi-1 gene, was susceptible (132 ± 9.9 galls/plant) to M. incognita infection. Exposure to a single 3 hr heat spike of 35°C was sufficient to increase the susceptibility of ‘Amelia’ but did not affect Rutgers. Despite this change in resistance, Mi-1 gene expression was not affected by heat treatment, or nematode infection. The heat-induced breakdown of Mi-1 resistance in ‘Amelia’ did recover with time regardless of additional heat exposures and M. incognita infection. These findings would aid in the development of management strategies to protect the tomato crop at times of heightened M. incognita susceptibility.