Rhizoctonia Limb Rot Research Articles

Pearl Millet as a Rotation Crop for Peanut

In the southeastern United States, there are limited options for crops that can be grown in rotation with peanut (Arachis hypogaea). Pearl millet (Pennisetum glaucum) has potential as a grain crop, and some hybrids have shown resistance to the peanut root-knot nematode (Meloidogyne arenaria), the primary nematode pest of peanut in this region. The objective of this study was to determine whether pearl millet reduces M. arenaria when planted in rotation with peanut. The experiment was arranged as a randomized, complete-block design with six replications. The rotations were peanut following either 2 years of corn, HGM-100 pearl millet, or TifGrain 102 pearl millet. There were two staggered sequences of each rotation so that a cycle was completed in 2004 and in 2005. Pearl millet did not increase either stem rot or Rhizoctonia limb rot in peanut. In both years, root galling from M. arenaria was lower on peanut following TifGrain 102 (4.6 on a scale of 0 to 10) and corn (4.9) than following HGM-100 (7.5). Peanut yields in 2004 were low and unaffected by the preceding rotation crop; however, in 2005, yields were greater in peanut following 2 years of TifGrain 102 (2320 kg/ha) and corn (2504 kg/ha) than following HGM-100 (1821 kg/ha). The lower yields following HGM-100 were likely due to greater populations of M. arenaria that had developed on the susceptible pearl millet hybrid. Economic analyses showed greater returns above variable costs from the grain crops than from the peanut crops. We conclude that the resistant pearl millet hybrid TifGrain 102 is as effective as corn in limiting population increase of M. arenaria and in enhancing peanut yield compared to the susceptible pearl millet hybrid, HGM-100. Additional research is needed to improve the profitability of pearl millet, and nematode resistance should be an important component of crop improvement programs. Accepted for publication 20 October 2006. Published 2 February 2007.

Effects of Broiler Litter in an Irrigated, Double‐Cropped, Conservation‐Tilled Rotation

Broiler production is increasing rapidly in the Southern Coastal Plain, and little research has been conducted to evaluate broiler litter applications on the sandy soils of the region. We conducted a 4‐yr field study to determine optimum rates of broiler litter, its economic value, changes in soil tests to a depth of 90 cm, and effects on pathogens and nematodes. Summer crops were cotton (Gossypium hirsutum L.), pearl millet [Pennisetum glaucum (L.) R. Br.] for grain, and peanut (Arachis hypogaea L.). Winter crops were wheat (Triticum aesitivum L.) and oilseed canola (Brassica napus L.). Litter rates were 0, 4.5, 9.0, and 13.5 Mg ha−1 for each crop. Litter application increased yields of cotton, pearl millet, wheat, and canola and decreased yield of peanut. Average crop value increase from application of a megagram of broiler litter was estimated to be $42 ha−1 yr−1 when the application was made to all crops and $68 ha−1 yr−1 when none was applied to peanut. The mean cost of applied litter was approximately $12 Mg−1. Surface soil P, K, Cu, Zn, and Mn were increased in direct relation to litter rate. Data indicate that it would be prudent to limit applications to about 4.5 Mg ha−1. Litter applications had little effect on soil nematodes, but Rhizoctonia limb rot (Rhizoctonia solani AG‐4) of peanut increased. Lodging of canola, due to Sclerotinia spp., was doubled by any application of broiler litter.

Tillage and Chlorpyrifos Treatment Effects on Peanut Arthropods—An Incidence of Severe Burrower Bug Injury

Abstract A 2-yr study was conducted on the effects of tillage and soil insecticide (chlorpyrifos) treatment on peanut arthropod pests. A 3 by 2 split-plot experiment with five replications was subjected to factorial ANOVA. Main plot treatments consisted of three tillage systems: conventional moldboard plow, strip tillage into a killed wheat cover crop, and strip tillage into corn stubble residue. Subplot insecticide treatments were granular chlorpyrifos applied at early pegging (growth stage R2) and untreated. Populations of corn earworn, Helicoverpa zea (Boddie), and velevetbean caterpillar, Anticarsia gemmatalis Hübner, were lower in strip tillage systems. Chlorpyrifos applications caused corn earworm outbreaks in all tillage systems, but these applications were more disruptive in strip tillage. Chlorpyrifos treatment also increased populations of fall armyworm, Spodoptera frugiperda (J.E. Smith), but had no measurable effect on velvetbean caterpillar populations. Pod damage from lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), and wire-worms, Conoderus spp., was lower in strip tillage systems, and chlorpyrifos suppressed pod damage in all systems. Threecornered alfalfa hopper, Spissistilus festinus (Say), damage to peanut was greater in the wheat residue strip tillage system. Chlorpyrifos treatment reduced threecornered alfalfa hopper damage in all systems. Spider mite injury was not affected by tillage, but chlorpyrifos treatments resulted in mite outbreaks in all tillage systems. Burrower bug, Pangaeus bilineatus Say, injury to peanut kernels was greater in the strip tillage systems in 1999; and burrower bug injury was suppressed in the strip tillage systems by chlorpyrifos treatment. There was a significant interaction effect for burrower bug injury between tillage and insecticide treatment. Incidence of tomato spotted wilt virus also was reduced by strip tillage. Use of an effective fungicide program and a 3-yr crop rotation out of peanut production probably obscured any potential tillage effects on fungal diseases (southern stem rot, Rhizoctonia limb rot, and leaf spot). However, chlorpyrifos treatment increased Rhizoctonia limb rot incidence. Weed populations were generally greater in strip tillage systems, but postemergence herbicides effectively eliminated any potential confounding effect on yield and grade. Yield was not affected by tillage in either year, and chlorpyrifos had no effect on yield in 1998. In 1999, however, chlorpyrifos increased yield in both strip tillage systems. Neither tillage nor insecticide treatment affected grade (percentage total mature kernels) in 1998, but in 1999 grade was highest in conventional tillage and grade was improved by chlorpyrifos treatment in strip tillage systems. Crop value losses of $249 and $388/ha were attributed to burrower bug injury in untreated corn and wheat residue strip tillage systems, respectively. This injury may have been an anomaly of drought conditions but, given the potential economic impact, burrower bug merits further study in conservation tillage peanut production.

Evaluation of Detached Shoot and Leaflet Inoculation Techniques to Screen Peanut Genotypes for Resistance to Rhizoctonia Limb Rot

Abstract Identifying peanut genotypes with resistance to Rhizoctonia limb rot in the field is slow and costly. The objectives of this study were to compare detached leaflet and shoot inoculations as methods of screening for resistance to Rhizoctonia limb rot and to assess the relationship between genotype reactions in vitro and in the field. Eleven peanut germplasm selections and four cultivars, which exhibited a range of susceptibility to limb rot in previous field experiments in 1996 and 1997, were selected for evaluation. Detached lower reproductive limbs were suspended in Hoagland's solution and inoculated using a mixture of soil and oat seeds infested with Rhizoctonia solani. Detached leaflets on moistened filter paper in petri dishes were inoculated with hyphal plugs. Georgia Green and selections 512 and 283 were the most susceptible of all the genotypes to leaflet infections although Georgia Green is partially resistant to limb rot in the field. Disease levels for all genotypes were higher in the detached shoot inoculation study than in previous field experiments and symptoms observed were typical of those seen in the field. However, there was no correlation in relative susceptibility of the genotypes between the detached leaflet, shoot, or previous field experiments. Susceptibility of genotypes in the field may be determined by the combined resistance of the different plant parts or by factors not evaluated in this study. The detached shoot inoculation technique did not reproduce the same range of disease reactions on diverse peanut genotypes that were observed in the field experiments, but it did prove to be a good method of generating high levels of disease in vitro. The technique could probably be adapted to evaluate other factors such as relative fungicide performance or effects of environment on disease.

Identification of Resistance to Rhizoctonia Limb Rot in a Core Collection of Peanut Germ Plasm.

Diseases caused by Rhizoctonia solani lead to significant reductions in peanut yields and quality throughout the world. A subset of accessions from the peanut germ plasm core collection plus the commercial cultivars Florunner, Southern Runner, Georgia Browne, and Georgia Green were evaluated for resistance to limb and seedling hypocotyl infections caused by R. solani. Georgia Green and core accessions 95 (PI 497351), 197 (PI 331326), 208 (PI 274193), 244 (PI 343361), 246 (PI 343398), and 524 (PI 288178) had levels of resistance comparable to Georgia Browne, the only commercial cultivar reported to have partial resistance to Rhizoctonia limb rot. Eleven core accessions, representing the full range of disease expression, and the commercial cultivars were evaluated in growth chambers to quantify their susceptibility to seedling hypocotyl infections and to determine if evaluating seedlings could serve as a primary screening method to identify potential sources of limb rot resistance. The most resistant core accessions to seedling hypocotyl infections were 234 (PI 159664) and 366 (PI 268968), and the most resistant commercial cultivar was Georgia Green. There was not a significant correlation between resistance to limb rot in the field and the severity of hypocotyl infections in growth chambers, indicating that resistance to hypocotyl infections is not a good indicator of resistance to Rhizoctonia limb rot.

Soil Insecticide and Fungicide Treatment Effects on Peanut Pod Damage, Disease Incidence, and Yield, 1994

Abstract Granular soil insecticides were evaluated in standard (Bravo) and alternative (Folicur, Moncut, and Tilt) fungicide programs for effects on pod damage, disease incidence, and yield. The test was conducted on a Varina loamy sand in Barnwell County, SC. The experimental design was a RCB with 6 replicates. The experimental unit was a plot 50 × 25 ft (8 rows on 38-inch spacing). Granular insecticides were applied at pegging (Jul 12, 53 DAP) with a 2-row electric Gandy applicator, using 5-inch banders centered over the row. Foliar fungicides were applied with a tractor-mounted 8-row boom (8003 nozzles, 40 psi, 16.9 gpa for the first 2 appl. dates; TX6 nozzles, 60 psi, 8.3 gpa for the last 4 appl. dates). Tire traffic was confined to rows 1—2 and 7—8 of each plot so there was no traffic on yield rows after granular insecticide application. Insect pod damage was evaluated after digging by examining four 25-pod samples per plot and recording external hull feeding and internal kernel damage. The external injury counts reported include those pods with internal injury. Pod injury was primarily due to wireworm feeding based on recovery of 1.0 wireworm larvae/ft2 from 4-in depth sieve samples taken on Sept 6. Disease incidence was evaluated within 1 h of digging by scanning 100 row ft per plot and estimating the total row ft symptomatic for southern stem rot (Sclerotium rolfsii) on the plant crown and Rhizoctonia limb rot on plant laterals. No measure of disease severity was taken. The middle four rows (two 100-ft subsamples per plot) were harvested for yield.

Suppression of Foliar and Soilborne Peanut Diseases in Bahiagrass Rotations

Florunner peanut was grown after 1, 2, or 3 years of Tifton 9 bahiagrass and in alternating years with bahiagrass. Continuous peanut was grown in nontreated plots and in plots treated with flutolanil (4.48 kg/ha). In continuous peanut, stem rot (Sclerotium rolfsii) incidence was 4, 18, 19, and 44% during 1990 to 1993, respectively, without flutolanil and 0, 4, 10, and 17% with flutolanil. In 1993, stem rot incidence was 39, 29, 17, and 23% in the third, second, first, and alternating year of peanut, respectively. Rhizoctonia limb rot severity was low to moderate and not affected by crop rotation. Leaf spot diseases caused by Cercospora arachidicola and Cercosporidium personatum were present each year and were more severe in the short-term rotations. Pod yield of peanut was 3,044, 3,616, 4,547, and 3,922 kg/ha during the third, second, first, and alternating year of peanut, respectively. Compared to continuous peanut, longer rotations or treatment with flutolanil increased peanut grades and reduced percent damaged kernels (seeds). Population densities of Rhizoctonia solani and Pythium spp. in the soil generally were low and not altered by crop rotation. Rotation had little effect on root-knot (Meloidogyne incognita), ring (Criconemoides curvatum), or lesion (Pratylenchus brachyurus) nematodes.

Effect of Application Techniques on Performance of Propiconazole for Peanut Disease Control

Abstract Propiconazole (Tilt®) was applied to Florunner peanut by injection into irrigation water (chemigation) or as a foliar spray. At rates of 0.12-0.25 kg/ha of propiconazole control of both Rhizoctonia limb rot (Rhizoctonia solani AG-4) and stem rot (Sclerotium rolfsii) was inconsistent. Chemigation resulted in the lowest incidence of stem rot, but the incidence of stem rot was only 26% less than the control. Yields from plots receiving chemigation were greater than expected based on disease ratings, indicating that some effects of the fungicide were not being evaluated. Where foliar sprays of chlorothalonil were applied for late leaf spot (Cercosporidium personatum), supplemental applications of propiconazole via chemigation improved leaf spot control. However, substituting chemigated propiconazole for foliar sprays of chlorothalonil consistently resulted in more severe leaf spot and, in one year, decreased yields. Propiconazole is most effective against leaf spot when applied as a foliar spray, whereas chemigation applications provide optimum efficacy against soilborne pathogens of peanut.

Evaluation of Runner Peanut Cultivars and Advanced Georgia Breeding Lines for Yield and Resistance to Late Leaf Spot Under Three Disease-Management Programs1

Abstract Podyield and resistance to late leaf spot, caused by Cercosporidium personatum (Berk. & M.A. Curtis) Deighton, were evaluated on nine advanced Georgia breeding lines and five cultivars of peanut (Arachis hypogaea L.): Florunner, Georgia Runner, GK-7, Southern Runner, and Sunrunner. Peanuts were grown at Tifton, GA during 1987-1988 under three leaf spot programs using diniconazole at 0.14 kg/ha with Agri-Dex® (0.5% v/v): 1) unsprayed, 2) 28-day, and 3) 14-day spray schedule. Final disease ratings (Florida 1 to 10 scale) were made approximately 1-wk prior to harvest. In unsprayed plots, Southern Runner and GaT-2566 had significantly lower leaf spot disease ratings than Florunner, GK-7, Sunrunner, and Georgia Runner. Across all fungicide treatments, yields of Georgia Runner averaged significantly higher than the four other cultivars and GaT-2566. Average yields were 5111, 4497, 4433, 4404, 4377, and 4022 kg/ha for Georgia Runner, Southern Runner, GK-7, GaT-2566, Sunrunner, and Florunner, respectively. In addition to low yield potential of GaT-2566, it was susceptible to Rhizoctonia limb rot (R. solani Kühn, anastomosis group 4). However, Georgia Runner was found to have moderate tolerance to late leaf spot and excellent yield potential.

White Mold and Rhizoctonia Limb Rot Resistance among Advanced Georgia Peanut Breeding Lines1

Abstract Sclerotium rolfsii Sacc. and Rhizoctonia solani Kuhn are soilborne pathogens causing two major diseases in peanut (Arachis hypogaea L.) production: white mold and limb rot, respectively. Chemical and cultural control has been relatively ineffective in the past, consequently disease resistance is actively being sought as an environmentally safer and cost efficient alternative. Seven advanced breeding lines were evaluated from the Georgia Peanut Breeding Program and compared to four commercial runner cultivars. Among the cultivars, Southern Runner was found to have the highest yield and resistance to white mold but not limb rot. GA T-2741 had the best overall yield and disease resistance to both white mold and Rhizoctonia limb rot of all cultivars and breeding lines.

Effects of Chlorpyrifos on Pod Damage, Disease Incidence, and Yield in Two Peanut Fungicide Programs1

Abstract The benefits of chlorpyrifos (Lorsban 15G) soil insecticide treatment in standard (chlorothalonil) and developmental (tebuconazole) peanut fungicide programs were compared in five field tests over a 3-yr period. Chlorpyrifos treatment reduced incidence of southern stem rot (Sclerotium rolfsii) and insect pod injury, while increasing yield in the standard fungicide program. In contrast, chlorpyrifos treatment did not measurably affect stem rot incidence or yield in the tebuconazole program, and insect pod injury was reduced in only one of three years. Tebuconazole reduced Rhizoctonia limb rot (R. solani AG-4) and stem rot incidence, and decreased pod injury relative to the standard chlorothalonil program. Tebuconazole increased yield 804 kg/ha (716 lb/ac) over the standard fungicide. Chlorpyrifos increased yield 503 kg/ha (448 lb/ac) for a net return of $315/ha ($128/ac) in the standard fungicide program. However, in the developmental program, chlorpyrifos increased yield only 79 kg/ha (70 lb/ac) for a net return of -$2/ha (-$1/ac). Labeling of ergosterol biosynthesis inhibitor (EBI) fungicides such as tebuconazole would significantly affect peanut insect management in some production areas by reducing the economic incentive for preventative treatments of organophosphate insecticides.

Tank-Mix Applications of Cyproconazole and Chlorothalonil for Control of Foliar and Soilborne Diseases of Peanut

Field tests were conducted during 1989-1991 at Tifton and Plains, Georgia, and Marianna, Florida, to evaluate the efficacy of full-season applications of tank-mix combinations of cyproconazole at rates of 0.062 kg a.i/ha and 0.093 kg a.i./ha with chlorothalonil at 0.63 kg a.i./ha for control of late leaf spot, caused by Cercosporidium personatum; southern stem rot, caused by Sclerotium rolfsii; and Rhizoctonia limb rot, caused by R. solani, of peanut (Arachis hypogaea) (.)

Effects of Two Cropping and Two Tillage Systems and Pesticides on Peanut Pest Management1

Abstract In one or more years of a 3-year study, white mold (Sclerotium rolfsii) and Rhizoctonia limb rot (Rhizoctonia solani) damaged peanuts less in a wheat-peanut than in the fallow-peanut cropping system, but velvetbean caterpillar (Anticarsia gemmatalis) damage was less in the fallow-peanut. Thrips (Frankliniella fusca) and Rhizoctonia limb rot damage was less in minimum tillage than in conventional tillage but root-knot nematode (Melodogyne arenaria) damage was less in conventional tillage. Aldicarb reduced root-knot and lesion nematode (Pratylenchus brachyurus), thrips, and potato leafhopper (Empoascafabae) damage, but increased numbers of three cornered alfalfa hoppers (Spissistilus festinus) and velvetbean caterpillar damage. Flutolanil reduced white mold and Rhizocotonia limb rot damage. There was a high negative correlation (P=0.0001) of number of white mold loci with yield (r=-0.70). Rhizoctonia limb rot, gall and lesion indices and number of lesion nematodes in the soil were also negatively correlated with yield, but at low levels. Cropping systems did not affect peanut yields; however, tillage systems and nematicide/insecticide and fungicide treatments had major effects. Mean yield in conventional-tillage plots were greater than in minimum-tillage plots for the control and each chemical treatment. Mean yields were 11.1%, 55.9%, and 77.3% greater than control of aldicarb, flutolanil, and aldicarb plus flutolanil treatments, respectively, across cropping systems, tillage systems, and years.

Sensitivity of Rhizoctonia solani isolates to fungicides and evaluation of peanut cultivars to Rhizoctonia limb rot1

Abstract Twenty-one isolates were made from typical Rhizoctonia limb rot lesions of Florunner peanuts (Arachis hypogaea L.) and one each from a peanut pod and cowpea (Vigna unguiculata Walp.). Isolates of Rhizoctonia solani were characterized for sensitivity to three sterol-inhibiting fungicides, PCNB and chlorothalonil. Diniconazole, cyproconazole, and tebuconazole were the most effective inhibitors of radial growth, with a mean EC50 of 0.028, 0.056, and 0.166 μg/μL, respectively. EC50s for PCNB and chlorothalonil were 4.06 and 4.85 μg/mL, respectively. A technique to reproduce the disease in the greenhouse was developed and used to evaluate 18 peanut cultivars for resistance to limb inoculation with R. solani. NC 6, NC 7, New Mexico Valencia A, and Florunner were the most susceptible cultivars based on lesion length. Wounding before inoculation resulted in significantly increased lesion length for 15 of 18 cultivars. In a three-year (1986–88) field trial, NC 6, Florigiant, and NC 7 were the most susceptible cultivars, while VA 81B and Toalson appeared to be the most resistant.

Effects of Fungicides, Cultivars, Irrigation, and Environment on Rhizoctonia Limb Rot of Peanut

Diniconazole, flutolanil, and PCNB + ethoprop were evaluated in field tests in Plains and Tifton, Georgia, for control of Rhizoctonia limb rot of peanut caused by Rhizoctonia solani AG-4. Diniconazole applications at 60 + 90 days after planting (DAP) or 60 + 90 + 120 DAP were generally the best treatments for reducing incidence of limb rot in Plains. Based on a visual rating of incidence of Rhizoctonia limb rot after inverting, applications of diniconazole at 60 + 90 DAP significantly reduced disease incidence over applications at 90 + 120 DAP in Florunner, Pronto, and late-planted Florunner peanuts. Flutolanil reduced Rhizoctonia limb rot but was less effective than the two best diniconazole treatments. PCNB + ethoprop generally did not reduce incidence or severity when compared to the control. In Tifton, application of diniconazole every 14 days at 0.28 kg a.i./ha provided the greatest reduction in disease incidence in Florunner and New Mexico Valencia A (NMVA) cultivars. Pronto had significantly less Rhizoctonia limb rot than Florunner, and Florunner had less than NMVA. Irrigation increased disease incidence by as much as 109% over plots that received no irrigation

Effects of Tractor Traffic and Chlorothalonil Applied via Ground Sprays or Center Pivot Irrigation Systems on Peanut Diseases and Pod Yields

Chlorothalonil (as Bravo 720) was applied at 1255 g/ha 7 times to groundnut cv. Florunner in 0.12, 17.8 or 1.7 kl of water/ha via ground sprays, centre pivot irrigation (chemigation) or pivot-mounted underslung boom, respectively. Some of the chemigated plots were subjected to tractor traffic. Rhizoctonia limb rot (caused by R. solani anastomosis group 4) was generally not controlled by chlorothalonil and tended to be more severe with tractor traffic. Plants in untreated plots had final defoliation of 96 and 68% because of late leaf spot (caused by Cercosporidium personatum [Mycosphaerella berkeleyi]) in 1987 and 1988, respectively. Ground sprays gave the best leaf spot control in both years, followed by the underslung boom and chemigation applications. In 1987, yields were significantly lower in plots that received the underslung boom or chemigation treatments than in ground-sprayed plots. With less disease in 1988, pod yields were equal in chemigated and ground-sprayed plots and were significantly higher in plots treated by means of the underslung boom.

Effects of Chemigated and Conventionally Sprayed Tebuconazole and Tractor Traffic on Peanut Diseases and Pod Yields

Tebuconazole (252 g a.i./ha) was applied as Folicur 1.2 EC seven times to Florunner peanuts via ground sprays or center-pivot irrigation (chemigation). Tebuconazole applied via chemigation was diluted in water or nonemulsifiable oil and applied in 25.4 kl/ha of water. Chemigated plots either did or did not receive tractor traffic after each application. Plants in nontreated plots were defoliated by late leaf spot (Cercosporidium personatum) in 1987 and 1988. Significant Rhizoctonia limb rot (R. solani AG-4) was present only in 1987 and symptoms were reduced by all fungicide treatments; plants in plots not receiving tractor traffic had the least limb rot

Control of Southern Stem Rot and Rhizoctonia Limb Rot of Peanut with Flutolanil

Abstract Flutolanil (SN 84364) was evaluated in vitro against Sclerotium rolfsii and Rhizoctonia solani AG-4. ED50 values were < 0.01 and < 0.1 μg/mL for S. rolfsii and R. solani, respectively, while Pentachloronitrobenzene (PCNB) had ED50 values of < 0.1 and < 1.0 μg/mL, respectively. Concentrations of flutolanil at 0.1 μg/mL greatly reduced sclerotia and sclerotia initial development of S. rolfsii. Field evaluations were conducted near Tifton, GA, during 1983–86 for control of southern stem rot (S. rolfsii) and Rhizoctonia limb rot (R. solani AG 4) on peanut (Arachis hypogaea L.). Flutolanil 50 WP applied as a banded (40 cm) foliar spray at rates of 1.12 – 5.6 kg ai/ha at pegging (about 60 days post seeding) significantly (P = 0.05) decreased both disease loci numbers caused by S. rolfsii and percentage of vines infected with R. solani. Yields were increased significantly (P = 0.05) in all treatments over the four years of trials. Flutolanil 7 G was significantly (P = 0.05) less effective in controlling southern stem rot and increasing yield than the 50 WP formulation.