Using Soil-Applied Fungicides to Manage Phytophthora Crown and Root Rot on Summer Squash

Phytophthora crown and root rot (Phytophthora capsici) of summer squash is especially difficult to manage because all commercial cultivars are highly susceptible to P. capsici. Producers have traditionally relied on foliar fungicide applications to control Phytophthora crown and root rot despite their limited efficacy. Soil fungicide applications, including via subsurface drip chemigation, have recently gained interest as a method of improving control of P. capsici infections. In this study, soil drenches and foliar applications of 11 fungicides were compared for control of Phytophthora crown and root rot of summer squash in replicated field and greenhouse trials. Fungicides were applied at 7-day intervals. Incidence (%) of plant death was assessed from 7 to 42 days post inoculation (dpi) in field trials. Crown rot severity was rated on a scale of 1 (no wilting) to 5 (plant death) from 5 to 21 dpi in greenhouse trials. Results of field and greenhouse trials were similar. Plant death of ‘Cougar’ following inoculation with P. capsici isolate 12889 occurred at all growth stages from first true-leaf to full maturity in field trials. Plant death 42 dpi differed significantly (P ≤ 0.0001) among fungicides and application methods. The fungicide–application method interaction also was significant. Some fungicides were ineffective regardless of application method. In general, soil drenches were more effective than foliar applications at limiting plant death but no treatment completely controlled disease symptoms. Mean plant death 42 dpi was 41% for soil drenches and 92% for foliar sprays. Drenches of fluopicolide, mandipropamid, or dimethomorph limited plant death to ≤10% and prevented yield loss associated with root and crown rot. Foliar applications generally did not reduce plant death compared with the untreated, inoculated control, and were unable to prevent yield loss in field trials. In greenhouse trials, crown rot severity differed significantly (P ≤ 0.0001) among fungicides, application methods, and cultivars when plants were inoculated with P. capsici isolate 12889 or SP98. Crown rot was less severe and disease progress was slower following soil drenches than foliar applications. Some fungicide treatments were more effective on ‘Leopard,’ which was less susceptible to P. capsici than ‘Cougar.’ Soil application methods, including soil drench and drip chemigation, should be evaluated when fungicides are registered for soilborne disease control, because these methods provide better control of Phytophthora crown and root rot than foliar application.

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Identification, Chemical and Biological Management of Phytopythium vexans, the Causal Agent of Phytopythium Root and Crown Rot of Woody Ornamentals

Plant Disease ◽

10.1094/pdis-05-20-0987-re ◽

2020 ◽

Author(s):

Milan Panth ◽

Fulya Baysal-Gurel ◽

Farhat A. Avin ◽

Terri Simmons

Keyword(s):

Cytochrome C ◽

Cytochrome C Oxidase ◽

Root Rot ◽

Field Trials ◽

Causal Agent ◽

Crown Rot ◽

Red Maple ◽

Woody Ornamentals ◽

Root And Crown Rot ◽

Crown And Root Rot

Soilborne diseases caused by pathogens such as Phytophthora, Rhizoctonia, Fusarium, Verticillium, and Pythium species are the most important diseases of woody ornamentals. Ginkgo (Ginkgo biloba) and red maple (Acer rubrum) ‘October Glory’ plants grown in containers and fields in Tennessee have shown root and crown rot symptoms with dark brown to black lesions in 2017 and 2018. The objective of this research was to isolate and identify pathogens affecting ginkgo and red maple plants in nurseries of Tennessee and develop fungicide/biofungicide management recommendations for nursery producers. Isolations were made from the infected roots. Several Phytophthora-like colonies with spherical zoospores, filamentous to globose oogoni, and whitish mycelium, were isolated on V8-PARPH medium. For confirming identity, total genomic DNA was extracted followed by the sequence analysis of the internal transcribed spacer (ITS) regions, and large subunit (LSU) of the nuclear ribosomal RNA (rRNA) as well as cytochrome c oxidase subunit I (Cox I) and cytochrome c oxidase subunit II (Cox II) of mitochondrial DNA (mtDNA). Based on morphological and molecular analysis, Phytopythium vexans was described as a causal agent of crown and root rot from the infected ginkgo and red maple plants. To complete Koch’s postulates, a pathogenicity test was performed by drenching 100 ml V8 agar medium slurry of P. vexans inoculum on 1-year-old potted ginkgo plant root systems as well as red maple ‘October Glory’. Necrotic lesion development was observed in the root system 45 days after inoculation and P. vexans was re-isolated from the roots of both ginkgo and red maple. All control ginkgo and red maple plants remained disease-free and no pathogen was re-isolated. In addition, the efficacy of fungicides, biofungicides, fertilizer and host-plant defense inducers (traditionally recommended for management of oomycete diseases) for control of Phytopythium crown and root rot was evaluated on ginkgo and red maple ‘October Glory’ seedlings in greenhouse and field trials. The fungicides such as Empress Intrinsic, Pageant Intrinsic, Segovis and Subdue MAXX were effective in both greenhouse and field trials, and the biofungicide Stargus reduced the disease severity caused by pathogen P. vexans on ginkgo and red maple plants in greenhouse trials. These results will help nursery producers to make proper management decisions for newly reported Phytopythium crown and root rot disease of ginkgo and red maple plants.

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Evaluation of Harvest-Aid Herbicides as Desiccants in Lentil Production

Weed Technology ◽

10.1614/wt-d-16-00007.1 ◽

2016 ◽

Vol 30 (3) ◽

pp. 629-638 ◽

Cited By ~ 5

Author(s):

Ti Zhang ◽

Eric N. Johnson ◽

Christian J. Willenborg

Keyword(s):

Adverse Effects ◽

Crop Yield ◽

Seed Yield ◽

Yield Loss ◽

Field Trials ◽

Growth Stages ◽

Yield And Quality ◽

Seed Field ◽

Dry Down ◽

General Reduction

Desiccants are currently used to improve lentil dry-down prior to harvest. Applying desiccants at growth stages prior to maturity may result in reduced crop yield and quality, and leave unacceptable herbicide residues in seeds. There is little information on whether various herbicides applied alone or as a tank-mix with glyphosate have an effect on glyphosate residues in harvested seed. Field trials were conducted at Saskatoon and Scott, Saskatchewan, Canada, from 2012 to 2014 to determine whether additional desiccants applied alone or tank mixed with glyphosate improve crop desiccation and reduce the potential for unacceptable glyphosate residue in seed. Glufosinate and diquat tank mixed with glyphosate were the most consistent desiccants, providing optimal crop dry-down and a general reduction in glyphosate seed residues without adverse effects on seed yield and weight. Saflufenacil provided good crop desiccation without yield loss, but failed to reduce glyphosate seed residues consistently. Pyraflufen-ethyl and flumioxazin applied alone or tank mixed with glyphosate were found to be inferior options for growers as they exhibited slow and incomplete crop desiccation, and did not decrease glyphosate seed residues. Based on results from this study, growers should apply glufosinate or diquat with preharvest glyphosate to maximize crop and weed desiccation, and minimize glyphosate seed residues.

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Integrated Control of Rhizoctonia Crown and Root Rot of Sugar Beet with Fungicides and Antagonistic Bacteria

Plant Disease ◽

10.1094/pdis.2001.85.7.718 ◽

2001 ◽

Vol 85 (7) ◽

pp. 718-722 ◽

Cited By ~ 61

Author(s):

Sebastian Kiewnick ◽

Barry J. Jacobsen ◽

Andrea Braun-Kiewnick ◽

Joyce L. A. Eckhoff ◽

Jerry W. Bergman

Keyword(s):

Sugar Beet ◽

Root Rot ◽

Integrated Control ◽

The United States ◽

Field Trials ◽

Sugar Yield ◽

Economic Losses ◽

Yield Increase ◽

Leaf Stage ◽

Crown And Root Rot

Rhizoctonia crown and root rot, caused by the fungus Rhizoctonia solani AG 2-2, is one of the most damaging sugar beet diseases worldwide and causes significant economic losses in more than 25% of the sugar beet production area in the United States. We report on field trials in the years 1996 to 1999 testing both experimental fungicides and antagonistic Bacillus sp. for their potential to reduce disease severity and increase sugar yield in trials inoculated with R. solani AG 2-2. Fungicides were applied as in-furrow sprays at planting or as band sprays directed at the crown at the four-leaf stage, or four- plus eight-leaf stage, while bacteria were applied at the four-leaf stage only. The fungicides azoxystrobin and tebuconazole reduced crown and root rot disease by 50 to 90% over 3 years when used at rates of 76 to 304 g a.i./ha and 250 g a.i./ha, respectively. The disease index at harvest was reduced and the root and sugar yield increased with azoxystrobin compared with tebuconazole. The combination of azoxystrobin applied at 76 g a.i./ha and the Bacillus isolate MSU-127 resulted in best disease reduction and greatest root and sucrose yield increase.

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First Report of a Phytopythium litorale Species Causing Crown and Root Rot on Rhododendron pulchrum in China

Plant Disease ◽

10.1094/pdis-04-21-0830-pdn ◽

2021 ◽

Author(s):

Yaxing Li ◽

Yangfan Feng ◽

Cuiping Wu ◽

Junxin Xue ◽

Binbin Jiao ◽

...

Keyword(s):

Root Rot ◽

Morphological Characters ◽

Morphological Features ◽

Crown Rot ◽

Sterile Water ◽

First Report ◽

Inoculation Method ◽

Platanus Orientalis ◽

Crown And Root Rot ◽

Root Tissues

During a survey of pathogenic oomycetes in Nanjing, China from June 2019 to October 2020, at least ten adjacent Rhododendron pulchrum plants at a Jiangjun Mountain scenic spot showed symptoms of blight, and crown and root discoloration . Symptomatic root tissues collected from three 6-year-old plants were rinsed with water, cut into 10-mm pieces, surface sterilized with 70% ethanol for 1 min, and plated onto 10% clarified V8 PARP agar (cV8A-PARP) containing pimaricin (20 mg/liter), ampicillin (125 mg/liter), rifampicin (10 mg/liter), and pentachloronitrobenzene (20 mg/liter). Four Pythium-like isolates were recovered after three days of incubation at 26°C, and purified using hyphal-tipping. Ten agar plugs (2×2 mm2) of each isolate were grown in 10 mL of 10% clarified V8 juice (cV8) in a 10 cm plate at 26°C for 3 days to produce mycelial mats, and then the cV8 was replaced with sterile water. To stimulate sporangial production, three to five drops of soil extract solution were added to each plate. Sporangia were terminal, ovoid to globose, and the size is 24 to 45.6 (mean 34.7) (n=10.8) in length x 23.6 to 36.0 (mean 29.8) (n=6.2) in width. Gametangia were not observed in cV8A or liquid media after 30 days. For colony morphology, the isolates were sub-cultured onto three solid microbial media (cV8A-PARP, potato dextrose agar, corn meal agar) . All isolates had identical morphological features in the three media. Complete ITS and partial LSU and cox2 gene regions were amplified using primer pairs ITS1/ITS4, NL1/NL4, and FM58/FM66 , respectively. The ITS, LSU, and cox2 sequences of isolate PC-dj1 (GenBank Acc. No. MW205746, MW208002, MW208003) were 100.00% (936/936 nt), 100.00% (772/772 nt), and 99.64% (554/556 nt) identical to those of JX985743, MT042003, and GU133521, respectively. We built a maximum-likelihood tree of Phytopythium species using the concatenated dataset (ITS, LSU, cox2) to observe interspecific differences. Based on the morphological characters and sequences, isolate PC-djl was identified as Phytopythium litorale . As the four isolates (PC-dj1, PC-dj2, PC-dj3 and PC-dj4) tested had identical morphological characters and molecular marker sequences, the pathogenicity of the representative isolate, PC-dj1, was tested using two inoculation methods on ten one-year-old R. pulchrum plants. For the first inoculation method, plants were removed from the pot, and their roots were rinsed with tap water to remove the soil. Each of these plants was placed in a glass flask containing 250 mL of sterile water and 10 blocks (10 x 10 mm2) of mycelial mats harvested from a three-day-old culture of P. litorale, while the other plant was placed in sterile water as a control, and incubated at 26°C. After three days, symptoms including crown rot, root rot and blight was observed on the inoculated plants whereas the control remained asymptomatic. For the second inoculation method, ten plants were dug up to expose the root ball. Ten three-day-old cV8A plugs (5×5 mm2) from a PC-dj1 culture or sterile cV8A plugs were evenly insert into the root ball of a plant before it was planted back into the original pots. Both plants were maintained in a growth chamber set at 26°C with a 12/12 h light/dark cycle and irrigated as needed. After 14 to 21 days, the inoculated plant had symptoms resembling those in the field , while the control plant remained asymptomatic. Each inoculation method was repeated at triplicate and the outcomes were identical. Phytopythium isolates with morphological features and sequences identical to those of PC-dj1 were recovered from rotted crown and root tissues of all inoculated plants. Previously, P. litorale was found causing diseases of apple and Platanus orientalis in Turkey, fruit rot and seedling damping-off of yellow squash in southern Georgia, USA. This is the first report of this species causing crown and root rot on R. pulchrum, an important ornamental plant species in China. Additional surveys are ongoing to determine the distribution of P. litorale in the city of Nanjing.

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USE OF THE EXCISED SHOOT ASSAY TO EVALUATE RESISTANCE TO Phytophthora cactorum OF APPLE ROOTSTOCK CULTIVARS

Canadian Journal of Plant Science ◽

10.4141/cjps88-102 ◽

1988 ◽

Vol 68 (3) ◽

pp. 851-857 ◽

Cited By ~ 12

Author(s):

R. S. UTKHEDE ◽

H. A. QUAMME

Keyword(s):

Malus Domestica ◽

Root Rot ◽

Crown Rot ◽

Lesion Length ◽

Malus Domestica Borkh ◽

Root Stock ◽

P 16 ◽

The Mean ◽

Crown And Root Rot ◽

Moderately Resistant

The excised shoot assay was used to evaluate crown and root rot (P. cactorum (Leb & Cohn) Schroeter) resistance of several apple (Malus domestica Borkh.) rootstock cultivars using relative lesion length as a measure of resistance. To determine the best time to assess crown rot resistance, three cultivars, M.26 (moderately resistant), MM.111 (moderately susceptible) and MM.106 (susceptible) were tested monthly for a 12-mo period. The best separation of the three cultivars of known resistance was from the period of February to June and again in November. In another test on 27 apple root-stock cultivars tested quarterly, good separation of known standards was achieved only on the April sampling date. In both tests the organism appeared to overwhelm resistance of the tissue during the most active stage of shoot growth in July and August. Based on the mean for the three dates (April, October and January) the cultivars P. 16, J9, P.2, M.4, 0.3, P.1, M.9, M.26, P.22 and P.18 were significantly more resistant than the field-susceptible rootstocks, MM.106. None was significantly more resistant than M.9 and M.4, the resistant standards.Key words: Crown rot, Malus domestica Borkh, root rot, P. cactorum, rootstocks, apple

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Performance and Resistance to Phytophthora Crown and Root Rot in Squash Lines

HortTechnology ◽

10.21273/horttech04636-20 ◽

2020 ◽

Vol 30 (5) ◽

pp. 608-618 ◽

Cited By ~ 1

Author(s):

Kyle E. LaPlant ◽

Gregory Vogel ◽

Ella Reeves ◽

Christine D. Smart ◽

Michael Mazourek

Keyword(s):

Root Rot ◽

Cucurbita Pepo ◽

Field Experiments ◽

Phytophthora Capsici ◽

Severe Disease ◽

Field Trials ◽

Disease Symptoms ◽

Resistant Lines ◽

Oomycete Pathogen ◽

Crown And Root Rot

Phytophthora crown and root rot, caused by the oomycete pathogen Phytophthora capsici, is a devastating disease of squash and pumpkin (Cucurbita pepo). No currently available cultivars provide complete resistance to this disease. Three newly developed squash lines and four hybrids were evaluated in greenhouse and field experiments for their resistance to phytophthora crown and root rot as well as for their horticultural performance. The three newly developed lines ranked among the most resistant entries included in 2 years of field trials. In addition, in a separate greenhouse experiment, one of the lines was shown to display the least severe disease symptoms among a group of accessions previously reported to possess partial resistance to phytophthora crown and root. Furthermore, the resistance was observed to be robust to several isolates of P. capsici. However, the phytophthora-resistant lines had reduced yield relative to standard squash cultivars. These lines are useful for continued breeding efforts toward a phytophthora crown and root rot-resistant cultivar.

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Morphological and Molecular Characteristics of Fungal Species Associated with Crown Rot of Strawberry in South Korea

10.21203/rs.3.rs-713894/v1 ◽

2021 ◽

Author(s):

Oliul Hassan ◽

Taehyun Chang

Keyword(s):

South Korea ◽

Root Rot ◽

Species Complex ◽

Sequence Data ◽

Morphological Characteristics ◽

Fungal Species ◽

Crown Rot ◽

Molecular Characteristics ◽

Pathogenicity Test ◽

Crown And Root Rot

Abstract Crown and root rot is the most important and destructive strawberry diseases in Korea as it causessubstantial economic loss. In August 2020, a severe outbreak of crown and root rot on strawberries (Fragaria×ananassa Duch.) was observed in the greenhouse at Sangju, South Korea. Infected plantlets displayed browning rot within the crown and root, stunted growth, and poor rooting. Thirty fungal isolates were procured from the affected plantlet. Isolates were identified based on morphological characteristics and pathogenicity test as well as sequence data obtained from internal transcribed spacer, large subunit ribosomal ribonucleic acid, translation elongation factor,and RNA polymerase Ⅱ-second largest subunit. Results showed that thecrown and root rot of strawberry in Korea was caused by three distinct fungal species:Fusarium oxysporum species complex, F. solani species complex, andPlectosphaerella cucumerina. To the best of our knowledge,F. solani species complex andP. cucumerinaare reported for the first time as the causal agents of the crown and root rot of strawberryin South Korea.Pathogenicity tests confirmed that these isolates are pathogenic to strawberry.Understanding the composition and biology of the pathogen population will be helpful toprovide effectivecontrol strategies for the disease.

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Resistance to Phytophthora Species among Rootstocks for Cultivated Prunus Species

HortScience ◽

10.21273/hortsci10391-17 ◽

2017 ◽

Vol 52 (11) ◽

pp. 1471-1476 ◽

Cited By ~ 2

Author(s):

Gregory T. Browne

Keyword(s):

Root Rot ◽

Phytophthora Species ◽

Crown Rot ◽

Phytophthora Cactorum ◽

Prunus Species ◽

Phytophthora Megasperma ◽

Soil Flooding ◽

Root And Crown Rot ◽

Crown And Root Rot ◽

Multiple Species

Many species of Phytophthora de Bary are important pathogens of cultivated Prunus L. species worldwide, often invading the trees via their rootstocks. In a series of greenhouse trials, resistance to Phytophthora was tested in new and standard rootstocks for cultivated stone fruits, including almond. Successive sets of the rootstocks, propagated as hardwood cuttings or via micropropagation, were transplanted into either noninfested potting soil or potting soil infested with Phytophthora cactorum (Lebert & Cohn) J. Schöt., Phytophthora citricola Sawada, Phytophthora megasperma Drechs, or Phytophthora niederhauserii Z.G. Abad & J.A. Abad. Soil flooding was included in all trials to facilitate pathogen infection. In some trials, soil flooding treatments were varied to examine their effects on the rootstocks in both the absence and presence of Phytophthora. Two to 3 months after transplanting, resistance to the pathogens was assessed based on the severity of root and crown rot. ‘Hansen 536’ was consistently more susceptible than ‘Lovell’, ‘Nemaguard’, ‘Atlas’, ‘Viking’, ‘Citation’, and ‘Marianna 2624’ to root and/or crown rot caused by P. cactorum, P. citricola, and P. megasperma. By contrast, susceptibility to P. niederhauserii was similarly high among all eight tested genotypes of peach, four genotypes of peach × almond, two genotypes of (almond × peach) × peach, and one genotype of plum × almond. Most plum hybrids were highly and consistently resistant to crown rot caused by P. niederhauserii, but only ‘Marianna 2624’ was highly resistant to both crown and root rot caused by all of the Phytophthora species. The results indicate that there is a broad tendency for susceptibility of peach × almond rootstocks and a broad tendency for resistance of plum hybrid rootstocks to multiple species of Phytophthora.

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EFFECT OF SEEDING DEPTH, SEEDING DATE AND SEED SIZE ON COMMON ROOT ROT OF SPRING BARLEY

Canadian Journal of Plant Science ◽

10.4141/cjps82-132 ◽

1982 ◽

Vol 62 (4) ◽

pp. 885-891 ◽

Cited By ~ 13

Author(s):

L. J. DUCZEK ◽

L. J. PIENING

Keyword(s):

Grain Yield ◽

Seed Size ◽

Root Rot ◽

Yield Loss ◽

Spring Barley ◽

Field Trials ◽

Common Root ◽

Common Root Rot ◽

Seeding Date ◽

Seeding Emergence

The effects of variable seeding depth and dates of seeding of barley on the incidence of root rot, and on emergence and grain yield were investigated in field trials at Saskatoon and Scott, Saskatchewan. The effect of variable seeding depth of barley on intensity of root rot, grain yield, loss of yield due to root rot, and the effect of variable seed size of barley on incidence of root rot and yield were also investigated in field trials at Lacombe, Alberta. Symptoms of common root rot, based on lesions on the subcrown internode, were not influenced by seed size or seeding date but the disease increased with depth of seeding. Grain yield decreased with depth and with late seeding. Emergence was not affected by seeding date but decreased with depth of seeding. Common root rot was not associated with the reduced yields of later seeding dates but was associated with reduced yields of increased seeding depths. The increased emergence and reduced disease at shallow depths resulted in a greater number of clean plants which probably accounts for some of the increased grain yield at shallow seeding depths.

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Relationship of binucleate Rhizoctonia isolates used for biocontrol of rhizoctonia crown rot of sugar beet to anastomosis systems

Canadian Journal of Microbiology ◽

10.1139/m91-055 ◽

1991 ◽

Vol 37 (5) ◽

pp. 339-344 ◽

Cited By ~ 3

Author(s):

Leonard J. Herr

Keyword(s):

Sugar Beet ◽

Root Rot ◽

Anastomosis Group ◽

The Other ◽

Crown Rot ◽

Considerable Heterogeneity ◽

Binucleate Rhizoctonia ◽

Crown And Root Rot ◽

Relationship Of ◽

Intraspecific Group

The relationships of 10 binucleate Rhizoctonia isolates used as biocontrol agents of rhizoctonia crown and root rot of sugar beet in Ohio to described binucleate Rhizoctonia anastomosis systems were investigated. Ten Ohio binucleate Rhizoctonia (Ohio BNR) isolates, paired in all combinations, cross anastomosed with one another, indicating that all belong to the same anastomosis group. Four representative Ohio BNR isolates failed to anastomose with any tester isolates of the Ceratobasidium anastomosis grouping system, indicating that none belong in that system. However, all 10 Ohio BNR isolates anastomosed with an AG-B (o) tester isolate (binucleate Rhizoctonia anastomosis grouping system), indicating that the Ohio agents belong in this anastomosis grouping system and to the (o) intraspecific group of AG-B. None of the Ohio BNR isolates anastomosed with either of the other two intraspecific group tester isolates (AG-Ba, AG-Bb) of the AG-B group. Moreover, the AG-B intraspecific group tester isolates, AG-Ba, AG-Bb, AG-B (o), self-anastomosed but did not cross anastomose with one another. Variations in cultural characteristics noted among the 10 Ohio BNR isolates indicated that considerable heterogeneity exists within these AG-B (o) isolates. Key words: binucleate Rhizoctonia, anastomosis, rhizoctonia crown rot, sugar beet.

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