Timing and Efficacy of Fungicide Applications for Diplodia Ear Rot Management in Corn

2015 ◽  
Vol 16 (3) ◽  
pp. 123-131 ◽  
Author(s):  
Martha P. Romero Luna ◽  
Kiersten A. Wise
Keyword(s):  
Fungal Growth ◽  
The United States ◽  
Field Trials ◽  
Individual Growth ◽  
Growth Stages ◽  
Ear Rot ◽  
Management Options ◽  
Vitro Assay ◽  
Stenocarpella Maydis

Diplodia ear rot, a corn (Zea mays L.) disease caused by the fungus Stenocarpella maydis (Berk.) B. Sutton, has been a persistent ear rot across the United States. Management options are currently limited. Field trials conducted under inoculated and non-inoculated conditions were established at two locations in Indiana from 2011 to 2013 to test the fungicides azoxystrobin plus propiconazole and prothioconazole against Diplodia ear rot. Fungicides were applied at three individual growth stages during each year. Fungicides did not consistently reduce Diplodia ear rot compared to non-fungicide-treated controls in any year. Applications also did not consistently increase yield at any timing under inoculated and non-inoculated plots compared with the non-fungicidetreated control. Fungicides were tested in an in vitro assay to determine the effective fungicide concentration at which 50% of mycelial growth or conidial germination of S. maydis was inhibited (EC50). Propiconazole and prothioconazole EC50 values indicated efficacy in reducing fungal growth under controlled conditions; however, current fungicide application methods and plant barriers to fungicide contact with the pathogen may prevent these products from effectively reducing Diplodia ear rot in a field setting. Accepted for publication 23 August 2015. Published 1 September 2015

scholarly journals Limited Genetic Diversity in North American Isolates of Phytophthora erythroseptica Pathogenic to Potato Based on RAPD Analysis

Plant Disease ◽  
2005 ◽  
Vol 89 (4) ◽  
pp. 380-384 ◽  
Author(s):  
Rick D. Peters ◽  
Rod J. Clark ◽  
Albert D. Coffin ◽  
Antony V. Sturz ◽  
David H. Lambert ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
North America ◽  
New Brunswick ◽  
Prince Edward Island ◽  
Random Amplified Polymorphic Dna ◽  
Geographic Origin ◽  
The United States ◽  
Vitro Assay ◽  
Phytophthora Erythroseptica

Pink rot of potato (Solanum tuberosum), caused by Phytophthora erythroseptica, is found wherever potatoes are grown, and in the last decade, it has reemerged as an economically important disease in Canada and the United States. A selection of isolates of P. erythroseptica from major potato-growing regions in North America, namely Prince Edward Island and New Brunswick, Canada, and Maine and Idaho, U.S.A., was assessed for genetic diversity with randomly chosen decanucleotide primers which were used to amplify regions of DNA to reveal polymorphisms among templates (random amplified polymorphic DNA [RAPD]). The isolates varied in their geographic origin as well as in their sensitivity to mefenoxam, as determined by an in vitro assay. In three separate RAPD screens (I, II, and III) with 23 isolates of P. erythroseptica chosen from a larger collection, 1,410, 369, and 316 robust, scorable bands were amplified, respectively. However, among the bands amplified in screens I, II, and III, only 3, 1, and 3 bands, respectively, were polymorphic. When three primers yielding polymorphisms were used to screen 106 isolates from Prince Edward Island and New Brunswick, or a representative collection of 32 isolates from Prince Edward Island, New Brunswick, Maine, and Idaho, no major variation was discovered. RAPD markers were not correlated with geographic origin or mefenoxam sensitivity of the isolates. From an evolutionary standpoint, the absence of genetic diversity among the isolates of P. erythroseptica we examined may be attributable to the relatively recent introduction of a small founding population of the pathogen in North America.

Research Note Infection and Ultrastructure of Conidia and Pycnidia of Stenocarpella maydis in Maize

2011 ◽  
Vol 74 (4) ◽  
pp. 676-680
Author(s):  
ZHENGJUN XIA ◽  
HONGYAN WU ◽  
PREMILA N. ACHAR
Keyword(s):  
The United States ◽  
Ear Rot ◽  
Callose Deposition ◽  
Term Survival ◽  
Embryonic Tissues ◽  
Maize Seeds ◽  
Transmission Electron ◽  
Stenocarpella Maydis ◽  
Host Tissues

Stenocarpella maydis is the most prevalent ear rot pathogen of maize (Zea mays) in South Africa, the United States, and other countries. Infection and ultrastructure of propagules of S. maydis in maize were observed by light, scanning, and transmission electron microscopy. Two-celled conidia of S. maydis were found in the tissues of husk and kernels. Mycelia colonized inter- and intracellularly in the host tissues. Pycnidia were found abundantly inside the seed tissues of susceptible cultivars; within a single seed, pycnidia propagated preferentially in embryonic tissues. A pycnidium is composed of morphologically different resting spores mingled with some degraded organelles of the host cell. In this study, various enzymatic activities led to cell wall degradation, lacunae in endosperm tissues, and disrupted organelles in susceptible cultivars. In contrast, callose deposition surrounding fungal hyphae was clearly visible in resistant cultivars. Heavy infection was detected by maceration, even though there was no apparent symptom on the seed coat. The saprophytic nature and structurally different forms of propagules could contribute to a long-term survival of this pathogen in the field and during grain storage. Furthermore, S. maydis might pose a threat of diplodiatoxin intoxication to human and domestic animals when infected maize seeds are consumed.

Yield losses of soybeans due to Phytophthora megasperma f.sp. Glycinea

1989 ◽  
Vol 40 (6) ◽  
pp. 1161 ◽  
Author(s):  
MJ Ryley ◽  
HF Mosetter ◽  
JL Rose
Keyword(s):  
The United States ◽  
Field Trials ◽  
Field Resistance ◽  
Growth Stages ◽  
Yield Losses ◽  
Phytophthora Megasperma ◽  
High Death Rate ◽  
High Death ◽  
Soybean Genotypes ◽  
Seed Yields

Field trials were conducted in two seasons to determine the influence of Phytophthora megasperma f.sp. glycinea on seed yields of soybean genotypes with different levels of resistance. The fungicide metalaxyl, applied as a seed dressing and soil drenches, was used to control the disease. The cultivar Davis, which has high field resistance, did not suffer significant losses in either year. whereas the yield depression of less resistant genotypes ranged up to 72%, depending on the genotype and year. In 198 1 - 82 high death rate of plants occurred early in the season, but yield losses were less than in 1982-83 when mortality occurred late in the season. The declining ability of surviving plants to compensate for disease losses during the latter growth stages may account for the differences in yield losses between seasons.Genotypes with immunity to P. megasperma f.sp. glycinea have been widely grown in the United States because they offer complete protection against some races. However, new pathogenic races have developed quickly, and previously immune genotypes have then suffered severe yield losses. The results of these trials demonstrate that yield losses can be prevented without resorting to fungicide treatments. It is likely that a stable long-term solution to phytophthora root and stem rot will be conferred by field resistance.

scholarly journals Effects of Temperature and pH on Fusarium oxysporum and Soybean Seedling Disease

Plant Disease ◽  
2019 ◽  
Vol 103 (12) ◽  
pp. 3234-3243
Author(s):  
David R. Cruz ◽  
Leonor F. S. Leandro ◽  
Gary P. Munkvold
Keyword(s):  
Fusarium Oxysporum ◽  
Root Rot ◽  
Radial Growth ◽  
Culture Media ◽  
Fungal Growth ◽  
Artificial Culture ◽  
Vitro Assay ◽  
Seedling Disease ◽  
Soybean Seedlings

Fusarium oxysporum (Fo) is an important pathogen that reduces soybean yield by causing seedling disease and root rot. This study assessed the effects of pH and temperature on Fo fungal growth and seedling disease. In an in vitro assay, 14 Fo isolates collected from symptomatic soybean roots across Iowa in 2007 were grown on artificial culture media at five pH levels (4, 5, 6, 7, and 8) and incubated at four temperatures (15, 20, 25, or 30°C). In a rolled-towel assay, soybean seeds from Fo-susceptible cultivar Jack were inoculated with a suspension of a pathogenic or a nonpathogenic Fo isolate; both isolates were previously designated for their relative aggressiveness in causing root rot at 25°C. The seeds were placed in rolled germination paper, and the rolls were incubated in all combinations of buffer solutions at four pH levels (4, 5, 6, and 7), and four temperatures (15, 20, 25, or 30°C). There was a significant interaction between temperature and pH (P < 0.05) for in vitro radial growth and root rot severity. Isolates showed the most in vitro radial growth after incubation at pH 6 and 25°C. For the rolled-towel assay, the pathogenic isolate caused the most severe root rot at pH 6 and 30°C. Gaussian regression analysis estimates for optimal conditions were pH 6.3 at 27.1°C for maximal fungal growth and pH 5.9 at 30°C for maximal root rot severity. These results indicate that optimal pH and temperature conditions are similar for Fo growth and disease in soybean seedlings and suggest that Fo may be a more important seedling pathogen when soybeans are planted under warm conditions in moderately acidic soils.

Occurrence of Stenocarpella macrospora Causing Ear Rot in Corn in the United States

2016 ◽  
Vol 17 (2) ◽  
pp. 152-154
Author(s):  
Martha P. Romero Luna ◽  
Carl A. Bradley ◽  
Heather M. Kelly ◽  
Kiersten A. Wise
Keyword(s):  
United States ◽  
South Africa ◽  
South America ◽  
The United States ◽  
Ear Rot ◽  
Stenocarpella Maydis ◽  
The U.S ◽  
Related Fungus

Diplodia ear rot of corn is primarily caused by the fungus Stenocarpella maydis in the United States. Stenocarpella macrospora is a closely related fungus present in the U.S. but primarily associated with Diplodia leaf streak. S. macrospora is recognized as a major ear rot pathogen in South America and South Africa, but has infrequently been associated with ear rot in the U.S. This brief presents the first reports of Diplodia ear rot in Illinois and Tennessee. This is also the first confirmation of S. macrospora causing ear rot in the U.S. in over 60 years. Accepted for publication 19 May 2016. Published 15 June 2016.

scholarly journals Fungicide Sensitivity Monitoring of Alternaria spp. Causing Leaf Spot of Sugarbeet (Beta vulgaris) in the Upper Great Lakes

Plant Disease ◽  
2019 ◽  
Vol 103 (9) ◽  
pp. 2263-2270 ◽  
Author(s):  
N. Rosenzweig ◽  
L. E. Hanson ◽  
S. Mambetova ◽  
Q. W. Jiang ◽  
C. Guza ◽  
...  
Keyword(s):  
Disease Management ◽  
Leaf Spot ◽  
Resistance Management ◽  
Fungal Growth ◽  
The United States ◽  
Cross Resistance ◽  
Management Approach ◽  
Dilution Method ◽  
Fungicide Sensitivity

Alternaria leaf spot (ALS), caused by Alternaria spp., can occur wherever sugarbeet is grown. Infection by Alternaria spp. and disease management has historically been considered a minor issue in sugarbeet production in the United States. An increase of both incidence and severity in 2016 of ALS high enough to cause yield loss has been observed in Michigan. With a renewed need to consider potential management of this disease, the sensitivity was determined for populations of Alternaria spp. to three classes of fungicides currently labeled for management of leaf spot on sugarbeet, including demethylase inhibitor (DMI), quinone outside inhibitor (QoI), and organo-tin fungicides. Leaves with symptoms of ALS were sampled from sugarbeet fields in east-central Michigan and southwestern Ontario, Canada. Monoconidial isolates were obtained to determine sensitivity to each fungicide class above. A spiral gradient dilution method was used to estimate the fungicide effective concentration (in milligrams per liter) that caused a 50% inhibition of fungal growth in vitro for all isolates. Significant temporal shifts were detected in the frequencies of sensitivity phenotypes to DMI and QoI but not organo-tin fungicides from 2016 through 2017. Individual isolates of Alternaria spp. were recovered with cross-resistance to DMI and multiple resistance to DMI, QoI, and triphenyltin hydroxide fungicides. To our knowledge, this is the first report of a fungus other than Cercospora beticola with resistance to organo-tin fungicides. Fungicide sensitivity monitoring indicates that an effective integrated disease management approach combining fungicide efficacy trials and monitoring pathogen biology is essential for developing effective resistance management recommendations.

scholarly journals Baseline Sensitivity of Ascochyta rabiei to Azoxystrobin, Pyraclostrobin, and Boscalid

Plant Disease ◽  
2008 ◽  
Vol 92 (2) ◽  
pp. 295-300 ◽  
Author(s):  
K. A. Wise ◽  
C. A. Bradley ◽  
J. S. Pasche ◽  
N. C. Gudmestad ◽  
F. M. Dugan ◽  
...  
Keyword(s):  
United States ◽  
Ascochyta Blight ◽  
Monitoring Program ◽  
The United States ◽  
Ascochyta Rabiei ◽  
Alternative Respiration ◽  
Baseline Sensitivity ◽  
Vitro Assay ◽  
Mean Values

Ascochyta rabiei, causal agent of Ascochyta blight on chickpea (Cicer arietinum), can cause severe yield loss in the United States. Growers rely on applications of fungicides with site-specific modes of action such as the quinone outside inhibiting (QoI) fungicides azoxystrobin and pyraclostrobin, and the carboximide fungicide boscalid, to manage disease. In all, 51 isolates collected prior to QoI fungicide registration and 71 isolates collected prior to boscalid registration in the United States were tested in an in vitro assay to determine the effective fungicide concentration at which 50% of conidial germination was inhibited (EC50) for each isolate–fungicide combination. The effect of salicylhydroxamic acid (SHAM) on conidia of A. rabiei in the presence and absence of azoxystrobin also was assessed to determine whether the fungus is capable of using alternative respiration. Five of nine A. rabiei isolates tested had significantly higher (P ≤ 0.05) EC50 values when SHAM was not included in media amended with azoxystrobin, indicating that A. rabiei has the potential to use alternative respiration to overcome fungicide toxicity in vitro. EC50 values of azoxystrobin and pyraclostrobin ranged from 0.0182 to 0.0338 μg/ml and from 0.0012 to 0.0033 μg/ml, with mean values of 0.0272 and 0.0023 μg/ml, respectively. EC50 values of boscalid ranged from 0.0177 to 0.4960 μg/ml, with a mean of 0.1903 μg/ml. Establishment of these baselines is the first step in developing a monitoring program to determine whether shifts in sensitivity to these fungicides are occurring in the A. rabiei pathogen population.

Variable adhesion and diurnal population patterns of epiphytic yeasts on creeping bentgrass

2006 ◽  
Vol 52 (5) ◽  
pp. 404-410 ◽  
Author(s):  
Tom W Allen ◽  
Leon L Burpee ◽  
James W Buck
Keyword(s):  
Creeping Bentgrass ◽  
Field Trials ◽  
Agrostis Palustris ◽  
Initial Field ◽  
Vitro Assay ◽  
Yeast Community ◽  
Epiphytic Yeast ◽  
Nonadherent Cells ◽  
Total Yeast

Irrigation and an in vitro agitation assay were used to determine the percentage of the epiphytic yeast community (Cryptococcus, Pseudozyma, Rhodotorula, and Sporobolomyces) adhering to the phylloplane of creeping bentgrass (Agrostis palustris (Huds.) Pers.). Colony-forming units (cfu) of total epiphytic yeast populations (adherent and nonadherent cells) and of adherent populations (cells not removed by agitation) were determined by leaf washing and dilution plating. In an in vitro assay, 40.0% and 57.1% of the yeast adhered to the leaves, whereas, in initial field trials the percentage of adherent yeasts ranged from 40.0% to 71.9% of the total population. Adherent yeast cfu on leaves in the morning were significantly lower on bentgrass (8.0 × 103to 3.1 × 104cfu·cm–2) compared with total yeast cfu (1.4 × 104to 4.7 × 104cfu·cm–2) on the nonirrigated control. No differences in yeast populations were observed between irrigated and nonirrigated plots 2 h after the 0900 treatments. Yeast populations followed a diurnal pattern, with larger cfu recovered from bentgrass leaves in the morning and significantly lower populations recovered in the afternoon. At 1400 the adherent yeast were 83.1%–100% of the total yeast population recovered from the leaves. The relative adhesiveness of the epiphytic yeast community on bentgrass leaves is dynamic with nonadherent cells making up a larger percentage of the population in the mornings than the afternoons.Key words: adherence, Cryptococcus, leaf surface, Rhodotorula, turfgrass.

scholarly journals Potential Impact of Fluopyram on the Frequency of the D123E Mutation in Alternaria solani

Plant Disease ◽  
2018 ◽  
Vol 102 (3) ◽  
pp. 656-665 ◽  
Author(s):  
Mitchell J. Bauske ◽  
S. K. R. Yellareddygari ◽  
Neil C. Gudmestad
Keyword(s):  
Disease Control ◽  
Solanum Tuberosum L ◽  
Management Strategies ◽  
Point Mutations ◽  
Fungal Growth ◽  
Alternaria Solani ◽  
Selective Advantage ◽  
Field Trials

Succinate dehydrogenase-inhibiting (SDHI) fungicides have been widely applied in commercial potato (Solanum tuberosum L.) fields for the control of early blight, caused by Alternaria solani Sorauer. Five-point mutations on three AsSdh genes in A. solani have been identified as conferring resistance to SDHI fungicides. Recent work in our laboratory determined that A. solani isolates possessing the D123E mutation, or the substitution of aspartic acid for glutamic acid at position 123 in the AsSdhD gene, were collected at successively higher frequencies throughout a 3-year survey. In total, 118 A. solani isolates previously characterized as possessing the D123E mutation were evaluated in vitro for boscalid and fluopyram sensitivity. Over 80% of A. solani isolates with the D123E mutation evaluated were determined to be highly resistant to boscalid in vitro. However, effective concentration at which the fungal growth is inhibited by 50% values of isolates with the D123E mutation to fluopyram, ranging from 0.2 to 3 µg/ml, were sensitive and only slightly higher than those of baseline isolates to fluopyram, which ranged from 0.1 to 0.6 µg/ml. Five A. solani isolates with the D123E mutation were further evaluated in vivo for percent disease control obtained from boscalid and fluopyram compared with two wild-type isolates, three isolates possessing the F129L mutation, two isolates possessing the H134R mutation, two isolates possessing the H133R mutation, and one isolate with the H278R mutation. Relative area under the dose response curve values for boscalid and fluopyram were significantly lower for all five D123E-mutant isolates, demonstrating reduced disease control in vivo. In field trials, the frequency of A. solani isolates with the D123E mutation recovered from treatments receiving an in-furrow application of fluopyram ranged from 5 to 37%, which was significantly higher compared with treatments receiving foliar applications of standard protectants, in which the frequency of the D123E mutation in isolates ranged from 0 to 2.5%. Results suggest that A. solani isolates possessing the D123E mutation have a selective advantage under the application of fluopyram compared with SDHI-sensitive isolates, as well as isolates possessing other mutations conferring SDHI resistance. These data illustrate the importance of implementing fungicide resistance management strategies and cautions the use of fluopyram for in-furrow applications that target other pathogens of potato.

scholarly journals Biotechnical control of tar spot (Rhytisma acerinum) disease on velvet maple (Acer velutinum Boiss) in vitro

2014 ◽  
Vol 60 (No. 8) ◽  
pp. 330-335
Author(s):  
S.M. Karami ◽  
M.R. Kavosi ◽  
G. Hajizadeh ◽  
H. Jalilvand
Keyword(s):  
Fungal Growth ◽  
Fungal Spore ◽  
Field Trials ◽  
Light Conditions ◽  
Northern Iran ◽  
Growth Coefficient ◽  
Significant Difference ◽  
Tar Spot ◽  
Pure Cultures

Several different fungi can cause tar leaf spot diseases in maple trees, including three fungi of the genus Rhytisma. Rhytisma acerinum (Pers.) Fries is an ascomycete that forms black stromata known as tar spot on the adaxial surface of the leaves of Acer species. The tar spot (R. acerinum) disease has been increasing in incidence and severity in maples of Hyrcanian forests, northern Iran, in recent years. One of the best ways to manage infestations by R. acerinum is through adequate biotechnical techniques. The isolation of fungal spore colonies was evaluated using different dosages of Oxywet 10% (50, 100, 200, 500 &micro;l), Gentamicin 5% (100, 200, 400; 1,000 &micro;l), and Amoxicillin antibiotics 20% (25, 50, 100, 250 &micro;l) in 100 ml of distilled water in each treatment. All possible combinations of single doses were applied using light and dark treatments. In light conditions, it appears that the Oxywet (200 &micro;l) had the significant effect on controlling R. acerinum. Reduced fungal growth, coefficient and inhibition of fungal growth were observed in the light treatment. The other antibiotics (Gentamicin, Amoxicillin) were not so effective in controlling this pathogen. Results of spore germination showed a significant difference between all treatments. All treatments were tested in pure cultures in the laboratory only. The results obtained cannot be expected of the same effectiveness in open field trials. &nbsp;

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