Fungicide Physical Mode of Action: Impacts on Suppression of Hop Powdery Mildew

Plant Disease ◽

10.1094/pdis-10-21-2131-re ◽

2021 ◽

Author(s):

Briana Claassen ◽

Sierra N Wolfenbarger ◽

David H. Gent

Keyword(s):

Powdery Mildew ◽

Disease Control ◽

Post Infection ◽

Mode Of Action ◽

Field Experiments ◽

Field Studies ◽

Post Inoculation ◽

Complete Control ◽

Application Timing ◽

Zones Of Inhibition

Understanding of the physical mode of action of fungicides allows for more efficient and effective application of fungicides and can improve disease control. Greenhouse and field studies were conducted to explore the pre-and post-infection duration and translocative properties of fungicides commonly used to control hop powdery mildew, caused by Podosphaera macularis. In greenhouse studies, application made 24 h before inoculation were almost 100% effective at suppressing powdery mildew, regardless of the fungicide evaluated. However, percent control of powdery mildew based on the number of pathogen colonies per leaf varied significantly between fungicides with increasing time from inoculation to application, ranging from 50 to 100% disease control (SE 0.168 and 0, respectively) depending on the fungicide. Fluopyram or fluopyram + trifloxystrobin were particularly efficacious, suppressing nearly all powdery mildew development independent of application timing. In translocation studies, fluopyram and flutriafol were the most effective treatments in each of two separate experiments, resulting in zones of inhibition of 1036 and 246.3 mm2, respectively, on adaxial leaf surfaces when a single droplet of each fungicide was applied to the abaxial surface of leaves. In field experiments, all fungicide treatments provided nearly complete control of powdery mildew infection when applied prior to inoculation. Levels of disease control decreased with time depending on treatment, showing trends similar to those observed in greenhouse studies. In the 2017 field experiments high levels of disease control (>75%) were observed at post-inoculation timepoints for all treatments tested, whereas the same fungicides were more sensitive to application timing in a different year. Findings from this research indicate that differences in efficacy between fungicides are relatively small when applications are made preventatively, but post-infection activity and translaminar movement of certain fungicides may render some more effective depending on application coverage and pre-existing infection.

Download Full-text

Pre- and Postinfection Activity of Fungicides in Control of Hop Downy Mildew

Plant Disease ◽

10.1094/pdis-10-14-1004-re ◽

2015 ◽

Vol 99 (6) ◽

pp. 858-865 ◽

Cited By ~ 3

Author(s):

David H. Gent ◽

Megan C. Twomey ◽

Sierra N. Wolfenbarger ◽

Joanna L. Woods

Keyword(s):

Disease Control ◽

Downy Mildew ◽

Field Experiments ◽

Resistance Management ◽

Field Studies ◽

Similar Efficacy ◽

Application Timing ◽

Pseudoperonospora Humuli ◽

Hazard Warnings ◽

Post Hoc

Optimum timing and use of fungicides for disease control are improved by an understanding of the characteristics of fungicide physical mode of action. Greenhouse and field experiments were conducted to quantify and model the duration of pre- and postinfection activity of fungicides most commonly used for control of hop downy mildew (caused by Pseudoperonospora humuli). In greenhouse experiments, control of downy mildew on leaves was similar among fungicides tested when applied preventatively but varied depending on both the fungicide and the timing of application postinfection. Disease control decreased as applications of copper were made later after inoculation. In contrast, cymoxanil, trifloxystrobin, and dimethomorph reduced disease with similar efficacy when applied 48 h after inoculation compared with preventative applications of these fungicides. When fungicides were applied 72 h after inoculation, only dimethomorph reduced the sporulating leaf area similarly to preinoculation application timing. Adaxial chlorosis, necrosis, and water soaking of inoculated leaves, indicative of infection by P. humuli, were more severe when plants were treated with cymoxanil, trifloxystrobin, and dimethomorph 48 to 72 h after inoculation, even though sporulation was suppressed. Trifloxystrobin and dimethomorph applied 72 h after inoculation suppressed formation of sporangia on sporangiophores as compared with all other treatments. In field studies, dimethomorph, fosetyl-Al, and trifloxystrobin suppressed development of shoots with systemic downy mildew to the greatest extent when applied near the timing of inoculation, although the duration of preventative and postinfection activity varied among the fungicides. There was a small reduction in efficacy of disease control when fosetyl-Al was applied 6 to 7 days after inoculation as compared with protective applications. Trifloxystrobin had 4 to 5 days of preinfection activity and limited postinfection activity. Dimethomorph had the longest duration of protective activity. Percent disease control was reduced progressively with increasing time between inoculation and application of dimethomorph. These findings provide guidance to the use of fungicides when applications are timed with forecasted or post hoc disease hazard warnings, as well as guidance on tank-mixes of fungicides that may be suitable both for resistance management considerations and extending intervals between applications.

Download Full-text

Multiyear Evaluation of Fungicide Efficacy and Application Timing for Control of Southern Rust in Hybrid Corn in Arkansas

Plant Disease ◽

10.1094/pdis-06-20-1247-re ◽

2021 ◽

Vol 105 (4) ◽

pp. 1108-1114

Author(s):

Travis R. Faske ◽

Michael Emerson

Keyword(s):

Disease Control ◽

Growth Stage ◽

Field Experiments ◽

Growth Stages ◽

Application Timing ◽

Quinone Outside Inhibitor ◽

Puccinia Polysora ◽

Dmi Fungicides ◽

Rust Severity ◽

Demethylation Inhibitor

The efficacy and timing of eight foliar fungicides to manage southern rust of corn (caused by Puccinia polysora Underwood) was investigated over 4 years in three field experiments. Each experiment consisted of one-, two-, or three-fungicide application timings at tassel, milk, or dent growth stages with quinone outside inhibitor (QoI), demethylation inhibitor (DMI), or QoI + DMI fungicides. Each year trace amounts of southern rust were observed in the field at tassel, except in 2018, when rust was not observed until physiological maturity. Southern rust severity on ear leaf and two leaves above the ear leaf was approximately 50, 35, 75, and 0% at dent in 2015, 2016, 2017, and 2018, respectively. Applications that contained a QoI or QoI + DMI fungicide provided greater southern rust control than DMI fungicides, with little variation within fungicide classes. Applications of QoI or QoI + DMI fungicides applied at tassel provided greater disease control (52.5%) than those applied at milk (5.8%) or dent (1.4%), and greater yield protection (40.4%) than those applied at milk (23.7%) or dent (2.6%) when final rust development was severe (>40%). When rust development increased later in the season, after milk growth stage, a trend of better disease control was observed with fungicides applied at milk (57.8%) compared with tassel (35.2%), but grain yield protection was similar, with an average yield protection of 7.4%. There was no yield benefit with fungicides applied in the absence of disease or at the dent growth stage. Southern rust was most effectively managed with QoI or QoI + DMI fungicides applied at tassel when southern rust was present and environmental conditions favored rust development.

Download Full-text

Characterization of multiple herbicide–resistant waterhemp (Amaranthus tuberculatus) populations from Illinois to VLCFA-inhibiting herbicides

Weed Science ◽

10.1017/wsc.2019.13 ◽

2019 ◽

Vol 67 (4) ◽

pp. 369-379 ◽

Cited By ~ 11

Author(s):

Seth A. Strom ◽

Lisa C. Gonzini ◽

Charlie Mitsdarfer ◽

Adam S. Davis ◽

Dean E. Riechers ◽

...

Keyword(s):

Dose Response ◽

Field Experiments ◽

Survival Rates ◽

Acetolactate Synthase ◽

Field Studies ◽

Complete Control ◽

Herbicide Resistant ◽

Amaranthus Tuberculatus ◽

Als Inhibitors ◽

And Control

AbstractField experiments were conducted in 2016 and 2017 in Champaign County, IL, to study a waterhemp [Amaranthus tuberculatus (Moq.) J. D. Sauer] population (CHR) resistant to 2,4-D and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-, photosystem II–, acetolactate synthase (ALS)-, and protoporphyrinogen oxidase–inhibiting herbicides. Two field experiments were designed to investigate the efficacy of very-long-chain fatty-acid (VLCFA)-inhibiting herbicides, including a comparison of active ingredients at labeled use rates and a rate titration experiment. Amaranthus tuberculatus density and control were evaluated at 28 and 42 d after treatment (DAT). Nonencapsulated acetochlor, alachlor, and pyroxasulfone provided the greatest PRE control of CHR (56% to 75%) at 28 DAT, while metolachlor, S-metolachlor, dimethenamid-P, and encapsulated acetochlor provided less than 27% control. In the rate titration study, nonencapsulated acetochlor controlled CHR more than equivalent field use rates of S-metolachlor. Subsequent dose–response experiments with acetochlor, S-metolachlor, dimethenamid-P, and pyroxasulfone in the greenhouse included three multiple herbicide–resistant (MHR) A. tuberculatus populations: CHR-M6 (progeny generated from CHR), MCR-NH40 (progeny generated from Mclean County, IL), and ACR (Adams County, IL), in comparison with a sensitive population (WUS). Both CHR-M6 and MCR-NH40 are MHR to atrazine and HPPD, and ALS inhibitors and demonstrated higher survival rates (LD50) to S-metolachlor, acetochlor, dimethenamid-P, or pyroxasulfone than ACR (atrazine resistant but HPPD-inhibitor sensitive) and WUS. Based on biomass reduction (GR50), resistant to sensitive (R:S) ratios between CHR-M6 and WUS were 7.5, 6.1, 5.5, and 2.9 for S-metolachlor, acetochlor, dimethenamid-P, and pyroxasulfone, respectively. Values were greater for MCR-NH40 than CHR-M6, and ACR was the most sensitive to all VLCFA inhibitors tested. Complete control of all populations was achieved at or below a field use rate of acetochlor. In summary, field studies demonstrated CHR is not controlled by several VLCFA-inhibiting herbicides. Greenhouse dose–response experiments corroborated field results and generated R:S ratios (LD50) ranging from 4.5 to 64 for CHR-M6 and MCR-NH40 among the four VLCFA-inhibiting herbicides evaluated.

Download Full-text

Meta-Analysis Reveals a Critical Period for Management of Powdery Mildew on Hop Cones

Plant Disease ◽

10.1094/pdis-04-14-0396-re ◽

2015 ◽

Vol 99 (5) ◽

pp. 632-640 ◽

Cited By ~ 13

Author(s):

Mark E. Nelson ◽

David H. Gent ◽

Gary G. Grove

Keyword(s):

Powdery Mildew ◽

Disease Control ◽

Mode Of Action ◽

Meta Analysis ◽

Field Trials ◽

Use Patterns ◽

Stage Of Development ◽

Action Committee ◽

Cone Development ◽

Individual Participant

Results of 28 field trials conducted over a 12-year period investigating management of hop powdery mildew caused by Podosphaera macularis were quantitatively summarized by meta-analysis to compare product efficacy and use patterns by mode of action as defined by Fungicide Resistance Action Committee (FRAC) groups. Availability of original observations enabled individual participant data meta-analysis. Differences in control of powdery mildew on leaves and cones were apparent among fungicide FRAC groups when individual products were evaluated over the course of a growing season. FRAC groups 13, 3, and U13 provided the most efficacious control of powdery mildew on leaves. Percent disease control on cones was influenced by midseason foliar disease and fungicide mode-of-action. FRAC 13 provided significantly better disease control on cones than all other groups except U13, 3, and premixes of 7 with 11. Disease control on leaves was similar when a rotational program of fungicides was used, independent of the modes of action, but improved on cones if FRAC groups 13 and 3 were both included compared with programs consisting of FRAC groups 11 and 3, 11 and 5, or 3 and 5. Disease control on cones was improved from 32 to 52%, on average, when the fungicide quinoxyfen (FRAC 13) was applied at least once during the early stages of cone development, defined in this analysis as 20 July to 10 August, as compared with all other treatments. Efficacy of disease control on cones by quinoxyfen was moderated by and interacted with the incidence of leaves with powdery mildew. Disease control on cones was further improved if two applications of quinoxyfen were made during this period. Collectively, these findings suggest that disease control during juvenile stages of cone development largely influences the success of fungicide programs and point to the critical importance of focusing management efforts during this stage of development, independent of what actual management strategy is employed.

Download Full-text

Fungicides and Application Timing for Control of Early Leafspot, Southern Blight, andSclerotiniaBlight of Peanut

International Journal of Agronomy ◽

10.1155/2016/1848723 ◽

2016 ◽

Vol 2016 ◽

pp. 1-7 ◽

Cited By ~ 3

Author(s):

W. James Grichar ◽

Jason E. Woodward

Keyword(s):

Disease Control ◽

Systems Approach ◽

Sclerotium Rolfsii ◽

Field Studies ◽

Yield Response ◽

High Dose ◽

Cercospora Arachidicola ◽

Application Timing ◽

Southern Blight ◽

Soilborne Disease

Field studies were conducted in 2013 and 2014 in south Texas near Yoakum and from 2008 to 2011 in central Texas near Stephenville to evaluate various fungicides for foliar and soilborne disease control as well as peanut yield response under irrigation. Control ofSclerotiniablight caused bySclerotinia minorJagger with penthiopyrad at 1.78 L/ha was comparable to fluazinam or boscalid; however, the 1.2 L/ha dose of penthiopyrad did not provide consistent control. Peanut yield was reduced with the lower penthiopyrad dose when compared with boscalid, fluazinam, or the high dose of penthiopyrad. Control of early leaf spot, caused byCercospora arachidicolaS. Hori or southern blight, caused bySclerotium rolfsiiSacc., with penthiopyrad in a systems approach was comparable with propiconazole, prothioconazole, or pyraclostrobin systems and resulted in disease control that was higher than the nontreated control. Peanut yield was also comparable with the penthiopyrad, propiconazole, prothioconazole, or pyraclostrobin systems and reflects the ability of the newer fungicides to control multiple diseases found in Texas peanut production.

Download Full-text

POSSIBLE MECHANISMS OF A BARLEY RESISTANCE TO THE MILDE

Vestnik of the Russian agricultural science ◽

10.30850/vrsn/2020/4/54-57 ◽

1970 ◽

pp. 54-57

Author(s):

B. А. Batasheva ◽

R. А. Abdullaev ◽

O. N. Kovaleva ◽

I. А. Zveynek ◽

Е. E. Radchenko

Keyword(s):

Powdery Mildew ◽

Field Experiments ◽

Spring Barley ◽

Field Studies ◽

Sources Of Resistance ◽

Protective Mechanisms ◽

Double Row ◽

Resistant Varieties ◽

Highly Sensitive ◽

Winter Crops

The work was performed at the Dagestan experimental station VIR. The research material was collected samples of barley. A field study of the resistance of 1089 samples of cultural barley to powdery mildew was carried out. Field experiments were laid in one term during winter sowing. Laboratory and field studies were conducted in accordance with the VIR Guidelines. The possibility of linking the variety's resistance to the pathogen with the plant's habitus is considered. The size and shape of the leaves, the nature of their location in space, height and productive bushiness create a special microclimate in sowing, both on small plots and on large areas. The differentiation of subspecies according to the studied feature is shown. There are more susceptible forms among the six-rowers. The probability of detecting resistant varieties is higher among double-row barley. Nudibranchs are highly sensitive to disease. No resistant samples were found. With increasing density of productive stalks, the frequency of mildew-resistant varieties increases. In the search for possible protective mechanisms, resistance has also been studied in relation to the type of development. Southern Dagestan has relatively mild winters, which allows simultaneous autumn sowing of spring and winter crops. Among spring barley, the share of resistant to the pathogen is higher than among winter barley. The results show that ultra-ripe and late barley are susceptible to the disease, and the former to a greater extent. Short -, medium-and mid-late varieties are differentiated by sensitivity to the pathogen. Precocious barley is more susceptible (72.3) than the average late (12.9%). The opposite trend is observed in the content of stable barley in the same variants: 0.89 and 10.5%, respectively. In both cases, the middle-aged forms occupy an intermediate position. It is shown that the frequency of susceptible forms among high – productive samples is minimal, and among low-productive samples-maximum. As a result of many years of research, the sources of resistance to powdery mildew are mainly selected from European countries, recommended as a source material for selection.

Download Full-text

Interaction between Preemergence Ethofumesate and Postemergence Glyphosate

Weed Technology ◽

10.1614/wt-d-12-00050.1 ◽

2013 ◽

Vol 27 (1) ◽

pp. 47-53 ◽

Cited By ~ 2

Author(s):

Andrew R. Kniss ◽

Dennis C. Odero

Keyword(s):

Weed Control ◽

Nonlinear Regression ◽

Field Experiments ◽

Field Studies ◽

Application Timing ◽

Common Lambsquarters ◽

Late Season ◽

Hairy Nightshade ◽

Redroot Pigweed ◽

Red Dye

Greenhouse and field experiments were conducted to determine whether PRE-applied ethofumesate increased POST spray retention and weed control with glyphosate. In greenhouse studies, ethofumesate was applied PRE at rates from 0 to 224 g ai ha−1followed by POST treatment with either water or glyphosate (840 g ae ha−1) to which a red dye had been added. Plants were immediately washed and spray retention determined spectrophotometrically. Common lambsquarters retained more glyphosate solution compared to water, regardless of PRE ethofumesate rate. Increasing the rate of PRE ethofumesate increased the POST spray retention of both water and glyphosate. PRE application of ethofumesate increased POST spray retention of water by 114% and glyphosate solution by 18% compared to no ethofumesate treatment as determined by nonlinear regression. Ethofumesate rates of 90 g ha−1increased POST spray retention to at least 95% of the total observed response. In field studies, common lambsquarters, redroot pigweed, and hairy nightshade densities were all reduced by ethofumesate, although the duration of ethofumesate effect varied by species and ethofumesate application timing. PRE ethofumesate had no significant effect on hairy nightshade density until after POST glyphosate was applied, whereas common lambsquarters densities were most affected by PRE ethofumesate early in the season. Late-season redroot pigweed density was reduced by ethofumesate regardless of application timing.

Download Full-text

Damping-off of sugar beet in Finland: II. Disease control

Agricultural and Food Science ◽

10.23986/afsci.72140 ◽

1983 ◽

Vol 55 (5) ◽

pp. 431-450

Author(s):

Mauritz Vestberg ◽

Risto Tahvonen ◽

Kyösti Raininko

Keyword(s):

Sugar Beet ◽

Disease Control ◽

Field Experiments ◽

Damping Off ◽

Good Protection ◽

Great Damage

In pot and field experiments carried out in 1979-1981, the systemic funqicide hymexazol prevented satisfactorily soil borne damping-off of sugar beet caused mainly by the fungus Pythium debaryanum auct. non Hesse. The results with the combination hymexazol + thiram were still better. This treatment gave very good protection against the disease up to about two to three weeks after emergence, increased the yield on the average by 5-10 % and produced considerably thicker and denser stands. Thereafter a large number of beets may have become infected, but no great damage was caused as only few died. Band spraying at emergence using hymexazol with a large amount of water as well as spraying into the seed furrow prevented the outbreak of the disease almost completely. Liming had little effect on damping-off.

Download Full-text

Evaluating the Impact of Two Generalist Predators on the Leafhopper Erasmoneura vulnerata Population Density

Insects ◽

10.3390/insects12040321 ◽

2021 ◽

Vol 12 (4) ◽

pp. 321

Author(s):

Stefan Cristian Prazaru ◽

Giulia Zanettin ◽

Alberto Pozzebon ◽

Paola Tirello ◽

Francesco Toffoletto ◽

...

Keyword(s):

Field Experiments ◽

Field Studies ◽

Generalist Predators ◽

Predator Species ◽

Potted Plants ◽

Naturally Occurring ◽

Orius Majusculus ◽

Limited Effectiveness ◽

Pest Outbreaks ◽

The Impact

Outbreaks of the Nearctic leafhopper Erasmoneura vulnerata represent a threat to vinegrowers in Southern Europe, in particular in North-eastern Italy. The pest outbreaks are frequent in organic vineyards because insecticides labeled for organic viticulture show limited effectiveness towards leafhoppers. On the other hand, the naturally occurring predators and parasitoids of E. vulnerata in vineyards are often not able to keep leafhopper densities at acceptable levels for vine-growers. In this study, we evaluated the potential of two generalist, commercially available predators, Chrysoperla carnea and Orius majusculus, in suppressing E. vulnerata. Laboratory and semi-field experiments were carried out to evaluate both species’ predation capacity on E. vulnerata nymphs. The experiments were conducted on grapevine leaves inside Petri dishes (laboratory) and on potted and caged grapevines (semi-field); in both experiments, the leaves or potted plants were infested with E. vulnerata nymphs prior to predator releases. Both predator species exhibited a remarkable voracity and significantly reduced leafhopper densities in laboratory and semi-field experiments. Therefore, field studies were carried out over two growing seasons in two vineyards. We released 4 O. majusculus adults and 30 C. carnea larvae per m2 of canopy. Predator releases in vineyards reduced leafhopper densities by about 30% compared to the control plots. Results obtained in this study showed that the two predators have a potential to suppress the pest density, but more research is required to define appropriate predator–prey release ratios and release timing. Studies on intraguild interactions and competition with naturally occurring predators are also suggested.

Download Full-text