Site-specific Fungicide Research Articles

Effect of site-specific fungicide mixtures combined with mancozeb on soybean rust control in north-western Paraguay

RESUMEN Debido a que la información sobre el uso de fungicidas para el control de la roya asiática de la soja (RAS) en Paraguay es escasa, el objetivo de este trabajo fue evaluar el efecto de 18 tratamientos (fungicidas sitio-específicos aplicados de forma aislada y en combinación con mancozeb) sobre la RAS. Se realizaron dos ensayos en La Paloma (Canindeyú, Paraguay) en dos épocas de siembra (S1: 10/10/2018 y S2: 20/01/2019) bajo un diseño factorial en bloques completos al azar (Factor A: fungicidas sitio-específicos, Factor B: fungicidas sitio-específicos + mancozeb) con cuatro repeticiones. Se realizó el análisis de varianza para cada experimento y la prueba de comparación de medias de Scott-Knott al 5 % de probabilidad. La interacción Factor A x Factor B no fue significativa para las variables evaluadas en ambas épocas de siembra. Sin embargo, el Factor A fue significativo para la severidad, ABCPE y la EC en ambas épocas de siembra, donde las mezclas picoxistrobina + benzovindiflupyr y azoxistrobina + benzovindiflupyr dieron lugar a la menor severidad de la RAS y mayor EC en S1, mientras que en S2 sobresalieron las mezclas de trifloxistrobina + prothioconazol + bixafen y trifloxistrobina + prothioconazol. Los fungicidas menos eficientes fueron picoxistrobina + ciproconazol y trifloxistrobina + ciproconazol. La adición de mancozeb a las mezclas de fungicidas sistémicos favoreció la EC en 7 % en S1 y en 3,8 % en S2 y el rendimiento en 174 kg ha-1 en S1 y 128 kg ha-1 en S2.

Synergistic Effects of Clonostachys rosea Isolates and Succinate Dehydrogenase Inhibitors Fungicides against Gray Mold on Tomato.

Gray mold caused by Botrytis cinerea is a devastating disease in tomatoes. Site-specific fungicide application is still key to disease management; however, chemical control has many drawbacks. Here, the combined application of a biological agent, Clonostachys rosea, with newly developed succinate dehydrogenase inhibitors (SDHI) fungicides showed stronger synergistic effects than the application of SDHI fungicides alone on tomato gray mold control. C. rosea 67-1 has been reported as an efficient biological control agent (BCA) for B. cinerea. Little information is currently available about the combination of C. rosea and fungicides in the control of gray mold. By testing the sensitivity to fungicides with different action mechanisms, C. rosea isolates showed high tolerance to SDHI fungicides (1000 μg mL-1) on PDA, and the conidial germination rate was almost not affected under 120 μg mL-1 of fluxapyroxad and fluopyram. In greenhouse experiments, the control effect of the combination of C. rosea and fluxapyroxad or fluopyram against tomato gray mold was significantly increased than the application of BCA or SDHI fungicides alone, and the combination allows a two-fold reduction of both the fungicide and BCA dose. Further, the biomass of B. cinerea and C. rosea on tomato plants was determined by qPCR. For B. cinerea, the trend of detection level for different treatments was consistent with that of the pot experiments, and the lowest biomass of B. cinerea was found when treated with C. rosea combined with fluxapyroxad and fluopyram, respectively. For C. rosea, qPCR assay confirmed its colonization on tomato plants when mixed with fluopyram and fluxapyroxad. These results indicated that combining C. rosea 67-1 with the SDHI fungicides could synergistically increase control efficacy against tomato gray mold.

Performance of prothioconazole solo or added to mancozeb in the control of Asian soybean rust

ABSTRACT The evolution of the reduction in Asian soybean rust (caused by Phakopsora pachyrhizi) control by site-specific fungicides has been reported season after season. In a field experiment, the effect of prothioconazole solo and added to multisite mancozeb was evaluated for rust control. Treatments were evaluated in a factorial design of four prothioconazole doses and three mancozeb doses. In a set of treatments, three applications were performed in one soybean cycle and four applications in another one. The first applications were performed at GS V8, 11 days before rust detection, with 2.56% leaflet incidence, while the other applications were at 12 to 14-day interval. Rust severity was quantified, control was calculated in relation to the unsprayed treatment, and soybean grain yield was estimated as kg/ha. Fifty-one to 61% control was obtained with three sprayings and 68% to 70% control with four sprayings of prothioconazole alone. Over 80% control was obtained with at least 0.3 L/ha prothioconazole + 2.0 kg/ha mancozeb, corresponding to 75 g a.i./ha prothioconazole + 1500 g a.i./ha mancozeb. Reduction in P. pachyrhizi control by the use of the site-specific fungicide alone was confirmed, while the addition of mancozeb can recover the efficacy of the site-specific fungicide.

Identification of Cotton Root Rot by Multifeature Selection from Sentinel-2 Images Using Random Forest

Cotton root rot is a destructive cotton disease and significantly affects cotton quality and yield, and accurate identification of its distribution within fields is critical for cotton growers to control the disease effectively. In this study, Sentinel-2 images were used to explore the feasibility of creating classification maps and prescription maps for site-specific fungicide application. Eight cotton fields with different levels of root rot were selected and random forest (RF) was used to identify the optimal spectral indices and texture features of the Sentinel-2 images. Five optimal spectral indices (plant senescence reflectance index (PSRI), normalized difference vegetation index (NDVI), normalized difference water index (NDWI1), moisture stressed index (MSI), and renormalized difference vegetation index (RDVI)) and seven optimal texture features (Contrast 1, Dissimilarity 1, Entory 2, Mean 1, Variance 1, Homogeneity 1, and Second moment 2) were identified. Three binary logistic regression (BLR) models, including a spectral model, a texture model, and a spectral-texture model, were constructed for cotton root rot classification and prescription map creation. The results were compared with classification maps and prescription maps based on airborne imagery. Accuracy assessment showed that the accuracies of the classification maps for the spectral, texture, and spectral-texture models were 92.95%, 84.81%, and 91.87%, respectively, and the accuracies of the prescription maps for the three respective models were 90.83%, 87.14%, and 91.40%. These results confirmed that it was feasible to identify cotton root rot and create prescription maps using different features of Sentinel-2 imagery. The addition of texture features had little effect on the overall accuracy, but it could improve the ability to identify root rot areas. The producer’s accuracy (PA) for infested cotton in the classification maps for the texture model and the spectral-texture model was 2.82% and 1.07% higher, respectively, than that of the spectral model, and the PA for treatment zones in the prescription maps for the two respective models was 8.6% and 8.22% higher than that of the spectral model. Results based on the eight cotton fields showed that the spectral model was appropriate for the cotton fields with relatively severe infestation and the spectral-texture model was more appropriate for the cotton fields with low or moderate infestation.

Metalaxyl resistance in Phytophthora infestans: An overview

Late blight is one of the major destructive diseases of two most important crops –potato and tomato. The disease is known to cause immense loss worldwide. The causal agent Phytophthora infestans, due to various reasons, developed resistance against Metalaxyl fungicide which was very effective against the pathogen, in its initial years of introduction. A number of possibilities have been estimated for the occurrence and development of resistance in the fungal pathogen isolates: existence of resistant isolates before the introduction of the fungicide, development of resistant mutants, presence of both the mating types A1 and A2 of pathogen in a locality leading to the possibilities of recombinants, migration of resistant isolates, excessive use of site specific fungicide etc. Since development of resistance in pathogen population against fungicide is an issue of serious concern and can pose a great threat to the potato and tomato production thus various anti resistance strategies need to be practiced.

Remote Sensing and Precision Agriculture Technologies for Crop Disease Detection and Management with a Practical Application Example

Abstract Remote sensing technology has long been used to detect and map crop diseases. Airborne and satellite imagery acquired during growing seasons can be used not only for early detection and within-season management of some crop diseases, but also for the control of recurring diseases in future seasons. With variable rate technology in precision agriculture, site-specific fungicide application can be made to infested areas if the disease is stable, although traditional uniform application is more appropriate for diseases that can spread rapidly across the field. This article provides a brief overview of remote sensing and precision agriculture technologies that have been used for crop disease detection and management. Specifically, the article illustrates how airborne and satellite imagery and variable rate technology have been used for detecting and mapping cotton root rot, a destructive soilborne fungal disease, in cotton fields and how site-specific fungicide application has been implemented using prescription maps derived from the imagery for effective control of the disease. The overview and methodologies presented in this article should provide researchers, extension personnel, growers, crop consultants, and farm equipment and chemical dealers with practical guidelines for remote sensing detection and effective management of some crop diseases.

Rapid Detection of Fungicide Resistance Phenotypes Among Populations of Nothopassalora personata in South Carolina Peanut Fields

We evaluated the occurrence of fungicide resistance phenotypes in populations of Nothopassalora personata, the causal agent of late leaf spot (LLS), sampled from South Carolina peanut fields in 2018 using a modified detached leaf assay (DLA). Spore suspensions obtained from each of 72 groups of LLS-symptomatic leaves collected from nine counties were used in the DLA to examine phenotypic resistance to four site-specific fungicides (azoxystrobin, benzovindiflupyr, prothioconazole, and thiophanate-methyl) and one multisite contact fungicide (chlorothalonil). Lesion development was measured as a binary event in which presence of a lesion indicated control failure (phenotypic resistance) and absence of a lesion indicated successful control (sensitivity). Phenotypic resistance probabilities of N. personata samples to each site-specific fungicide were compared against the control fungicide (chlorothalonil). Variation in phenotypic resistance probabilities to the four single-site fungicides was observed from most counties (6 of 9), with frequencies of phenotypic resistance having differed among counties. The DLA facilitated rapid evaluation of N. personata phenotypic resistance to azoxystrobin, benzovindiflupyr, prothioconazole, and thiophanate-methyl. This assay has potential to be used as an alternative method for routine monitoring of phenotypic resistance, identification of populations to test for the presence of resistance genes, and improving reliability of current fungicide recommendations.

Addition of mancozeb to the fungicide mixtures DMI + QoI and SDHI + QoI on the control of wheat leaf blights

ABSTRACT Wheat leaf blights caused by Drechslera siccans, D. tritici-repentis, especially D. tritici-repentis, are difficult to be controlled by site-specific fungicide mixtures. Due to development of resistance, the use of double site-specific mixtures has shown control inferior to 50%. In an experiment conducted in the field with the wheat cultivar Jadeite 11, in 3 x 6 m plots and four replicates, the effect of a muli-site fungicide added to fungicide mixtures on the control of leaf blights was evaluated. The effect of the following mixtures was evaluated: picoxystrobin + cyproconazole, kresoxim-methyl + epoxiconazole, azoxystrobin + cyproconazole, pyraclostrobin + epoxiconazole, pyraclostrobin + fluxapyroxad, trifloxystrobin + prothioconazole and azoxystrobin + propiconazole, added of five mancozeb levels, 0; 1.5; 2.0; 2.5 and 3.0 kg/ha. The first application occurred after 30% leaf incidence, and the remaining two occurred at 15 and 18-day intervals. The fungicides were applied with a backpack sprayer pressurized by CO2, delivering 180 L/ha. Leaf blights severity was quantified, control was calculated, the percentage of chlorophyll in flag leaves was determined, and grain yield was assessed. The mean control of leaf blights by the mixtures without addition of the multi-site fungicide was 44%. The disease severity reduced as a function of the addition of mancozeb levels for all treatments. Control superior to 80% was obtained with the mixtures kresoxim methyl + epoxiconazole and pyraclostrobin + epoxiconazole, both added at least 2.0 kg/ha mancozeb. There was a positive reflex on the increase in wheat grain yield as a function of control, varying from 3005 kg/ha for the best treatment to 2026 kg/ha for control.

Site-Specific Management of Cotton Root Rot Using Airborne and High-Resolution Satellite Imagery and Variable-Rate Technology

Abstract. Cotton root rot is a century-old cotton disease that now can be effectively controlled with Topguard Terra fungicide. Because this disease tends to occur in the same general areas within fields in recurring years, site-specific application of the fungicide only to infested areas can be as effective as and considerably more economical than uniform application. The overall objective of this research was to demonstrate how site-specific fungicide application could be implemented based on historical remote sensing imagery and using variable-rate technology. Procedures were developed for creating binary prescription maps from historical airborne and high-resolution satellite imagery. Two different variable-rate liquid control systems were adapted to two existing cotton planters, respectively, for site-specific fungicide application at planting. One system was used for site-specific application on multiple fields in 2015 and 2016 near Edroy, Texas, and the other system was used on multiple fields in both years near San Angelo, Texas. Airborne multispectral imagery taken during the two growing seasons was used to monitor the performance of the site-specific treatments. Results based on prescription maps derived from historical airborne and satellite imagery of two fields in 2015 and one field in 2016 are reported in this article. Two years of field experiments showed that the prescription maps and the variable-rate systems performed well and that site-specific fungicide treatments effectively controlled cotton root rot. Reduction in fungicide use was 41%, 43%, and 63% for the three fields, respectively. The methodologies and results of this research will provide cotton growers, crop consultants, and agricultural dealers with practical guidelines for implementing site-specific fungicide application using historical imagery and variable-rate technology for effective management of cotton root rot. Keywords: Airborne imagery, Cotton root rot, High-resolution satellite imagery, Prescription map, Variable-rate application.

Change detection of cotton root rot infection over 10-year intervals using airborne multispectral imagery

Cotton root rot is a very serious and destructive disease of cotton grown in the southwestern United States. Accurate information regarding its spatial and temporal distribution within fields is important for effective management of the disease. The objectives of this study were to examine the consistency and variation of cotton root rot infections within cotton fields over 10-year intervals using airborne multispectral imagery and to assess the feasibility to use historical imagery to create prescription maps for site-specific management of the disease. Airborne multispectral images collected from a 102-ha cotton field in 2001 and 2011 and from a 97-ha field in 2002 and 2012 in south Texas were used in this study. The images were rectified and resampled to the same pixel size between the two years for each field. The normalized difference vegetation index (NDVI) images were generated and unsupervised classification was then used to classify the NDVI images into root rot-infected and non-infected zones. Change detection analysis was performed to detect the consistency and change in root rot infection between the two growing seasons for each field. Results indicate that the spatial patterns of the disease were similar between the two seasons, though variations existed for each field. To account for the potential expansion and temporal variation of the disease, buffer zones around the infected areas were created. The buffered maps between the two years agreed well. The results from this study demonstrate that classification maps derived from historical images in conjunction with appropriate buffer zones can be used as prescription maps for site-specific fungicide application to control cotton root rot.

Development of potato late blight (Phytophthora infestans) in differently developed potato crops and the potential to graduate the fungicide dose according to crop biomass

Phytophthora infestans is a serious disease in potato production and control of the disease often requires 10 or more fungicide applications during the growing season. Control is typically carried out using a constant fungicide dose in the entire field although there may be large differences in crop development and biomass across the field. The objective of the study reported in this paper was to test whether the fungicide dose response curve controlling P. infestans was dependent on the crop development and biomass level. If such a biomass-dependent dose response was found it was further the purpose to evaluate the potential to optimize fungicide inputs in potato crops applying a site-specific crop density-dependent fungicide dose. The study was carried out investigating the fungicide dose response controlling P. infestans in potatoes at three biomass densities obtained growing the potato crop at three nitrogen levels. Furthermore, the field experiments included four levels of fungicide dose rate at each nitrogen rate, an untreated control, the recommended fungicide dose rate and two reduced dose rates and the experiments were replicated for three years. Nitrogen level and thus crop density had a limited although significant influence on attack of P. infestans whereas fungicide dose rate by far was the most influential variable. In contrast the interaction of nitrogen rate and fungicide dose rate that would indicate a biomass-dependent dose response was insignificant. If the variation in crop density and biomass level obtained in the study is representative for the variation found cultivating potatoes in heterogeneous fields there seem to be limited potential for fungicide optimization applying fungicides against P. infestans site-specific according to crop density or biomass.

Baseline sensitivity of Monilinia laxa from Greece to fenhexamid and analysis of fenhexamid-resistant mutants

Fenhexamid is a hydroxyanilide fungicide with excellent performance against Botrytis cinerea but also effective against Monilinia spp. which cause brown rot disease in apple and stone fruit. A total of 75 Monilinia laxa field isolates were utilized to determine baseline sensitivity while a number of fenhexamid-resistant laboratory mutants were used to evaluate the resistance risk associated with the longevity of the effectiveness of fenhexamid. Fenhexamid was found to be highly effective against all field isolates. EC50 values ranged from 0.02 to 1 μg mL−1 and were distributed unimodaly around an average of 0.1 μg mL−1. M. laxa laboratory strains with moderate and high resistance levels to fenhexamid were isolated after UV mutagenesis. All fenhexamid-resistant strains showed parental sensitivity to carbendazim, iprodione, fludioxonil, pyraclostrobin, flusilazole and prochloraz. Interestingly, some of the mutant strains were also resistant to tridemorph, fenpropimorph and spiroxamine. Studies on fitness parameters of fenhexamid-resistant strains revealed a fitness cost on sporulation and pathogenicity but not on mycelial growth. These results suggest that fenhexamid should be a good alternative site-specific fungicide for the control of brown rot disease caused by M. laxa. However, appropriate anti-resistance strategies should be considered to ensure the successful commercial use of fenhexamid in the long run.

Growth Sensitivity of Corynespora cassiicola to Thiophanate-methyl, Iprodione, and Fludioxonil

An African violet production facility has relied solely on thiophanate-methyl, a site-specific fungicide that possesses a high risk for pathogens to develop resistance, to manage a devastating Corynespora leaf spot problem. During a disease outbreak in September 2007, 325 isolates of C. cassiicola were collected and 40 isolates were randomly selected to determine the pathogen's sensitivity for mycelium growth on agar amended with various concentrations of thiophanate-methyl, iprodione, or fludioxonil. EC50 values, concentration resulting in a 50% reduction in mycelium growth, were determined and indicate a population that currently is sensitive to all three fungicides. Due to the high risk of the pathogen developing resistance to thiophanate-methyl and iprodione, a moderate risk for cross-sensitivity between iprodione and fludioxonil, and phytotoxicity and visual residue problems with protective fungicides such as chlorothalonil, a fungicide rotation is recommended with fludioxonil as the main chemical selection. Accepted for publication 22 July 2011. Published 26 September 2011.

Multi-temporal wheat disease detection by multi-spectral remote sensing

For the implementation of site-specific fungicide applications, the spatio-temporal dynamics of crop diseases must be well known. Remote sensing can be a useful tool to monitor the heterogeneity of crop vitality within agricultural sites. However, the identification of fungal infections at an early growth stage is essential. This study examines the potential of multi-spectral remote sensing for a multi-temporal analysis of crop diseases. Within an experimental field, a 6 ha plot of winter wheat was grown, containing all possible infective stages of the powdery mildew (Blumeria graminis) and leaf rust (Puccinia recondita) pathogens. Three high-resolution remote sensing images were used to execute a spatio-temporal analysis of the infection dynamics. A decision tree, using mixture tuned matched filtering (MTMF) results and the Normalized Difference Vegetation Index (NDVI), was applied to classify the data into areas showing different levels of disease severity. Classification results were compared to ground truth data. The classification accuracy of the first scene was only 56.8%, whereas the scenes from May 28th and June 20th achieved considerably higher accuracies of 65.9% and 88.6% respectively. The results showed that high-resolution multi-spectral data are generally suitable to detect in-field heterogeneities of crop vigour but are only moderately suitable for early detection of crop infections.

Identification of powdery mildew (Erysiphe graminis sp. tritici) and take-all disease (Gaeumannomyces graminis sp. tritici) in wheat (Triticum aestivum L.) by means of leaf reflectance measurements

Abstract The ability to identify diseases in an early infection stage and to accurately quantify the severity of infection is crucial in plant disease assessment and management. A greenhouse study was conducted to assess changes in leaf spectral reflectance of wheat plants during infection by powdery mildew and take-all disease to evaluate leaf reflectance measurements as a tool to identify and quantify disease severity and to discriminate between different diseases. Wheat plants were inoculated under controlled conditions in different intensities either with powdery mildew or take-all. Leaf reflectance was measured with a digital imager (Leica S1 Pro, Leica, Germany) under controlled light conditions in various wavelength ranges covering the visible and the near-infrared spectra (380–1300 nm). Leaf scans were evaluated by means of L*a*b*-color system. Visual estimates of disease severity were made for each of the epidemics daily from the onset of visible symptoms to maximum disease severity. Reflectance within the ranges of 490780 nm (r2 = 0.69), 510780nm (r2 = 0.74), 5161300nm (r2 = 0.62) and 5401300 nm (r2 = 0.60) exhibited the strongest relationship with infection levels of both powdery mildew and take-all disease. Among the evaluated spectra the range of 490780nm showed most sensitive response to damage caused by powdery mildew and take-all infestation. The results of this study indicated that disease detection and discrimination by means of reflectance measurements may be realized by the use of specific wavelength ranges. Further studies have to be carried out, to discriminate powdery mildew and take-all infection from other plant stress factors in order to develop suitable decision support systems for site-specific fungicide application.

Laboratory studies to assess the risk of development of resistance to zoxamide.

Laboratory studies were conducted to evaluate the risk of developing field resistance to zoxamide, a new Oomycete fungicide which acts on microtubules. Zoxamide, metalaxyl and dimethomorph were compared with respect to the ease with which fungicide-resistant mutants could be isolated and their level of resistance. Attempts to generate mutants of Phytophthora capsici and P infestans with resistance to zoxamide by mycelial adaptation on fungicide-amended medium were unsuccessful. Similarly, changes in sensitivity to zoxamide were small (resistance factors < or = 2.2) in mutants of P capsici isolated by chemical mutagenesis of zoospore cysts. In parallel experiments with metalaxyl, highly resistant mutants were obtained using both adaptation (P capsici or P infestans) and chemical mutagenesis (P capsici). For dimethomorph, chemical mutagenesis (P capsici) yielded moderately resistant mutants (maximum resistance factor = 20.9), and adaptation (P capsici or P infestans) did not induce resistance. It is proposed that failure to isolate mutants resistant to zoxamide results from the diploid nature of Oomycete fungi and the likelihood that target-site mutations would produce a recessive phenotype. Our studies suggest that the risk of a highly resistant pathogen population developing rapidly in the field is much lower for zoxamide than for metalaxyl. However, as with any site-specific fungicide, appropriate precautions against resistance development should be taken.