Control of Microdochium albescens in pre-germinated and dryland rice seeds

ABSTRACT: The fungus Microdochium albescens can interfere in the germination of seeds and in the death of rice seedlings; however, there is not technical indication for its control by seed treatment. This research evaluated the efficiency of fungicides in the treatment of pre-germinated and dryland rice seeds in the control of M. albescens. Seeds of the cultivars, Epagri 109, SCS116 Satoru, SCS121 CL and SCS122 Miura were treated with the following fungicides (g a.i./100 kg of seeds): fluazinam + thiophanate methyl (9.45 + 63), pyraclostrobin + thiophanate methyl (5 + 45), carboxin + thiram (60 + 60), metalaxyl-M + thiabendazole + fludioxonil (3 + 22.5 + 3.75), carbendazim + thiram (45 + 105), carbendazim (45). Seeds without fungicide treatment constituted the control. The treated seeds were sown in potato-sucrose-agar (PSA) culture medium and incubated at 25 ± 2 °C and photoperiod of 12 hours for 14 days. Treated seeds were also submitted to the germination test. Fluazinam + thiophanate methyl and metalaxyl-M + thiabendazole + fludioxonil showed greater control of M. albescens, not differing statistically between them, in the five cultivars and in the two cultivation systems. The tested fungicides provided seed germination above 90% in the four cultivars.

Assessment of a Postharvest Treatment with Pyrimethanil via Thermo-Nebulization in Controlling Storage Rots of Apples

Apples are very susceptible to infections from various fungal pathogens during the growing season due to prolonged exposure to environmental influences in the field. Therefore, a strict and targeted fungicide strategy is essential to protect fruit and trees. Increased environmental and health concerns and pathogen resistance have resulted in a rising demand to reduce fungicide usage and residues on marketed fruit. Thus, producers must develop new plant protection strategies to conform to the legal and social demands while still offering high-quality apples. This study assessed the efficacy of a post-harvest fungicide treatment with pyrimethanil via thermo-nebulization for controlling storage rots and compared the results to those of standard pre-harvest fungicide strategies. The results showed that a single post-harvest application of pyrimethanil successfully controlled storage rots and is comparable to strategies using multiple pre-harvest fungicide applications. The control of fungal rot was sustained even after 5 months of storage and 2 weeks of shelf life. Thermo-nebulization into the storage facility allowed for a lower dosage of fungicide to be used compared to pre-harvest applications, while still maintaining optimal rot control. Residue analyses showed that the post-harvest fungicide treatment did not exceed legal or retailer’s standards.

Characterization of the Molecular Mechanisms of Resistance against DMI Fungicides in Cercospora beticola Populations from the Czech Republic

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most important foliar pathogen of sugar beet worldwide. Extensive reliance on fungicides to manage CLS has resulted in the evolution of fungicide resistance in C. beticola worldwide, including populations in the Czech Republic. One important class of fungicides used to manage CLS is the sterol demethylation inhibitors (DMI). The aim of our study was to assess DMI resistance in C. beticola from the Czech Republic and elucidate the molecular basis of DMI resistance in this population. A total of 50 isolates were collected in 2018 and 2019 from the major sugar beet growing regions of the Czech Republic and assessed for in vitro sensitivity to the DMI fungicides propiconazole, prochloraz, and epoxiconazole. These analyses identified three strains that exhibited 50% effective concentration (EC50) values > 1.0 μg mL–1 against respective fungicides, which were therefore considered resistant. In contrast, strains that exhibited lowest EC50 values were considered sensitive. To explore the molecular basis of resistance in these three strains, the cytochrome P450-dependent sterol 14α-demethylase (Cyp51) gene was sequenced. Sequence analysis identified a Y464S mutation in all three resistant strains. To assess whether Cyp51 gene expression may play a role in DMI resistance, selected strains were grown in vitro with and without fungicide treatment. These analyses indicated that Cyp51 gene expression was significantly induced after fungicide treatment. Thus, we conclude that Y464S point mutation along with induced Cyp51 gene overexpression is likely responsible for resistance against DMI fungicides in C. beticola from the Czech Republic.

Fungal and seed treatment interference in the viability of coriander seeds

ABSTRACT The determination of the sanitary quality is important to diagnose if the commercialized lots are free of pathogens and to make a decision about the need for seed treatment. The objective was to evaluate the interference of fungi associated with coriander seed lots in their physiological performance and the effect of seed treatment with the fungicide Metalaxyl-m + Fludioxonil. The study was carried out in two steps. In experiment I, the physiological potential and sanitary characterization of 18 coriander seed lots were evaluated, using the tests, water content, tetrazolium test and health test. In experiment II, we evaluated the physiological performance of coriander seeds with and without fungicide treatment using the first count and germination test. Coriander seed lots showed high physiological potential, however, not all lots expressed their maximum potential in the germination test without treatment, due to the negative effect of fungi associated with seeds, mainly A. dauci and in association with A. alternata. There was an improvement in the physiological performance of coriander seeds treated with Metalaxyl-m + Fludioxonil fungicide.

Temporal Dynamics and Severity of Cucurbit Downy Mildew Epidemics as Affected by Chemical Control and Cucurbit Host Type

Cucurbit downy mildew caused by the oomycete Pseudoperonospora cubensis is an important disease that affects members of Cucurbitaceae family globally. However, temporal dynamics of the disease have not been characterized at the field scale to understand how control strategies influence disease epidemics. Disease severity was assessed visually on cucumber and summer squash treated with weekly alternation of chlorothalonil with either cymoxanil, fluopicolide or propamocarb, during the 2018 spring season and 2019 and 2020 fall seasons in North Carolina, and the 2018 and 2020 fall seasons in South Carolina. Disease onset was observed around mid-June during the spring season and early September during the fall season, followed by a rapid increase in severity until mid-July in the spring season and late September or mid-October in the fall season, typical of polycyclic epidemics. The Gompertz, logistic and monomolecular growth models were fitted to disease severity using linear regression and parameter estimates used to compare the effects of fungicide treatment and cucurbit host type on disease progress. The Gompertz and logistic models were more appropriate than the monomolecular model in describing temporal dynamics of cucurbit downy mildew, with the Gompertz model providing the best description for 34 of the 44 epidemics examined. Fungicide treatment and host type significantly (P < 0.0001) affected standardized area under disease progress curve (sAUDPC), final disease severity (Final DS) and weighted mean absolute rates of disease progress (ρ), with these variables, in most cases, being significantly (P < 0.05) lower in fungicide treated plots than in untreated control plots. Except in a few cases, sAUDPC, Final DS and ρ were lower in cases where chlorothalonil was alternated with fluopicolide or propamocarb than in cases where chlorothalonil alternated with cymoxanil or when chlorothalonil was applied alone. These results characterized the temporal progress of cucurbit downy mildew and provided an improved understanding of the dynamics of the disease at the field level. Parameters of disease progress obtained from this study could serve as inputs in simulation studies to assess the efficacy of fungicide alternation in managing fungicide resistance in this pathosystem.

Alternative products to control powdery mildew in soybeans culture in field

The occurrence of powdery mildew (Microsphaera diffusa) in soybean (Glycine max L.) has increased in the last harvests. In order to study the efficiency of powdery mildew control due to the application of alternative products and conventional fungicide, trials were conducted in Ponta Grossa, PR, Brazil, during the 2013/2014 and 2014/2015 growing seasons. The design used was randomized blocks with four replications. The treatments for the experiments were: 1 - control; 2 - acibenzolar-S-methyl (Bion 500 WG®); 3 - calcium (Max Fruit®); 4 - Micronutrients: copper, manganese and zinc (Wert Plus®); 5 - Micronutrients: manganese, zinc and molybdenum (V6®); 6 - NK fertilizer (Hight Roots®); 7 - Ascophyllum nodosum (Acadian®) and 8 - fungicide (azoxystrobin + cyproconazole) (Priori XTRA®) with the addition of the adjuvant. Four applications of alternative products (phenological stages V3, V6, R1 and R5.1) and two of fungicide (phenological stages R1 and R5.1) were carried out. The parameters evaluated were powdery mildew severity and productivity. The severity data made it possible to calculate the area under the disease progress curve (AUDPG). Alternative products didn’t reduce powdery mildew in the two harvests. The conventional fungicide treatment was the only one that controlled powdery mildew and didn’t reduce the productivity in both experiments.

Effects of Calcium, Magnesium and Potassium on Sweet Basil Downy Mildew (Peronospora belbahrii)

Downy mildew (Peronospora belbahrii) is a major disease of sweet basil (Ocimum basilicum). We examined the effects of potassium, calcium and magnesium, individually and in combination, on sweet basil downy mildew (SBDM) in potted plants and under commercial-greenhouse conditions over six growing seasons. An increased K concentration in the fertigation solution increased SBDM severity, whereas foliar-applied KCl and K2SO4 suppressed SBDM. The application of higher concentrations of those salts increased the K concentrations in the shoots and significantly alleviated SBDM. Increased concentrations of Ca or Mg in the fertigation solution decreased SBDM severity, as did foliar-applied CaCl2. However, the combination of Ca and Mg did not have any synergistic effect. Foliar-applied K2SO4 provided better disease suppression than some of these treatments. The 3.3 mM Mg + fungicide treatment and the 5.0 mM Mg + fungicide treatment each provided synergistic disease control in one of two experiments. SBDM severity was significantly reduced by MgCl2 and MgSO4 (both 3.3 mM Mg), as compared with the basic Mg fertigation (1.6 mM), with MgCl2 providing better control. The combined Mg salts + fungicide treatments reduced SBDM better than any of those treatments alone. These results demonstrate that macro-elements can contribute to SBDM control.

Late harvest and chemical treatment of cowpea seeds

Reduced quality ofcowpea due to late harvest and therefore pathogen incidence may influence the results of the germination test, whenever losses are associated with the agentsadhered to seed coat;in that context, chemical treatmentof seeds during the evaluations may reflect more accurately physiological quality of the samples, which in turn may assurethe emergence results of healthy seedlings and establishment of appropriate plant populations inthe field. This study had the objective ofevaluating the effects of fungicide treatment on minimizing physiological quality losses of cowpea seedsdue to lateharvestin germination and seedling development tests. The experimental design was the completely randomized with four replications. Treatments consisted of cowpea, cultivar BRS Guariba, harvested at different times (0, 3, 6, 9, 12 and 15 days after physiological maturity)andtreated or not with fungicide carboxim+thiramfor seed quality tests. Seeds were initially characterized by seed moisture and mass. Afterwards, sampleswere evaluated by tests ofgermination percentage, germination first count, seedling length and dry matter. Data was submitted to variance analysisand means were analyzed as a 2x6 factorial. Means from chemical treatment and harvest times were compared by the Tukey test and regression analysis (p≤0.05), respectively, with subsequent unfolding of any significant interactions. Delayed harvest of cowpea seeds sharply reduces germination and vigor; fungicide treatment before performing physiological tests enables to establish thatseed quality losses can bein part caused by pathogen vehiculationonthe seed coat.

Efficacy of fungicides against brown spot on walnuts in the Western Forest-Steppe of Ukraine

Goal. To study the effectiveness of fungicides against brown spot of walnut in the Western Forest-Steppe of Ukraine. Methods. The studies were carried out during 2018—2019. in agrocenoses of the walnut garden of the Ukrainian Research Station of Plant Quarantine of the Institute of Plant Protection of the NAAS. At the detailed account inspected not less than 3—4 accounting trees from four parties of a crown and analyzed on 25 accounting bodies (leaves, shoots, fruits) and determined intensity of defeat. The study of the effectiveness of fungicides against brown spot was carried out on the nut variety Bukovynsky 2 using drugs: Bordeaux liquid, 1-percent solution — the standard; Kuproksat, s. c., (copper sulphate tribasic, 345 g/l), Medyan Extra 350 SC s. c., (copper chloride, 350 g/l). Results. Defeat of leaves at the last account in variants with the drug Medyan Extra 350 SC s. c., decreased in comparison with control in 2.6 times, development of a disease — in 2.8 times. By all indicators, the variant with the drug Kuproksat, hp was more effective, where the brown leaf spot was 20.5% (64.5% in the control), the disease was 9.3% (31.4% in the control). Fetal damage in the last account in the experimental variants was respectively 2.7—3.9 times less, and the development of the disease — 3.1—4.2 times weaker than in the control. Conclusions. The obtained data show that in the conditions of the western Forest-Steppe of Ukraine the application of fungicides on walnut both in the experimental and in the reference variants provided good and approximately identical protection of the nut against brown spot Ophiognomonia leptostyla (Fr.) Sogonov. The effectiveness of fungicides was the highest in the variant with the drug Kuproksat, hp, (on the leaves — 70.4%, on the fruits — 75.9%). Technical efficiency of the drug Medyan Extra 350 SC, s. c. on leaves and fruits was 64.6 and 67.9%, respectively. Fungicide treatment of experimental plots helps to reduce the incidence of the disease, which makes it possible to obtain a yield of 0.9—1.1 t/ha higher than in the control.