Combining sanitation and disease modelling for control of grapevine powdery mildew

Chasmothecia of Erysiphe necator form in one season, survive winter and discharge ascospores that cause primary infections and trigger powdery mildew epidemics in the next season. A strategy for powdery mildew control was developed based on (i) the reduction in overwintering chasmothecia and on (ii) spring fungicide applications to control ascosporic infections timed based on estimate risk (two to five sprays per season). Several fungicides, the hyperparasite Ampelomyces quisqualis, and a mineral oil product were first tested as separate applications in a greenhouse and in vineyards. In the greenhouse, A. quisqualis suppressed chasmothecia formation by 41 %; fungicides and mineral oil suppressed chasmothecia formation by 63 % and ascospore viability by 71 %. In vineyards, application of boscalid + kresoxim-methyl or meptyldinocap once after harvest, as well as application of A. quisqualis pre- and post-harvest, delayed disease onset and epidemic development in the following season by 1 to 3 weeks and lowered disease severity (up to the pea-sized berry stage) by 56 to 63 %. Risk-based applications of sulphur and of synthetic fungicides provided the same control as the grower spray program but required fewer applications (average reduction of 47 %). Sanitation strategies were then tested by combining products and application times (late-season, and/or pre-bud break, and/or spring). Adequate disease control with a reduced number of sprays was achieved with the following combination: two applications of A. quisqualis (pre- and post-harvest), one application of mineral oil before bud break, and model-based applications of sulphur fungicides between bud break and fruit set.     

A model for the development of Erysiphe necator chasmothecia in vineyards

A temperature‐driven, mechanistic model predicting the development of Erysiphe necator chasmothecia in vineyards was developed and validated in 38 vineyards in the Po Valley (northern Italy), Baden‐Württemberg (Germany), and South Australia between 2005 and 2011. The model, which begins operating when the first ascocarp initials are formed, predicts on a daily basis the proportions of chasmothecia at the yellow, brown and black maturity stage. The initialization date was estimated with an iterative procedure that minimized the residuals of predicted versus observed values. In all vineyards, a drop to more favourable temperatures for ascocarp production over 2–4 days in the week or in the 2 weeks before the model initialization date probably triggered chasmothecia production. Model predictions provided a good fit of observed data (coefficients of determination, model accuracy, efficacy and efficiency were all ≥0·90), with some overestimation. When predicted production of black chasmothecia (on leaves) was compared with observed dispersal of chasmothecia from vines, lack of splashing rain was probably the main cause of overestimation. When observed numbers of yellow, brown or black chasmothecia on leaves were compared with model predictions, removal of the developing chasmothecia by rainfall was probably the main cause of overestimation. Inclusion of the effect of rainfall on the removal of immature and mature chasmothecia from the powdery mildew colonies could improve the model. The model could be used to time the application of fungicides or biocontrol agents for reducing ascocarp formation and reducing primary inoculum in the following season.     

Effects of fungicide application on physiological and molecular responses of grapevine (Vitis vinifera L.): a comparison between copper and sulfur fungicides applied alone and in combination with novel fungicides

BACKGROUND

Chemical products against fungi and oomycetes pose serious environmental issues. In the last decade, the use of less impacting active ingredients was encouraged to reduce chemical inputs in viticulture. In this study, the effect of different antifungal compounds on grapevine agronomic, physiological, and molecular responses in the vineyard was evaluated in addition to protection against powdery and downy mildews.

RESULTS

In 2 years and in two Vitis vinifera cultivars (Nebbiolo and Arneis), a conventional crop protection approach, based on traditional fungicides (sulfur and copper), was compared to combined strategies. A well-known resistance inducer (potassium phosphonate), Bacillus pumilus strain QST 2808 and calcium oxide, both active ingredients whose biological interaction with grapevine is poorly characterized, were applied in the combined strategies in association with chemical fungicides. Despite a genotype effect occurred, all treatments optimally controlled powdery and downy mildews, with minimal variations in physiological and molecular responses. Gas exchange, chlorophyll content and photosystem II efficiency increased in treated plants at the end of season, along with a slight improvement in the agronomic performances, and an activation of molecular defense processes linked to stilbene and jasmonate pathways.

CONCLUSION

The disease control strategies based on potassium phosphonate, Bacillus pumilus strain QST 2808 or calcium oxide combined with traditional chemical compounds did not cause severe limitations in plant ecophysiology, grape quality, and productive yields. The combination of potassium phosphonate and calcium oxide with traditional fungicides can represent a valuable strategy for reducing copper and sulfur inputs in the vineyards, including those organically managed. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Identification and distribution of mating‐type idiomorphs in populations of Podosphaera macularis and development of chasmothecia of the fungus

Podosphaera macularis, the causal agent of hop powdery mildew, is known to produce chasmothecia (formerly cleistothecia) in eastern North America and Europe. Ascocarps have not yet been reported from the Pacific Northwestern region of North America. Reasons for the apparent absence of chasmothecia in the Pacific Northwest were unknown. This study established that P. macularis is heterothallic and ascocarp ontogeny, maturation, dehiscence and ascospore infection proceed similarly to other powdery mildew fungi. Genome sequencing of a MAT1‐1 isolate revealed the structure of the MAT1 locus and presence of MAT1‐1‐3, demonstrating further similarities to other powdery mildew fungi. PCR assays with primers designed from conserved domains of the MAT1 idiomorphs were developed to characterize the frequency of idiomorphs in populations of P. macularis. Amongst 317 samples of P. macularis collected during 2012 and 2013 from the Pacific Northwest only the MAT1‐1 idiomorph was found. In contrast, among 56 samples from the eastern United States and Europe, MAT1‐1 and MAT1‐2 idiomorphs were detected at equivalent frequencies. At temperatures representative of late season conditions in the Pacific Northwest, chasmothecia formed readily when a Pacific Northwest MAT1‐1 isolate was paired with a MAT1‐2 isolate collected from outside the region. Although these findings do not encompass all climatic, geographic or temporal barriers that could inhibit the formation of chasmothecia, the current absence of the ascigerious stage of P. macularis in the Pacific Northwest could be explained by the absence of the MAT1‐2 mating type idiomorph.     

Laboratory assay of the effectiveness of the entomopathogenic fungus Isaria farinosa (Holmsk.) Fries (Sordariomycetes: Hypocreales) against the vine mealybug Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), even under the use of fungicides

The vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), is one of the main pests in vineyards. At present biological control of the pest is based on the release of hymenopterous parasitoids and coccinellid predators. The effectiveness of an entomopathogenic fungus, Isaria farinosa, as an alternative biological control agent on vine mealybug P. ficus was investigated by using different inoculum densities and different relative humidity levels. The fungus caused more than 80% mortality at 95% relative humidity and at 1 × 10⁸ conidia ml^?1 inoculum density. The mortality effects of the fungus decreased in lower humidity levels and lower spore densities. The inhibitory effects of common fungicides, used in vineyards, on I. farinosa were also investigated. Sulphur, copper oxychloride, fosetyl-Al and chlorothalonil did not decrease the effectiveness of I. farinosa as a pathogen of vine mealybug. With the application of tebuconazole, penconazole and mancozeb, the most inhibitory fungicides on the entomopathogen, the mortality rates of mealybugs, inoculated with I. farinosa, decreased from 86% to 42%, 34% and 45%, respectively, in the adult females; from 94% to 51%, 45% and 45%, respectively, in the first nymphal stages; and from 86% to 56%, 49% and 63%, respectively, in ovisacs.     

Evaluation of Inhibitory Effect of Some Bicarbonate Salts and Fungicides Against Hazelnut Powdery Mildew

Hazelnut (Corylus avellana L.) which is intensively grown in the Black Sea region is the most important agricultural product of Turkey. Hazelnut production and quality are negatively affected by several diseases and pests. Powdery mildew is nowadays one of the most common diseases in almost whole hazelnut producing areas. The disease is caused by two different species, Phyllactinia guttata (Wallr. et Lev.) Fr. and Erysiphe corylacearum U. Braun & S. Takam. For the last 4 years, E. corylacearum, a newly invasive fungus in Turkey, has been caused significant economic losses. In the present study, the efficacy of ammonium, potassium and sodium bicarbonates, and two fungicides were evaluated in field trials against powdery mildew on hazelnuts in Samsun in 2016. The application rates of compounds used in the experiment were as follows: ammonium, potassium and sodium bicarbonates (Sigma-Aldrich, Seelze, Germany) at 1.5, 3, 4.5 and 6% (w/v); Collis® SC (100?g/l Kresoxim methyl +200?g/l Boscalid, BASF, Spain) at 30?ml/100?l and Sulflow® 80 WG (Sulphur 800?g/l, Agrofarm, Turkey) at 400?g/100?l. Of the compounds tested, except for fungicides, sodium was found to be the most effective in controlling the powdery mildew on hazelnuts, followed by potassium and ammonium, respectively. Among those three, ammonium bicarbonate was ineffective against fruit infections of the disease. There was also no significant difference between inhibitory effects of 6% sodium bicarbonate, Collis and Sulflow against the disease (P < 0.05). In addition, bicarbonate salts was phytotoxic to hazelnut leaves at concentrations greater than 1.5%. The results indicate that sodium or potassium bicarbonate solutions seems to be a useful biocompatible fungicide for controlling the powdery mildew on hazelnuts.     

Development of a grower‐conducted inoculum detection assay for management of grape powdery mildew

Management of grape powdery mildew (Erysiphe necator) and other polycyclic diseases often relies on calendar‐based pesticide application schedules that assume the presence of inoculum. An inexpensive, loop‐mediated isothermal amplification (LAMP) assay was designed to quickly detect airborne inoculum of E. necator to determine when to initiate a fungicide application programme. Field efficacy was tested in 2010 and 2011 in several commercial and research vineyards in the Willamette Valley of Oregon from pre‐bud break to véraison. In each vineyard, three impaction spore traps were placed adjacent to the trunk. One trap was maintained and used by the grower to conduct the LAMP assay (G‐LAMP) on‐site and the other two traps were used for laboratory‐conducted LAMP (L‐LAMP) and quantitative PCR assay (qPCR). Using the qPCR as a gold standard, L‐LAMP was comparable with qPCR in both years, and G‐LAMP was comparable to qPCR in 2011. Latent class analysis indicated that qPCR had a true positive proportion of 98% in 2010 and 89% in 2011 and true negative proportion of 96% in 2010 and 64% in 2011. An average of 3·3 fewer fungicide applications were used when they were initiated based on spore detection relative to the grower standard practice. There were no significant differences in berry or leaf incidence between plots with fungicides initiated at detection or grower standard practice plots, suggesting that growers using LAMP to initiate fungicide applications can use fewer fungicide applications to manage powdery mildew compared to standard practices.     

New tools for studying epidemiology and resistance of grape powdery mildew to DMI fungicides

Using a Random Amplified Polymorphic DNA (RAPD) assay, we investigated the genetic polymorphism existing among 62 European isolates of the grape powdery mildew fungus (Uncinula necator [Schw.] Burr.). Isolates overwintering as mycelium in buds were genetically distinct from isolates overwintering as ascospores, suggesting the existence of two genetically isolated powdery mildew populations, and consequently of two independent sources of inoculum in the vineyard. Isolates resistant to fungicides inhibiting sterol 14α-demethylation (DMIs) were found in both populations, suggesting that resistance to DMIs may arise independently in the two powdery mildew populations. A PCR assay targeting the gene encoding U. necator 14α-demethylase has been developed which will permit an early, specific detection of U. necator infections, and may be useful for spraying programmes. ©1997 SCI     

Additive and synergistic antifungal effects of copper and phenolic extracts from grape cane and apples

Background

Organic viticulture seeks sustainable alternatives for eco-toxic copper fungicides to control downy mildew caused by Plasmopara viticola. (Poly)phenol-rich extracts of agricultural byproducts are known to possess antifungal activity, but high production costs often limit their actual implementation.

Results

We developed and produced novel ligninsulfonate-based grape cane extract (GCE) formulations and an apple extract on a pilot plant scale, including a detailed (poly)phenol characterization by high-performance liquid chromatography photodiode array mass spectrometry (HPLC-PDA-MS). Our GCE formulations alone reduced downy mildew disease severity in greenhouse trials by 29%–69% in a dose-dependent manner, whereas a standard application of the copper-based agent alone reached ~56%. When applied together, disease severity was diminished by 78%–92%, revealing a synergistic effect that depended on the mixture ratio. Combining GCE formulations with the apple extract, additive effects were found (80% disease severity reduction).

Conclusion

The studied plant extracts are proposed to both substitute for and synergistically reinforce copper fungicides in grapevine downy mildew control. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Bicarbonate solutions control powdery mildew (Leveillula taurica) on sweet red pepper and reduce the development of postharvest fruit rotting

Disease severity of powdery mildew (causal agentLeveillula taurica (Lév.) Arn.) on pepper (Capsicum annuum), defoliation and fruit sunscald rating were significantly reduced (P=0.05) by foliar applications of sodium or potassium bicarbonate solutions, compared with water or penconazole (Ophir). Preharvest application of bicarbonate solutions significantly reduced (P=0.05) postharvest decay development on sweet red pepper fruits.     

Detection of Erysiphe necator in Air Samples Using the Polymerase Chain Reaction and Species-Specific Primers

ABSTRACT A polymerase chain reaction (PCR) assay employing species-specific primers was developed to differentiate Erysiphe necator from other powdery mildews common in the northwest United States. DNA was extracted from mycelia, conidia, and/or chasmothecia that were collected from grape leaves with a Burkard cyclonic surface sampler. To differentiate E. necator from other erysiphaeceous fungi, primer pairs Uncin144 and Uncin511 were developed to select unique sequences of the internal transcribed spacer regions of E. necator. Using these primers in PCR amplifications, a 367-bp amplicon specific to E. necator was generated, but no amplicons were generated from other erysiphaceous species collected from 48 disparate hosts representing 26 vascular plant families. The PCR limit of detection was one to five conidia of E. necator placed directly into reaction mixtures or 100 to 250 conidia placed on glass rods coated with silicon grease. During field studies, this PCR assay facilitated the detection of E. necator inoculum in air samples within hours of sample rod collection and prior to disease onset. Amplification of E. necator DNA did not occur when the PCR assay was conducted on vineyard air samples collected while grapes were dormant or during periods when vine growth occurred but E. necator remained dormant. The initial PCR detection of E. necator of the season occurred during seasonal ascospore releases caused by precipitation events between bud burst and the prebloom period during the 3 years of the study. Detection ceased for 7 to 11 days following ascospore release and then resumed several days prior to the observance of microscopic symptoms and signs of powdery mildew in the field. Results of this study represent the initial step toward the goal of incorporating an inoculum availability component into current and future grapevine powdery mildew risk assessment models.     

Erysiphe trifolii– a newly recognized powdery mildew pathogen of pea

Diversity of powdery mildew pathogens infecting pea (Pisum sativum) in the US Pacific Northwest was investigated using both molecular and morphological techniques. Phylogenetic analyses based on rDNA ITS sequences, in combination with assessment of morphological characters, defined two groups of powdery mildews infecting pea. Group I (five field samples and three glasshouse samples) had ITS sequences 99% similar to those of Erysiphe pisi in GenBank and exhibited simple, mycelioid type of chasmothecial appendages typical of E. pisi. Erysiphe pisi is normally considered as the powdery mildew pathogen of pea. Group II (four glasshouse samples and two field samples) had ITS sequences 99% similar to those of E. trifolii and produced chasmothecia with dichotomously branched appendages similar to those of E. trifolii. There are fourteen nucleotide differences in the ITS region between the two groups. The correlation of rDNA ITS sequences with teleomorphic features for each of the two groups confirms their identity. Repeated samplings and artificial inoculations indicate that both E. pisi and E. trifolii infect pea in the US Pacific Northwest. Erysiphe trifolii is not previously known as a pathogen of pea. The existence of two distinct powdery mildew species infecting pea in both glasshouse and field environments may interfere with the powdery mildew‐resistance breeding programmes, and possibly explains putative instances of breakdown of resistance in previously resistant pea breeding lines.     

Prior Inoculation with Non-pathogenic Fungi Induces Systemic Resistance to Powdery Mildew On Cucumber Plants

A spray inoculation of the first leaf of 2-leaf stage cucumber plants with a non-pathogenic isolate of Alternaria cucumarina or Cladosporium fulvum before a challenge inoculation with the pathogen Sphaerotheca fuliginea induced systemic resistance to powdery mildew on leaves 2–5. Systemic resistance was expressed by a significant (p < 0.05) reduction in the number of powdery mildew colonies produced on each leaf of the induced plants, as compared with water-sprayed plants. Systemic resistance was evident when a prior inoculation with each of the inducing fungi was administered 1, 3 or 6 days before the challenge inoculation with S. fuliginea. Increasing the inoculum concentration of A. cucumarina or C. fulvum enhanced the systemic protection and provided up to 71.6% or 80.0% reduction, respectively, in the number of colonies produced on upper leaves, relative to controls. Increasing the inoculum concentration of S. fuliginea used for challenge inoculation, increased the number of powdery mildew colonies produced on both induced and non-induced plants. Pre-treated plants, however, were still better protected than controls, indicating that the level of systemic protection was related to the S. fuliginea inoculum concentration. The induction of systemic resistance against powdery mildew by biotic agents, facilitates the development of a wide range of disease management tools.     

Fungicide sensitivity of populations of wheat powdery mildew (Erysiphe graminis f.sp. Tritici) in Central Europe in 1993

In 1993 we observed the sensitivity of wheat powdery mildew populations (Erysiphe graminis DC f.sp. tritici Marchal) from the Czech Republic, Austria, Hungary and Slovakia to the fungicides triadimenol, tebuconazole, propiconazole, flutriafol and fenpropimorph. The highest resistance value was shown to triadimenol, which attained a mean resistance factor (MRF) of 29 (expressing how many times the population is more resistant than are standard sensitive isolates) in the mildew population from the Czech Republic. The mildew populations from eastern Slovakia and eastern Hungary, populations geographically isolated from the other populations, showed very high sensitivity to all fungicides tested. There was most sensitivity to fenpropimorph (smallest MRF values) compared with the other fungicides. Cross-resistance was established among all triazoles used, but not between triazoles and fenpropimorph. Sensitivity of wheat powdery mildew populations from Central Europe to these fungicides is considered adequate, and the development of resistance has shown a decreasing tendency in recent years.     

Chemical Control of Botrytis cinerea on Grapes in New York (USA)1

Control of gray mold in New York vineyards is difficult to achieve at the present time. Benomyl-resistant strains of Botrytis cinerea have been isolated from vineyards in all grape-growing regions of New York State. Because of this resistance and lack of governmental registration of new fungicides, growers must choose among only moderately effective fungicides such as captan, folpet, dicloran and copper. Current research indicates that either vinclozolin or iprodione at 850 g/ha to 1100 g/ha applied twice, beginning at about 5 % sugar content and two weeks later, will provide excellent control of gray mold on ripening berries, whereas sprays applied at 5 % or 90 % bloom and at berry touch are not effective. An application of gibberellic acid (GA3) (10 or 25 (µg/ml) on Aurore (S.5279) at 10–15 cm shoot growth reduced the severity of gray mold on clusters of ripe fruit, but not the incidence of it. A single application of triadimefon at 30 mg/1 sprayed on Vignoles (Ravat 51), when fruit clusters averaged 17 % surface area infected with Uncinula necator and 2.6 % sugar content, retarded the development of powdery mildew and subsequent berry splitting, and ultimately reduced the severity of gray mold by 50 % at harvest, 6 weeks later.     

Evaluation of systemic fungicides for use in the glasshouse industry

The primary evaluation of ten fungicides for the control of cucumber powdery mildew (Sphaerotheca fuliginea), tomato leaf mould (Cladosporium fulvum) and tomato grey mould (Botrytis cinerea) indicated that nine of them were systemically active against one or more of the pathogens when applied as soil drenches. Benomyl, thiophanate, thiophanate-methyl, thiabendazole and Cela W52A showed activity against all three diseases, but dimethirimol, triarimol and dodemorph were more specific and mainly active against cucumber powdery mildew. An in vitro bioassay generally indicated that fungitoxicity was not translocated from sprayed to unsprayed leaves, and though toxicity to B. cinerea, following soil drenches of benomyl, thiophanate and thiophanate-methyl, was detected by bioassay in leaf sap and calyces it was not detected in fruit. Furthermore, extended evaluation of benomyl for the control of grey mould on cropping tomotoes showed that in the presence of abundant B. cinerea inoculum, benomyl soil drench treatment effectively controlled flower and leaf infection but not fruit ghost-spotting.     

Dynamics of ascospore maturation and discharge in Erysiphe necator, the causal agent of grape powdery mildew

Dynamics of ascocarp development, ascospore maturation, and dispersal in Erysiphe necator were studied over a 4-year period, from the time of ascocarp formation to the end of the ascosporic season at the end of June in the following spring. Naturally dispersed chasmothecia were collected from mid-August to late November (when leaf fall was complete); the different collections were used to form three to five cohorts of chasmothecia per year, with each cohort containing ascocarps formed in different periods. Chasmothecia were exposed to natural conditions in a vineyard and periodically sampled. Ascocarps were categorized as containing mature or immature ascospores, or as empty; mature ascospores inside chasmothecia were enumerated starting from late February. Ascospore discharge was determined using silicone-coated slides that were placed 3 to 4 cm from sections of the vine trunk holding the chasmothecia. Before complete leaf fall, 34% of the chasmothecia had mature ascospores, 48% had immature ascospores, and 18% were empty; in the same period, the trapped ascospores represented 56% of the total ascospores trapped in an ascosporic season (i.e., from late summer until the next spring or early summer). The number of viable chasmothecia diminished over time; 11 and 5% of chasmothecia had mature ascospores between complete leaf fall and bud break and after bud break, respectively. These ascocarps discharged ≈2 and 42% of the total ascospores, respectively. All the ascocarp cohorts released ascospores in autumn, survived the winter, and discharged viable ascospores in spring; neither ascospore numbers nor their pattern of temporal release was influenced by the time when chasmothecia were collected and exposed in the vineyard. Abundance of mature ascospores in chasmothecia was expressed as a function of degree-days (DD) (base 10°C) accumulated before and after bud break through a Gompertz equation (R2 = 0.92). Based on this equation, 90% of the ascospores were mature when 153 DD (confidence interval, 100 to 210 DD) had accumulated after bud break. Most ascospores were trapped in periods with >2 mm of rain; however, a few ascospores were airborne with <2 mm of rain and, occasionally, in wet periods of ≥3.5 h not initiated by rain.     

Monitoring of QoI fungicide resistance in Plasmopara viticola populations in Japan

BACKGROUND: The increasing occurrence of QoI fungicide resistance in Plasmopara viticola (Berk. & MA Curtis) Berl. & DeToni populations is becoming a serious problem in the control of grapevine downy mildew. In Japan, the existence of QoI‐fungicide‐resistant P. viticola was reported in 2009. RESULTS: The QoI fungicide resistance in P. viticola samples collected from vineyards in Japan in 2008 and 2009 was monitored. Resistant P. viticola were detected in the regions where QoI fungicides have been introduced in accordance with the pest management programme, whereas in Hokkaido vineyards, where QoI fungicides have not yet been introduced, QoI‐fungicide‐resistant P. viticola were not found. CONCLUSION: Japan comprises thousands of islands and is physically isolated from other countries by the sea. Monitoring the emergence, incidence and distribution of QoI fungicide resistance in P. viticola populations in Japan is necessary to improve pest management strategies for downy mildew disease in Japanese vineyards. Copyright © 2010 Society of Chemical Industry     

Integrated Control of Powdery Mildew on Field-grown Mango Trees by Foliar Sprays of Mono-potassium Phosphate Fertilizer, Sterol Inhibitor Fungicides and the Strobilurin Kresoxym-methyl

Foliar sprays of solutions of di-potassium hydrogen orthophosphate, K2HPO4 (DKP) and potassium di-hydrogen orthophosphate, KH2PO4 (MKP), commercial systemic fungicides, and an alternating treatment with phosphate fertilizer and systemic fungicides inhibited development of the powdery mildew fungus, Oidium mangiferae, on flowers and bloom clusters of field-grown mango trees. The effectiveness of the alternation treatments with an appropriate systemic fungicide and 1% solution of mono-potassium phosphate (MKP) in controlling powdery mildew on bloom clusters was similar to that of the commercial treatment with the systemic fungicides. However, application of the systemic fungicides alone, on the same dates on which they were applied in the alternation treatment, without application of the phosphate treatment was significantly less effective in controlling the disease than either the phosphate or the alternation treatment. This indicates that the use of phosphate fertilizer has a significant role in disease control and that it can reduce the number of fungicide treatments necessary against powdery mildew by up to 50%. These results were confirmed in large-scale demonstration trials conducted in commercial orchards in 1994 and 1995. Our 1997 findings also revealed that tank-mix treatments of 1% MKP solution with half the recommended quantity of sterol inhibitor fungicide applied at 14-day intervals provided a protection against powdery mildew comparable with or superior to that given by the standard fungicides-based treatment applied at 7-day intervals. Tank-mix treatments of MKP (1%) with sterol inhibitor at the recommended rate or with the new strobilurin Kresoxym-methyl (BAS 490F, strobi), or the BAS 490F alone, were the most effective, and provided >95% protection against O. mangiferae, compared with the control. Phosphate solutions were found not to be phytotoxic to plant tissue. These treatments affected the yield of mango trees: a significantly lower yield was observed on control untreated trees, probably because of powdery mildew infection on flowers. The inhibitory effectiveness of phosphate salts makes them a potential major component of an integrated pest management program.     

Efficacy of biocontrol agents and natural compounds against powdery mildew of zucchini

The activity of different types of natural compounds and of two biofungicides based on Bacillus subtilis and Ampelomyces quisqualis alone and in combination with fungicides was tested against powdery mildew of zucchini. The efficacy was compared to the activity of fungicides used alone in four experimental trials carried out in the open field and under greenhouse conditions. The Podosphaera xanthii population used throughout the work was partially resistant to azoxystrobin, whereas it was susceptible to mychlobutanil. Sulphur plus terpenes and mustard oil consistently controlled powdery mildew, followed by mychlobutanil alone or in combination with A. quisqualis. B. subtilis and A. quisqualis when tested alone were partially effective. The combination of azoxystrobin and B. subtilis only delayed the spread of the pathogen.