CERCBET 3 – a forecaster for epidemic development of Cercospora beticola*

Cercospora beticola is the most prevalent and damaging fungal disease in German sugar beet growing. Control strategies are based on action thresholds. A model has been developed which forecasts epidemic development (expressed as disease incidence) and signals when action thresholds are overridden. The plot‐specific model, CERCBET 3 uses as input meteorological parameters (temperature, relative humidity), easily accessible agronomic field characteristics and a single recording of C. beticola disease incidence. Extensive validation in 2001–03 showed that, in 80–95% of the cases, CERCBET 3 correctly forecasted the dates when thresholds were overridden. Cultivar diversity in German sugar beet growing is increasing, thus a module has been included into CERCBET 3 which reflects susceptibility to C. beticola by introducing a sporulation factor. In some cases a second or even third fungicide treatment could be necessary to control Cercospora leaf spot and so a further module which models fungicide efficacy has been elaborated. CERCBET 3 is available for sugar beet growers in an interactive form on the Internet platform ISIP, which is provided by the governmental crop protection services of Germany.     

Bioassays using detached tobacco leaves to determine the sensitivity of Peronospora tabacina to fungicides

Two bioassay methods are described which use detached tobacco leaves to measure the sensitivity of Peronospora tabacina to systemic fungicides. Tobacco leaves (13–15 cm²), treated with fungicides before or after detachment from the plant, were inoculated with sporangia in water drops and, after incubation in beakers and Petri plates, the disease severity and/or production of sporangia was determined 4–7 days after treatment with the fungicides. Of 15 systemic fungicides applied to detached leaves, eight N-phenylamides at 0.066?1.0 μg ml^?1 controlled blue mould; metalaxyl was the most effective fungicide. Isolates of P. tabacina, collected in the field from tobacco plants grown in soil treated with metalaxyl, were not resistant to the fungicide applied to detached leaves prior to inoculation. The fungicide, applied to leaves before detachment, was used to measure the efficacy of five systemic N-phenylamide fungicides sprayed on the basal and unsprayed distal portions of the leaves. Blue mould was controlled on the basal portion of the leaf by all the fungicides at 0.66?1.0 μg ml^?1, but it required the application of 3–30 times more chemical on the basal portion to achieve comparable blue mould control on the distal part of the leaf.     

Uptake and distribution of [14C]metalaxyl by detached tobacco leaves

When the petioles of detached tobacco leaves (10–17 cm²) were incubated in aqueous solutions containing [¹⁴C]metalaxyl, uptake of the fungicide was dependent on the temperature and photoperiod. Detached leaves took up 78% more [¹⁴C]metalaxyl at 26°C than at 16°C. The rate of uptake in the light at 21°C was linear, but after an additional 20h in the dark, there was only twice as much fungicide in the leaves. Different sized leaves contained the same amount of fungicide per cm² area. Uptake by detached leaves of the ¹⁴C-labelled anilide lactones ofurace and RE-26940 [2-methoxy-N-(tetrahydro-2-oxo-3-thienyl)acet-2′,6′-xylidide] was similar to that of metalaxyl. At the concentration of metalaxyl (66 ng ml^?1) that controlled blue mould (Peronospora tabacina) on detached tobacco leaves, the amount of fungicide in the leaves was found to be 7.25 ng. Autoradiography showed that the distribution of [14C]metalaxyl in detached leaves after incubation for 23h was uniform, although higher concentrations of the label were present in the smaller veins of the leaves.     

多菌灵等4种杀菌剂对烟草灰霉病菌的室内生物活性

采用菌丝生长速率法和孢子萌发法,分别测定了烟草灰霉病菌对多菌灵、嘧霉胺、异菌脲和丙环唑的敏感性,同时通过离体叶片法评估了这4种杀菌剂对烟草灰霉病的保护和治疗作用。结果表明:4种杀菌剂对烟草灰霉病菌的菌丝生长和孢子萌发均表现出了不同程度的抑制活性,并对灰霉病同时具有保护和治疗作用。其中多菌灵对菌丝生长的抑制活性最强,EC₅₀平均值为0.06 mg/L,其次为丙环唑、嘧霉胺和异菌脲,EC₅₀平均值分别为0.36、0.53和0.60 mg/L;异菌脲和丙环唑对烟草灰霉病菌孢子萌发的抑制活性较强,EC₅₀平均值分别为2.05和2.21 mg/L,其次为嘧霉胺和多菌灵,EC₅₀平均值分别为10.56和131.23 mg/L。异菌脲和多菌灵对灰霉病的保护作用和治疗作用均最强,当药剂质量浓度为200 mg/L时,其对离体叶片的保护和治疗作用防效分别为100%、100%和98.3%、91.8%。研究结果可为烟草灰霉病的科学防治提供依据。     

Tillage and herbicide treatments with inter‐row cultivation influence weed densities and yield of three industrial crops

Field experiments were conducted in northern Greece in 2003 and 2004 to evaluate effects of tillage regimes (moldboard plowing, chisel plowing, and rotary tilling), cropping sequences (continuous cotton, cotton‐sugar beet rotation, and continuous tobacco) and herbicide treatments with inter‐row hand hoeing on weed population densities. Total weed densities were not affected by tillage treatment except that of barnyardgrass (Echinochloa crus‐galli), which increased only in moldboard plowing treated plots during 2003. Redroot pigweed (Amaranthus retroflexus) and black nightshade (Solanum nigrum) densities were reduced in continuous cotton, while purple nutsedge (Cyperus rotundus), E. crus‐galli, S. nigrum, and johnsongrass (Sorghum halepense) densities were reduced in tobacco. A. retroflexus and S. nigrum were effectively controlled by all herbicide treatments with inter‐row hand hoeing, whereas E. crus‐galli was effectively reduced by herbicides applied to cotton and tobacco. S. halepense density reduction was a result of herbicide applied to tobacco with inter‐row hand hoeing. Yield of all crops was higher under moldboard plowing and herbicide treatments. Pre‐sowing and pre‐emergence herbicide treatments in cotton and pre‐transplant in tobacco integrated with inter‐row cultivation resulted in efficient control of annual weed species and good crop yields. These observations are of practical relevance to crop selection by farmers in order to maintain weed populations at economically acceptable densities through the integration of various planting dates, sustainable herbicide use and inter‐row cultivation; tools of great importance in integrated weed management systems.     

Derivation and testing of a model to predict selection for fungicide resistance

A mathematical model was derived to predict selection for fungicide resistance in foliar pathogens of cereal crops. The model was tested against independent data from four field experiments quantifying selection for the G143A mutation conferring resistance to a quinone outside inhibitor (QoI) fungicide in powdery mildew (Blumeria graminis f.sp. hordei) on spring barley (Hordeum vulgare). Fungicide treatments with azoxystrobin differed in the total applied dose and spray number. For each treatment, we calculated the observed selection ratio as the ratio of the frequency of the resistant strain after the last and before the first spray. The model accurately predicted the variation in observed selection ratios with total applied fungicide dose and number of sprays for three of the four experiments. Underprediction of selection ratios in one experiment was attributed to the particularly late epidemic onset in that experiment. When the equation representing epidemic development was modified to account for the late epidemic, predicted and observed selection ratios at that site were in close agreement. On a scatter plot of observed selection ratios on predicted selection ratios, for all four experiments, the 1:1 line explained 89–92% of the variance in the mean of observed selection ratios. To our knowledge, this is the first fungicide resistance model for plant pathogens to be rigorously tested against field data. The model can be used with some degree of confidence, to identify anti‐resistance treatment strategies which are likely to be effective and would justify the resources required for experimental testing.     

Downy mildew outbreaks on grapevine under climate change: elaboration and application of an empirical‐statistical model*

The global climate is changing. Much research has already been carried out to assess the potential impacts of climate change on plant physiology. However, effects on plant disease have not yet been deeply studied. In this paper, an empirical disease model for primary infection of downy mildew on grapevine was elaborated and used to project future disease dynamics under climate change. The disease model was run under the outputs of the General Circulation Model (GCM) and future scenarios of downy mildew primary outbreaks were generated at several sites all over the word for three future dates: 2030, 2050, 2080. Results suggested a potential general advance of first disease outbreaks, both in the Northern and Southern Hemispheres, for all three future decades considered. The advance is predicted to be from about a minimum of one day in South Africa in 2030 to a maximum of 28 days in Chile and China in 2080. The advance in the outbreak time could lead to more severe infections, due to the polycyclic nature of the pathogen. Therefore, changes in the timing and frequency of fungicide treatments could be expected in the future, with a possible increase in the costs of disease management.     

Optimal application timing of simeconazole granules for control of rice kernel smut and false smut

We investigated the optimal timing of simeconazole (RS-2-(4-fluorophenyl)-1-(1H-1,2,4-triazol-1-yl)-3-trimethylsilylpropan-2-ol) application for controlling rice kernel smut in field trials in Miyagi Prefecture, Japan, using formulations of simeconazole (1.5% granules). The field tests revealed that a submerged application of simeconazole granules (450–600 g ai/ha) at 1–5 weeks before heading was highly effective against kernel smut, with treatments 1–2 weeks before heading being the most effective. Submerged application of the fungicide at 2–5 weeks before heading was also highly effective against false smut, with treatment 3 weeks before heading being the most effective. These periods overlap the timing for optimal application of simeconazole to control rice sheath blight and ear blight. Consequently, we concluded that treatment with simeconazole 2–3 weeks before heading can be a useful tool for controlling all four diseases.     

Effects of fungicide on growth of Leptosphaeria maculans and L. biglobosa in relation to development of phoma stem canker on oilseed rape (Brassica napus)

Controlled‐environment and field experiments were done to investigate effects of the fungicide Punch C (flusilazole plus carbendazim) on growth of Leptosphaeria maculans and L. biglobosa in oilseed rape. In controlled‐environment experiments, for plants inoculated with L. maculans, fungicide treatment decreased lesion size and amount of L. maculans DNA in leaves; for plants inoculated with L. biglobosa, fungicide did not affect lesion size or amount of pathogen DNA. When release of ascospores was monitored using a Burkard spore sampler, the timing and pattern of ascospore release differed between the four seasons. In 2006/2007, the majority of ascospores released were L. maculans, whilst in 2007/2008 the majority were L. biglobosa; in both seasons L. maculans ascospores were released before L. biglobosa ascospores. In field experiments in 2002/2003 and 2003/2004, fungicide treatment decreased severity of stem canker on cv. Apex, but gave no significant yield response. In 2006/2007 and 2007/2008, fungicide treatment decreased phoma leaf spot incidence in autumn and stem canker severity at harvest, and increased yield. Fungicide treatment decreased stem canker severity more on cv. Courage, with a good yield response, than on cv. Canberra. In 2002/2003 and 2003/2004, fungicide treatment decreased the frequency of spread of L. maculans into stem pith tissues and in 2006/2007 fungicide decreased the amount of L. maculans DNA in stem tissues (measured by quantitative PCR). These results are used to suggest how effects of fungicides on interactions between L. maculans and L. biglobosa might affect severity of phoma stem canker and yield response.     

Integrated control of potato late blight: predicting the combined efficacy of host resistance and fungicides

Integrating cultivars that are partially resistant with reduced fungicide doses offers growers an opportunity to decrease fungicide input but still maintain disease control. To use integrated control strategies in practice requires a method to determine the combined effectiveness of particular cultivar and fungicide dose combinations. Simple models, such as additive dose models (ADM) and multiplicative survival models (MSM), have been used previously to determine the joint action of two or more pesticides. This study tests whether a model based on multiplicative survival principles can predict the joint action of fungicide doses combined with cultivars of differing partial host resistance. Data from eight field experiments on potato late blight (Phytophthora infestans) were used to test the model; the severity of foliar blight was assessed and scores used to calculate the area under the disease progress curve (AUDPC). A subset of data, derived from the most susceptible cultivar, King Edward, was used to produce dose–response curves from which parameter values were estimated, quantifying fungicide efficacy. These values, along with the untreated values for the more resistant cultivars, Cara and Sarpo Mira, were used to predict the combined efficacy of the remaining cultivar by fungicide dose combinations. Predicted efficacy was compared against observations from an independent subset of treatments from the field experiments. The analysis demonstrated that multiplicative survival principles can be applied to describe the joint efficacy of host resistance and fungicide dose combinations.     

Assessment of sanitation and fungicide application directed at cocoa tree trunks for the control of <Emphasis Type="Italic">Phytophthora</Emphasis> black pod infections in pods growing in the canopy

Studies were conducted in two cocoa-growing areas of Ghana, one solely affected by Phytophthora palmivora and the other predominantly by Phytophthora megakarya, to determine the effectiveness of sanitation practices and fungicide application on tree trunks for the control of black pod disease in the canopy. Sanitation practices including weeding, pruning, thinning, shade reduction and removal of mummified pods were carried out prior to fungicide applications, and diseased pods were routinely removed at monthly intervals during harvesting. Three types of fungicides were used: systemic (Foli-R-Fos 400) applied as injection into the main trunks, semi-systemic (Ridomil 72 plus) and contact (Nordox 75, Kocide 101, Kocide DF, Blue Shield and Funguran-OH) applied as sprays onto pods on the main trunk. Sanitation combined with fungicide application on the trunk significantly reduced black pod disease incidence in the tree canopy. For fungicides applied as a spray, Ridomil 72 plus at 3.3 g l⁻¹ and Kocide DF at 10 g l⁻¹ and as injection, 40 ml Foli-R-Fos 400 injected twice a year, performed better than the other fungicide treatments. The position of pods significantly influenced the incidence of canopy black pod infection in the P. megakarya predominantly affected area but to a lesser extent in the P. palmivora solely affected area. However, no significant interactions were found between fungicide treatments and the position of pods on the tree in both disease areas. The determined trunk-canopy relationship in the development of black pod disease on cocoa can be used in disease control programmes to maximise the impact of sanitation practices, achieve judicious application of fungicides, thereby reducing the environmental impact of fungicides on the cocoa ecosystem, and ultimately increase the economic returns.     

Control of post‐harvest decay of apples by pre‐harvest and post‐harvest application of ammonium molybdate

Ammonium molybdate was tested as a potential fungicide for use in apples (cv Golden Delicious) against blue and grey mould, important post‐harvest diseases of pome fruits. In tests in vivo at 20 °C, ammonium molybdate (15 mM ) reduced lesion diameters of Penicillium expansum, Botrytis cinerea and Rhizopus stolonifer by 84%, 88% and 100% respectively. When apples treated with ammonium molybdate were stored at 1 °C for three months, a significant reduction in severity and incidence of P expansum and B cinerea was observed in both years of study (1998 and 1999). In the second year of the experiment the reduction in disease severity was greater than 88% for both pathogens, and the level of control was similar to, or greater than, that observed with the fungicide imazalil. When ammonium molybdate was applied as a pre‐harvest treatment, a significant reduction in blue mould decay was observed after three months in cold storage. In vitro, ammonium molybdate greatly inhibited spore germination of P expansum and B cinerea, although better inhibition was obtained against grey mould. Ammonium dimolybdate, sodium molybdate and potassium molybdate were also tested in vitro in comparison with ammonium molybdate as inhibitors of spore germination, but only ammonium molybdate inhibited spore germination by more than 50%. © 2001 Society of Chemical Industry     

STREP: a brown‐spot disease predictor for scheduling fungicide sprays against Stemphylium vesicarium on pear*

Brown spot of pear (Pyrus communis) caused by Stemphylium vesicarium is an important disease in fruit‐growing areas of Europe. The control of brown spot is based on protectant sprays of fungicide applied, at 7‐ to 15‐day intervals depending on the type of fungicide, from fruit set to preharvest regardless of the risk of infection. A forecasting model has been developed and can be used for timing the fungicide applications and to eliminate unnecessary sprays. The model quantifies the relationship between wetness duration and temperature in disease severity and can be used as a tool for the prediction of disease infection periods. The capacity of risk prediction was validated over 2 years. The fungicide sprays scheduled by the STREP forecaster were evaluated in commercial orchards during 3 years in different climatic areas in Spain and Italy. The results showed consistently that use of the STREP model minimized the number of fungicide sprays compared with a protectant schedule, but without decreasing the quality of commercial disease control. The susceptibility of selected European pear cultivars to infection by S. vesicarium and the influence of fruit age were also determined. The implementation of the model in warning stations will require the combination of predictions by the STREP model, the level of inoculum and the sensitivity of phenological stage and pear cultivar.     

Integration of partial resistance,plant density and use of fungicide for management of white mould in common bean

In-row plant densities have not been studied for common beans with type II growth habit and contrasting reactions to white mould. Advanced breeding lines with partial resistance or susceptibility to white mould were combined with 4, 7, 10 or 13 plants m⁻¹ and with or without fungicide at a constant between-row spacing of 0.5 m in five sprinkler-irrigated field trials conducted during the autumn–winter season in Brazil. White mould pressures in the trials covered the whole range from zero to moderate/high (46–60% of white mould severity index). In all trials, means of white mould incidence, severity and yield did not vary significantly between 7 and 13 plants m⁻¹ for the partially resistant line, regardless of the fungicide levels. For the susceptible line, 13 plants m⁻¹ increased white mould incidence and severity under moderate disease, regardless of the fungicide levels, and decreased yield compared with 10 plants m⁻¹ when fungicide was applied twice under moderate/high disease pressure. For the susceptible line, 7 or 10 plants m⁻¹ maximized yield in all trials, with or without fungicide applications. The results suggest that the current recommendation of 11–13 plants m⁻¹ could be used for type II beans with partial resistance to white mould in either a conventional or organic system. For susceptible genotypes, 7–10 plants m⁻¹ seems to be the most appropriate in-row plant density. This study may improve the recommendation of in-row plant density for type II beans cultivated under white mould pressure.     

Management of <Emphasis Type="Italic">Monosporascus</Emphasis> sudden wilt of melon by soil application of fungicides

Sudden wilt (vine decline) of melon caused by Monosporascus cannonballus is a problem in arid and semiarid regions worldwide. Preplanting soil disinfestation with methyl bromide, a common treatment for disease management, has been banned in many countries, raising the need for alternative disease-control measures. Soil fungicide application during the growing season is one possible treatment. Twelve fungicides were evaluated in vitro for M. cannonballus suppression, seven of those were evaluated under field conditions. The fungicides azoxistrobin, prochloraz and pyraclostrobin + boscalid exhibited high and similar efficacies in controlling sudden wilt disease under field conditions. Fludioxonil applied at high rates was also effective but was phytotoxic. Fluazinam, the first fungicide found capable of suppressing sudden wilt and one which has been used in Israel since 2000, was less effective. The results indicate that two applications of a fungicide during the short fall season should be sufficient for effective control of the disease. In the long spring season, at least three applications are needed to protect the melon crop. Melon fruits were examined for fungicide residues and only boscalid residues were found. This fungicide was therefore limited to the first application before fruit set.     

The effect of timing of fungicide applications on control of frogeye leaf spot and grain yield of soybeans

Soybean cultivar Samsoy 1, and the breeding lines TGx 849-313D and TGx 996-26E, grown in a field with a heavy epidemic of frogeye leaf spot caused byCercospora sojina, were treated with double foliar applications of the fungicide benomyl. The treatments were made using four application schedules at six different growth stages, starting from V₃ (fully developed leaves, beginning with trifoliate nodes) to R₅ (beginning seed_, to determine the effect of the fungucide timing on frogeye leaf spot severity, soybean grain yield and grain quality. Generally, applications at R₁ (beginning bloom) and R₃ (beginning pod) significantly (P<-0.05) reduced disease severity in the 2 susceptible genotypes, Samsoy 1 and TGx 849-313D. Plot yields of these genotypes were also significantly greater than the untreated controls when the fungicide applications were made at R₁ and R₃. There was no significant difference in diseave severity or grain yield, between the untreated control and the different times of application, on the resistant genotype TGx 996-26E. Improved seed germination and lower levels of seed infection byC. sojina occurred for all fungicide timings in the susceptible genotypes. The results suggest that fungicide spraying initiated at R₁ and followed up at R₃ is most effective in frogeye leaf spot control and can also result in higher grain yields, than applications made earlier or later in the season. Control of frogeye leaf spot, however, is best achieved by growing resistant cultivars.     

Trichoderma Biocontrol of Colletotrichum acutatum and Botrytis cinerea and Survival in Strawberry

Trichoderma isolates are known for their ability to control plant pathogens. It has been shown that various isolates of Trichoderma, including T. harzianum isolate T-39 from the commercial biological control product TRICHODEX, were effective in controlling anthracnose (Colletotrichum acutatum) and grey mould (Botrytis cinerea) in strawberry, under controlled and greenhouse conditions. Three selected Trichoderma strains, namely T-39, T-161 and T-166, were evaluated in large-scale experiments using different timing application and dosage rates for reduction of strawberry anthracnose and grey mould. All possible combinations of single, double or triple mixtures of Trichoderma strains, applied at 0.4% and 0.8% concentrations, and at 7 or 10 day intervals, resulted in reduction of anthracnose severity; the higher concentration (0.8%) was superior in control whether used with single isolates or as a result of combined application of two isolates, each at 0.4%. Only a few treatments resulted in significant control of grey mould. Isolates T-39 applied at 0.4% at 2 day intervals, T-166 at 0.4%, or T-161 combined with T-39 at 0.4% were as effective as the chemical fungicide fenhexamide. The survival dynamics of populations of the Trichoderma isolates (T-39, T-105, T-161 and T-166) applied separately was determined by dilution plating and isolates in the mixtures calculated according to the polymerase chain reaction (PCR) using repeat motif primers. The biocontrol isolates were identified to the respective species T. harzianum (T-39), T. hamatum (T-105), T. atroviride (T-161) and T. longibrachiatum (T-166), according to internal transcribed spacer sequence analysis.     

Computer‐aided design of improved warning systems – a case study for Botrytis control in flower bulbs*

Development and improvement of warning systems are often done empirically, relying on extensive field testing. As this approach is both costly and time‐consuming, there is a need for a more rational and efficient alternative. In a study to explore the options for improvement of a Botrytis warning system in flower bulbs, we applied a computer‐based approach to systems design. The approach consisted of the construction and evaluation of modified versions of the warning system using epidemiological knowledge, data sets of recorded and forecast weather and a simulation model of epidemic development and fungicide spray impact. Performance of modified versions was evaluated with regard to fungicide input, efficacy of disease control and sensitivity to the prediction error in weather forecasts. This approach can be more efficient than a purely empirical one, as it enables the designer to limit the number of alternative versions to be field‐tested on the basis of explicit performance criteria. It also has the advantage that it provides insight into the potentials for improvement of the warning system.     

β-1,3-Glucanase, chitinase, and peroxidase activities in tobacco tissues resistant and susceptible to blue mould as related to flowering, age and sucker development

Tobacco becomes naturally resistant to blue mould caused by Peronospora tabacina as it ages. This age-related resistance is correlated to the time of normal floral development and the senescence of lower leaves: however, it is dependent on neither. β-1,3-Glucanase, chitinase and peroxidase activities increase in tobacco with age. These increases correlate with the development of age-related resistance to blue mould and were independent of floral development. Additionally. β-1,3-glucanase, chitinase, and peroxidase activities were higher in leaf tissue from the main stalk resistant to blue mould) as compared to leaf tissue from suckering stems (susceptible to blue mould) on the same plant. Isozyme patterns of β-1,3-glucanase and chitinase in all resistant tissues are typical of those of tissues systemically protected by either stem injection with Peronospora tabacina or foliar inoculation with TMV.     

Dose and number of applications that maximize fungicide effective life exemplified by Zymoseptoria tritici on wheat – a model analysis

Two key decisions that need to be taken about a fungicide treatment programme are (i) the number of applications that should be used per crop growing season, and (ii) the dosage that should be used in each application. There are two opposing considerations, with control efficacy improved by a higher number of applications and higher dose, and resistance management improved by a lower number of applications and lower dose. Resistance management aims to prolong the effective life of the fungicide, defined as the time between its introduction onto the market for use on the target pathogen, and the moment when effective control is lost due to a build‐up of fungicide resistance. Thus, the question is whether there are optimal combinations of dose rate and number of applications that both provide effective control and lead to a longer effective life. In this paper, it is shown how a range of spray programmes can be compared and optimal programmes selected. This is explored with Zymoseptoria tritici on wheat and a quinone outside inhibitor (QoI) fungicide. For this pathogen–fungicide combination, a single treatment provided effective control under the simulated disease pressure, but only if the application timing was optimal and the dose was close to the maximum permitted. Programmes with three applications were generally not optimal as they exerted too much selection for resistance. Two‐application fungicide programmes balanced effective control with reasonable flexibility of dose and application timing, and low resistance selection, leading to long effective lives of the fungicide.