Sclerotinia Stem Rot Incidence Research Articles

An improvement in oilseed rape (Brassica napus L.) productivity through optimization of rice-straw quantity and plant density

• The highest yield obtained at the highest density with the most rice-straw returning. • Pod area index (PAI) increased with denser planting and more rice-straw returning. • The radiation and nitrogen use efficiency increased together with PAI. • More lignin in stem reduced the lodging risk and the incidence of sclerotinia stem rot. It was known that plant density and rice-straw returning affect the oilseed rape ( Brassica napus L.) yield in oilseed-rice rotation system. But it was not clear if their interaction influences on oilseed yield and lodging resistance. Therefore our study aimed to study role of interaction between two plant densities (D1; 45 × 10 4 plants ha −1 and D2; 75 × 10 4 plant ha −1 ) and three levels of rice-straw returning (R1; 6 × 10 3 kg ha −1 , R2; 9 × 10 3 kg ha −1 and R3, 12 × 10 3 kg ha −1 ) in improving seed yield and lodging resistance in oilseed-rice rotation system. Our results showed that the plant height and branch height increased, but the root crown diameter, branch number, pods per plant, yield per plant and lodging index decreased with the increase in plant density. Root crown diameter, branch height, pods per plant and lodging index increased while the plant height and seedling survival rate decreased due to increase in rice-straw returning. And the stem near the canopy was more prone to lodging. Low amount of rice-straw returning (R1) combined with low plant density (D1) can get high seed yield as the high seedling survival rate, while more rice-straw returning (R3) with higher plant density (D2) can elevate the seed yield by increasing the population pods and decreasing lodging index. Leaf area index (LAI), above ground nitrogen content and root nitrogen content decreased and the light transmittance (LT) increased at the bolting stage with the increase in plant density and rice-straw returning. However, the lower light transmittance (LT) associated with the increased pod area index (PAI) at the pod filling stage, which resulted in higher radiation use efficiency (RUE) and population biomass (PB). And in the pod filling stage, the above ground nitrogen content and root nitrogen content increased with the increase in rice-straw returning, but decreased with the increase in plant density, which resulted in the higher plant density and rice-straw returning, the higher nitrogen use efficiency (NUE). Besides, the activities of photosynthesis related enzymes fructose-1, 6-diphosphatase (FBP) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and the lignin synthesis related enzymes phenylalanine ammonia-lyase (PAL) and peroxidase (POD) in stem increased at the flowering stage under high plant density and large amount of rice-straw returning, resulted in increasing lignin content and decreasing incidence of sclerotinia stem rot. Present study highlights that large amount of rice-straw returning with high plant density could be used as efficient agronomic practices to improve the productivity of oilseed rape under oilseed rape-rice rotation system.

Foliar fungicides and their optimum timing reduce sclerotinia stem rot incidence, improve yield and profitability in canola (Brassica napus L.)

Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum (Lib.) de Bary causes significant economic losses in canola worldwide. The use of fungicides is an alternative in-field control option for SSR due to a lack of genetic resistance in commercial canola cultivars. The objectives of this study were to evaluate the efficacy and timing of foliar fungicide application for managing SSR, improving seed yield and profitability in canola. Thirteen field trials over eight years were conducted at several sites in Western Australia. In the fungicide effectiveness trials, fungicides were applied as either two-spray applications at 10 and 40% bloom or single application at 30% bloom stages. In the fungicide timing trials, fungicides were applied at various timings including 6–7 leaf, and 10, 30, 50, 60% bloom and late bloom stages. All fungicides evaluated significantly reduced the SSR incidence and improved seed yield in most years except for years of low disease pressure. Among fungicide timing treatments, the fungicides sprayed at between 10 and 50% bloom were more effective compared with earlier or later timing treatments. While both single and two spray regimes were effective, the single spray was more economical. A preliminary analysis based upon the current canola price and cost of fungicide application indicates that a yield increase of 90 kg ha−1 is required to cover the cost of a single spray regime. Yield increases greater than this were achieved in nine out of ten trials that had disease incidence above 5%.

Evaluation of different dates of sowing on PDI of Sclerotinia stem rot of lentil

Pulse crops play an important role in Indian agriculture and economy and they are the major source of protein and complementary to cereals both in production and consumption. The fungus Sclerotinia sclerotiorum is one of the most destructive pathogens of lentils. Yield losses can be attributed to fungal growth within stems and resulting lodging, which leads to smaller and fewer seeds, premature ripening, shattered pods, loss of smaller, shrunken seeds during harvesting. The stem rot fungus overwinters as sclerotia in the soil, in stubble at the soil surface and mixed with seed. Sclerotia can remain viable in the field for five years or more. Each year some sclerotia will germinate when conditions are suitable but others will remain dormant. Germination is either myceliogenically which directly infect plants or may be carpogenic (spore-producing apothecia) heavy infections result from airborne spores produced by apothecia at the soil surface. The present investigation experiments were conducted to find out the effect of different dates of sowing on Sclerotinia stem rot incidence in lentil, starting form 05 October to 15 November at 10 days interval, irrespective of the year.

Selenium (Se) reduces Sclerotinia stem rot disease incidence of oilseed rape by increasing plant Se concentration and shifting soil microbial community and functional profiles

Sclerotinia stem rot (SSR), a soil-borne plant disease, cause the yield loss of oilseed rape. Selenium (Se), a beneficial element of plant, improves plant resistance to pathogens, and regulates microbial communities in soil. Soil microbial communities has been identified to play an important role in plant health. We studied whether the changes in soil microbiome under influence of Se associated with oilseed rape health. SSR disease incidence of oilseed rape and soil biochemical properties were investigated in Enshi district, “The World Capital of Selenium”, and soil bacterial and fungal communities were analyzed by 16S rRNA and ITS sequencing, respectively. Results showed that Se had a strong effect on SSR incidence, and disease incidence inversely related with plant Se concentration. Besides, soil Se enhanced the microbiome diversities and the relative abundance of PGPR (plant growth promoting rhizobacteria), such as Bryobacter, Nitrospirae, Rhizobiales, Xanthobacteraceae, Nitrosomonadaceae and Basidiomycota. Furthermore, Soil Se decreased the relative abundance of pathogenic fungi, such as Olpidium, Armillaria, Coniosporium, Microbotryomycetes and Chytridiomycetes. Additionally, Se increased nitrogen metabolism, carbohydrate metabolism and cell processes related functional profiles in soil. The enrichment of Se in plants and improvement of soil microbial community were related to increased plant resistance to pathogen infection. These findings suggested that Se has potential to be developed as an ecological fungicide for biological control of SSR.

The role of precipitation, and petal and leaf infections in Sclerotinia stem rot of spring oilseed Brassica crops in Norway

Sclerotinia stem rot (SSR) is the most important disease of oilseed Brassica crops in Norway. Fungicide applications should be aligned with the actual need for control, but the SSR prediction models used lack accuracy. We have studied the importance of precipitation, and the role of petal and leaf infection for SSR incidence by using data from Norwegian field and trap plant trials over several years. In the trials, SSR incidence ranged from 0 to 65%. Given an infection threshold of 25% SSR, regression and Receiver Operating Characteristics (ROC) analysis were used to evaluate different precipitation thresholds. The sum of precipitation two weeks before and during flowering appeared to be a poor predictor for SSR infection in our field and trap plant trials (P = 0.24, P = 0.11, respectively). Leaves from three levels (leaf one, three, five), and petals were collected at three to four different times during flowering from nine field sites over two years and tested for SSR infection with real-time PCR. Percentage total leaf and petal infection explained 57 and 45% of variation in SSR incidence, respectively. Examining the different leaves and petals separately, infection of leaf three sampled at full flowering showed the highest explanation of variation in later SSR incidence (R2 = 65%, P < 0.001). ROC analysis showed that given an infection threshold of 45%, both petal and leaf infection recommended spraying when spraying was actually needed. Combining information on petal and leaf infection during flowering with relevant microclimate factors in the canopy, instead of the sum of precipitation might improve prediction accuracy for SSR.

Spatiotemporal Distribution Pattern of Sclerotinia sclerotiorum Apothecia is Modulated by Canopy Closure and Soil Temperature in an Irrigated Soybean Field.

Identifying the optimal timing for fungicide application is crucial in order to maximize the control of Sclerotinia stem rot (SSR), which is caused by Sclerotinia sclerotiorum. In this study, the impact of canopy closure and soil temperature on apothecia production was investigated to optimize fungicide application timing. Replicated soybean plots with a row spacing of 0.36 and 0.38 or 0.76 m were established in 2015 and 2016 in an irrigated soybean field at Michigan State University's Montcalm Research Center. The number of apothecia and ascospores and the incidence of SSR were monitored two times per week for 10 to 12 weeks. In both row-spacing trials, apothecia were observed earlier in 2016 (before the R1 growth stage) than in 2015 (between R1 and R2). The maximum number of apothecia was 50 times higher with the 0.36-m row spacing than with the 0.76-m row spacing in 2015 but was 2.5 times higher with the 0.76-m row spacing than with the 0.38-m row spacing in 2016, though the overall numbers were much lower in 2016. The apothecia distribution pattern was synchronized with the canopy closure pattern and the soil temperature profile. The peak number of apothecia was observed when canopy closure reached at least 50% and when average soil temperature in the row was between 21.5 and 23.5°C. In 91% of the cases, the presence of apothecia was observed when the percentage of light blocked was 70%, and no apothecia germinated in the absence of light or under full light exposure. During the first 50 days after plant emergence, the rate of canopy closure was higher in 2016 than in 2015, and the first diseased plant was observed earlier in 2016 (R2) than in 2015 (R5). Canopy closure and the distance of the sampling point from the soybean row explained much of the variability in the number of apothecia. These results can partially explain the inconsistent efficacy of fungicide applications based on the soybean growth stage and will be helpful for informing disease models and fine-tuning fungicide application strategies.

Biological control of Sclerotinia disease by Aspergillus sp. on oilseed rape in the field

ABSTRACTSclerotinia sclerotiorum causes serious yield losses to many crops worldwide. Aspergillus sp. Asp-4, previously shown to inhibit germination of sclerotia of S. sclerotiorum in vitro and in the field, was evaluated in field trials for suppression of this pathogen on oilseed rape. Spray application of Asp-4 to the soil prior to sowing rice in a rice–oilseed rape rotation resulted in a significant reduction in incidence of Sclerotinia stem rot on oilseed rape compared with the non-treated control in two field trials. This application of Asp-4 also resulted in a significant reduction in germination of sclerotia relative to the non-treated control in these field trials, suggesting that this reduction in sclerotial germination led to disease control. Microscopic examination demonstrated that Asp-4 could effectively colonise external and internal portions of sclerotia of S. sclerotiorum in vitro. Incubation of Asp-4 with sterile sclerotial material induced production of β-glucanase and chitinase activities by this isolate; β-glucanase and chitinase being potentially capable of degrading the glucan and chitin polymeric components of sclerotia. Incubation of Asp-4 with sterile sclerotial material also resulted in a significant reduction in dry weight of this sclerotial material relative to the non-treated control in 96 h in vitro experiments. Experiments reported here indicate that Aspergillus sp. Asp-4 has promise as a biological control agent for S. sclerotiorum on oilseed rape. Experiments reported here suggest that disease control results from inhibition of germination of sclerotial resting structures due to mycoparasitic colonisation by Asp-4.

Modelling inoculum dispersal and Sclerotinia stem rot gradients in canola fields

Dispersal of Sclerotinia sclerotiorum ascospores and sclerotinia stem rot (SSR) incidence were studied in commercial canola fields in two North Dakota locations from 2005 to 2007. Ascospores were collected on dishes containing a semi-selective medium that were placed on the soil, within plant canopies, at various distances from an area source of inoculum. SSR incidence was recorded at the end of the growing season. SSR incidence and inoculum gradients declined with distance from the area source in 2005 and 2007. In 2006, neither ascospores nor SSR were detected. The number of S. sclerotiorum colonies per dish (COL) declined between 30% and 75% within 40 m from the source, whereas SSR incidence declined by 50% within 12–17 m from the source. Ascospore dispersal and SSR gradients across years and locations were best described by Lambert's model (pseudo-R2 ≥ 0.98; P < 0.001) although the negative exponential model also provided a good fit for both (R2 ≥ 0.81; P ≤ 0.001). Every unit increase in the weekly mean COL represented an increase in SSR incidence that ranged between 0.5 and 0.75% (R2 = 0.96; P ≤ 0.0001) in 2005 and between 0.13 and 0.17% (R2 = 0.96; P ≤ 0.0001) in 2007. The existence of short distance dispersal, disease gradients, and the close association between inoculum concentration and disease incidence highlight the importance of within-field produced inoculum and provides support for the use of control tactics that emphasize reduction of sclerotia in canola fields as an effective way to reduce inoculum and control this disease.

Infection routes for Sclerotinia sclerotiorum in apetalous and fully petalled winter oilseed rape

Near‐isogenic lines (NILs) of apetalous (AP) and fully petalled (FP) winter oilseed rape were used to investigate infection by Sclerotinia sclerotiorum, which occurs mainly via infected petals adhering to leaves in FP oilseed rape. AP1 flowers had an average of 1·4 and 0·8 petals per flower in field and polytunnel experiments, respectively. In field experiments there were no significant differences between counts of FP1 petals, FP1 stamens and AP1 stamens adhered to leaves during flowering. At any one sample time, significantly more stamens tested positive for S. sclerotiorum on AP1 than FP1 NILs, e.g. in 2004, at early flowering 37·5% and 24·2% of stamens tested positive on AP1 and FP1 NILs, respectively. In polytunnel experiments, there were significantly more sclerotinia lesions per plant in the FP1 than in the AP1 NIL. The AP1 NIL did not avoid infection completely, probably because it produced some petals, and lesions were initiated from adhered stamens as well as petals. However, while 8·5% and 16·3% of petals initiated lesions in FP1 and AP1 NILs, respectively, only 2·5% and 1·0% of stamens initiated lesions in FP1 and AP1 NILs, which suggests stamens may be less infective than petals. In field experiments the AP1 NIL had significantly less incidence of sclerotinia stem rot than the FP1 NIL in 2004 (4·9% and 7·0%, respectively). However, there was no significant difference in stem rot incidence between AP and FP lines in 2005 (3·6% and 4·3%, respectively) or 2006 (5·5% and 3·9%, respectively).

Residue burning and tillage effects on diseases and yield of barley ( Hordeum vulgare) and canola ( Brassica napus)

Crop residue is often managed by tillage or burning in western Canada. This study was conducted to test the hypothesis that burning crop residues reduces the severity of barley ( Hordeum vulgare L.) and canola ( Brassica napus L.) diseases, and increases seed or grain yield or quality. Experiments were conducted at 2 sites, a Gray Luvisol (Typic Cryoboralf) and a Dark Gray Luvisol (Mollic Cryboralf) over 5 years in northeast Saskatchewan, Canada, with treatments of: zero (ZT) and conventional (CT) tillage, and burning (B) or no burning (NB) of previous crop residue. At each site, an experiment for barley and another for canola was established in a 2-year barley–canola rotation. Severity of leaf spotting diseases of barley, mainly net blotch [ Pyrenophora teres Drechsler], and incidence of sclerotinia stem rot [ Sclerotinia sclerotiorum (Lib.) de Bary] of canola were sometimes greater in the B treatment than the NB. Leaf spot severity of barley was usually slightly reduced under CT compared with ZT, but regardless of severity, barley yields were either similar, or more often higher under ZT than CT (337–766 kg ha −1 or 11–57%). There were occasionally effects of B on barley yield, but results were inconsistent and sometimes depended on tillage system. Canola yield tended to be greater under ZT than CT (141–233 kg ha −1 or 9–44%), but the effect of B was inconsistent. Tillage system had the greatest impact on crop yields with higher yield more often under ZT than CT, most likely as a result of improved soil moisture under the ZT system. We conclude that use of fire to manage diseases of barley and canola is ineffective.

Detection and quantification of airborne inoculum of Sclerotinia sclerotiorum using quantitative PCR

This paper reports the development of a new specific diagnostic technique to accurately quantify airborne inoculum of Sclerotinia sclerotiorum and discusses its potential use in disease‐forecasting schemes, using examples of three contrasting epidemic seasons: 2007, when there was a severe epidemic of sclerotinia stem rot (SSR) in England and high numbers of airborne ascospores were trapped at Rothamsted, and, in contrast, 2003 and 2004, when the incidence of SSR in England was low and low numbers of airborne ascospores were trapped at Rothamsted. DNA was extracted from wax‐coated plastic tapes, such as those used in Burkard (Hirst‐type) spore traps and rotating‐arm traps. A SYBR‐green quantitative PCR (qPCR) method produced a linear relationship between ascospore numbers and S. sclerotiorum DNA (mean 0·35 pg DNA per spore) and was able to detect DNA representing as few as two ascospores. The technique was insensitive to DNA of the host plant, Brassica napus, and other plant pathogens, including Sclerotinia minor, S. trifoliorum and Botrytis cinerea, and common airborne fungal genera such as Cladosporium and Penicillium. There was no relationship between rainfall and numbers of airborne ascospores of S. sclerotiorum present at Rothamsted during the period of infection in the severe SSR season (2007).

Effects of seeding rate and plant density on sclerotinia stem rot incidence in canola

Sclerotinia stem rot (Sclerotinia sclerotiorum Lib. deBary) affects canola wherever it is grown. Seeding rates, which are believed to affect the microclimate beneath the canopy, were evaluated for their impact on sclerotinia stem rot incidence. A study with five seeding rates (2.2 kg/ha, 3.3 kg/ha, 6.7 kg/ha, 13.3 kg/ha and 20.0 kg/ha) and four canola cultivars chosen for their variation in canopy structure and lodging resistance was conducted in Carman, Manitoba, Canada, in 2001 to 2003. A significant relationship between sclerotinia stem rot disease incidence (DI) and seeding rate was found. With an increase in seeding rate, the DI was significantly increased in the mean of the canola cultivars, and individually, only in the lodging-prone cultivar AC Excel. Lodging significantly increased for all cultivars when seeding rates exceeded the standard 6.7 kg/ha. Multiple regression analysis revealed that both plant density and lodging explain the majority of the variation in DI. Both plant density and lodging resistance varied in having a larger influence on DI depending on the year and cultivar analysed. Our results indicate that increasing seeding rate does modify the microenvironment and increases the potential for lodging, which may be responsible for plant-to-plant spread of this disease.

A Crop Loss-Related Forecasting Model for Sclerotinia Stem Rot in Winter Oilseed Rape

Sclerotinia stem rot (SSR) is an increasing threat to winter oilseed rape (OSR) in Germany and other European countries due to the growing area of OSR cultivation. A forecasting model was developed to provide decision support for the fungicide spray against SSR at flowering. Four weather variables-air temperature, relative humidity, rainfall, and sunshine duration-were used to calculate the microclimate in the plant canopy. From data reinvestigated in a climate chamber study, 7 to 11 degrees C and 80 to 86% relative humidity (RH) were established as minimum conditions for stem infection with ascospores and expressed as an index to discriminate infection hours (Inh). Disease incidence (DI) significantly correlated with Inh occurring post-growth stage (GS) 58 (late bud stage) (r(2) = 0.42, P </= 0.001). Using the sum of Inh from continuous infection periods exceeding 23 h significantly improved correlation with DI (r(2) = 0.82; P </= 0.001). A parallel GS model calculates the developmental stages of OSR based on temperature in the canopy and starts the model calculation at GS 58. The novel forecasting system, SkleroPro, consists of a two-tiered approach, the first providing a regional assessment of the disease risk, which is assumed when 23 Inh have accumulated after the crop has passed GS 58. The second tier provides a field-site-specific, economy-based recommendation. Based on costs of spray, expected yield, and price of rapeseed, the number of Inh corresponding to DI at the economic damage threshold (Inh(i)) is calculated. A decision to spray is proposed when Inh >/= Inh(i). Historical field data (1994 to 2004) were used to assess the impact of agronomic factors on SSR incidence. A 2-year crop rotation enhanced disease risk and, therefore, lowered the infection threshold in the model by a factor of 0.8, whereas in 4-year rotations, the threshold was elevated by a factor 1.3. Number of plants per square meter, nitrogen fertilization, and soil management did not have significant effects on DI. In an evaluation of SkleroPro with 76 historical (1994 to 2004) and 32 actual field experiments conducted in 2005, the percentage of economically correct decisions was 70 and 81%, respectively. Compared with the common practice of routine sprays, this corresponded to savings in fungicides of 39 and 81% and to increases in net return for the grower of 23 and 45 euro/ha, respectively. This study demonstrates that, particularly in areas with abundant inoculum, the level of SSR in OSR can be predicted from conditions of stem infection during late bud or flowering with sufficient accuracy, and does not require simulation of apothecial development and ascospore dispersal. SkleroPro is the first crop-loss-related forecasting model for a Sclerotinia disease, with the potential of being widely used in agricultural practice, accessible through the Internet. Its concept, components, and implementation may be useful in developing forecasting systems for Sclerotinia diseases in other crops or climates.

Seeding rate, fertilizer level and disease management effects on hybrid versus open pollinated canola (Brassica napus L.)

New canola cultivars have much higher yield potential than conventional canola cultivars and changes in production practices may be needed to achieve optimum yield from these cultivars. Studies were conducted to investigate the influence of seeding rates (2.8, 5.6 and 8.4 kg ha-1), fertilizer level (67% – low, 100% – medium, 133% – high of the commercial recommendation) and fungicide application on growth, dry matter accumulation, seed yield and seed quality using two high-yielding canola cultivars [cv. Quantum, open pollinated (OP), and cv. Invigor™, hybrid (HYB)]. The studies were conducted from 1999 to 2001 at three sites in the Parkland region of the Canadian prairies. The two cultivars did not differ in their responses to seeding and fertilizer rates, or fungicide application. Plant density was lower for the HYB than the OP because the HYB had larger seeds, with fewer seeds per kilogram. Emergence declined slightly at high fertilizer levels in some site-years due to fertilizer induced seedling damage, but increased with seeding rate. Time to onset of flowering and maturity showed no consistent influence of cultivar, and tended to be somewhat prolonged with an increase in fertilizer levels, but reduced by an increase in seeding rate. On average, the HYB produced 822 kg ha-1 more biomass and 200 kg ha-1 more seed yield than the OP. Sclerotinia stem rot incidence was very low, except at Melfort in 2000, and fungicide application generally failed to benefit the crop. Seed yield was generally increased when seeding rate was increased, with the largest increase occurring from 2.8 to 5.8 kg ha-1. Seed yield responses to the high rates of seeding or fertilizer only occurred where both inputs were at the highest level, indicating that the optimum level of one was dependent upon the level of the other input. Oil and protein concentration in the seed was higher for the HYB than the OP. High fertilizer levels generally increased the total yield of biomass and seed, and protein concentration in the seed, but usually reduced oil concentration in the seed. Increased seeding rate resulted in a small increase in oil concentration and a small reduction in protein concentration in the seed. Net returns were greatest and least variable for the HYB cultivar. Overall, the HYB performed better than the OP, and the full economic value of high-yielding canola cultivars was only realized when fertilizer and seeding rates were at or above the current recommended rates. Key words: Canola (Brassica napus L.), fertilizer rate, fungicide, hybrid canola, oil content, open pollinated canola, protein content, seeding rate, seed quality, yield

Impact of Sclerotinia Stem Rot on Yield of Canola.

Sclerotinia sclerotiorum is the causal agent of Sclerotinia stem rot (SSR) of canola (Brassica napus). In North Dakota, the leading canola producer in the United States, SSR is an endemic disease. In order to estimate the impact of this disease on canola yield, field experiments were conducted from 2000 to 2004 at several locations in North Dakota and Minnesota. Experimental plots were either inoculated with laboratory-produced ascospores or infected by naturally occurring inoculum in commercial fields. Applying fungicides at different concentrations and timings during the flowering period created epiphytotics of diverse intensities. Disease incidence was measured once prior to harvesting the crop on 50 to 100 plants per plot. Results of the study indicated that 0.5% of the potential yield (equivalent to 12.75 kg/ha) was lost for every unit percentage of SSR incidence (range of 0.18 to 0.96%). Considering the current cost of fungicide applications and the market value of this commodity, a 17% SSR incidence could cause losses similar to the cost of a fungicide application. Additional efforts are required to improve current levels of tolerance of canola plants to this pathogen.

Efficacy of Fungicides for Control of Sclerotinia Stem Rot of Canola.

Sclerotinia stem rot (SSR), incited by Sclerotinia sclerotiorum, causes yield reductions to canola (Brassica napus) grown in North Dakota and Minnesota. Field trials were conducted in North Dakota and Minnesota from 2000 to 2004 to evaluate the effect of foliar fungicides on SSR and canola yield. Levels of SSR varied among years and location. In general, fungicides that consistently reduced SSR incidence compared with an untreated control were azoxystrobin, benomyl, boscalid, iprodione, prothioconazole, tebuconazole, thiophanate-methyl, trifloxystrobin, and vinclozolin. Significant reductions in SSR incidence with fungicides did not always translate into differences in canola yield, however. Inconsistent results were observed with different timings of applications based on percent bloom. This indicates that application timing should be based on factors in addition to percent bloom.

Timing Fungicide Applications for Managing Sclerotinia Stem Rot of Potato.

Fungicides were applied to potato foliage at row closure (between rows) and at full bloom of primary inflorescences to control Sclerotinia stem rot during replicated trials in 2003, 2004, and 2005. Application at row closure followed labeled recommendations from manufacturers. Incidence of Sclerotinia stem rot did not vary significantly among fungicides when full labeled rates of thiophanate-methyl, fluazinam, and boscalid were applied at full bloom of primary inflorescences. Incidence of Sclerotinia stem rot was significantly less when fungicides thiophanatemethyl, fluazinam, or boscalid were applied to potato foliage at full bloom of primary inflorescences than at row closure or when fungicides were not applied in 2004 and 2005, and when thiophanate-methyl or fluazinam was applied to potato foliage at full bloom of primary inflorescences than at row closure or when fungicides were not applied in 2003. Mean percentage of control for the fungicides combined, relative to the nontreated control, was 43, 48, and 20% in 2003, 2004, and 2005, respectively, when application was made at row closure; whereas, it was 77, 83, and 80% in 2003, 2004, and 2005, respectively, when application was at full bloom of primary inflorescences. Mean disease incidences of infected stem were significantly less when fluazinam was applied at 100% bloom of primary inflorescences than at 20% drop of blossoms from primary inflorescences in 2004 and 2005. In summary, control of Sclerotinia stem rot was significantly better when fungicides were applied at full bloom of primary inflorescences than at row closure during all 3 years of the study.

First Report of Sclerotinia Stem Rot of Chickpea Caused by Sclerotinia sclerotiorum in North Dakota and Washington

Chickpea (Cicer arietinum L.) is cultivated as a rotational crop in the cereal-based production system in the U.S. Pacific Northwest (PNW) and its production is expanding to other northern tier states. During July 2005, symptoms of Sclerotinia stem rot were observed on chickpea cv. Dwelley and Dylan in fields near Spangle, WA and Carrington, ND, respectively, with disease incidence of approximately ≤1% in affected areas at both locations. Symptoms included stem whitening, wilting, and stem breakage. Occasionally, white fluffy mycelium was observed; however, production of sclerotia on infected plants was rarely observed. Sclerotinia sclerotiorum was isolated from diseased stems collected from both states. The isolates produced a ring of sclerotia near the edge of potato dextrose agar (PDA) plates in 7 days and produced neither conidia nor other fruiting bodies in culture after 30 days. PCR amplification of the rDNA internal transcribed spacer region from two representative isolates and subsequent digestion with restriction enzymes, Mbo I and Taq I, produced identical banding patterns to previously identified isolates of S. sclerotiorum from pea from the PNW (2). Chickpea cvs. Dwelley and Spanish White (eight plants of each) were inoculated by fastening mycelial agar plugs from an actively growing colony on PDA onto the stems with Parafilm. Symptoms of stem whitening were observed as early as 2 days after inoculation, and the lesions extended upward and downward from the inoculation site. Wilting and stem breakage were also observed. Control inoculations of four plants of each cultivar with PDA plugs without mycelium produced no visible symptoms. S. sclerotiorum was consistently reisolated from inoculated plants but not from control plants. Chickpea had been grown in the PNW for more than 20 years without any reported incidence of Sclerotinia stem rot although the disease has been reported from Arizona (3) and Asian countries (1). This is likely because of the upright growth habit of the chickpea plant coupled with relatively dry conditions late in the growing season. Previous chickpea cultivars were very susceptible to Ascochyta blight, an early-season disease of chickpea in the PNW that reduced chickpea stands and canopy coverage. Current cultivars possess much improved resistance to Ascochyta blight, allowing greater vegetative growth to occur and creating microenvironmental conditions conducive to Sclerotinia stem rot. In North Dakota, where humid conditions prevail late in the growing season, symptoms of Sclerotinia stem rot had been observed in previous years but had not been documented because of a recent history of chickpea cultivation there. To our knowledge, this is the first report of confirmed Sclerotinia stem rot of chickpea in North Dakota and Washington.

Application of thiophanate-methyl at different host growth stages for management of sclerotinia stem rot in soybean

Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, is an important disease of soybean ( Glycine max L.) in the North Central United States. The incidence of SSR can be reduced by planting partially resistant cultivars and by implementation of cultural practices that limit pathogen activity. Fungicides such as thiophanate-methyl are another option for control of SSR, but usually recommended in situations where susceptible cultivars must be grown or modification of cultural practices are not disease control options. Previous studies have shown that control of SSR with fungicides is possible, but that the degree of control is inconsistent especially when incidence of SSR surpasses 50%. This study was designed to evaluate the efficacy of single or multiple applications of thiophanate-methyl in relation to timing of inoculation and early reproductive growth stages of the host. Inoculum was introduced at growth stage R2 at the Illinois location, and naturally occurring inoculum was relied upon to initiate SSR at the Wisconsin location. Thiophanate-methyl was effective when applied at R1 prior to inoculation at R2, but not if applied at R3, after inoculation. Two applications of thiophanate-methyl starting at R1 or the R2 growth stage and a second 2 weeks later lowered the incidence of SSR at the naturally infested Wisconsin site compared to one application with one exception. The incidence of SSR was identical for one and two applications starting at R1.5. Soybean yield was improved by fungicides at both experimental locations, and coincided with timing, and number of applications. Data from both locations suggested that fungicides need to be applied prior to inoculum arrival to the infection court. One application was effective in the controlled inoculation study, but two applications were needed at the naturally infested location. Two applications of thiophanate-methyl improved yield of a partially resistant soybean cultivar even though the incidence of SSR was <10% at the Wisconsin location. Thiophanate-methyl is an effective option for control of SSR, especially to reduce seedborne inoculum in commercial seed production systems.

Effect of crop rotation and tillage system on sclerotinia stem rot on soybean

Sclerotinia stem rot (SSR) of soybean is a major disease in the North Central region of the United States. A 3-year study was done to determine if crop rotation and tillage, moldboard plowing then mulch tillage (MP + MT), mulch tillage (MT), and no-till (NT), affected the population density of sclerotia and apothecia, incidence of SSR, and soybean yield. Crop rotation did not significantly affect the number or distribution of sclerotia or SSR incidence, but did affect the number of apothecia and the yield. The highest number of apothecia per square metre was observed in the plots in the continuous soybean rotation. Tillage affected both the number and distribution of sclerotia in the soil profile. Moldboard plowing lowered the number of sclerotia per litre of soil, compared to MT and NT plots, and buried the sclerotia deeper than 10 cm into the soil. Tillage did not affect the total number of apothecia observed, but moldboard plowing did delay emergence of apothecia compared to no-till. The MP + MT plots had the lowest disease incidence and the highest yield, while the NT plots had the highest disease incidence and the lowest yields. One year of moldboard plowing will bury sclerotia at least 10 cm in soil and delay the production of apothecia. How this affects SSR development depends on the other factors involved with disease development.