Fungicides For Management Research Articles

Temporal analysis and fungicide management strategies to control mango anthracnose epidemics in Guerrero, Mexico

The temporal progress of anthracnose (Colletotrichum gloeosporioides) epidemics was studied in mango (Mangifera indica) orchards treated with fungicides from different chemical groups, mode of action, and application sequences in two regions of contrasting climates (sub-humid and dry tropics) in Guerrero, Mexico. Full flowering, initial setting, and 8-15mm O fruits were identified as critical stages for infection. Epidemics started 20-26 days after swollen buds, and maximum severity was attained at 40-42 days after the first symptoms were detected. The Weibull model described (r2>0.89) anthracnose epidemics in both floral and vegetative flushes. Active ingredients of different fungicide groups, mode of action, and residuality such as myclobutanil, azoxystrobin, cyprodinil+fludioxonil, quinoxyfen, and chlorotalonil + sulfur led to significantly low values (LSD 30oC (rFl=0.79-0.86; rVeg=0.80-0.95) and relative humidity > 90% (rFl=0.66-0.86; rVeg=0.67-0.94). In both regions, conidial sporulation was related to temperature >30oC (r=0.72-0.74), relative humidity <60% (r=0.66), severity (rFl=0.62-0.98; rVeg=0.75-0.97) and dew point <25oC (r=0.68-0.69).

Efficacy and Stability of Integrating Fungicide and Cultivar Resistance to Manage Fusarium Head Blight and Deoxynivalenol in Wheat

Integration of host resistance and prothioconazole + tebuconazole fungicide application at anthesis to manage Fusarium head blight (FHB) and deoxynivalenol (DON) in wheat was evaluated using data from over 40 trials in 12 U.S. states. Means of FHB index (index) and DON from up to six resistance class-fungicide management combinations per trial (susceptible treated [S_TR] and untreated [S_UT]; moderately susceptible treated [MS_TR] and untreated [MS_UT]; moderately resistant treated [MR_TR] and untreated [MR_UT]) were used in multivariate meta-analyses, and mean log response ratios across trials were estimated and transformed to estimate mean percent control ( ) due to the management combinations relative to S_UT. All combinations led to a significant reduction in index and DON (P < 0.001). MR_TR was the most effective combination, with a of 76% for index and 71% for DON, followed by MS_TR (71 and 58%, respectively), MR_UT (54 and 51%, respectively), S_TR (53 and 39%, respectively), and MS_UT (43 and 30%, respectively). Calculations based on the principle of treatment independence showed that the combination of fungicide application and resistance was additive in terms of percent control for index and DON. Management combinations were ranked based on percent control relative to S_UT within each trial, and nonparametric analyses were performed to determine management combination stability across environments (trials) using the Kendall coefficient of concordance (W). There was a significant concordance of management combinations for both index and DON (P < 0.001), indicating a nonrandom ranking across environments and relatively low variability in the within-environment ranking of management combinations. MR_TR had the highest mean rank (best control relative to S_UT) and was one of the most stable management combinations across environments, with low rank stability variance (0.99 for index and 0.67 for DON). MS_UT had the lowest mean rank (poorest control) but was also one of the most stable management combinations. Based on Piepho's nonparametric rank-based variance homogeneity U test, there was an interaction of management combination and environment for index (P = 0.011) but not for DON (P = 0.147), indicating that the rank ordering for index depended somewhat on environment. In conclusion, although the magnitude of percent control will likely vary among environments, integrating a single tebuconazole + prothioconazole application at anthesis with cultivar resistance will be a more effective and stable management practice for both index and DON than either approach used alone.

Reduced fungicide use on a new Australian peanut cultivar, highly resistant to the late leaf spot and rust pathogens

Rust (caused by Puccinia arachidis) and late leaf spot (LLS, caused by Mycosphaerella berkeleyi) can cause significant yield losses in Australian peanut crops. Until recently, all commercial peanut varieties were highly susceptible to these pathogens, but the new Australian cultivar Sutherland has significantly higher levels of resistance than the older cultivars. Field trials were conducted at two sites in Queensland to (a) confirm the improved resistance of cv. Sutherland over another commercial cultivar, Menzies, (b) study the effects of timing of first spray, spray interval and cultivar on disease severity and yield, and (c) develop a suitable fungicide management program for cv. Sutherland. In the 2006 and 2007 trials, rust and LLS developed slower and had lower final disease ratings and AUDPC values on unsprayed plots of cv. Sutherland than on cv. Menzies. The timing of the first spray is critical in managing both rust and late leaf spot, with the results demonstrating that the first fungicide spray on cv. Sutherland should be applied as soon as rust and LLS are first seen on cv. Menzies. In most trials spray intervals of 14 days or 21 days were suitable to effectively control rust and LLS. In years with low disease pressure, few, if any, fungicide applications will be needed to manage the diseases, but in other years up to four sprays may be necessary.

Epidemiology of the Groundnut (&amp;lt;i&amp;gt;Arachis hypogaea&amp;lt;/i&amp;gt; L.) Leaf Spot Disease: Genetic Analysis and Developmental Cycles

Groundnut leaf spot is one of the important factors limiting groundnut productivity in Africa particularly in the Democratic Republic of Congo (DR Congo). Early and late leaf spot disease of groundnut caused by Cercospora arachidicola Hori and Cercosporidium personatum (Berk & Curt.) Deighton, respectively, can cause considerable yield losses without fungicide management. The main objectives of this research were to analyze plant and disease developmental cycles. Significant differences were observed among the groundnut varieties evaluated for resistance to the leaf spot disease. The results show that plant development cycle can be divided into three developmental stages. A first stage characterized by a low production of leaves, a second stage with a significant leaf development and finally a third stage with a reduction of leaves. Interestingly, the leaf spot disease cycle was also divided in three stages. The disease stage characterized by the highest level of symptom expression was not associated with the plant phase with the highest emerged leaves. Disease symptoms reached the highest pick only after the phase of intense leaf development. The molecular analysis revealed that all the groundnut varieties analyzed were genetically closely related even though they showed different reactions to the leaf spot disease.

Fungicidal management of wilt complex of scented geranium

Systemic fungicides, carbendazim + mancozeb and carbendazim alone completely inhibited the mycelia growth even at 100 and 200 ppm, whereas among non-systemic fungicides, thiram was found to be the most effective and gave 52.77, 62.77 and 85.00% inhibition at 500, 1000 and 1500 ppm concentrations, respectively. Thiram was found to be most effective fungicides in inhibiting the both fungi (68.84 and 58.69%) followed by the indofil M 45 (47.59 and 51.38%). In pot house condition, carbendazim + mancozeb (0.2%) and carbendazim (0.1%) were most effective fungicides in reducing cent percent disease incidence and severity, but it was at par with thiram (82.35; 87.50). In field condition, mulching with transparent polyethylene mulch (25 μm) resulted in highest survival rate (95.83%) and least mortality rate (4.16%) of rooted geranium cuttings after 30 days of germination. The application of carbendazim (Bavistin) at 0.1% when applied individually was also found almost complete control as is evident from low disease incidence (1.04%) and severity (0.52%), considered to be second best treatment. Apparent infection rate (0.0) was observed in carbendazim + mancozeb and carbendazim followed by copper oxychloride (0.006) and carboxin (0.009). Area under disease progress curve was less than 100 in cabendazim + mancozeb and carbendazim.

Fungicidal management of chocolate spot of faba bean and assessment of yield losses due to the disease

This work was carried out at Sers El-Lyain Agriculture Research Station Farm, El-Minufiya Governorate during 2007/08 and 2008/09 growing seasons to evaluate the amount of losses in the seed yield of the five faba bean cultivars Giza 3 Mohassen, Giza 716, Giza 40, Sakha 1 and Sakha 2 under. In vitro studies show that Dithan M45 was the most effective agent against Botrytis fabae than Galben manozeb and copper oxychloride. Application Dithan M45 of under greenhouse conditions, 2 days before inoculation reduced the disease severity (3.11%) at 200ppm compared with the control treatment (18.59%) on Giza 40 cv., while the symptoms did not appear at the same concentration on other tested cultivars. It was observed that, the cvs. Giza 716 and Sakha 2 showed lower infection than the other tested cvs, except with Giza 40 which was highly susceptible. Field studies showed significant differences under the influence of chocolate spot disease. The area under the disease progress curve (AUDPC) was higher on Giza 40 followed by Sakha 1, Giza 3 Mohassen, Sakha 2 and Giza 716, respectively, with higher disease infection in the first season 2007/08 than 2008/09 season. High negative significant correlation (r) was obtained between AUDPC and the yield of the five tested cultivars in the two seasons. High negative correlation was observed between disease severity and each of plant height, number of branches, number of pods, weight of pods and weight of 100 seeds of Giza 40 and Sakha 1 in the first season. High negative regression coefficient (b) was found between each of the five studied characters and disease severity of five cultivars. However, plant height and number of branches were not significant for the Giza 716 and Sakha 2. The regression coefficient (b) values were found significant for number of pods (X3) with 0.532 and 0.096, for weight of pods (X4) with 0.422 and 0.0126 and for weight of 100 seed (X5) with 0.753 and 0093 for Giza 716 in the two seasons, respectively. While for Giza 40 these values were 0.644 and 0.226, 0.115 and 0.64 and 0.159 and 0.222, respectively. Coefficient of determination (R2) values were 0.63 and 0.341 for Giza 716 and were 0.757 and 0.854 for Giza 40 for the weight of pods in the two seasons, respectively.

Sensitivity of Venturia inaequalis Chilean Isolates to Difenoconazole, Fenarimol, Mancozeb, and Pyrimethanil

Apple scab (Venturia inaequalis) is the most important disease in Chilean apple (Malus domestica Borkh.) orchards where fungicide management is the main tool to control disease. Sensitivity tests to difenoconazole, fenarimol, mancozeb, and pyrimethanil fungicides were conducted on V. inaequalis wild isolates to construct local baseline sensitivity distributions, and compare them with a collection of isolates from seven different commercial orchards with no evidence of practical resistance. In vitro assays were conducted and sensitivity was measured as inhibition of mycelial growth (difenoconazole, fenarimol, pyrimethanil) or conidial germination (mancozeb). Departure from the baseline distribution to less sensitivity was found for difenoconazole, fenarimol, and mancozeb with resistance factors of 4.7, 5.8, and 2.1, respectively. The highest difference between baseline and orchard populations was observed for fenarimol which showed the highest shift to less sensitivity. Discriminatory doses of 0.04, 1.0, 0.6, and 0.2 µg mL -1 are proposed for in vitro monitoring of sensitivity to difenoconazole, fenarimol, mancozeb, and pyrimethanil, respectively.

Invasion of Phytophthora infestans at the Landscape Level: How Do Spatial Scale and Weather Modulate the Consequences of Spatial Heterogeneity in Host Resistance?

Strategic spatial patterning of crop species and cultivars could make agricultural landscapes less vulnerable to plant disease epidemics, but experimentation to explore effective disease-suppressive landscape designs is problematic. Here, we present a realistic, multiscale, spatiotemporal, integrodifference equation model of potato late blight epidemics to determine the relationship between spatial heterogeneity and disease spread, and determine the effectiveness of mixing resistant and susceptible cultivars at different spatial scales under the influence of weather. The model framework comprised a landscape generator, a potato late blight model that includes host and pathogen life cycles and fungicide management at the field scale, and an atmospheric dispersion model that calculates spore dispersal at the landscape scale. Landscapes consisted of one or two distinct potato-growing regions (6.4-by-6.4-km) embedded within a nonhost matrix. The characteristics of fields and growing regions and the separation distance between two growing regions were investigated for their effects on disease incidence, measured as the proportion of fields with ≥1% severity, after inoculation of a single potato grid cell with a low initial level of disease. The most effective spatial strategies for suppressing disease spread in a region were those that reduced the acreage of potato or increased the proportion of a resistant potato cultivar. Clustering potato cultivation in some parts of a region, either by planting in large fields or clustering small fields, enhanced the spread within such a cluster while it delayed spread from one cluster to another; however, the net effect of clustering was an increase in disease at the landscape scale. The planting of mixtures of a resistant and susceptible cultivar was a consistently effective option for creating potato-growing regions that suppressed disease spread. It was more effective to mix susceptible and resistant cultivars within fields than plant some fields entirely with a susceptible cultivar and other fields with a resistant cultivar, at the same ratio of susceptible to resistant potato plants at the landscape level. Separation distances of at least 16 km were needed to completely prevent epidemic spread from one potato-growing region to another. Effects of spatial placement of resistant and susceptible potato cultivars depended strongly on meteorological conditions, indicating that landscape connectivity for the spread of plant disease depends on the particular coincidence between direction of spread, location of fields, distance between the fields, and survival of the spores depending on the weather. Therefore, in the simulation of (airborne) pathogen invasions, it is important to consider the large variability of atmospheric dispersion conditions.

Soybean Response to Preplant and Foliar‐Applied Potassium Chloride with Strobilurin Fungicides

Potassium chloride (KCl) preplant or foliar applied with fungicides to soybean [Glycine max (L.) Merr.] may allow farmers to increase yields when soil K availability is reduced and/or when Septoria brown spot (SBS) (Septoria glycines), frogeye leaf spot (FLS) (Cercospora sojina), or sudden death syndrome (SDS) (Fusarium solani (Mart.) Sacc. f. sp. glycines) are present. Interactions between fertilizer and fungicide management programs have not been examined in the central United States. Our objective was to evaluate the effect of preplant‐ and foliar‐applied KCl alone or combined with pyraclostrobin, azoxystrobin, or azoxystrobin plus lambda‐cyhalothrin on soybean response and severity of SBS, FLS, and SDS. Experiments were conducted in northeastern (Novelty) and southeastern (Qulin) Missouri in 2006 and 2007 on soils with low to medium K. Leaf K concentrations increased 1.4 to 6.1 g kg−1 following preplant KCl compared to nontreated or foliar KCl. Leaf Cl concentrations increased significantly with preplant KCl at Qulin and foliar KCl at R4 at Qulin and Novelty. At Novelty, preplant KCl reduced the severity of SBS and FLS up to 6%, and increased yield 340 kg ha−1, while foliar KCl increased yield 110 kg ha−1 An R4 application of strobilurin fungicides increased yields 230 to 360 kg ha−1 at Novelty. At Qulin, soybean yield increased 390 kg ha−1 with preplant KCl, while there were variable effects of fungicides on the severity of SBS, FLS, or SDS, and no yield increase due to fungicides or foliar KCl. Foliar applications of KCl were no substitute for preplant KCl.

Seed treatment and foliar application of insecticides and fungicides for management of cercospora leaf spots and yellow mosaic of mungbean (Vigna radiata)

Field experiments were conducted during the rainy seasons of 2006 and 2007 at the Indian Agricultural Research Institute, New Delhi for the management of yellow mosaic (Mungbean Yellow Mosaic Virus) and cercospora leaf spots (Cercospora canescens and Pseudocercospora cruenta) of mungbean. Insecticides and fungicides as seed dressings, with or without foliar sprays, were evaluated. Amongst the treatments, a combination of seed treatment with thiamethoxam (Cruiser™) at 4 g kg−1 and carbendazim (Bavistin™) + TMTD (Thiram™) at 2.5 g kg−1 (1:1 ratio) followed by foliar applications of thiamethoxam (Actara™) 0.02% and carbendazim 0.05% at 21 and 35 d, respectively after sowing produced the highest seedling establishment, shoot and root lengths, number of pods, plant biomass, 1000-seed weight, and grain yield in mungbean with the lowest intensity of cercospora leaf spots and mungbean yellow mosaic. Vector (whitefly) populations were also the lowest in this treatment during all stages of the crop. This treatment was cost-effective, as it provided the highest return per Rupee of input. It was second best for the number of Rhizobium root nodules per plant.

Powdery Mildew of Dogwoods: Current Status and Future Prospects.

Cornus is a large genus of trees and shrubs that are collectively referred to as dogwoods. Flowering dogwood (C. florida L.) and kousa dogwood (C. kousa (F. Buerger ex Miq.) Hance) and interspecific hybrids of these species are popular ornamental trees that are known for their showy bracts, red berries (drupes), and/or fall color. Other species that are commercially grown for specialty markets include the pagoda dogwood (C. alternifolia L.), giant dogwood (C. controversa Hemsl.), cornelian cherry (C. mas L.), Pacific dogwood (C. nuttallii Aud.), and redosier dogwood (C. sericea L.). The foliage of native species, such as flowering dogwood and pagoda dogwood, is high in calcium (12) in quantities above what is needed for skeletal growth of wildlife; it is the preferred browse material for lactating does in late spring while many other trees are still leafless (13,22). The berries of flowering dogwood have high oil content and provide mast for numerous species of migrant songbirds, wild turkeys, and large and small mammals (22). For many years, nurseries that produced flowering and kousa dogwoods had the luxury of working with relatively diseasefree crops. Disease management and control costs were minimal and estimated at approximately $120/ha/year. In the late 1970s, flowering and kousa dogwoods were threatened by a new disease, dogwood anthracnose, caused by Discula destructiva (39), which was reviewed by Daughtrey et al. (3). In 1994, another disease, powdery mildew, reached epiphytotic levels in flowering dogwoods. Tens of millions of dollar’s worth of dogwoods were destroyed and millions of cultivated seedlings lost their commercial value because formal management strategies were not formulated. In subsequent years, fungicide management costs were estimated to be $1,975/ha/year. Many small producers of dogwoods terminated production of the tree because they could not afford the additional overhead or were not inclined to continue routine fungicide sprays every 2 weeks from May to October. Powdery mildew on C. florida was first reported in 1887 by Burrill and Earle (1), but this disease was rarely reported on flowering dogwood in the United States before 1994. However, the disease appeared simultaneously in forest, landscape, and nursery plantings statewide in Alabama in 1994 (8). Similar outbreaks of powdery mildew were observed in Tennessee, where many nursery fields of flowering dogwood were abandoned (Fig. 1). Powdery mildew has emerged as a nationwide disease of flowering dogwood (2). Although the host side of the disease triangle remained constant, we do not know whether the change of frequency and severity of powdery mildew in flowering dogwood was due to a change in the pathogen or a change in the environment.

Scenario Approach for Assessing the Utility of Dispersal Information in Decision Support for Aerially Spread Plant Pathogens, Applied to Phytophthora infestans

Opportunities exist to improve decision support systems through the use of dispersal information gained from epidemiological research. However, dispersal and demographic information is often fragmentary in plant pathology, and this uncertainty creates a risk of inappropriate action whenever such information is used as a basis for decision making. In this article, a scenario-based simulation approach is used to evaluate crop and economic risks and benefits in the use of dispersal information for decision making using the potato late blight pathosystem (Phytophthora infestans-Solanum tuberosum) as a case study. A recently validated spatiotemporal potato late blight model was coupled to submodels for crop growth, tuber dry matter production, and fungicide efficacy. The yield response of a range of management scenarios to a single influx of primary inoculum (the initial spore load) was calculated. Damage curves (relative yield loss versus initial spore load) from a range of combinations of varietal susceptibility and fungicide treatments were used to classify the various management scenarios as either sensitive to initial spore load or tolerant to initial spore load, thus identifying where a high degree of accuracy would be required in dispersal information for appropriate decision making, and where a greater degree of uncertainty could be tolerated. General epidemics, resulting from spatially homogeneous initial spore loads, responded more strongly to the size of the initial spore load than focal epidemics, resulting from an initial spot infection. Susceptible cultivars responded with sizeable yield losses even at low levels of initial spore load, regardless of the fungicide management regime used. These results indicated that, for susceptible cultivars (late cultivars in particular), the degree of accuracy that would be required in dispersal information for appropriate decision making is unlikely to be practically attainable. The results also indicated that, contrary to "folk wisdom," spore loads of a few hundred spores per square meter do not lead to appreciable crop loss in resistant cultivars and are therefore acceptable. We conclude that scope exists for including dispersal information in decision making for potato late blight with resistant potato cultivars but not for susceptible cultivars. The modeling framework used in this study can be extended to investigate the scope for inclusion of dispersal information in decision support for other aerially transmitted pathogens.

RESEARCH EXPERIENCE ON POTATO LATE BLIGHT DISEASE MANAGEMENT IN BANGLADESH

Potato is an important commercial crop in Bangladesh. Unfortunately, potato suffers from many destructive diseases, of which late blight, caused by Phytophthora infestans is the most important one. In Bangladesh, late blight causes serious yield loss in potato every year. Late blight was first reported in Bangladesh in 1922. In recent years more than 300 varieties, 2050 germplasm lines and 250 true potato seed (TPS) progenies were evaluated for resistance to major diseases under field conditions. Screening for late blight resistance was carried out under both natural and artificial conditions. So far more than 300 germplasm (exotic and local) and TPS progenies were screened through artificial inoculation. Of these only three lines (CIP-607, CIP-272 and CIP-616) were found to be tolerant to late blight. Some of the field resistant TPS progenies are: TS-6 × TS-9, HPS-7/67, HPS-II/13, TS-5 × TS, LM × 501, 501 × 9, 801000 and 300999. A set of 15 late blight resistant germplasm lines received from CIP, Peru in 2005 was evaluated under natural conditions of which 6-7 were found to be resistant to the disease. Attempts were made to develop late blight resistant transgenic potato varieties by transforming the RB resistance gene into two commercial varieties. Twenty races of P. infestans have so far been identified in Bangladesh. The frequency of races differed greatly with maximum occurrence of race 2. Existence of metalaxyl resistant strains of P. infestans have been identified which might be due to indiscriminate spraying of metalaxyl (Ridomil) fungicide. Both fungicide management and farmer training with farmer field schools are discussed.

Efficacy of Organically Acceptable Fungicides for Management of Early and Late Leaf Spot Diseases on Partially Resistant Peanut Cultivars

Field experiments were carried out in Georgia and North Carolina to evaluate the efficacy of fungicides approved for the organic management of early leaf spot, caused by Cercospora arachidicola, and late leaf spot, caused by Cercosporidium personatum, in peanut (Arachis hypogaea) fields planted to cultivars with partial resistance to one or both pathogens. Copper treatments alone or in mixtures resulted in less disease than a non-treated control. In Georgia, sulfur provided some disease suppression, but not as much as treatments with copper sulfate. Neem oil did not affect disease severity. Mean pod yields across years were significantly greater than the non-treated control only for copper sulfate in Georgia and cupric hydroxide in North Carolina. The minimal yield response to treatments suggests that under similar situations, the frequency of copper-based fungicide applications may be reduced with little affect on yield. Accepted for publication 16 January 2008. Published 17 March 2008.

Fungicide management strategies for control of strawberry fruit rot diseases in Louisiana and Mississippi

Sixteen fungicide treatments were evaluated for control of strawberry fruit diseases in five fungicide studies conducted at Hammond, LA and Poplarville, MS during the 2002, 2003 and 2005 fruiting seasons. The most frequent fruit rots at harvest were anthracnose fruit rot caused by Colletotrichum acutatum, stem-end rot caused by Gnomonia comari, and Botrytis fruit rot caused by Botrytis cinerea. Fungicides from seven groups were shown to be effective for control of strawberry fruit rot diseases in these trials, and the commercial combination fungicides were often the most effective. In at least two trials when compared to the untreated control, total fruit rot was less on berries from the pyraclostrobin+boscalid, cyprodinil+fludioxonil, azoxystrobin, fenhexamid+captan, and captan treatments; anthracnose fruit rot was less on berries from the cyprodinil+fludioxonil and azoxystrobin treatments; and stem-end rot was less on berries from the cyprodinil+fludioxonil, pyraclostrobin+boscalid, captan, azoxystrobin, and pyraclostrobin treatments. While low in all trials, a significant reduction in Botrytis fruit rot incidence occurred in four trials. Berries from the cyprodinil+fludioxonil, fenhexamid, fenhexamid+captan, pyraclostrobin+boscalid, captan, pyrimethanil, and azoxystrobin treatments had the lowest incidence of Botrytis fruit rot. Efficacious fungicides from various FRAC groups will provide strawberry growers with more options for controlling diseases while managing fungicide resistance.

Mitochondrial heteroplasmy for the cytochrome b gene Controls the level of strobilurin resistance in the apple powdery mildew fungus Podosphaera leucotricha (Ell. &amp; Ev.) E.S. Salmon

In single-spore isolates of the apple powdery mildew fungus Podosphaera leucotricha collected at various sites in Germany, Great Britain and India, we have identified different levels of strobilurin resistance. Sequence analyses of the mitochondrial cytochrome b gene and cleaved amplified polymorphic sequences (CAPS) analyses showed heteroplasmy with respect to the G143A mutation in all isolates tested. The quantity of mitochondria carrying this mutation correlated with strobilurin resistance in germination assays on isolated apple cuticles and in growth assays on strobilurin-treated leaves. In contrast to other plant pathogenic fungi, including powdery mildews of cereals and cucumber, heteroplasmy was stable even after six years of cultivation in the absence of strobilurin fungicides. These data are discussed with respect to disease and fungicide management.

Reviving Chickpea Production in Nepal Through Integrated Crop Management, with Emphasis on Botrytis Gray Mold.

This paper describes the current status of chickpea production and assesses the damage caused by the grey mould disease (Botrytis cinerea) in Nepal. It also discusses the effects of different integrated crop management components (host plant resistance, fungicide management, forecasting model-based fungicide application, row spacing variation, and seed treatment with Rhizobium) in the control of Botrytis grey mould and improvement of chickpea production in the country.

The Spatiotemporal Genetic Structure of Phytophthora capsici in Michigan and Implications for Disease Management

Root, crown, and fruit rot caused by Phytophthora capsici Leonian is a limiting factor for the production of peppers, tomatoes, and cucurbit crops in Michigan and the United States. Like many species in the genus Phytophthora, P. capsici has the potential for rapid polycyclic disease development from a limited amount of initial inoculum (6). P. capsici produces caducous sporangia that can be spread by wind-blown rain or release 20 to 40 motile zoospores in the presence of free water. The polycyclic phase of disease development is thought to be driven primarily by asexual spore dispersal at a local scale (within and down rows). Sexual reproduction requires both the A1 and A2 compatibility types (CTs) and results in the production of thick-walled oospores. Oospores are thought to serve as the primary survival structure outside of host tissue. Recommended disease management strategies stress the importance of avoiding excess water in the plant rhizosphere by using well-drained fields, conservative irrigation, and planting on raised beds. Additional recommendations include rotation to nonsusceptible hosts for at least 2 years and the use of fungicides. The phenylamide fungicide (PAF) mefenoxam is a systemic compound with high activity against P. capsici and has been used by growers throughout the United States to control P. capsici. Insensitivity to PAF has been reported for a number of other oomycetous organisms (Bremia lactucae, P. infestans, and P. sojae, etc.) and appears to be conferred by a single incompletely dominant gene of major effect (1). Growers in Michigan practicing 2+-year rotation in well-drained fields using an array of fungicidal management tools have experienced significant losses to P. capsici. Michigan is the number one producer of cucumbers for pickling in the United States and it was at the request of grower groups associated with this industry that research into the epidemiology and reproductive biology of P. capsici on cucurbit hosts was initiated. Although many researchers cite oospores as the most likely propagule for survival outside of host tissue, there have been very few investigations specifically aimed at determining the impact of sexual reproduction in natural populations of P. capsici. Our hypothesis was that the sexual stage may play an important role not only in survival but also in the adaptation of P. capsici populations to environmental stresses (e.g., fungicides). Our goal was to perform a comprehensive investigation of the phenotypic and genetic diversity present in P. capsici populations from the major vegetable production regions of Michigan, with the implicit intention of addressing questions concerning epidemiology, reproductive biology, and the durability of currently recommended management strategies.

Optimal Fungicide Management of Purple Spot of Asparagus and Impact on Yield.

Purple spot disease of asparagus, caused by the fungus Stemphylium vesicarium, results in lesions on spears and ferns and defoliation of ferns. In two newly established commercial asparagus fields (cvs. Jersey Giant and Jersey Knight), chlorothalonil or mancozeb was applied every 7, 10, or 14 days or according to Tom-Cast with a threshold of 15 disease severity values, and not applied to the control. Tom-Cast prompted four sprays, resulting in a 60% reduction in the number of fungicide applications when compared with the 7-day-interval treatment. When disease pressure was severe, lesions on ferns were significantly less for both cultivars when fungicides were applied according to Tom-Cast or every 7 days compared with spray intervals of 10 or 14 days. Applying fungicides according to Tom-Cast or every 7 days resulted in an increased Jersey Giant fern stand compared with applying fungicides every 10 or 14 days. Unsprayed control plots yielded 77 to 83% (depending on cultivar) of those plots treated according to Tom-Cast using chlorothalonil. Significantly higher yields of Jersey Knight were obtained for chlorothalonil versus mancozeb. When mancozeb was used, Jersey Knight yield was significantly increased with a 7-day versus Tom-Cast application regime. Using chlorothalonil in a Tom-Cast program provided a benefit per hectare (BPH) of $1,005.24 (Jersey Knight) to $2,057.69 (Jersey Giant). In comparison, using mancozeb in a Tom-Cast program provided a BPH of -$484.27 (Jersey Knight) to $1,030.55 (Jersey Giant) over a 2-year period.

Early Brown Rot Infections in Sweet Cherry Fruit Are Detected by Monilinia-Specific DNA Primers

ABSTRACT Visible and nonvisible quiescent infections of immature and mature fruit are an integral component of the disease cycle of brown rot of sweet cherry in California. Detection of these infections is critical for developing efficient and efficacious fungicide management programs. The previously published DNA amplification primers mfs3 and NS5 for the identification of Monilinia fructicola were very specific in amplifying DNA of M. fructicola only and not M. laxa. This primer set, however, only detected DNA from some of the California isolates of M. fructicola. This genetic diversity was supported by random amplified polymorphic DNA (RAPD) analysis. Using eight 10-mer primers, seven M. fructicola isolates from California were all identified as genetically distinct. Using the same primers, only one polymorphism was detected among seven isolates of M. laxa. The multiple genotypes identified within the small population sample of M. fructicola, but not of M. laxa, using RAPD analysis could be indicative of genetic recombination within M. fructicola but not within M. laxa. To detect early brown rot infections in fruit, two primer sets that were developed from DNA sequences of either ribosomal DNA (MF5/ITS4/ITS3) or a RAPD fragment (X-09intF3/X-09R) specifically amplified DNA from isolates of M. fructicola and Monilinia species, respectively. No amplification products were present when using DNA from Botrytis cinerea or from other fungi commonly found on sweet cherry fruit. Primers X-09intF3 and X-09R were more sensitive and reliable for detecting small amounts of target DNA either extracted from conidia or from laboratory-inoculated cherry fruit with early brown rot infections that showed no visual symptoms or with visible quiescent infections. Furthermore, these primers also were effective for detecting visible quiescent infections in cherry fruit that were collected in the field.