Protectant Fungicides Research Articles

Field evaluation of weather-based spray programs for the control of downy mildew of lettuce (Lactuca sativa), caused by Bremia lactucae, in Quebec and Ontario

Each year, downy mildew caused by Bremia lactucae occurs in lettuce-producing regions of Quebec and Ontario. Trials were conducted to determine if the disease could be managed with fewer fungicide applications, using disease forecasting. Disease-forecasting programs designed to time the application of fungicide sprays were evaluated for control of downy mildew of lettuce in 1997 and 1998 at 9 field sites. Disease forecasting was based on lesion development following a recorded sporulation-infection period (SIP), with leaf wetness between 3:00 AM and 10:00 AM and temperature between 5 and 20 °C. Presymptom sprays with the protectant fungicide mancozeb were applied before lesions were expected; they were based on 110 accumulated degree-days following a SIP, but not within 7 days of a previous spray. Post-latent-period sprays with the systemic fungicide metalaxyl-M in combination with mancozeb were applied after forecasted lesion development; they were based on 135 accumulated degree-days, but not within 14 days of a previous spray. The effects of forecasted sprays were compared with those of weekly applications of mancozeb and with those of metalaxyl-M or metalaxyl applied in furrow at the time of seeding or transplanting. Downy mildew developed at 7 of the 9 sites. The number of SIPs recorded at all sites ranged from 7 to 17. In 8 of the 9 sites, there were fewer mancozeb applications with the presymptom program than with the weekly sprays, that is a reduction of one, two, and three sprays at six, one, and one sites, respectively. This resulted in a 16%–60% reduction in applied fungicide. When metalaxyl-M plus mancozeb was applied according to the post-latent-period forecast, one or two sprays were required, that is a reduction of two, three, and four applications at four, three, and two sites, respectively, compared with the weekly application of mancozeb alone. Metalaxyl-M or metalaxyl applied in furrow provided control for 30–40 days after seeding or transplanting. The number of fungicide applications can be reduced with acceptable disease control if a forecasting program is followed.

Evaluations of New and Current Management Strategies to Control Phomopsis Cane and Leaf Spot of Grape

To extend our understanding of the epidemiology and control of Phomopsis cane and leaf spot of grape, caused by Phomopsis viticola, studies were conducted to: (i) determine efficacy of a dormant fungicide spray program for controlling the disease in its early stage of development (e.g., spring); (ii) evaluate a disease warning system by applying fungicides and fungicide-adjuvant combinations in response to predicted infection periods based on weather conditions; and (iii) correlate commercial control practices and environmental conditions with disease incidence based on a state-wide survey of commercial fields. With the warning system, control was equal to that obtained with a 7-day protectant fungicide program, but with fewer fungicide applications per season. A dormant application provided consistent, yet only moderate, control of the disease. Growers who applied a dormant-season application or early spring protectant fungicides tended to have lower disease incidence than those who did not. There was high variability in disease incidence within vineyards and farms, but no significant difference in incidence among regions of the state. Overall, early season application of protective fungicides was shown to be a key factor for successful management of P. viticola. Accepted for publication 29 March 2007. Published 26 July 2007.

Development of Alternaria leaf blight on north Australian cotton (Gossypium hirsutum), species prevalence, and its control using mancozeb

Alternaria leaf blight is the most prevalent disease of cotton in northern Australia. A trial was conducted at Katherine Research Station to determine ( i) the efficacy of the protectant fungicide mancozeb on disease suppression, and subsequent yield and quality of upland cotton; ( ii) the disease development at various canopy levels; and ( iii) the prevalence of the Alternaria pathogen during the cotton growing season. The protectant fungicide, mancozeb, significantly ( P < 0.05) reduced disease incidence ( 85% to <= 74%), severity ( 2 to <= 1.94) and leaf shedding ( 1.59 to <= 1.32). It also reduced disease severity on cotton bolls from 2.28 ( control) to <= 1.04 ( fungicide treated). No significant effects of Alternaria leaf blight were observed on the yield and quality of cotton fibre. Significantly ( P < 0.05) higher disease incidence, severity and defoliation were observed at the lower canopy ( 1-7 nodes) level irrespective of treatments. The middle canopy ( 8-14 nodes) had the next highest incidence, severity and defoliation. The least disease and defoliation were observed at the top canopy level ( 15+ nodes). Disease development at various canopy levels of cotton plants during the growing season were predicted by a logistic model ( R-2 ranges from 0.58 to 0.98). For all treatments, predicted disease development on control plots was faster than that on treated plots. A. macrospora was the most prevalent pathogen during the early growing season and A. alternata was more prevalent towards the end of the growing season. In total, 16-65% of lesions were colonised by both A. macrospora and A. alternata.

사과 경엽 살포용 살균제의 겹무늬썩음병균에 대한 포자형성 억제작용과 그것이 병 방제에 미치는 영향

Control of white rot which is one of the most serious apple diseases in Korea has mainly relied on periodical spray of protective fungicides. As the main inoculum source of the disease is pycnidiospores produced in the warts formed on affected stems of apple tree, it can be conceivable that inhibition of spore production might be an effective means for controlling the disease. Inhibitory efficacy of eight selected fungicides against sporulation of the fungus was assessed by counting the number of spores produced at detached warts treated with the fungicides of recommended dilution. They showed diverse effect on sporulation. Carbendazim and azoxystrobin suppressed sporulation almost completely, the former irreversively. Thiram and folpet promoted sporulation as producing much more number of spores than untreated control. Others showed almost no effect on sporulation. Effects of suppression and promotion in the sporulation shown by the fungicides on the control of white rot were examined by incidences of disease and infection at the plots adopted the spray programs of which the fungicide at late May was substituted by carbendazim, azoxystrobin, folpet and thiram, respectively. Disease incidence and infection frequency at the plots sprayed former two chemicals which suppressed sporulation were much lower than those of the plots adopted latter two chemicals and untreated plot at which the fungicide spray was skipped at that time. These facts were reconfirmed in the experiments conducted with carbendazim and thiram, in which 100 fruits were bagged just prior to each spray from late May to late July for elucidating the effect of the two fungicides on the action of subsequent ones. Disease incidence and infection frequency on the fruit bagged just prior to each spray were gradually increased as the seasons going on. The increase rate at the carbendazim plot was much lower than that of thiram. Especially, the fruit infected till late July at the carbendazim plot were almost completely cured by the three fungicides, iminoctadine-triacetate, tebuconazole and samzinwang, a combined formular of iminoctadine-triacetate and difenoconazole, sprayed at late July and hence. In thiram plot, infected fruit were also cured by the 3 fungicides but not remarkable. From these results, it can be concluded that control efficiency of white rot can be greatly enhanced by selecting the fungicide capable of suppress the sporulation of white rot fungus at the season when the mass dispersal of spores is not initiated.

Analysis of Factors That Influence the Epidemiology of Sclerotinia minor on Peanut.

In North Carolina, sclerotia of Sclerotinia minor germinate myceliogenically to initiate infections on peanut. The effects of soil temperature and soil matric potential (ψM on germination and growth of S. minor have not been well characterized, and little is known about relative physiological resistance in different parts of the peanut plant. Laboratory tests examined the ability of the fungus to germinate, grow, and infect detached peanut leaflets at soil temperatures ranging from 18 to 30°C at ψM of -100, -10, and -7.2 kPa. In addition, detached pegs, leaves, main stems, and lateral branches from three peanut lines varying in field resistance were examined for resistance to infection by S. minor. Sclerotial germination was greatest at 30°C and ψM of -7.2 kPa. Final mycelial diameters decreased with decreasing ψM, whereas soil matric potential did not affect lesion development. Mycelial growth and leaflet lesion expansion were maximal at 18 or 22°C. Soil ψM did not affect leaflet infection and lesion expansion. Lesions were not observed on leaves incubated at temperatures of 29°C or above, but developed when temperatures were reduced to 18 or 22°C 2 days after inoculation. Pegs and leaflets were equally susceptible to infection and were more susceptible than either main stems or lateral branches. Results of this work, particularly the effects of temperature on S. minor, and knowledge of peanut part susceptibility has application in improving Sclerotinia blight prediction models for recommending protective fungicide applications.

Comparison of deposition patterns in two programs for applying protectant fungicides to potato stems and leaves for the control of late blight (Phytophthora infestans)

Fungicides are applied by air, chemigation, and ground in the Columbia Basin of Oregon and Washington. These methods of fungicide application differ in deposition of fungicide to the canopy and cost. This study compared the alternate use of air and chemigation application of fungicides (AIRCHEM) with chemigation alone (CHEM), by either measuring chlorothalonil or manganese (mancozeb) amounts in three canopy levels (upper, middle, lower), both on leaflets and stems, after multiple fungicide applications on a 7-day schedule. Greater amounts of chlorothalonil or mancozeb were usually found on the leaflets in the upper and middle canopy locations from AIRCHEM compared to CHEM, the day of fungicide application and 7 days later. Deposition of fungicides on stems generally follow the same pattern as leaflets, but the amount deposited and maintained on stems was significantly less than leaflets. Mancozeb deposition in the three canopy levels followed the same pattern as was found for chlorothalonil. The greater the amounts of chlorothalonil on leaflets and stems resulted in better disease reduction during inoculation assays. Reduced fungicide amounts on stems compared to leaflets may be the reason for increased stems infections in recent years by more aggressive strains of late blight. This is the first report quantifying chlorothalonil or mancozeb amounts on potato stems and the first to report amounts of mancozeb on potato foliage after fungicide application.

상주 지역 감나무로부터 분리한 Colletotrichum gloeosporioides 균주들의 방제 약제에 대한 반응

상주 지역의 곶감용 감 생산 농가의 과수원으로부터 채집한 탄저병 감염 부위로부터 90 개의 감 탄저병균 (Colletotrichum gloeosporioides)을 분리하였다. 두 종의 benzimidazole계 약제 (thiophanate-methyl, carbendazim), 3 종의 egosterol 합성 저해제 (difenoconazole, myclobutanil, tebuconazole) 및 4 종의 보호 살균제 (propineb, mancozeb, chlorothalonil, dithianon) 등 총 9 종의 살균제에 대하여 분리한 균주들의 약제반응을 조사하였다. 상용농도로 약제가 첨가된 배지에서 대조구 대비 균사생육지수를 평가함으로서 조사하였다. Carbendazim(<TEX>$415{\mu}g/ml$</TEX>)과 thiophanate-methyl(<TEX>$750{\mu}g/ml$</TEX>) 에 대한 반응은 각각 82%와 78%의 균주가 0.1 이하의 대조구 대비 균사생육지수를 보였다. 모든 실험 대상 균주는 myc1obutanil(<TEX>$40{\mu}g/ml$</TEX>)과 tebuconazole (<TEX>$75{\mu}g/ml$</TEX>)이 첨가된 배지에서 균사생육이 완전히 억제되었으며, difenoconazole(<TEX>$50{\mu}g/ml$</TEX>)이 첨가 배지에서는 단지 l 균주만이 0.03 의 대조구 대비 균사생장지수를 보였다. 4 종의 보호 살균제 중 propineb(<TEX>$1,500{\mu}g/ml$</TEX>) 에 대한 감수성이 가장 높게 나타났다. In 2005, 90 isolates of Colletotrichum gloeosporioides causing persimmons tree anthracnose were obtained from infected twigs and fruits of persimmon trees. Their responses to nine fungicides, consisting of two benzimidazoles (thiophanate-methyl, carbendazim), three ergosterol-biosynthesis inhibitors (difenoconazole, myclobutanil, tebuconazole), and four protective fungicides (propineb, mancozeb, chlothalonil, and dithianon), were investigated with relative mycelial growth index to untreated control on PDA treated with field application rate of each fungicide. At response to carbendazim (<TEX>$415{\mu}g/ml$</TEX>) and thiophanate-methyl (<TEX>$750{\mu}g/ml$</TEX>), 82% and 78% of isolates showed relative mycelial growth index under 0.1 to untreated control, respectively. All of them did not grow on PDA incorporated with myclobutanil (<TEX>$40{\mu}g/ml$</TEX>) and tebuconazole (<TEX>$75{\mu}g/ml$</TEX>). Only one isolate (PER 36) grew on PDA amended with difenoconazole (<TEX>$50{\mu}g/ml$</TEX>), but its relative mycelial growth index to untreated control was very low with a values of 0.03. They were most sensitive to propineb (<TEX>$1,500{\mu}g/ml$</TEX>) among four protective fungicides.

Effect of Leaf Rust on Grain Yield and Yield Traits of Durum Wheats with Race-Specific and Slow-Rusting Resistance to Leaf Rust.

Leaf rust, caused by Puccinia triticina, is an important disease of durum wheat (Triticum turgidum) in many countries. We compared the effectiveness of different types of resistance in International Maize and Wheat Improvement Center-derived durum wheat germ plasm for protecting grain yield and yield traits. In all, 10 durum wheat lines with race-specific resistance, 18 with slow-rusting resistance, and 2 susceptible were included in two yield loss trials sown on different planting dates in Mexico with and without fungicide protection under high disease pressure. Eight genotypes with race-specific resistance were immune to leaf rust. Durum wheat lines with slow-rusting resistance displayed a range of severity responses indicating phenotypic diversity. Mean yield losses for susceptible, race-specific, and slow-rusting genotypes were 51, 5, and 26%, respectively, in the normal sowing date trial and 71, 11, and 44% when sown late. Yield losses were associated mainly with a reduction in biomass, harvest index, and kernels per square meter. Slow-rusting durum wheat lines with low disease levels and low yield losses, as well as genotypes with low yield losses despite moderate disease levels, were identified. Such genotypes can be used for breeding durum wheat genotypes with higher levels of resistance and negligible yield losses by using strategies that previously have been shown to be successful in bread wheat.

Sensitivity of Uncinula necator to quinoxyfen: evaluation of isolates selected using a discriminatory dose screen

Quinoxyfen is a protectant fungicide that provides excellent control of many powdery mildew diseases. Prior to the launch of quinoxyfen in vines in 1998, a leaf disc sporulation assay was developed to assess the sensitivity of Uncinula necator (Schw) Burr to quinoxyfen. The distribution of EC(50) values from 56 monoconidial U. necator isolates collected from six countries between 1993 and 1996 was found to range from less than 0.03 to 2.6 mg litre(-1). Although this range of EC(50) values was quite broad, the inability to establish a minimum inhibitory concentration (MIC) for the majority of these isolates, including some of the most sensitive isolates, was unexpected and suggested that the leaf disc sporulation assay may not reflect the true activity of quinoxyfen in the field. In 2002, following the detection of isolates resistant to quinoxyfen in Blumeria graminis Speer f. sp. tritici Marchal, a discriminatory dose screen was developed to test large populations of U. necator for rare individuals with significantly decreased sensitivity to quinoxyfen. The individual isolates selected by this method were tested with the leaf disc sporulation assay. Although a significant proportion were found to have EC(50) values within the original distribution, a number of isolates with apparent reduced sensitivity to quinoxyfen were also detected. However, further examination of a subset of these isolates in a more quantitative germination/germ tube elongation inhibition assay suggested that the magnitude of the reduction in sensitivity for some of these isolates was much less than predicted by the sporulation assay. Thus, for an exclusively protectant fungicide such as quinoxyfen, a leaf disc sporulation assay may overestimate the frequency of isolates with significantly reduced sensitivity and the threat of decreased performance due to resistance.

다양한 작물로부터 분리한 탄저병균(Colletotrichum spp.)의 살균제에 대한 반응

This study has been conducted to investigate the responses of various isolates of four Colletotrichum species such as C. gloeosporioides, C acutatum, C. coccodes, and C. dematium isolated from infected tissues of several crops to fungicides such as carbendazim, carbendazim+diethofencarb, four protective fungicides, and three ergosterol biosynthesis-inhibiting (EBI) fungicides. All the isolates of C. acutatum showed values in a range of 0.001-3.040 against carbandazim, a benzimidazole fungicide. As for the response to carbendazim, the isolates of C. gloeosporioides obtained from pepper, apple, and strawberry were clearly divided into two groups, resistant or sensitive isolates. All the resistant isolates showed values above 1000 , whereas the sensitive isolates had lower values than 0.550 . The isolates of C. gloeosporioides exhibited a negative cross resistance between carbendazim and diethofencarb (a N-phenylcarbamate fungicide), but isolates of C. acutatum did not. Toward carbendazim, C. coccodes and C. dematium isolates showed a similar response to C. acutatum isolates and the sensitive isolates of C. gioeosporioides, respectively. As for response of Protective fungicides, all the isolates of C. acutatum showed a more resistant reaction than all the isolates of C. gloeosporioides. However, there was no difference among 4 species of Colletotrichum against EBI fungicides.

The effect of a preparation from Chaetomium fungi on the growth of phytopathogenic fungi

We studied the fungicidal activity of a biological preparation from the fungi of the genus Chaetomium against soil phytopathogenic fungi Rhizoctonia solani and Fusarium oxysporum. The inhibitory effect of the preparation under study depended on its concentration, duration of storage, and growth characteristics of pure cultures of the phytopathogens. The highest (98.8%) inhibitory activity was observed on day 3 of the interaction with Rhizoctonia solani. After a 2-year storage, this preparation was capable of inhibiting the growth of the phytopathogens only at high doses. The preparation precluded the development of bare patch and increased the productivity of potato plants. The preparation may serve as an alternative to chemical fungicides for plant protection.

보호용 살균제와 ergosterol 생합성 저해 살균제에 대한 고추 탄저병균의 약제 반응

전국의 고추 재배지에서 1999년과 2002년에 채집한 병든 고추로부터 각각 130개와 258개의 고추 탄저병균을 분리한 후, 4종의 보호용 살균제와 3종의 ergosterol생합성 저해 살균제에 대한 균사 생장 저해 정도를 측정함으로서 살균제들에 대한 저항성 모니터링을 실시하였다. 1999년에 분리한 균주는 세 가지 보호용 살균제, 즉 dithianon, chlorothalonil 및 propineb에 대해서는 2002년의 균주보다 더 저항성을 보였다. 이에 반하여 다른 보호용 살균제인 iminoctadine에 대해서는 오히려 2002년의 균주가 더 저항성인 것으로 나타났다. 세 개의 ergosterol 생합성 저해(EBI) 살균제, 즉 tebuconazole, hexaconazole 및 prochloraz에 대해서는 2002년의 균주가 1999년의 균주보다 더 저항성이 컸으며, 2002년도의 균주들의 <TEX>$EC_{50}$</TEX> 값은 1999년 균주들보다 1.2배 내지 4.4배가 높았다 위의 살균제들에 대한 탄저병균의 반응을 보면, 채집한 지역 간에 저항성을 차이가 크게 나타나고 있었다. 단기간내에 충북에서 분리한 균주들은 채집한 시기가 늦어질수록, 고추의 생육 초기에 주로 많이 사용되는 보호용 살균제들에 대한 <TEX>$EC_{50}$</TEX>값은 감소하였다. 그러나 ergosterol 생합성 저해 살균제에 대한 균주들의 반응은 정해진 생육 기간 중에는 변화가 거의 없었다. In 1999 and 2002, 130 and 258 isolates of Colletotrichum spp. causing red pepper anthracnose were obtained from infected red pepper fruits, respectively. Their responses to 4 protective and 3 ergosterol biosynthesis-inhibiting(EBI) fungicides were investigated by observing their mycelial growth on PDA incorporated with different concentrations of each fungicide. The Colletotrichum isolates obtained in 1999 showed higher <TEX>$EC_{50}$</TEX> values than those isolated in 2002 against three protective fungicides such as dithianon, chlorothalonil, and propineb, whereas the response was reversed toward other protective fungicide, iminoctadine. On the other hand, the isolates of year 1999 were more resistant against three EBI fungicides such as tebuconazole, hexaconazole, and prochloraz than those of year 2002; the <TEX>$EC_{50}$</TEX> values of the former were 1.2-4.4 times higher than those of the latter, The responses of the Colletotrichum isolates toward protective and EBI fungicides were fluctuated according to regions, where the infected fruits were collected. On the other hand, the resis tance of Colletotrichum isolates to protective fungicides increased during monitoring from July to September, However, their responses towards EBI fungicides were not changed.

Sensitivity of Brazilian Isolates of Phytophthora infestans to Commonly Used Fungicides in Tomato and Potato Crops.

Isolates of the US-1 and BR-1 clonal lineages of Phytophthora infestans, collected from tomato and potato fields of two main producing regions of Brazil (south and southeast), were tested for sensitivity to the systemic fungicide metalaxyl, plus the three protectant fungicides mancozeb, chlorothalonil, and cymoxanil. For metalaxyl, one agar test and two leaf-disc tests were carried out. For all tests, metalaxyl insensitive (I), intermediately insensitive (II), and sensitive (S) isolates were detected. There was no association among metalaxyl sensitivity and region, lineage, or host. In the agar test, 35.0% of 210 isolates were classified as I, 36.0% as II, and 29.0% as S. US-1 isolates were classified as 36.1% I, 30.6% II, and 33.3% S. BR-1 isolates were 33.3% I, 23.8% II, and 42.9% S. In leaf-disc test 1 (240 isolates tested), 24.3% were classified as I, 35.0% as II, and 40.7% as S. Isolates of US-1 were 21.0% I, 39.8% II, and 39.2% S, whereas BR-1 isolates were 36.0% I, 20.0% II, and 44.0% S. In leaf-disc test 2 (96 isolates tested), which was based on an effective dose for 50% sporulation inhibition (ED50), most isolates were either I (44.8%) or II (51.0%), and only three (4.2%) were S. The US-1 isolates were 46.0% I, 51.0% II, and 3.0% S. Isolates of the BR-1 lineage were 45.0% I, 52.0% II, and 3.0% S. For mancozeb, the ED50 for 53 of 59 isolates was below 1.0 μg/ml. No isolate grew on medium amended with more than 100 μg of chlorothalonil/ml and the ED50 for 38 of 50 isolates was below 1.0 μg/ml. For cymoxanil, the ED50 for all 47 isolates tested was below 1 μg/ml. There is no evidence of resistance of resistance of P. infestans to protectant fungicides commonly used in Brazil.

Efficacy of fungicidal protection of newly developing potato leaves against Phytophthora infestans

Three experiments aiming to explore the efficacy of fungicides to protect newly developing potato leaves were carried out between 2000 and 2002. Contact, translaminar and systemic fungicides were applied in field trials at Lelystad in the centre of the Netherlands. Efficacy of the fungicides was established using a bioassay in which detached new grown leaflets (cv Bintje) were inoculated with Phytophthora infestans. The interval between the last fungicide application and picking the leaves to be used in the bioassay varied between 4 and 11 d. Disease incidence was assessed after incubation for approximately a week. Protection of the newly developed leaves depended on the intrinsic property of the fungicides, time since the last fungicide application and growth rate of potato leaves in the field since the last fungicide application. Shorter time intervals between spraying and inoculation resulted in better (re)distribution of (contact) fungicides on newly developed leaves resulting in better protection. Also, there was less dilution of the fungicide due to less leaf expansion during a 4 d compared with 7 d spray interval. A similar effect occurs when crop growth rate decreases. Ridomil Gold MZ, with the systemic active ingredient metalaxyl and Ranman (cyazofamid) resulted in the best protection of newly developed leaves at the beginning of the growing season when crop growth rate was high. Contact fungicides containing cyazofamid or to a lesser extent, mancozeb can protect newly developing leaves, due to good redistribution of the compounds.

Dissipation of pencycuron in rice plant

Pencycuron is a non-systemic protective fungicide for controlling sheath blight of rice. However, information on the fate of pencycuron in rice plant is lacking. The degradation of pencycuron in waterlogged tropic rice field was investigated. Pencycuron was applied at recommended field dose (187.5 g a.i./ha) and double recommended dose to cropped plots for three consecutive years. Pencycuron was rapidly degraded in rice plant at all doses of pencycuron application with first order half-lives of 1.57 approximately 2.77 d. The study revealed that pencycuron is safe from the human and environmental contamination point of view.

Field comparison of sterol-biosynthesis-inhibiting fungicides used alone and in combination with protectant fungicides for apple scab control

Several sterol-biosynthesis-inhibiting (SBI) fungicides were tested alone and in combination with a broad-spectrum protectant material in field trials for control of Venturia inaequalis. When used in a 10-day spray schedule, SBI fungicides, whether used alone or in a mixture, provided improved scab control as compared to the protectant material used alone. With bitertanol, diniconazole, and penconazole, the mixture also provided better scab control than when the SBI fungicide was used alone. However, with flusilazole and myclobutanil, no improvement in disease control occurred with the mixture as compared to the SBI fungicide alone. Fruit russeting was observed after a post-bloom application of hexaconazole and growth-regulating effects on the foliage were observed following cyproconazole and hexaconazole use. The use of SBI fungicides in mixtures to avoid or delay the development of fungus resistance is discussed.

Toxicity of Fungicides to Urediniospores of Six Rust Fungi That Occur on Ornamental Crops.

The recent introduction and rapid spread of rust on daylilies, caused by Puccinia hemerocallidis, suggested a need for fungicide treatments that reduce urediniospore viability on plant surfaces. Twelve fungicides in seven chemical classes were evaluated in vitro for toxicity to urediniospores of rust fungi that occur on daylily (P. hemerocallidis), geranium P. pelargonii-zonalis), iris (P. iridis), oxalis (P. oxalis), mint (P. menthae), and Florida azalea (Pucciniastrum vaccinii). Germination of urediniospores of all six rust fungi on potato dextrose agar in the absence of fungicides ranged from 54 to 88%. Germination of urediniospores of all rust species during and after exposure to azoxystrobin, chlorothalonil, copper sulfate pentahydrate, mancozeb, and trifloxystrobin was less than or near 1%. Germination during exposure to fenhexamid, iprodione, myclobutanil, propiconazole, thiophanate-methyl, triadimefon, and triflumizole ranged from 0 to 60% and usually was greater (0 to 75%) after fungicide residues had been removed. Germination of urediniospores of P. pelargonii-zonalis decreased when exposed to azoxystrobin, copper sulfate pentahydrate, and mancozeb for 1 min and was nearly eliminated after a 30-min exposure, while exposure to trifloxystrobin and chlorothalonil eliminated germination after 4 and 8 h, respectively. Urediniospores that had been allowed to imbibe water for 4 h had no further germination or germ tube growth after a 24-h exposure to azoxystrobin, chlorothalonil, copper sulfate pentahydrate, mancozeb, and trifloxystrobin. Less than one lesion per plant developed on seedlings inoculated with urediniospores of P. pelargonii-zonalis that had been sprayed with azoxystrobin, chlorothalonil, copper sulfate pentahydrate, and mancozeb, whereas seedlings inoculated with spores not exposed to fungicides developed 148 lesions per plant. The strobilurin (azoxystrobin and trifloxystrobin), broad-spectrum protectant (chlorothalonil and mancozeb), and inorganic copper (copper sulfate pentahydrate) fungicides were fungicidal to urediniospores of the six rust fungi. However, the benzimidazole (thiophanate-methyl), dicarboximide (iprodione), hydroxyanilide (fenhexamid), and demethylation-inhibiting (myclobutanil, propiconazole, triadimefon, and triflumizole) fungicides were only fungistatic to rust urediniospores.

Control strategies with reduced fungicide input for Botrytis leaf blight in lily—a simulation analysis

Leaf blight, caused by the pathogen Botrytis elliptica (Berk.) Cooke, is the most important foliar disease in ornamental lily cultivation. The conventional control strategy of Dutch bulb growers is to apply protective fungicides at weekly intervals from crop emergence until harvest. We applied simulation models to complement experimental studies in the search for control strategies with less fungicide input at minimum yield loss.Effects of cultural measures that reduce primary infection, were investigated across 5 years of historic weather assuming season-specific influx patterns of only primary inoculum. The results indicate that reduction of influx of external primary inoculum by cultural measures is a necessary basis of an effective strategy to control fire disease in lilies. A modest degree of spatial isolation, i.c. maintaining a distance of at least 10m to fields where lilies were grown in the previous year, was much more effective than post-harvest measures aiming at reduced production or survival of sclerotia. Results showed that when cultural measures are combined with a relatively resistant cultivar, non-chemical control may well be a feasible option.Different chemical control strategies were evaluated across combinations of 5 years of historic weather and inoculum influx levels that had been derived in a previous study. Simulation results indicate that fungicide input can be strongly reduced, even with a highly susceptible cultivar and under a scenario of high disease pressure. Under such high-risk conditions, fungicides with a high initial and residual efficacy and weather forecasts of better-than-actual quality appear to be the prerequisites to make a warning system-based control strategy as reliable as the strategy with weekly applications of a low-cost fungicide.The conclusions concerning the strong beneficial effect of modest degrees of spatial isolation rely critically on our assumptions with regard to the dispersal distance of conidiospores. We therefore recommend that field studies on dispersal of B. elliptica spores be conducted, whereas system-level experiments are required to validate the conclusions.

Deposition and redistribution of fungicides applied by air and chemigation for control of late blight in commercial potato fields

The fungicides metiram, mancozeb, metiram + triphenyltin hydroxide, propamocarb hydrochloride + chlorothalonil, dimethomorph + mancozeb, cymoxanil + mancozeb, and chlorothalonil were applied by aircraft and through center-pivot irrigation systems (chemigation) to replicated plots in commercial fields of ‘Russet Burbank’ potato. Fungicide deposition and redistribution were indirectly determined by inoculation of excised leaves withPhytophthora infestans and directly by chlorothalonil residue analysis from upper, middle, and lower crop canopies. The effectiveness of two surfactants added with fungicide and applied by aircraft, an increased water volume rate used by aircraft, and a reduced water volume used with chemigation was also determined. The addition of synthetic latex and siliconepolyether surfactants did not increase efficacy of metiram or mancozeb in controlling late blight when applied by aircraft. The protectant fungicides metiram, mancozeb, and chlorothalonil were not significantly different from dimethomorph + mancozeb, cymoxanil + mancozeb, and propamocarb hydrochloride + chlorothalonil in late blight control when applied by aircraft. However, cymoxanil + mancozeb had limited efficacy when applied by chemigation. Fungicide deposition through the canopy differed when air applications were made before or after canopy closure (row closure). Fungicides applied by aircraft prior to row closure protected the entire canopy; whereas, fungicide application after row closure initially protected the top and middle canopies, and subsequent applications and redistribution of the fungicides were needed for adequate protection throughout the canopy. The fungicides and fungicide mixtures tested were evenly deposited throughout the potato canopy with each chemigation application. Severity of late blight did not differ on leaves treated with mancozeb or chlorothalonil applied by aircraft at water volumes of 47 L/ha and 94 I/ha and then inoculated withP. infestans, nor did severity of late blight differ on inoculated leaves previously treated with chlorothalonil by chemigation at water volumes of 15,145 and 50, 571 L/ha.

A PROBLEM CASE STUDY: INFLUENCE OF CLIMATIC TRENDS ON LATE BLIGHT EPIDEMIOLOGY IN POTATOES

A PROBLEM CASE STUDY: INFLUENCE OF CLIMATIC TRENDS ON LATE BLIGHT EPIDEMIOLOGY IN POTATOES