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.     

Synergy of cymoxanil and mancozeb when used to control potato late blight

Summary Synergism between fungicides could be used to reduce the application dosage. Synergism between cymoxanil and mancozeb was studied using potted potato plants under field conditions. In three experiments the preventive efficacy of the fungicides and fungicide mixtures in the treatments were studied using a bio-assay. Potato plants were sprayed with the fungicides or fungicide mixtures. Leaves were picked from the potato plants with regular intervals after fungicide application. The efficacy of the fungicides was studied in a bioassay by inoculating the leaves withPhytophthora infestans zoosporangia. The Abbot method was used to show synergistic effects of the cymoxanil/mancozeb mixtures tested. In two of three experiments synergy of the fungicide mixtures was found.     

Challenges to Organic Potato Farming: Disease and Nutrient Management

For organic potato producers the two main challenges are disease and nutrient management. Both factors are limited by regulations that on the one hand prohibit the use of chemical fertilisers, especially nitrogen and, on the other hand, most synthetic pesticides. Late blight, caused by Phytophthora infestans is commonly thought to be the factor most limiting yield. However, because there is no really effective fungicide available to control late blight, there are virtually no yield loss data available for organic farming conditions. In this paper the state of the art of organic potato management with respect to disease and nutrient management is summarised. In a second part, the interactive effects of N-availability in the soil, climatic conditions and late blight were studied in the presence and absence of copper fungicides from 2002–2004 for the mid-early main-crop potato cv. Nicola. From the experimental work it became clear that copper fungicides in most cases do slow down epidemics adding an average of 3 days to the growth duration. However, only 30% of the variation in yield could be attributed to disease reduction. A model including disease reduction, growth duration and temperature sum from planting until 60% disease severity was reached, and soil mineral N contents at 10 days after emergence could explain 75% of the observed variation in yield. However, the model failed when N-supply was extremely high. The implications of the results on the management of organic potatoes with respect to cultivar choice, nutrient and disease management are discussed. In conclusion, several points emerge from the results: In organic farming, yields are foremost limited by nutrient availability in spring and early summer. The effects of late blight on yields may often be overestimated and cannot be deducted from results in conventional farming because of the strong interaction with nutrient status. Resistance clearly remains the most important strategy against late blight in organic potato production. However, as important or even more important than resistance is the early development and bulking behaviour and the ability of a cultivar to make use of organic nutrients efficiently. In the absence of efficient organic pesticides it is possible to reduce blight pressure to a certain extent by arranging the crop in small narrow fields perpendicular to the main wind direction neighboured either by non-hosts or completely resistant potatoes.     

Are there alternatives to copper for controlling grapevine downy mildew in organic viticulture?

Downy mildew caused by the obligate biotrophic oomycete Plasmopara viticola is one of the most important and devastating diseases of grapevine. Copper-based fungicides are used to control the disease in organic vineyards. However, since 2006, copper use has been limited by an European Commission regulation. In this study conducted from 2004 to 2007, we tested materials that might replace copper in organic viticulture, under controlled greenhouse and field conditions at two locations in Europe (northern Italy and Switzerland). We tested 112 different treatments, including biocontrol agents, materials of animal origin, homeopathic preparations, inorganic materials, microbial extracts, natural derivatives, plant extracts, physical methods and synthetic materials. Good control results were observed for two new copper formulations, but one of them induced phytotoxic effects. Two of the plant extracts provided good control on both leaves and clusters, and six of them controlled the infection on clusters only. One biocontrol agent reduced symptoms on leaves and bunches. Three of the other treatments provided good control on leaves, and four of them provided good control on bunches. Clay was as effective as copper on both leaves and bunches. Currently, even if there is no treatment that is as effective as copper for controlling grapevine downy mildew in organic vineyards, Yucca schidigera and Salvia officinalis extracts and Trichoderma harzianum, could be considered as promising candidates to be developed. This study may help the development of an integrated management program in which a less effective product is applied in combination with copper, to reduce the total quantities of copper applied.     

Interaction of dosage,spray interval and fungicide action in blister blight disease control in tea

Copper oxychloride at three dosage rates, nickel chloride at two rates and a combination of the two at three rates were tested against blister blight of tea (caused by Exobasidium vexans Massee) at six different treatment intervals from June to November, 1981. Under severe monsoon weather conditions, disease incidence exceeded the critical economic threshold limit with both fungicides when applied at intervals longer than 3 days. Only with the combination of copper and nickel was blister blight infection below the critical limit at 5-day spray intervals. When weather conditions were mild in October and November the treatment interval could be safely extended to 11 days with either copper or nickel alone, or both used together. The eradicant nickel chloride was superior to the protectant copper fungicide under severe weather conditions. A strong interaction was evident between dosage, treatment interval, the mode of action of the fungicide and weather conditions in blister blight disease control. The results point to the need in practice for short spray intervals with a copper-nickel combination at 210 g/ha of each from June to September and longer intervals thereafter, for maximum economic control.     

Changes in the distribution of phenylamide-resistant strains ofPhytophthora infestans (Mont.) de Bary in Ireland 1985–89

Summary Phenylamide-based fungicides were reintroduced to the Irish market in 1985. Mixtures of phenylamides and mancozeb were recommended for no more than 3 sprays in potato late blight control programmes with the last systemic spray to be applied not later than 31 July. Samples of potato foliage infected withP. infestans were collected from the main potato growing areas in Ireland over a five-year period starting in 1985. Using the floating disc method, 11% of the crops sampled in 1985 were found to have phenylamide-resistant strains ofP. infestans present. The number of crops with resistant strains increased rapidly up to 1988 when 83% of the crops sampled had resistance. Factors affecting the distribution of resistance and the efficacy of a phenylamide-based spray programme are discussed.     

河北省一季作区马铃薯病虫害发生及综合防控

河北省一季作区马铃薯主要病虫害有晚疫病、早疫病、黑痣病和二十八星瓢虫,此外,病毒引起的品种退化比较普遍,造成不同程度的损失。本文根据河北省一季作区马铃薯病虫害发生特点总结出一套综合防控技术体系,包括将马铃薯与玉米、大白菜等非茄科作物轮作3年减轻黑痣病危害;采用脱毒薯克服病毒引起的品种退化问题;种薯和(或)土壤消毒控制黑痣病和晚疫病;待马铃薯生长至封垄后,遇到适宜晚疫病发生的天气,喷施1～3次保护性杀菌剂预防晚疫病和早疫病;一旦监测到晚疫病中心病株后即拔除并装入塑料袋带出田外,并交替喷施有治疗效果、能兼治早疫病且作用机制不同的内吸性杀菌剂及混剂;田间出现马铃薯二十八星瓢虫成虫,在杀菌剂中混入高效氯氰菊酯或高效氯氟氰菊酯等高效杀虫剂防虫;马铃薯成熟前1～2周将地上部分割掉并运出田外后收获块茎。     

Potassium phosphite combined with reduced doses of fungicides provides efficient protection against potato late blight in large-scale field trials

Potato late blight caused by the oomycete Phytophthora infestans is a devastating disease of potato worldwide. Most of the potato cultivars grown in conventional agriculture are susceptible, or at best moderately resistant, and require frequent applications of fungicides to avoid heavy yield losses.In field trials spanning four years, we have investigated the effect of potassium phosphite, an inorganic salt on potato late blight. Potassium phosphite is known to induce defence responses in potato and to also have direct toxic effects on oomycetes, which in turn counteract late blight and tuber blight development. However, the use of this salt is not yet implemented and approved in European potato cultivation. We compared the effect of phosphite alone with fungicides currently used in Swedish potato cultivation. We also investigated the combined use of potassium phosphite and reduced doses of fungicides. Table potato cultivars and starch potato cultivars with different levels of resistance were used.We found that potassium phosphite in combination with reduced doses of fungicides results in the same level of protection as treatments with the recommended full dose of fungicides. These combined treatments reduce the need of traditional fungicides and may also decrease the selection pressure for fungicide resistance development in the pathogen. In relatively resistant starch potato cultivars using phosphite alone gave sufficient protection against late blight. Furthermore, in starch potato a combination of phosphite and fungicides at two-week intervals provided similar protection to weekly applications of fungicide at the recommended dose. Foliar treatment with phosphite also gave protection against tuber blight at similar levels to that of the best-performing fungicide. Our data suggests that potassium phosphite could be used in potato cultivation in temperate regions such as in Sweden, at least in combinations with reduced rates of fungicides. The implementation of the use of phosphite in practical potato crop protection as part of an IPM strategy is discussed. Doses, intervals and combinations could be adjusted to the level of cultivar resistance.     

Impact and Interaction of Nitrogen and Phytophthora infestans as Yield-limiting and Yield-reducing Factors in Organic Potato (Solanum tuberosum L.) Crops

For organic potato producers, the two main challenges are disease and nutrient management. Both are limited by regulations that on the one hand prohibit the use of chemical fertilizers, especially nitrogen, and on the other hand prohibit most synthetic pesticides. Late blight caused by Phytophthora infestans is commonly thought to be the most yield-reducing factor. However, because there is no really effective fungicide available to control late blight, there are virtually no yield loss data available for organic farming conditions. In this paper, the state of the art of organic potato tuber growth under on-farm conditions with respect to disease and nutrient management is summarized by field trials and on-farm surveys on commercial organic crops carried out in the years 1995–1998. Soil nitrogen (N) levels, plant N uptake, disease development of P. infestans and potato yield were measured. Results indicated that N availability was most important in limiting yields in organic potato crops. From on-farm data, a model including disease development, growth duration of the crops until foliage decay and different parameters related to N status of the crop could explain 73% of the observed variation in yield. Only 25% of this variation in yield could be attributed to the influence of late blight. Differences in N availability explained 48%. In conclusion, several points emerged from the results. In organic farming, yields are mainly limited by nutrient availability in spring and early summer. The effects of late blight on yields may often be overestimated and cannot be deduced from results in conventional farming because of the strong interaction with nutrient status. Depending on N availability, tubers stop growing between mid-July (70–90 kg N ha⁻¹ uptake), the end of July (110–140 kg N ha⁻¹ uptake) and mid-August (140–180 kg N ha⁻¹ uptake) due to N limitations. The higher the N status of a potato crop, the longer the growing period needed to achieve the attainable yield and the higher the probability that late blight stops further tuber growth and becomes the key tuber-yield-limiting factor. In the second part of this paper, the interactive effects of soil N availability and the impact of P. infestans on yield in the presence and absence of fungicides from 1996 to 1998 for mid-early main crops are reported. An empirical schematic model of disease impact depending on N availability was developed.     

Indications of soil borne inoculum ofPhytophthora infestans

Summary In this paper we present observations made during three years in a potato field in Sweden that indicated the presence of soil borne inoculum ofPhytophthora infestans. In 1994, a fungicide trial against late blight was left in the field with various degrees of late blight infection. In 1995, cereals was grown in the field. In 1996, certified potato seed tubers were planted and blight appeared early in the season in a pattern corresponding to the heavily infected areas in 1994. No volunteer potato plants were found in 1995 or 1996. Both mating types A1 and A2 were isolated in 1996 and 1997 and oospores were found in leaves, stems as well as in stolons.     

Evaluation of sprinkler application of fungicides for control of potato early blight in Colorado

Sprinkler application of four fungicides, Du-Ter 47.5% W.P. (0.70 kg/ha), Difolatan 4F (3.51 1/ha), Bravo W-75 (1.68 kg/ha) and Bravo 500 (1.17 1/ha, 1.761/ha and 2.341/ha) were evaluated in Colorado for control of potato early blight caused byAlternaria solani (Ellis & G. Martin) L.R. Jones and Grout and compared to the conventional method of airplane application. Fungicides applied through center pivot irrigation systems generally achieved disease control equal to airplane application. Application of fungicides through both center pivot sprinklers and by airplane effectively reduced early blight infection. Control of early blight by airplane or sprinkler application of fungicides significantly (P = 0.05) increased potato yields in 1978. In other years (1977, 1979 and 1980) fungicide applications which reduced disease severity generally increased tuber yields but the increases were not significant when compared to the control.     

Potato fungicides interfere with entomopathogenic fungi impacting population dynamics of green peach aphid

Fungicides applied to potato can enhance green peach aphid,Myzus persicae (Sulzer), outbreaks by interference with entomopathogenic fungi. (Order Entomophthorales). Late season aphid numbers were highest in potatoes sprayed with metalaxyl + mancozeb, captafol, or mancozeb, and lowest in potatoes sprayed with benomyl, triphenyltin hydroxide, chlorothalonil, or copper hydroxide. In field-collected aphids,Pandora (= Ernyia) neoaphidis (Remaudière et Hennebert) andEntomophthora planchoniana Cornu (F. Entomophthtoraceae) were the predominant cause of mycoses, 66.7% and 22.3%, respectively.Conidiobolus obscurus (Hall and Dunn) Remaudièe and Keller (F. Ancylistaceae) accounted for 8.5% of mycoses. In the laboratory, fungicides were shown to have direct effects on these entomopathogens. Metalaxyl + mancozeb, mancozeb and captafol were strongly inhibitory of germination of conidia, copper hydroxide was intermediate, and chlorothalonil had little effect. Triphenyltin hydroxide, benomyl, metalaxyl + mancozeb, and mancozeb were strongly inhibitory of growth of mycelia, copper hydroxide was intermediate, and chlorothalonil and copper hydroxide had least effect. Benomyl was highly toxic to green peach aphid, copper hydroxide and chlorothalonil intermediate, and captafol, mancozeb, and metalaxyl + mancozeb least toxic. Possible interference of potato fungicides with aphid pathogens is now an important consideration because of the intensity of spraying required to protect the crop from infection by metalaxyl-resistant strains of the late blight pathogen,Phytophthora infestans (Mont.) de Bary. Minnesota potato growers reported high green peach pressure in both 1995 and 1996, years of intensive fungicide spraying. Concomitantly, there was a marked increased in the incidence of PLRV in seed lots entered for winter testing.     

Differential diagnosis ofVerticillium dahliae in potato with antisera to partially purified pathogen-produced extracellular antigens

Summary An extracellular protein-lipopolysaccaride antigen (PLP) was purified from culture fluids ofVerticillium dahliae. Antiserum produced in rabbits to the PLP detected the antigen in homogenates of tubers, stems and leaves ofV. dahliae-infected potato plants but not in extracts of healthy potato tissue or extracts of potato plants infected by other fungal pathogens. The antigen was not detectable in extracts of potato isolates ofV. tricorpus, V. nigrescens andV. nubilum or various other fungi. The antigen was shown to be different from cross-reactive antigens detected by antisera to mycelial antigens. When used as a tool for specific diagnosis ofV. dahliae infection in potato, antiserum to PLP was more reliable than that prepared against fungal body antigens. Publication of the Agricultural Research Organization No 245-E.     

5种药剂对马铃薯晚疫病的防治效果分析

试脸在田间测定了克露、迭克宁、银法利、瑞凡和中药杀菌剂5种药剂对马铃薯晚疫病的防治效果。结果表明：5种药剂对马铃薯晚疫病均具有明显的防治效果和增产效果,防治效果最好的是银法利,其次为瑞凡、达克宁、克露和中药杀菌剂,增产62%-155％,晚疫病烂薯率为1．20％-8．09％。根据病害发展曲线,病害发展前期使用5种药剂。均可达到显著防治效果。病害发展后期,建议选择银法利和瑞凡药剂。注意每种药剂交替使用,避免产生抗药性。     

Application of acibenzolar-S-methyl and standard fungicides for control of Phytophthora blight on squash

A plant systemic acquired resistance inducer, acibenzolar-S-methyl (ASM), was evaluated to determine the efficacy for suppression of Phytophthora blight of squash caused by Phytophthora capsici under field conditions. ASM was applied as foliar sprays before and after transplanting at rates of 17.5, 8.8, and 4.4 g a.i. ha⁻¹. Application of ASM did not significantly reduce final Phytophthora blight incidences in 2 out of 3 field experiments; however, area under the disease progress curve (AUDPC) values were reduced significantly by ASM in all experiments conducted. Disease suppression by the three application rates of ASM was not significantly different. To determine the effect of application of ASM in conjunction with standard chemical fungicides, ASM was applied with mefenoxam (Ridomil Gold), copper hydroxide, and mandipropamid (Revus). AUDPC values and final disease incidences were consistently lower in field plots treated by the combination of ASM and standard fungicides than applications of these chemicals alone. Application of ASM resulted in significantly higher squash yield than the non-treated control in 2 of 3 experiments and plots treated with the combined use of ASM and standard fungicides produced the highest yields. These results suggest that ASM may induce plant resistance under field conditions, providing suppression of Phytophthora blight of squash, and that there may be some benefit to the integration of ASM and standard chemical fungicides.     

Assessment of retention and persistence of copper fungicides on orange fruit and leaves using fluorometry and copper residue analyses

High volumes of copper hydroxide, cuprous oxide and copper oxychloride were sprayed under natural conditions onto mature orange trees to compare the retention on citrus leaves and fruit over a period of 56 days by means of copper residue analyses and a spray deposition assessment protocol using fluorometry, photomacrography and digital image analyses. Rainfall and increase in fruit size were also recorded to determine if it had an influence on weathering of copper residues. Initial retention following application of the different fungicides differed on Valencia leaves and fruit: applications with cuprous oxide retained significantly more copper residue and fluorescent pigment, while copper hydroxide retained higher copper and pigment levels on Navel leaves and fruit. Nonetheless, persistence of copper residues deposited by the three copper fungicide formulations was similar and decreased at the same tempo during both seasons; initially a fast reduction (48 and 60% for year one and two respectively) in residue during the first 14 days followed by a more gradual decline (41 and 24% for year one and two respectively) from 14 to 56 days. The loss of copper residues was attributed to weathering (days after treatment), fruit growth and cumulative rainfall as these factors were inversely correlated with copper residue levels (Pearson's r = −0.840, −0.722 and −0.733 respectively). A 76% and 90% correlation was observed between the copper residue analyzed and the quantitative fluorescent pigment measurements on mature leaves and fruit, respectively; showing that fruit is more reliable for fluorometry analyses and that this technique proved to be an effective tool for spray deposition and persistence assessment of copper fungicides. All copper formulations tested at these registered rates at 35-day spray intervals were effective in controlling Guignardia citricarpa.     

The economic impact of potato late blight on US growers

Summary Potato growers have been able to control the fungus,Phytophthora infestans, that causes late blight with fungicides, but at an increasingly higher cost. A Delphi survey was conducted with thirteen experts to estimate the impact of late blight on potato yields, storage losses and fungicide use. It was estimated late-blight fungicides cost $77.1 million and lost revenue for US growers was an additional $210.7 million. These total costs, which average $507 per hectare, do not include non-fungicide control practices.     

不同杀菌剂对马铃薯晚疫病的防治效果

通过田间试验调查,研究了7种化学药剂对马铃薯植株和薯块晚疫病的防治效果。结果表明:7种药剂对马铃薯晚疫病均可达到显著防治效果。防治效果最好的4种药剂为25%瑞凡、50%福帅得、0.5%苦参碱和30%甲霜.嘧菌酯,防治效果均达到80%以上;其次为45%三苯乙酸锡和68.75%银法利,防治效果达到70%以上;较差为52.5%抑快净,防治效果达到65%。建议在生产上交替使用,避免产生抗药性。     

Toxicity of some pesticides to Trichoderma viride Pers.

The toxicity of several fungicides, insecticides and acaricides to the important biological control agent Trichoderma viride Pers. has been evaluated in the laboratory. The effects of the pesticides on the spores and mycelium of T. viride and on the antagonistic activity of this fungus to Fusarium graminearum are reported. The insecticides cypermethrin, deltamethrin, fenvalerate, kelevan, carbaryl, carbaryl plus gamma-HCH (lindane), dimethoate, trichlorfon, diazinon, ethion and permethrin and the fungicides wettable sulfur, quinomethionate, dinocap, copper oxychloride and folpet were non-toxic to both the spores and the mycelium of T. viride.     

Application of fungicides to reduce yield loss in anthracnose-infected lupins

A range of fungicides were evaluated for control of anthracnose (Colletotrichum lupini) in lupin. Glasshouse investigation identified fungicides that reduced disease severity with varying degrees of efficacy. When applied 1 d prior to infection, azoxystrobin, chlorothalonil, mancozeb and copper oxychloride fungicides were highly effective. Systemic fungicides such as tebuconazole, benomyl and carbendazim were less effective. Application timing was important; fungicides such as chlorothalonil and mancozeb were less effective when applied 5 d prior to infection compared with 1 d prior. Application after infection was ineffective for all fungicides. In field experiments application of azoxystrobin, mancozeb or chlorothalonil during flowering and podding reduced incidence of anthracnose infection on pods. Yield responses occurred in moderately susceptible, moderately resistant or resistant cultivars. Seed infection was reduced but not eradicated. Application of foliar fungicides for anthracnose control is potentially a viable management option for lupin production in high anthracnose risk areas of Western Australia.