Failure of metalaxyl to eradicate late blight on potatoes (cv. Green Mountain)

Eradication of potato late blight with metalaxyl was examined in field studies from 1980 to 1983. In 1980 disease outbreak and subsequent progression were late and moderate. In 1981 and 1983, they were early and moderate to severe, while in 1982 the disease became established later in the season but developed rapidly and resulted in moderate to severe damage to foliage. There were no significant differences in foliar disease severity among metalaxyl treatments. While treated plots generally showed significantly less foliar damage throughout the season than untreated plots, except in 1983, the reduction in foliar damage in September was only 30–50% in 1980, 10–20% in 1981, 20–30% in 1982, and less than 10% in 1983. Sporulation of the pathogen occurred readily on infected leaves of both treated and untreated plants. There were no significant differences in yield, but application of metalaxyl to foliage significantly reduced the incidence of late blight tuber rot.     

Metalaxyl and other fungicides for control ofPhytophthora infestans on potato in northwest Washington State

In northwest Washington State, fungicidal control of late blight caused byPhytophthora infestons was evaluated for three years. During 1977, a high rainfall year with supplemental sprinkler irrigations, all metalaxyl and chlorothalonil treatments reduced tuber rot at harvest, but only metalaxyl extended control of tuber rot after 4 months’ storage. During 1978, a high rainfall year, one application of metalaxyl sprayed over or dusted on potato seed pieces at planting or applied five times to foliage at 2 or 4 wk intervals gave excellent blight control equal to that with chlorothalonil applied to foliage every 2 wk. In 1979, a low rainfall year,P. infestons did not kill plants in untreated plots until October. Five applications of metalaxyl sprayed every 2 wk on foliage did not control foliage blight. However, metalaxyl reduced foliage blight when dusted on cut potato seed pieces. Mancozeb sprayed every 2 wk also gave excellent control. The possibility that metalaxyl applied to foliage is effective in late blight control only when washed into the soil by rainfall or irrigation for uptake by roots is discussed. Yields and percent U.S. No. 1 grade tubers were not significantly affected by any treatment in these 3-year trials.     

Control of late blight (Phytophthora infestans (Mont.) de Bary) with fungicide applied by hydraulic and electrostatic sprayers

Summary Similar amounts of metalaxyl were deposited onto potato leaves on the middle and lower parts of the stem by different tractor-mounted sprayers, but much more was deposited onto apical leaves by an electrostatic sprayer. Late blight spread into plots from inoculated guard plants but was controlled by Fubol (metalaxyl+mancozeb) at least as well when applied electrostatically (4.4 or 91/ha) as hydraulically (200l/ha).     

Optical density variation in aerial photographs of potato plots infected withPhytophthora infestans

Optical density signatures were developed from infrared photographs of plots infected with late blight caused byPhytophthora infestans (Mont.) d By. Slight differences between optical density signatures of plots with different spray schedules preceded corresponding differences in infection levels that were not visually apparent on the date of photography but were visually apparent later. The technique of density signature development allowed consistent and quantitative differences to be recorded.     

Evaluation of fungicides to control circular leaf spot of persimmon caused by Mycosphaerella nawae

The efficacy of ten fungicides against Mycosphaerella nawae, the causal agent of circular leaf spot (CLS) of persimmon, was evaluated in vitro and in field experiments. Field trials were conducted in 2009 and 2010 to investigate the comparative efficacy of the fungicides alone or combined using alternating sequences in spray programmes based on two, three or four applications. Disease incidence was assessed by estimating the percentage of affected leaves, which included leaves showing at least one necrotic spot and defoliation. Fenpropimorph, pyraclostrobin, tebuconazole and thiophanate-methyl were the most effective fungicides in inhibiting mycelial growth of M. nawae isolates (EC₅₀ < 2 ppm). In field experiments, the most effective fungicides using two spray applications were captan, chlorothalonil, mancozeb and pyraclostrobin which significantly reduced disease incidence compared with untreated plots. Regarding the number of spray applications, two applications of captan and mancozeb were less efficient than three to control the disease. However, the percentage of affected leaves provided by three applications of captan and mancozeb alone or combined with pyraclostrobin using alternating sequences in spray programmes, was not significantly different from that provided by four applications. Experimental results demonstrated that spray programmes based on three applications of these fungicides could effectively control CLS of persimmon. The advantages of spray programmes based on alternated use of strobilurins and protective fungicides are discussed.     

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.     

Quantitative analysis of host resistance,fungicide and weather effects on potato early and late blight using computer simulation models

Models which simulate the development of potato early blight, potato late blight and fungicide dynamics were used to analyze the effects of host resistance, fungicide and weather on individual and combined epidemics of these diseases. Fungicide and host resistance effects were based on (and accurately reflected) products and cultivars available to commercial potato growers in northeastern USA. Moderate resistance to early blight had a 2-3 fold greater effect than did moderate resistance to late blight in suppressing early and late blight, respectively. Analysis of simulation experiments indicated that replacement of an early blight susceptible cultivar with a cultivar moderately resistant to the disease would permit a reduction in the fungicide application frequency from once every week to once every two weeks without loss of disease suppression. Fungicide effect in suppressing late blight was 2-3 fold greater than in suppressing early blight. Variation in seasonal weather (typical of northeastern USA) influenced late blight development more strongly than it affected early blight development, and it affected epidemics of individual diseases more than combined epidemics.     

Efficacy over time of cymoxanil mixtures in controlling late blight in potatoes incited by a phenylamide-resistant isolate of Phytophthora infestans

Field-grown potatoes (cv. Alpha) were sprayed with fungicides at the commercially recommended rates 0–15 days before being inoculated with a phenylamide-resistant isolate of Phytophthora infestans (Mont.) DeBary. Numbers of lesions, or disease severity, in fungicide-treated versus fungicide-free plants were used to calculate the percentage control efficacy of fungicides over time. Efficacy over time fitted a declining logistic model in 26 out of 31 cases. Non-transformed data showed a significantly longer duration of > 90% efficacy of the cymoxanil mixtures Mancur (mancozeb + cymoxanil, 4 + 1), Pulsan (mancozeb + oxadixyl + cymoxanil, 7 + 1 + 0 · 4) and Sandocur-M (mancozeb + oxadixyl + cymoxanil, 7+1+2) (9–11 days) compared with SAN-518 (mancozeb + oxadixyl, 7+1), Ridomil-MZ (mancozeb + metalaxyl, 1 + 7 · 5), mancozeb or Curzate (4–6 days). Predicted T₅₀ values (number of days with >50% efficacy) were significantly larger for Pulsan and Sandocur-M (16 days) than for Ridomil-MZ (11 days), SAN-518 (10 days), mancozeb (9 · 5 days) and Curzate (7 · 5 days). Numeric integration of the area under the predicted control efficacy curves gave significantly larger values for Pulsan and Sandocur-M compared with the other fungicides except Mancur. Linear regression of logit disease control values over time resulted in the smallest slope for Sandocur-M. Analysis of variance showed no significant interaction between fungicide and cumulative rain. We predict that Pulsan and Sandocur-M may effectively control phenylamide-resistant Phytophthora infestans in the field at 14-day spray intervals, and Mancur at 10-day intervals.     

Comparison of two strategies for use of translaminar and contact fungicide in the control of potato late blight in the highland tropics of Ecuador

Strategies based on using the translaminar fungicide cymoxanil for control of potato late blight, caused by Phytophthora infestans, were compared in the highland tropics of Ecuador in three separate field experiments. In one strategy, a commercial formulation of cymoxanil mixed with mancozeb was sprayed sequentially three times early in the season; this was then followed by three sequential sprays of a commercial product containing mancozeb alone. For the other strategy, the same commercial products were alternated. For each strategy, a spray interval of 14 d was used after the contact/translaminar mixture and 10 d after sprays containing mancozeb alone. Both strategies were evaluated with a manually operated knapsack sprayer but with two levels of application quality. High quality was achieved with a constant pressure valve and a new nozzle, while for low quality, fungicide was applied without a valve and using a damaged nozzle. All treatment combinations gave adequate disease control and no consistent effect of application strategy or application quality could be measured on disease severity or yield. However, approximately twice the volume of fungicide was applied using poor quality equipment, regardless of the application strategy. Advantages and disadvantages of the strategies and their potential effects on fungicide resistance are discussed.     

Comparison of the NegFry decision suport system with routine fungicide application for the control of potato late blight in Ireland

Summary Field experiments between 1996 and 2000 compared the efficacy of fungicide programmes applied in accordance with the NegFry and Met éireann (Mé) decision support systems (DSS) for the control of late blight with 7- and 10-day routine fungicide programmes. The Mé DSS reduced fungicide use by 68% and 54% respectively while NegFry reduced fungicide use by 49% and 27% compared with the 7- and 10-day programmes. The NegFry DSS was similar to the 10-day routine programme in terms of late blight control, quality and marketable yield. A similar result was found when the NegFry DSS was compared with a 7-day routine mancozeb programme (included for two seasons only). Within the NegFry DSS the use of fluazinam resulted in improved yield, foliage blight and tuber blight control compared with mancozeb, but this benefit was significant for tuber blight only. The Mé DSS resulted in inferior disease control, yield and quality.     

Fungicidal control of metalaxyl-insensitive strains of Bremia lactucae on lettuce

Strains of B. lactucae insensitive to 0.01 g a.i. l⁻¹ metalaxyl have been detected in all the lettuce-growing districts of South Australia. Despite this, applications of a formulated mixture of 0.25 g a.i. l⁻¹ metalaxyl and 2 g a.i. l⁻¹ mancozeb every 7–10 days controlled downy mildew in field experiments, where similar applications of either metalaxyl or mancozeb alone were ineffective. Protectant schedules of either 0.3 g a.i. l⁻¹ dimethomorph or 2–2.4 g a.i. l⁻¹ phosphonic acid also controlled downy mildew, but were less effective than the metalaxyl/mancozeb formulation. Mixtures of either dimethomorph or phosphonic acid with mancozeb enabled the time between the sprays to be increased to 14 days without significantly reducing control. Fungicide applications increased marketable yield by 60% compared with that of the unsprayed plants. Drenching seedlings with 4 g a.i. l⁻¹ phosphonic acid controlled downy mildew for at least 14 days and should prevent the spread of the disease from plant production areas.     

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.     

不同药剂组合对马铃薯晚疫病的防治效果

马铃薯晚疫病是马铃薯生产中的重要病害,是影响马铃薯产量和品质的重要因素之一,在云南春作马铃薯上普遍发生,且危害较重,给当地马铃薯产业带来了巨大的经济损失。为减轻马铃薯晚疫病对马铃薯生产造成的损失,试验研究了11种药剂7种药剂组合(包衣剂+保护剂+治疗剂)通过播种期种薯包衣,现蕾期叶面喷施一次保护剂,发病初期和发病中期叶面各喷一次治疗剂的方法防治马铃薯晚疫病。结果表明,药剂组合种薯包衣+甲霜·锰锌+氟吡菌胺·霜霉威的防治效果最好,防治效果达到60.99%,增产率176.28%,增效率152.27%;其次是种薯包衣+霜脲·锰锌+氟吡菌胺·霜霉威组合,防治效果达到60.15%,增产率173.20%,增效率150.55%。这2个药剂组合对马铃薯晚疫病均有极显著的防治效果,增产增效明显。     

Effect of nitrogen fertilization on Fusarium head blight in spring barley

Nitrogen fertilization has been shown to influence the occurrence and the impact of Fusarium head blight in wheat. It also plays a key role in adjusting barley quality to the requirements of the malting industry, implying specific contents of protein. The present study investigated the effect of nitrogen input on the incidence of relevant Fusarium species in spring barley under field and greenhouse conditions. Grain material from differently fertilized field plots was analyzed for fungal DNA and mycotoxins by qPCR and LC-MS/MS, respectively. Under natural pathogen pressure no effect of nitrogen on infection was observed. When pathogen pressure (Fusarium culmorum and Fusarium avenaceum) was increased via species-specific soil-surface inoculation, nitrogen application reduced contents of Fusarium DNA and mycotoxins in barley grain. Nitrogen-dependent canopy parameters were recorded over the season and correlated with DNA and mycotoxin data. Apparently, sparser canopy permitted more Fusarium infections in unfertilized plots. In addition, well nitrogen-fertilized plants allowed less fungal development in the barley spike after spray inoculation in the greenhouse. These results suggest that nitrogen fertilization restricts Fusarium grain infection of barley by influencing canopy characteristics and possibly plant physiology.     

Elba: A late maturing,blight resistant potato variety

Elba is a high yielding cultivar which combines resistance to the golden nematode, foliar infection byPhytophthora infestans andAlternaria solani, andVerticillium wilt. Elba is a late maturing tablestock cultivar especially well adapted to organic soils. In small plots and on farmers’ fields it has demonstrated its worth in reducing the need for foliar fungicides to prevent blight.     

Control of chickpea blight disease caused by Didymella rabiei by mixing resistance inducer and contact fungicide

Elicitors of systemic acquired resistance are well known to reduce severity of several plant pathogenic diseases caused by fungi, bacteria and viruses. Their field applications for management of plant diseases are, however, limited because of yield penalties. Our studies on affect of Benzo (1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), an elicitor of systemic acquired resistance, on chickpea blight caused by a fungal pathogen Didymella rabiei showed that multiple foliar applications of the chemical were effective in management of the disease under economic threshold levels. Multiple applications, however, affected chickpea grain yield adversely. The BTH induced yield penalties could be prevented by foliar spray schedule comprised of BTH and a contact fungicide mancozeb. One spray of BTH (50 ppm) followed by another of mancozeb (0.2%) was less effective (8.3% severity) than three sprays of BTH (4.2% severity) in blight control, however, this treatment enhanced grain yield significantly (1.241 t ha⁻¹) over three sprays of BTH (0.922 t ha⁻¹).     

The Use of Mineral Oil in Potato Protection: Dynamics in the Plant and Effect on Potato Virus Y Spread

The focus of this study was to evaluate two mineral oils (Superior 70 and Vazyl-Y) in reducing the seasonal spread of Potato Virus Y (PVY). Three concentrations of oil (0, 5, and 10 L ha^?1 of Superior 70; 0, 7.5, and 15 L ha^?1 of Vazyl-Y) and three spray regimes for both oils (every 3–4, 7, and 10–11 days) were tested. Two weeks after top-kill, two tubers from each of 49 plants free of virus at emergence were harvested from treatment plots, sprouted, and tested for PVY with enzyme-linked immunosorbent assay (ELISA). Results revealed that in the case of Superior 70, PVY spread in mineral oil treated plots ranged from 2.1 to 12.2 %, while in the control plots it ranged from 20.4 to 37.7 % across three cultivars. In the case of Vazyl-Y, PVY spread in mineral oil treated plots ranged from 2.1 to 26.5 %, while in the control plots it ranged from 49.9 to 85.7 % across three cultivars. These data show that there was a significant reduction in PVY due to spray of mineral oils. In addition, mineral oil was quantified in plants from the Superior 70 treated and the control plots to understand the dynamics of mineral oil during the season. While there was little to no oil measured in the leaves at the early stages of plant growth, a considerable amount of mineral oil was detected close to plant maturity. A basic model of the concentration of oil in the treated foliage was formulated to confirm our understanding of the factors at play. The model could explain from 50 to 90 % of the variation in oil content observed in the field. Plant growth and size are important factors affecting oil content in mineral oil treated foliage.     

Management of the Colorado potato beetle using the entomogenous fungusBeauveria bassiana

Small field plots of Katahdin potatoes on Long Island, NY were treated 6 times in 1980 for control of Colorado potato beetle (CPB)Leptinotarsa decemlineata (Say), Coleoptera: Chrysomelidae, using either the entomogenous fungusBeauveria bassiana (Balsamo) Vuill. (Bb) at 5x 10¹³ colony forming units/ha or fenvalerate at 0.227 kg active ingredient/ha. No significant differences were found between Bb and fenvalerate treatments in egg mass size and viability or in the total foliage consumed by first generation CPBs. First generation CPB larval populations were significantly higher in Bb plots. Oviposition by first generation adults and second generation beetle populations were higher in fenvalerate plots. Average yield was 29.4 metric tons/ha in fenvalerate plots and 24.6 metric tons/ha in Bb plots (a 16% reduction), but nearby untreated plots were completely defoliated by July 24 and yielded <7 metric tons/ha (> 60% reduction).     

Spraying potatoes to prevent leaf roll spread by the green peach aphid

Studies were made at Presque Isle, Maine, 1962–1966, to determine the suppressive effects of several materials against spread of the potato leaf roll cirus,Corium solani Holmes, transmitted by the green peach aphid,Myzus persicae (Sulzer), when applied as foliar sprays to Kennebec, Green Mountain, or Chippewa potatoes in field cages or in field plots. The early cage tests showed that spray mixtures containing 1% of the systemic plant growth regulant chlorocholine chloride (2-chloroethyltri-methylammonium chloride) or 1% of mineral oil were more effective than the insect antifeeding compound AC-24,055^® (=ENT-25,651), the aphid-repellent compounds ENT 20,430 or ENT 21,178, or the surfactants Sarkosyl-O^® (bis (2-ethylhexyl) sodium sulfosuccinate) or Aerosol-OT^® (CH₃ (CH₂)_n CON (CH₃) CH₂ COOH). Field tests disclosed that chlorocholine chloride at 5.2 lb or 2.6 lb/a/a was more effective when healthy green peach aphids were placed on infector plants in the plots soon after the plants were sprayed, 1 week later, or soon after the 2nd of 2 weekly applications than when the aphids were introduced before spraying. The difference in leaf roll suppression at these two dosages was not significant at the 5% level; as high as 90% control of leaf-roll spread was obtained. When only natural infestations of aphids were involved and field spread of the virus was light, the 86% control of leaf roll spread that was obtained from 4 weekly applications made in late June and in July was not significantly different (P=0.05) from the 79% control obtained from 2 biweekly applications made during the same period of time. The potato plants soon recovered from the slight chlorosis resulting from the spray treatment and there was no reduction in weight of US 1 tubers at harvest. Aphid population trends in treated plots were not affected.     

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.