Chemical control of potato early blight and its effect on potato yield

Potato early blight infection was reduced significantly by Daconil 2787, Difolatan and Manzate D. Rates of 0.50 1b/A to 1.5 1b/A were effective until inoculum loads increased as the season progressed then the higher rates were significantly more effective than the lower ones. Consistent yield increases in the range of 18 to 39% were demonstrated when early blight was controlled. Statistically significant yield increases were shown in seasons when severe Verticillium wilt or early killing frosts did not shorten the growing season and negate the beneficial effects of early blight control.     

Estimating potato yield responses from chemical control of early blight in Minnesota

The effect of early blight on tuber yield of two potato (Solanum tuberosum L.) cultivars (Russet Burbank and Norland) was evaluated using number and timing of applications of three chemicals to generate different disease epidemics in 1981 and 1982. Under the non-irrigated farming conditions in Minnesota, there were no significant differences among captafol, triphenyltin hydroxide and maneb-Zn in blight control to increase yield. Of the five spray schedules tested, a 7–10 day spray schedule initiated when blight severity exceeded 0.01%, and a 7–10 day schedule initiated when blight was found above the lower third of the plant, generally gave significant, positive yield responses with all three chemicals. At Rosemount in 1982, the greatest yield increases (relative to unsprayed) obtained were 34.9% and 48.6% in total tuber yields for Norland and Russet Burbank, respectively. At Rosemount in 1982, the highest yield increases (relative to unsprayed) obtained were 92.2% and 56.6% in total tuber yields for Norland and Russet Burbank respectively. At Grand Forks in 1981, the highest yield increases were 126.8% and 34.6% in total tuber yields for Norland and Russet Burbank respectively. Across all three experiments, maximum yield losses (percentage of [[yield of ‘healthy’—yield of unsprayed check]/yield of ‘healthy’’]) were 58.4% (US #1 tubers) and 55.9% (total tubers) for cv. Norland and 34.4% (US #1 tubers) and 36.2% (total tubers) for cv. Russet Burbank.     

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.     

The critical period for control of early blight (Alternaria solani) of potato

The purpose of this study was to identify when the critical period for control of early blight occurs and thus the need to initiate a spray schedule of protectant fungicides. The initiation of weekly fungicide spray schedules was staggered to identify the critical period. The accumulation of 400 P-Days, environmental conditions favorable for sporulation, spore dissemination and plant infection and airborne spores ofA. solani were detected prior to the critical period each year. Since early blight is a disease of old plants, host susceptibility appeared to be involved in the timing of the critical period in addition to favorable weather and the presence of the pathogen. A measure of potato plant development, and therefore susceptibility toA. solani, is needed to adequately predict the critical period. The accumulation of 400 P-Days may aid in the prediction of the critical period by estimating the time of plant susceptibility and therefore the timing of the first necessary fungicide spray.     

Assessing progenies of potato for resistance to early blight

Summary Progenies from crosses between cultivars varying widely in resistance to early blight (Alternaria solani Sor.), were assessed for resistance as true seedlings in a glasshouse in Scotland. The resistance of a representative sample of surviving genotypes from each progeny was compared with samples of the same progenies not previously exposed to the fungus, both in the glasshouse in Scotland and in the field in Israel. The exposed population was more resistant. Resistance was identified more effectively in adult plants from tubers in the glasshouse than in true seedlings and agreement between glasshouse and field assessment was better when progenies were compared rather than individual genotypes. The mid parent and progeny mean scores of the unexposed population were correlated at both sites, thus confirming that the resistance is heritable. Selecting resistant individuals at the seedling stage is suggested as a useful tool for resistance breeding, having first chosen the best parents for crossing.     

Influence of potato cultivars on the effectiveness of fungicide control of early blight

Three potato cultivars differing in degree of susceptibility to early blight were grown under crop management practices typical for Pennsylvania in 1987 and 1988. There were three experimental treatments: no fungicides, mancozeb with weekly applications initiated at 7 or 8 weeks after planting (early treatment), and weekly applications initiated at first symptoms of disease (late treatment). The no-fungicide control treatment had significantly higher AUDPC values than either treatment with fungicides and the no-fungicide treatment had significantly lower yield in 1987 but not in 1988. Tubers from the no-fungicide control had lower specific gravity. Norchip, the cultivar most susceptible to early blight examined in this study, responded the most in yield increases by the increased fungicide applications.     

Tests of aphicides for possible systemic control of potato blight

Summary The systemic aphicide disulfoton, applied as “Disyston” granules to the soil, can decrease the amount of potato blight in the field. However, neither disulfoton nor two other systemic aphicides, menazon and dimethoate, were systemically fungicidal, in glasshouse-grownKing Edward plants, to zoospores ofP. infestans. Disulfoton probably affects blight in the field indirectly, untreated plants becoming more susceptible when attacked by aphids, rather than treated plants becoming more resistant.

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Zusammenfassung Forrest, Hoare undSmith (1965) stellten in ihren Feldversuchen 1963 mit “Disyston”-Granulat (Bodenbchandlung), dass das systemische Blattlaus-Bek?mpfungsmittel Disulfoton (0,0-Di?thyl S-[2-(?thylthio)?thyl] dithiophosphat) enth?lt, eine Verminderung des Kraut- und Knollenf?ulebefalles fest. Die vorliegende Ver?ffentlichung befasst sich mit Untersuchungen über die m?gliche systemisch-fungizide Wirkung von Disulfoton und von zwei anderen systemischen Blattlaus-Bek?mpfungsmitteln, n?mlich Menazon (0,0-Dimethyl S-[4,6-Diamino-1,3,5-triazin-2-ylmethyl]-methyl-dithiophosphat) und Dimethoate (0,0 Dimethyl (S-[N-methylcarbomixid]-methyl-dithiophosphat). W?sserige Dispersionen der Aphizide wurden rund um jung eingetopfte, im Glashaus herangewachsene Pflanzen der SorteKing Edward auf den Boden gegossen: 9 bis 22 Tage sp?ter, je nach Entwicklung der Pflanzen usw., wurden Bl?ttchen abgenommen und ihre Oberseiten mit einzelnen Tropfen von Suspensionen mit Zoosporen vonPhytophthora infestans (Mont.) de Bary nach der Methode vonMcKee (1964) inokuliert. Die Konzentrationen variierten von 1 bis 256 Zoosporen pro Tropfen zu 0,02 ml. Nach der Inkubation in feuchter Luft bei 15°C w?hrend 8 Tagen wurden die Bl?ttchen als befallen oder nicht befallen beurteilt, und die EC50-Werte (Anzahl der pro Tropfen zu 0,02 ml n?tigen Zoosporen, um 50% der Bl?ttchen zu infizieren) wurden nach der Probit-Methode errechnet. Behandelte und unbehandelte Bl?ttchen wurden verglichen, und jeder Vergleich wurde 4- bis 5 mal wiederholt. Die entsprechenden EC50-Werte (gewogenes Mittel in Fettdruck) sind in dertabelle aufgeführt. Die gleichetabelle enth?lt auch die Ergebnisse von K?fig-Untersuchungen mit Kartoffelblattl?usen (Macrosiphum euphorbiae [Thos.]). die best?tigen, dass die Pflanzen systemischaphizid wirksam waren. Keines der Blattlaus-Bek?mpfungsmittel hatte irgendeine systemisch-fungizide Wirkung, noch erh?hten sie die Phytophthora-Anf?lligkeit. Die Art und Weise, wie Disulfoton den Krautf?ulebefall im Feld beeinflussen kann, ist wahrscheinlich indirekter Natur. Behandelte Pflanzen sind kaum als resistenter zu betrachten, viel eher dürfte zutreffen, dass unbehandelte, von Blattl?usen befallene Pflanzen anf?lliger werden. Wenn die Blattl?use zahlreich auftreten, werden die Bl?tter oft stark besch?digt und mit Honigtau bedeckt. Krautf?ulesporen k?nnen m?glicherweise die durch Blattl?use besch?digten Bl?tter unbehandelter Pflanzen leichter infizieren als die unbesch?digten Bl?tter von behandelten Pflanzen. Der Honigtau, eine klebrige, zuckerhaltige L?sung, k?nnte entweder als Sporenfalle oder als Nahrung für die Sporen dienen, oder er kann indem er eine gewisse Feuchtigkeit der Bl?tter bewirkt, die Infektion durch Krautf?ulesporen erm?glichen, w?hrend diese trockene Bl?tter nicht infizieren.

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Résumé Forrest, Hoare etSmith (1965) ont, en 1963, observé dans les champs des diminutions de manifestations de mildiou sur le feuillage et les tubercules de pommes de terre à la suite d’applications sur le sol de granules de “disyston”, contenant l’aphicide systémique disulfoton (diethyl S-[2-(ethylthio)ethyl] phosphorothiolothionate). Le présent rapport concerne l’examen d’une possible action fongicide systémique du disulfoton et de deux autres aphicides systémiques, menazon (S-[4,6-diamino-1,3,5-triazin-2-ylmethyl] dimethyl phosphorothiolothionate) et dimethoate (dimethyl S-[N-methylcarbamoylmethyl] phosphorothiolothionate). On répand les dispersions aqueuses des aphicides sur le sol autour de jeunes plantes deKing Edward poussées en pots en serre; 9 à 22 jours plus tard, suivant la vitesse de croissance des plantes, etc. on détache des folioles et on inocule leur surface supérieure avec des gouttes isolées de suspensions de zoospores dePhytophthora infestans (Mont.) de Bary suivant la méthode deMcKee (1964). Les concentrations varient de 1 à 256 zoospores par goutte de 0,02 ml. Après incubation en atmosphère humide à 15°C pendant 8 jours, les folioles sont classées en infectées ou non infectées et les valeurs EC50 (les nombres de zoospores nécessaires par goutte de 0,02 ml pour infecter 50% des folioles) sont calculés par la méthode du probit. On compare les folioles traitées et non traitées et chaque comparaison est répété 4 ou 5 fois. Letableau montre, pour chaque type de produit, les valeurs EC50 avec les charges moyennes en gros chiffres et les résultats de tests sur des aphides de la pomme de terre en cage (Macrosiphum euphorbiae [Thos]), résultats qui confirment que les plantes étaient systémiquement aphicides à ce moment. Aucun des aphicides ne révèle une quelconque action fongicide systémique, ni n’accro?t la susceptibilité au mildiou. La manière ou les manières par lesquelles le disulfoton pourrait influencer le mildiou au champ est probablement indirecte: ce serait les plantes non traitées qui deviendraient plus susceptibles quand elles sont attaquées par les aphides plut?t que les plantes traitées qui deviendraient plus résistantes. Quand les aphides sont nombreux, les feuilles sont souvent gravement endommagées et couvertes de miélat. Il se peut que les spores dePhytophthora infectent plus aisément les feuilles endommagées par les aphides des plantes non traitées que les feuilles non endommagées des plantes traitées: ou que le miélat, qui est une solution sucrée collante, puisse agir en tant que trappe à spores ou comme nourriture des spores, ou encore qu’il maintienne les feuilles humides et favorise ainsi l’infection par les spores qui n’infecteraient pas les feuilles sèches.

     

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.     

Bacillus thuringiensis a potential control agent for the Colorado potato beetle

In laboratory tests conducted to determine the effectiveness of the exotoxin ofBacillus thuringiensis against the Colorado potato beetle,Leptinotarsa decemlineata (Say), applications sprayed on tomato foliage at dilutions ranging from 10^?1 through 10^?4 killed 90% of the 1st and 2nd stage beetle larvae. As the dosage decreased, the time to achieve this level of mortality increased from 4 to 9 days. Adult beetles were not killed by these treatments; however they did cease feeding. In field tests, the highest dosages ofB. t. sprayed on either tomato or potato plants provided adequate or nearly complete protection when applied weekly. Young larvae that ingested sub-lethal doses developed into adults with atrophied mouthparts and antennae, transformations of the paired parts of the labial palps into an unpaired part, the appearance of a tarsal-like claw on a palp, and malformation of the cranial sclerities.     

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.