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.     

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.     

Breeding for resistance to late blight in the potato

American Journal of Potato Research -     

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.     

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.     

Crop loss prediction tables for potato late blight epidemics

American Journal of Potato Research - The yield loss prediction equation of MacKenzie and Petruzzo was used to determine expected yield losses resulting from over 1000 computer-generated late...     

Resistance to late blight inAndigena potatoes

Summary Andigena clones derived from mass-selected seedling populations which had been subjected to several generations of natural selection in the field for late blight resistance were studied. The average level of resistance (score about 3 on scale 1–5) was better than a sample ofTuberosum potatoes (score about 4) and the best individual clones were very resistant indeed. It is concluded thatAndigena has the genetic capacity for excellent response to selection for resistance and that thus one major obstacle to the use of the Group in potato breeding has been removed.

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Zusammenfassung Es wurdenAndigena-Klone verwendet, die durch Massenauslese aus S?mlingspopulationen gewonnen wurden. Diese S?mlingspopulationen wurden w?hrend mehrerer Generationen der natürlichen Auslese aulPhytophthora-resistenz im Feld unterworfen. Ungef?hr 100 Klone wurden mittels des Einzelblatt-Testes mit einer gr?sseren Zahl vonTuberosum-Klonen verglichen. Aus den Ergebnissen in Tabelle 1 geht hervor, dass der durchschnittliche Resistenzgrad vonAndigena (ungef?hr Note 3 bei einer Skala von 1 bis 5) bedeutend besser war als der vonTuberosum (ungef?hr Note 4); derjenige der bestenAndigena-Einzelklone war wirklich sehr gut (Note 1 bis 2). Andere Ergebnisse (Tabelle 2) betreffen das Verh?ltnis zwischen Krautf?uleresistenz und Reifezeit; in diesem Material gab es keine signifikante Kor relation, und es war offensichtlich, dass eine befriedigende Resistenz h?tte aufrechterhalten werden k?nnen, sogar ohne durch Auslese auf Frühreife gef?hrdet zu werden. Daraus wird geschlossen, dass dieAndigena-gruppe, obwohl in ihrem Urzustand sehr anf?llig für Krautf?ule, die genetische F?higkeit zu ausgezeichneter Reaktion in der Resistenzzucht besitzt und dass ein Haupthindernis für die Anwendung dieser Gruppe in der Kartoffelzüchtung beseitigt wurde. In diesem Zusammenhang wird auf die von Paxman kürzlich gemachte Feststellung hingewiesen, dass es im Vergleich mit reinenTuberosum-Familien inAndigena Tuberosum F₁-Hybrid-Familien ungef?hr 60% Ertragsheterosis gibt.

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Résumé Les auteurs ont utilisé les clonesAndigena provenant d’une sélection massale dans des populations de plantules soumises pendant plusieurs générations à la sélection naturelle au champ vis-à-vis du mildiou. Ils ont comparé quelque 100 clones au moyen d’un test sur foliole détachée avec un vaste échantillon de clonesTuberosum. Les résultats (Tableau 1) montrent que le niveau moyen de résistance des Andigena (cote: 3 environ sur une échelle 1–5) est significativement meilleur que ceux deTuberosum (cote de 4 environ) et que les meilleurs clones individuels sont réellement très bons (cote 1–2). D’autres résultats (Tableau 2) concernent la relation entre la résistance au mildiou et la maturité; il n’y a aucune corrélation significative dans ce matériel et il apparait qu’une résistance satisfaisante peut être maintenue sans risque sérieux de perte due à la sélection pour la précocité. Il est conclu que le groupeAndigena, quoique hautement susceptible au mildiou dans son état primitif, possède la capacité génétique de répondre excellemment à la sélection pour la résistance et qu’un obstacle majeur à l’utilisation du groupe dans l’amélioration de la Pomme de terre a été éliminé. A ce sujet, l’attention est attirée sur la récente découverte de Paxman qu’il y a approximativement 60% de production d’hétérosis dans les familles hybrides F₁ Andigena × Tuberosum en comparaison avec les familles puresTuberosum.