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.     

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.     

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.     

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.     

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.     

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.     

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.     

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...     

Breeding for resistance to late blight in the potato

American Journal of Potato Research -