J. R. Wallin

The relation of cumulative amount and frequency of rainfall and mean temperature to late blight in Indiana

SummaryTemperature and rainfall amount and frequency data from Bluffton, Hungtington, Washington, Princeton and Shoals, Indiana were analyzed in relation to the occurrence of late blight in northern and southern Indiana for the period 1915 through 1951.Highly significant differences between group means were obtained for the northern Indiana rainfall amount slopes. The southern Indiana slope means were not significantly different.The means of the slopes of the cumulative rainfall frequency lines were significantly different for southern but not northern Indiana.A ‘critical’ slope for the cumulative amount and frequency of rainfall was computed as the slope midway between the means of the severe- and no-blight year groups.Four combinations of temperature and rainfall were employed to formulate hypothetical late blight forecasts for northern and southern Indiana.The greatest percentage of accurate forescasts for both sections of the state was obtained from the use of the combination of weekly mean temperature 75° F. or less and cumulative rainfall equal to or greater than the critical slope. However, all forecasts for northern and southern Indiana were only 65 and 67 per cent accurate, respectively.In both sections of the state the no-blight years were predicted with the greatest accuracy by all temperature-rainfall combinations.

Influence of post-inoculum air temperature maxima on survival ofPhytophthora infestans in potato leaves

SummaryFive cultures ofP. infestans, growing in potato leaves, were subjected to air temperatures of 105° F. 22 hours; 106° F. 21, 22 and 27 hours; 108° F. 43 hours; 109° F. 45 hours; 110° F. 24 hours and 115° F. 47 hours after inoculation.Cultures survived 105° F. Only culture 1 survived 106° F. 21 hours after inoculation although two cultures (1 and SB) survived exposure to 106° F. 22 hours after inoculation. All cultures survived this temperature 27 hours after inoculation. All cultures survived 108° F. 43 hours after inoculation. Moreover, the five cultures survived 109° F. and 110° F. 45 and 24 hours, respectively, after inoculation. Three cultures, (1, 35 and SB) survived exposure to 115° F. 47 hours after inoculation. The same five cultures, growing in detached potato leaves, were exposed to air temperatures of 83, 95, ]05 and 108° F. 14, 14, 20 and 18 hours respectively, after inoculation. The five cultures varied in their tolerance to 105° F. and none survived the maximum of 108° F.

Prediction of potato late blight incidence from samples of blighted seed tubers

SummaryEleven seed tuber lots at Albert Lea and Hollandale, Minnesota, were sampled for the presence of tubers with symptoms of late blight in April, 1955.Tubers with late blight were found in two of four lots sampled at Farm 1, Albert Lea. During the season, the disease was found in two fields planted to the blighted seed lots and in one field planted to an unblighted lot.At Farm 2, Albert Lea, late blight was not found in a field of Cherokee potatoes planted with seed whose sample yielded a trace of blight.At Hollandale, Minnesota, tuber blight was found in three of five seed lots sampled. During the season, late blight developed in the fields planted to the blighted lots and in one field planted to Cherokee potatoes whose seed sample was blight free.

Forecasting potato late blight in Minnesota

SummaryPeriods of 10 hours or more concurrent temperature ≤75° F. and relative humidity ≥90 per cent followed by temperature maxima < 95° F. were used to predict potato late blight development. One favorable period a week was considered sufficient for limited reproduction and subsistence of the fungus in the foliage.During 1950. 1951. 1952. and 1953. blight developed as forecast in those areas near the weather-blight observation posts.The results thus far warrant continued efforts to forecast late blight on the basis of the same temperature and relative humidity relationships, with more consideration devoted to the influence of high temperature maxima immediately succeeding a period favoring secondary infection processes.Because the early part of the record on each hygrothermograph chart is at least a week old when it reaches the forecaster any further delay in the receipt of these records decreases the practical value of the forecasts.

Abstracts of papers presented at Annual Meeting

HEILIGMAN, F., AND I. R. W A G N E R EFFECTS OF CHLORO-IPC ON SPROUTING AND LOSSES IN WHITE POTATOES DURING STORAGE The use of 3-Chloro-lsopropyl-N-Phenyl Carbamate (Chloro-IPC) reduced losses in white potatoes stored at 55, 72, and 85 ° F. when compared to untreated controls. The material was effective when used as a dip, as a spray, or when incorporated in water emulsion potato wax. The treatment controlled sprouting and reduced weight losses during storage. There is some evidence that the material may have some indirect effect in controlling losses caused by microbial decay. H O Y M A N , WM. G. COMPARATIVE REACTIONS OF ATTACHED AND DETACHED LEAVES TO P H Y T O P H T H O R A I N F E S T A N S Thirty potted potato selections 6 to 12 inches in height and detached leaves from them were simultaneously inoculated with zoospores from a culture of race 0. The inoculations were made in a plastic-covered chamber at 70 ° F. and 100 per cent relative humidity. The reaction of each of the 30 selections was recorded as soon as symptoms appeared and the final reading was made the eighth day following inoculation. Sporulation occurred on attached and detached leaves of 8 selections. Sporulation also occurred on the attached leaves of one selection, whereas the reaction of the detached leaf consisted of large lesions. The symptoms on both types of leaves of the 3 selections consisted of necrotic spotting. The attached leaves of 4 selections showed no symptoms, whereas the detached leaves showed definite necrotic spotting. No reaction was evident on leaves of 14 selections.