Study Of Potato Blight Forecasting

Press, Volume XCVIII, Issue 28805, 28 January 1959, Page 15

Study Of Potato Blight Forecasting

Instructors in agriculture in sev-1 eral parts of New Zealand are keeping records of maximum and minimum temperatures and air humidity and keeping an eye on potato crops for development of blight, so that in the course of a year they may be able to work out in graph form a relationship between these factors. This might enable a pattern to be visualised for the development of blight in potato crops and will show whether it is possible to develop a system of forecasting of potato blight outbreaks on weather information. Giving this information last week, Mr C. M. Driver, of the Crop Research of the Department of Scientific and Industrial Research, said that officers of the Department. of Agriculture at Palmerston North, Christchurch, Ashburton, Timaru, Waimate, and Dunedin were keeping these records. Blight occurs 10 days to about three weeks after a period of 48 hours in which -temperatures are between 50 and 77 degrees Fahrenheit and the humidity is over 75 per cent.

While he did not have specific figures to show the position, Mr Driver said at the end of the week that conditions had been such last Week to bring on blight if humid conditions persisted. The severity of the appearance of blight after the development period was dependent on the 'sort of weather in the interim. Hot dry weather reduces the infection and a temperature of over 90 degrees was needed to really suppress it, but even then it would still survive. If moderate conditions persisted now Mr Driver said that blight could be very evident in crops in two weeks’ time following the earlier blight period in December of last year. Blight conditions prevailed in the Darfield district last week and they existed in areas such as Belfast. CoUtts Island, and Ellesmere, he said.

that lime there was ■<> sign of the disease on potato crops, but a warning was given to farmers that they had a period of grace in which to spray as a preventive measure. Dr. Blair said yesterday that a question prevalent in the minds of farmers at the present was whet was the outcome of the warning and what was happening to the blight. With the recent period of very dry weather some farmers have suggested that although a warning was given, the disease has not occurred because of ths continued drought. "We observed the disease on four varieties on January 8." Dr Blair said. This was about two ' and a half weeks after the warning was given. "This fact, together with the evidence a year ago. indicates 1 that there is some solid ' foundation for following the socalled ‘English rules’ of blight forecasting, but the intensity of ■ the disease on January 8 was 1 slight and would hardly attract 1 notice. It has been distinctly advantageous that this very dry ' weather has stabilised the situation. "In other words, the disease has been initiated, but has not ; progressed to a destructive level Warning Hooded “What about the farmers who . have sprayed their crops in the ; light of the warning? Has their ; money been spent to no avsil? “I would say they have prevented the disease from becoming . established in their erbps. So that . if the weather breaks and beI comes very wet and humid there ' should be very little, if any, sud- ’ den build up of the blight, com- , pared with those crops which have , not been sprayed and in which . the disease has been established • and is at present lying dormant. “If, on the other hand, the ! weather stays dry the farmer who 1 did not spray may say cynically. • ‘I didn’t lose any money on that.’ 1 The farmer who did spray will have to view the situation philosophically with the thought that he has spent a relatively (mail amount on a sound form of crop insurance," Dr. Blair said.