FROST CONTROL in ORCHARDS and MARKET GARDENS
For the next few weeks growers will be on tenterhooks wondering about frost. We are really very fortunate when we consider the few drastic frosts we have had over the past few years. There have been losses, but there has not been a widespread loss for a long time. That is no reason to think that we can sit back and do nothing. Destruction of fruit by frost is something we can do a great deal to eliminate entirely or reduce to a point where crops are not seriously affected. Any orchardist who does not prepare for frost in most parts of Hawke’s Bay is throwing away a very sound insurance premium in the form of firepots and a supply of fuel oil.
NEW METHODS NEEDED
The present system of 100 gallon pots or so to the acre of ground, and burning various grades of fuel oil, will control any frost likely to be experienced in our district. It is, however, a dirty, costly job, and we are still looking for something more efﬁcient and less costly. The poor combustion of an open oil flame without forced draught results in very low heat unit output. It also brings the “smog” problem, which must get worse as more areas are planted. It is reasonable to suppose that the time must come when this method will be disallowed, as it has in other parts of the world.
J. Wattie Canneries Ltd. spent a considerable sum last year in an endeavour to distribute warm air from burning fuel oil and blowing it over a large area. It was only partially successful. This year we are trying another device imported from South Africa, where it has been very successful. We are not entirely sold on the idea, but it is worth thorough investigation. It could be that it would have a place in conjunction with the present set-up of fuel pots. It also has very deﬁnite possibilities as a sprayer and the present unit is adaptable for this purpose.
The principle of this trial machine, known as the “Rypkul,” is not to generate a large amount of heat, but to produce a fog over the cropping area preventing the loss of heat by radiation. It prevents frost by conserving the heat constantly being radiated by the earth and every object on it. Flat country is essential, as it would be impossible to maintain the blanket fog effect where the country is too steep or undulating.
The fog is produced by vapourising fuel oil and water. One machine is capable of covering a very large area up to 150 acres, and if it was successful, several orchards could be covered by a single unit. The unit is portable, so that it can cope with drift.
Market gardeners or strawberry growers will welcome this machine if it proves successful here. Ground crops are difﬁcult to protect because frost is heaviest just above the earth’s surface. Heat from frost pots rises quickly, often leaving a shallow layer above the ground not effectively controlled. Fruit trees, being off the ground, are easier to protect.
Unlike frost pots, which actually heat the air over a great depth, no heat is produced by this unit at all. It is necessary then to create the protecting fog before the temperature reaches danger level. This, of course, requires someone on the job over a longer period, but one man can do this, where the other method requires more men plus the added labour for refueling, and placing the pots out and taking them in each year. Its actual operating costs are also light, burning about 15 gallons of diesel oil per hour.
Our main concern, until it is tried, is drift. It remains to be seen if the fog can be held just where it is required under our actual conditions.
(a) Damp, ﬁnely worked ﬁrm soil will radiate heat over a longer period than a rough and dry soil. It is advisable to roll the land before putting the ﬁre-pots out.
(b) Grassed orchards should be kept mowed reasonably short, even if it means moving the pots occasionally.
(c) New pots are slow to light. It is as well to light them during the day and allow them to burn for half an hour or so beforehand. The soot which builds up