Frost Protection In Orchards

Hawke's Bay Herald-Tribune, Issue 211, 22 September 1937, Page 7

Frost Protection In Orchards

ADVICE TO GROWERS Temper atures Which Are Injurious To Fruit DANGEROUS STAGES (By N. J. Adamson, Orchard Instructor) . Numerous enquiries have been made in regard to temperatures which are injurious to fruit. TJnfortunately, we have limited local data sufiiciently reliable on Which to base an estimate of the temperatures which cause injury and mUSt thereford rely Ujwn outside experience to some extent. The following table is taken from the Bulletin of the Berkfeley College of Agriculture of the UnivCrsity of California: — Temperature endured for thirty mihutes or less (sheltered thermometers) by deciduous fruits and various stages of deveionmeht:—

The fruit buds of nearly all deciduous fraits are extremely susceptfble to damage during the period of from twenty-four to forty-eight hours before ihey open. The petals are still folded, but the flowers are growing rapidly aiid are extremely tender. Buds in this condition are often injured by temperatUtes as higli as those given in the table for small green fruits. kortunately, most deciduous liuittfees come into full bioom gradually, so that even if all the buds about to open at one tihife are kilied, the siae of the crop is iiot reduced materially. ' Buds of the Bcisc pear often open RimuJtaneously, and a low temperature just before the flowers open sometimes. destroys most of the crop. At the time^ genCrally designated "full blDoHi" most deciduous fruittrees have large Uumbcfs of firuitbtids which Ure still tightly bloscd, in addition to the flowers Which afe fully upen. This makes the loss of the entire crop, or eveu the gfeater portlon of the crop. ofl one cold Uight, extremely improbable at this Stage. ' This has led fruitgrowerg in some districts tO believe that frost can do no damage before the fruit has sbt. fcome growers even follow the hazardous practice of leaving heafers unlighted on frosty iiights during this period. While a smgle frost at full bloom scldom affects tho eize of the linal crop, a series of/ heavy fOosts, each killing a portion of the blossoms, may leave too feW undamaged blossoms for a full crOp. Most Dangerous Stago The most dangerous stage in general is after all the petals have fallen and tho fruit has set. All the fruit beiug in nearly -the same condition, the entirfe Crop may be killed in a siflgle xiight. It is at tllis timo that Orchard-lieatfeg operations should be most carefully cOhduCted. Apples and peafs at this stage of devClopment usually are iiot seriously injured by a temperature of 28.5 degfes F. for thirty minutes or leSS, provided the duratioU of temperatures below 32 degrees F. doeS iiot exceed three houfs. If the temperature drops to 29 degrees F. only a shOrt timo before suhrlSe and has not been below 32 degrees F. more than three lioui's heating is urinecessary. However, if it appears that the lowest temperature during the night Will be below 29 degrcOs F., 0r if the temperature falls below 82 degrees F. more than three hours before sunrise, huarere should be liglited and the temperature mamtained as near 31 degrees as possible throughout the remaiuder of the night, Small green aprieots aro extremely tender just after the shucks (dried caliees) have dropped and before the pits have bsrdened. ApricOls in this condition have be-eu injured at long contiuued temperatures of 31 degrees F. and many growers think it iiecessary not to allow the temperature k) fall below 32 degrees F. as long as the pits are soft. Siisceptibility to Frost Damage Djfferent varieties of the same fruit often • diifer considerably in their susccptibility to frost damage. The Delieious apple appoars to be more tender than most other varieties of apples grown eommercially. The Bosc pear is more, susceptiblo to damage by frost than most other varieties of pears at similar siages of development, wliile the "Winter Nelis is liardicr than most varieties. Stundard temperatures are usually taken at a height of four feet to four feet six inches from the ground. Thermometers, if fully exposed to the sky at night radiate ,heat aud becorne colder than the air, consequently they register a lower temperature than they should: They should therefore be placed under a shelter, which may be conveuijeutly constructed by placfing -jva p a bcard

fifteeu inches long by nine inches deep is screwed a few inclics from the top. On the top of this board is a hinged lid of the same size, bovelled on the edge so that it may hang down liko a roof as a protection to the thermometer which should be liuug horizontally on two screws as higlx up on the first i board as possible. The bulb end should be very slightly lower than the other, Warning thermometers should be placed at the lowest level of the crop to be proteeted and set to give adequatc warning ot approaching dangerous temperatures. Followlng the frosts which occurred on the nights of last Friday aud Saturday a survey of orchards on the flats revealod no appreciable damage to either plums or peaclies which were in full bloom at the timo. Temperatures of 28 degrees F„ were racorded

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