Jack Frost is not wel­come

Crops halved due to dry, frosty con­di­tions

The Western Star - - RURAL WEEKLY - PETER McMEEKIN Nidera Aus­tralia

THERE has been plenty of media chat­ter in re­cent weeks, not about the for­get­table 1988 thriller movie Jack’s Back, but the po­ten­tial 2017 win­ter crop hor­ror story star­ring the enig­matic Jack Frost.

Frost risk is an ac­cepted part of grow­ing win­ter crops in Aus­tralia. Ev­ery sea­son, some­where across the coun­try, grain pro­duc­tion is lost to frost.

The ex­tent of those losses vary from year to year ac­cord­ing to lo­ca­tion and land­scape fac­tors as well as the cli­mate.

Clear, calm and dry nights fol­low­ing cold days are the pre­cur­sor con­di­tions for a ra­di­a­tion frost (or hoar frost).

Th­ese con­di­tions are most of­ten met where high pres­sures fol­low a cold front, bring­ing cold air, ac­com­pa­nied by set­tled, cloud­less weather.

When the loss of heat dur­ing the night de­creases the tem­per­a­ture at ground level to zero, a frost oc­curs. Wind and cloud re­duce the like­li­hood of frost by de­creas­ing the loss of heat to the at­mos­phere.

The ex­tent of frost dam­age is de­ter­mined by how quickly the tem­per­a­ture takes to get to zero, the length of time it stays be­low zero and how far be­low zero it gets.

A frost event dur­ing flow­er­ing can cause ster­il­i­sa­tion of the flo­ret.

In gen­eral, wheat is more sus­cep­ti­ble than bar­ley to such events due to the length of its flow­er­ing pe­riod. That said, very few ce­real crops are at the flow­er­ing stage so it is too early to see wide-scale frost-aborted flow­ers.

How­ever, it is not too early to suf­fer stem frost dam­age.

Stem frost oc­curs when a small amount of wa­ter set­tles inside the leaf sheath above the penul­ti­mate node and ad­ja­cent de­vel­op­ing tis­sue of the boot.

Many re­ports em­a­nat­ing from the Rive­rina re­gion of

❝ How­ever, it is not too early to suf­fer stem frost dam­age. — Peter McMeekin

south­ern New South Wales re­late to the morn­ing of Au­gust 28.

The overnight low in some ar­eas was re­ported to be less than - 6 de­grees, with be­low-zero tem­per­a­tures for more than six hours.

Sim­i­lar re­ports are also sur­fac­ing in the Mur­ray Mallee re­gion of South Aus­tralia.

Iden­ti­fy­ing stem frost dam­age can be very dif­fi­cult and it usu­ally takes quite some time for the ex­tent of such events to be­come ev­i­dent to the mar­ket.

Ce­real losses of up to 70% have been re­ported, but such ex­am­ples are few and quite iso­lated at this point. The one bright light is that af­fected plants, de­pend­ing on avail­able mois­ture, will send up new tillers to com­pen­sate.

In north­ern NSW and south­ern Queens­land, frost dam­age to the chick­pea crop is wide­spread. Many pad­docks have been flow­er­ing for weeks and fre­quent frost events are tak­ing their toll.

Chick­peas have a low tol­er­ance to frost. How­ever, as long as the plant can ac­cess suf­fi­cient mois­ture, they will sim­ply re­flower and pro­duce new pods, min­imis­ing over­all pro­duc­tion loss.

In 2016 the rain didn’t stop un­til late Oc­to­ber and the chick­pea plants re­flow­ered for weeks. This year al­most the en­tire chick­pea grow­ing re­gion has had less than 40% of av­er­age rain­fall since April 1.

This sim­ply means the plants will not have mois­ture to re­place aban­doned flow­ers and sig­nif­i­cant pro­duc­tion losses will re­sult.

The lack of rain­fall and re­cent frost dam­age means this sea­son’s pro­duc­tion will fall to less than 50% of last year’s record.

It is the ex­tent and the ge­o­graphic spread of the dam­age that will tell the tale in terms of lost pro­duc­tion.

PHOTO: FILE

POOR SEA­SON: Last year’s record chick­pea crop will be a dis­tant mem­ory this year thanks to a chal­leng­ing sea­son for grow­ers.

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