RESEARCH & EVENTS
Varietal issues : What ’ s different about season 2023-24
By Josh Fielke ABA Industry Development Officer
OVER the past month , I have driven around orchards and spoken to a number of growers , about the industry-wide issue of floral and vegetative bud development . The varieties that are most affected are Carmel and Shasta . There seems to be no correlation to crop load , nutrition , irrigation or hedging practices or other variables . Weather conditions appear to be the contributing factor . This took me to the work of Prue McMichael on Carmel Growth Disorder ( AL08015 ). In her final report , Californian Non-infectious bud failure ( NBF ) researchers found that spring temperatures and in particularly those over 27 degrees celcius throughout May and June ( Northern hemisphere – November and December here ) correlate to vegetative bud failure the following spring in Carmel . Using this information , I set up analysis for five weather stations and catergorised these months to align with crop stages . These are Renmark Airport ( Station 024048 , 1995 to 2024 ), Balranald RSL ( Station 049002 , 1965 to 2024 ), Griffith Airport ( Station 075041 , 1970 to 2024 ), Mildura Airport ( Station 076031 , 1964 to 2024 ) and Shepparton ( made up of station 074106 , 1970 to 2022 , and station 081125 , 2022 to 2024 ). Each crop stage date is explained in table 1 , and weather findings are in table 2 . Each of these weather stations report against the counted number of days in season 2023-24 that were over 27 degrees celcius . In the brackets is the average number of days over 27 since the weather station has been commissioned . The results of this analysis align with the symptoms described in McMichael ’ s report . An example of this is that on average Griffith has 50 days over 27 degrees throughout the growing period ( August 15 to January 16 ) and in the same time period , in season 2023 / 24 Griffith had 91 days over 27 degrees . Using McMichael ’ s referenced range of November and December , Griffith observed 52 days over 27 degrees in 2023 / 24 , where on average Griffith normally only has 32 ( not seen in table ). McMichael also referenced the same strong NBF symptoms in 2007 which
Table 1 : Crop stage categorisation .
is also seen in the data , observing a total of 45 days over 27 degrees in November and December of 2006 . For Shasta , while the symptoms are not the same as NBF , perhaps these weather conditions contributed to a lower number of flower buds being developed . The reason I have included Shepparton in this evaluation is because there was no issue with the Shasta trees at this farm and they flowered as expected . This aligns with the thought process above , as Shepparton observed the average
LEFT : Floral and vegetative bud development was impacted in Carmel and Shasta varieties in the 2023-24 season .
number of days over 27 degrees during the growing period and in November / December in 2023 / 24 . It is also important to note , within the affected regions there are some farms that have good flowering but still have lower than expected flower counts . In summary , with the data collected , I think that the number of days over 27 degrees throughout the growing season has triggered a genetic response within some varieties . Certainly , on Carmel contributing to NBF and potentially the reduction of flower buds that have developed on Shasta this year . How and what these climatic conditions have triggered needs to be discussed further , as well as how we manage it . But overall , I think the weather has contributed to the issue and is something to be aware of moving forward in managing our orchards .
Table 2 : Weather data from five different weather stations near almond growing regions .
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