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Agrometeorological Analysis on the Freeze Damage Occurrence of Yuzu Trees in Goheung, Jeonnam Province in 2018

2018년 전라남도 고흥 유자나무 동해 발생에 대한 기상학적 구명

  • Received : 2019.03.28
  • Accepted : 2019.05.15
  • Published : 2019.06.30

Abstract

In 2018, severe diebacks have occurred on yuzu trees cultivated in Goheung, Jeonnam Province. On-farm surveys at 18 randomly selected orchards revealed the dieback incidence ranged from 7.5% to 100% with an average of 43.6%, and 56.6% of the affected yuzu trees were eventually killed. In order to find the reason for this sudden epidemic, we investigated the weather conditions that are exclusively distinct from previous years, hypothesizing that certain weather extremes might have caused the dieback epidemic on yuzu trees. Since different temperatures can cause freeze damage to plants depending on their dormancy stages, we investigated both periods when yuzu becomes hardy under deep dormancy (January-February) and when yuzu loses its cold hardiness (March-April). First, we found that daily minimum air temperatures below $-10^{\circ}C$ were recorded for 7 days in Goheung for January and February in 2018, while no occasions in 2017. In particular, there were two extreme temperature drops ($-12.6^{\circ}C$ and $-11.5^{\circ}C$) beyond the yuzu cold hardiness limit in 2018. In addition, another occasion of two sudden temperature drops to nearly $0^{\circ}C$ were occurred right after abnormally-warm-temperature-rises to $13^{\circ}C$ of daily minimum air temperatures in mid-March and early April. In conclusion, we estimated that the possible damages by several extreme freeze events during the winter of 2018 could be a major cause of severe diebacks and subsequently killed the severely affected yuzu trees.

2018년 전남 고흥군에서 발생한 유자나무의 집단 고사가 발생했다. 이에 대한 원인 조사를 위해 고흥군 풍양면에 있는 18개 유자 과수원을 무작위로 선정하여 조사를 수행한 결과 과수원별 고사증상을 보인 나무의 비율은 평균 43.6%(7.5%~100% 피해율), 증상을 보인 나무 중 56.5%는 나무 전체가 완전 고사되는 피해를 입은 것으로 나타났다. 고사 증상을 보인 대부분의 유자나무에서는 동해의 전형적인 증상인 표피 안 형성층과 목부의 갈변, 잎눈과 꽃눈의 무 발아, 가지나 줄기에 쪼개짐 증상 등이 관찰되었다. 따라서 기상 조건과 유자나무의 고사 증상이 연관 되어있을 것이라는 가설을 바탕으로 고흥지역의 과거 기상 자료를 분석하였다. 2017년 1월과 2월 고흥지역의 일평균 기온은 $-10^{\circ}C$ 이상이었으나, 2018년의 동 기간에는 $-10^{\circ}C$ 아래로 떨어진 날이 7일이나 되었다. 특히 2018년에는 1월과 2월에 유자의 내한성을 훨씬 넘어선 극최저기온(각각 $-12.6^{\circ}C$$-11.5^{\circ}C$)이 관측되었다. 또한 그해 3월 중순과 4월 초에 일 최저기온이 $13^{\circ}C$로 상승한 이상고온 직후 급격히 기온이 $0^{\circ}C$로 떨어지는 현상이 발생하였다. 결론적으로, 2018년 겨울철에 기록적인 극최저기온과 이상고온에 이은 급격한 기온의 저하로 인한 동해가 고흥지역에 대발생한 고사증상의 주요 원인이 되었을 것으로 추정하였다.

Keywords

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Fig. 1. Symptoms of different levels of dieback on damaged or killed yuzu trees in Goheung-gun in 2018.

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Fig. 2. Plant hardiness zone map based on the average annual minimum winter temperature for 2000-2010 in Korea.

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Fig. 3. Annual variations of the monthly minimum value of daily minimum temperatures in Goheung for January and February from 2000 to 2018. Red dotted lines indicate a climatological value of the monthly minimum of daily minimum temperature during 1981-2010 as a reference for comparison.

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Fig. 4. Daily variations of the minimum temperature during Jan-Apr in Goheung in 2018 (black line), compared to the one in 2017 (gray line). Dotted circles indicate the days with a minimum temperature below -10°C, and two incidences (1st and 2nd shocks) where possible freeze damage may happen were marked on the graph.

Table 1. Incidence of severe diebacks on yuzu trees in the investigated orchards in Pungyang-myeon, Goheung-gun in 2018

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