太阳辐射与苹果树腐烂病早春发病的关系以及树干保护的防腐作用

 苹果树腐烂病在早春有一次发病高峰,在此高峰期,主干、主枝上的原发病斑的分布具有明显的方位倾向。不同方位的树皮受日光照射后,皮温比气温高,其增温幅度愈大,增温持续时间愈长,则该方位上的发病点愈密集。因而认为腐烂病早春发病所表现的方位性与此期间树皮受日光照射后的增温有关。按风速1.1~3.8米/秒、低云量0~2级,12~14点阳光直射面树皮温度与气温间的关系可以直线回归式表之;t_{b (皮温)}=7.70+1.93t_{a (气温)}。河北省二、三月份由阳光辐射引起树皮增温的条件经常存在。采用秋后涂白保护树体的常发病部位可以降低早春树皮增温、减轻病害,推荐桐油皂白涂剂。

SOLAR RADIATION IN RELATION TO THE EARLY SPRING OUTBREAK OF VALSA CANKER (VALSA MALI MIYABE ET YAMADA) OF APPLE TREES

Valsa canker (Valsa mali Miyabe et Yamada) is one of the most des-tructive diseases of apple trees in North China. The development of the canker usually reaches a peak in the early spring (March) in Hebei Province. Observations revealed that most of the primary cankers on the trunk and limb often produced and spread along definite directions during this season. The cankers occurred at the south side of the tree trunk with a higher density and then in the order of south-west, west and south-east, usually at a height within 100 cm above the ground. Re-sults of field investigations proved that the bark temperature was always higher than the surrounding air temperature under the influence of solar radiation. The correlation between bark temperature (t_b) and air tem-perature (t_a) can be expressed in the following linear regression.