The effects of covering cabbage crops to prevent cold injury were investigated using cheesecloth made of Vinylon.
Two types of cheesecloth, #200 and #300 were used. The floating row cover method in which the cheesecloth is at a height 50cm above the ground and the contacting row cover method in which the cheesecloth is kept just above the top of the cabbages were employed.
The air temperatures under the floating and the contacting row covers, using cheesecloths #300 and #200 were 3°C and 2°C, respectively, higher than that of the control during clear nights with wind speed below 50cm/s. However, with increasing wind speed the difference between the air temperatures in the control and the row covering were slight especially in the contacting row covering, using #300. The leaf temperatures under the floating row cover with #300 and #200, were 3°C and 2°C, respectively, higher than the control when the wind speed was less than 50cm/s on clear nights. With increasing wind speed over 100cm/s, there was no difference between the leaf temperatures in the contacting row cover with cheesecloths #200 and #300, and that of the control. However, there was a difference between the leaf temperatures in the floating row cover with #300 and the control. In the case of the contacting row cover, the leaf temperature increased slightly under #200 and #300, leading to a small temperature difference between the contacting row cover and the control.
These results show that the floating row cover with cheesecloth #300 was useful irrespective of wind speed. The incidence of head rot caused by cold injury under the floating row cover with cheesecloth #300 was lower than it was in the control in open field. The contacting row cover and the floating row cover with cheesecloth #200 were ineffective.
The influence of the height of the floating row cover with cheesecloth #300 on keeping the leaf temperature higher by taking off or retaining all the sides of cheesecloth was investigated. Leaf temperature under the floating row cover, stretched 30cm above the ground was about 1.5°C higher than that of the control when the wind speed was less than 50cm/s on clear night. However, the difference in leaf temperature was counterbalanced when wind speed was more than 1m/s. When the cheesecloth was ctretched 50cm and 1m above the ground, the leaf temperature was about 2.5°C higher than that of the control irrespective of wind speed. With increasing wind speeds of more than 1m/s, the leaf temperature under the cheesecloth stretching 1m high was about 1°C higher than that at 50cm.
By covering all sides with cheesecloth #300 stretched at 50cm high, the leaf temperature was about 1°C lower than that it was without the side cheesecloth.
These results indicate the advantages of choosing cheesecloth #300 rather than #200, and stretching the cheesecloth at a height greater than 50cm in order to effectively prevent cold injury to cabbage crops in the open field.
