WEATHER IN CRANBERRY CULTURE 23 



after the water has been drawn out from under the ice and much before the time 

 for the winter flood to be taken off, the bog may be reflowed at any time. If 

 the ice remains over most of the bog until within two to three weeks of the time 

 for the winter flood to be taken off, it would not be necessary, ordinarily, to reflow; 

 thus, the winter flooding period would be shortened to that extent. 



The risk of having the vines pulled up by the lifting of the ice when a bog is 

 reflowed or flooded by a heavy rainfall, after the water has been drawn out from 

 under the ice, is not nearly as great as is usually thought. Cranberry vines are 

 sometimes pulled out in that way, but in such cases a few to several inches of 

 vines are frozen firmly into the i:e. When the water is drawn out from under the 

 ice, allowing it to drop down onto the vines, they usually freeze onto the lower 

 surface of the ice but do not become embedded in it to any considerable extent. 

 When the bog is reflowed, some of the under side of the ice melts when the water 

 comes in contact with it, since the water is warmer than the ice, thus freeing the 

 vines again. This allows the ice to rise without pulling the vines. It is only on 

 the more shallowly flooded parts of a bog where the vines probably would be 

 frozen into the ice, that they might be pulled out by the lifting of the ice; but 

 even there it would not happen if the bog were flooded to no greater depth than 

 when the ice first formed. 



Sufficient water to reflow a bog, if necessary, must be available in case the water 

 is drawn out from under the ice and, ordinarily, would be available for most bogs. 

 For those who do not have enough water to reflow, protection of the vines against 

 injury due to lack of oxygen during the winter-flooding period would have to be 

 obtained by flooding shallowly and by shortening the winter-flooding period as 

 much as possible. 



From what is now known as to the course of the dissolved oxygen content of 

 the water on winter-flooded bogs in Massachusetts, it seems very probable that 

 the oxygen content of the water usually does not become low enough to cause 

 injury to the vines until sometime in January; in Wisconsin, it is known that it 

 becomes low enough in December. Measurements have shown, too, that on 

 winter-flooded bogs In Massachusetts, even when there is 5 to 6 Inches of Ice, the 

 dissolved oxygen content of the water may increase, if there is no snow on the 

 ice. Moreover, there have been winters in Massachusetts when the supply of 

 dissolved oxj'gen In the water of winter-flooded bogs remained well above the 

 level at which Injury to the vines was apt to occur. These were the warmer 

 winters when bogs did not become covered with Ice at any time, or for only a few 

 days at a time. The winter of 1936-37 undoubtedly was such a one; it was one 

 of the warmest and least snowy on record. 



It may not be necessary to draw the water from under the ice every winter on 

 bogs in Massachusetts, but it should be done whenever a winter is cold enough 

 to make 5 to 6 Inches of ice, especially when there Is snow on It. The water should 

 be withdrawn as soon as possible after the snow falls, since with snow on the ice 

 the oxygen content of the water decreases rapidly and within a few days may be 

 low enough to cause decided injury. 



SUMMARY 



Injury to cranberry vines as a result of a lack of dissolved oxygen In the winter- 

 flooding water has for many years been known to occur. It has been more fre- 

 quent and more severe In Wisconsin than In Massachusetts, but often causes a 

 very appreciable reduction In the size of the crops produced in Massachusetts. 



External manifestations of injury are: Dead stems, loss of leaves, dead terminal 

 buds, dead flower buds, failure of flowers to set fruit after pollination, and re- 

 tardation in the development of flower buds. 



