cause of infestation. The uplands around cranberry bogs, often from ten to 

 forty feet high and usually wooded, furnish ideal conditions for wind disper- 

 sion. Infestations from wind drift often are thickest near the bog margin and 

 diminish toward the center. They seldom, if ever, develop in round patches. 



Often there is a high mortality among the wind-borne larvae after they reach 

 a cranberry bog. It seems to be greatest in their first stage and probably is due 

 mainly to reduced vitality, this making them readily subject to disease and other 

 killing agents. The nature of cranberry foliage as a food may be a factor. 



3. By the Worms Falling on the Bog Margin from Overhanging Trees. — The 

 uplands around most bogs now are cleared of trees and brush well back from the 

 margin, so the chances of this generally are small. 



4. By the Caterpillars Crawling Across the Marginal Ditch in Their Later 

 Stages. — When the surrounding upland is heavily infested, complete defoliation 

 of the trees commonly occurs, and then the hungry worms often crawl onto the 

 bog. 



Treatment 



LATE HOLDING OF THE WINTER FLOOD 



Holding the winter flood till May 25 kills the eggs laid on the bog the year 

 before and usually catches most of the wind drift. (See pages 12 and 26.) 



REFLOODING 



The wind drift is generally about over by the last of May, and reflooding 

 about May 29 for twentyfour hours kills the worms before they do much harm 

 unless they are very numerous. A twelvchour flood kills them after they are a third 

 grown, but if they are abundant, treatment should not be delayed after the above 

 date most years. The date for the earliest springs is May 24 and for the latest 

 June 3. Many of the small worms cling to the vines with a bubble of air as the 

 water rises and never come to the surface. As they grow they lose this habit. 

 This may explain their greater resistance to drowning in their first stages. The 

 larger worms thrash themselves to death on the surface of the water. 



Late May is also the time to flood to control rose-bloom. If the water is held 

 thirty-six hours, the swollen pink shoots (Plate Two, fig. 6) caused by the 

 disease collapse and dry up a day or two later. 



The flooding also destroys other pests that may be at work, such as false 

 armyworms, blossom worms, black-headed fireworms, and green spanworms. 



SPRAYING OR DUSTING 



Spraying with 3 pounds of 50 percent wettable DDT powder in 100 gallons of 

 water, 300 gallons to the acre, is recommended whenever the worms are too preva- 

 lent. Dusting with 50 pounds of 5 percent DDT dust to the acre is also very ef' 

 fective. 



PREVENTION 



Keeping the maturing worms from crawling onto the bog is best accomplished 

 by: 



(a) Removing the trees, especially the oaks, and the brush for 150 feet 

 from the bog margin. This also helps to prevent frosts somewhat by allowing 

 freer air movements across the bog at night. 



(b) Spraying the upland for 200 feet from the bog margin with the DDT 

 spray already mentioned. This is always advisable if the upland has not been cleared 

 and is thickly infested. 



(c) Keeping the marginal ditch cleaned out and partly full of water, with a 

 film of kerosene or fuel oil on the water, during the worm-crawl. Sometimes the 

 ditch must be deepened considerably for this. 



[50] 



