CRANBERRY STATION. 163 



under such conditions of light reduction, the forty-eight-hour flooding 

 period hitherto advocated for treating this insect may be much reduced, 

 for the oxygen deficiency should affect the worms as well as the plants. 



The Gypsy Moth (Porthetria dispar L.). 



In 1919 this insect hurt the bogs more than any other. In 1920 it did 

 little harm, as it was generally less prevalent and was treated much more 

 effectively by the growers. 



In 1920 Mr. Walter F. Holmes, the gypsy-moth division superintendent 

 for Cape Cod, and the wi-iter tested the open nozzle for treating this pest 

 on the bogs. This is the nozzle used in the gypsy-moth work to spray 

 tall trees from the ground. As tested it proved unsatisfactory for bog 

 spraying, as it was hard to spray at such long range without skipping 

 considerable areas; but it should be tried further, with smaller nozzle 

 holes and lower pressures. 



Experience and experiments in recent years have showii that this insect 

 can be controlled readily on the bogs by — 



1. Holding the winter flowage until May 25. This will kill the eggs laid 

 on the bog the season before, and in most years it also will catch most of 

 the worm wind-drift. 



2. Rejlowing about May 29 for thirty-six hours. The wind-drift is about 

 over then, and the water will kill the worms before they do much harm 

 unless they are unusually numerous. This flooding also will destroy 

 other pests that may be at work, such as the false army worm (Calocampa), 

 blossom worm (bud worm) and fireworm. After the gypsy caterpillars are 

 one-third grown, a fourteen-hour flooding kills them, few getting ashore 

 with life enough to eat afterward. They seem to thrash themselves to 

 death in the water, as do apparently all other growing foliage-eating 

 worms of the cranberry, except those that sew the leaves together. If 

 the worms are very numerous, however, it is better not to delay the flood- 

 ing after the above date in average seasons. The date for the earliest 

 springs is May 24 and for the latest June 3. 



3. Spraying with lead arsenate {3 pounds of powder or 6 pounds of paste 

 to 50 gallons of water) about May 24. WeU applied, this treatment is sure 

 death to the w^orms when they are small. They are hard to poison when 

 over half growTi. In very early springs the spraying should be done about 

 May 18; in very late ones about May 30. 



4. Keeping the maturing worms from getting onto the bogs. This is done 

 best by: — 



(a) Removing the trees, especially the oaks, for some distance back from the 

 bog margin. The removal of the underbrush (scrub oaks, etc.) also would 

 help, but this seems too costly. 



{b) Keeping the marginal ditch cleaned out and partly full of water, and 

 maintaining a film of kerosene or crude oil on the water during the worm- 

 crawl period. 



