162 MASS. EXPERIMENT STATION BULLETIN 206. 



reported as injuring corn or grass in the following towns in eastern Massa- 

 chusetts: Wilmington, Canton, Bourne, Falmouth, Barnstable, Brewster 

 and Chatham. That year it destroyed 20 acres of corn on one farm in 

 Bourne. In 1920 it seriously hurt several acres of com in Bourne. 



The army worm and the fall army worm are the two more common of 

 the three harmful insects known to infest the bogs as a result of letting off 

 the winter water in midsummer. The outbreaks of both species nearly 

 always start in the southern States. They are noted there by the Bureau 

 of Entomology which forecasts their spread into the North. Such fore- 

 casts were published in both 1919 and 1920. Cranberry growers contem- 

 plating holding winter flowage very late should consult the Bureau as to 

 the prospective abundance of these pests. The army worm probably 

 never greatly harms cranberry bogs reasonably free of grasses except in 

 infestations following very late removal of the winter flood. 



The Cranberry Fruit Worm (Mineola vaccinii Riley) . 



In 1919 this pest did less harm than in any previous year of the writer's 

 experience. Its reduction was to be expected from the mildness of the 

 previous winter and the wetness of the growing season. ^ The egg para- 

 sitism {Trichogramma) examined ranged from 16 to 88 per cent on dry 

 bogs, and from to 37 on flowed ones. 



In 1920 the insect did much more harm than in 1919, the winter before 

 having been severe. The egg parasitism ranged from 14 to 50 per cent 

 on dry bogs, and from to 25 per cent on flowed ones. 



The Black-head Fireworm {Rhopobota vacciniana (Pack.)). 



This pest was less harmful in 1919 than in any previous year of the 

 writer's experience. The second brood seemed to be entirely suppressed 

 on some bogs; on others it began hatching freely, but for some cause, 

 perhaps disease, as a rule faded out without doing much damage. In 1920 

 this worm was less harmful than usual, but more so than in 1919. 



Results of spraying tests in 1920 support previous experience in indicat- 

 ing that while 1 part of Black-Leaf 40 in 800 parts of water, with 2 pounds 

 of soap to 50 gallons added, is fairly effective in killing the worms, it is 

 probably better economy, all things considered, to use the insecticide at 

 the rate of 1 part to 400 parts of water. One part to 800, with the soap, 

 kills the moths satisfactorily. At either strength the spray is safe to use 

 when the vines are in bloom. Lead arsenate may be used with Black- 

 Leaf 40 if the soap is left out,^ but it should not be so used unless other 

 pests, such as the gypsy moth or spanworms, are also to be treated, for the 

 soap makes the Black-Leaf 40 more effective. 



As cloudiness or dark water, by reducing the light reaching the plants 

 and so lessening photosynthesis, causes a marked decrease of oxygen in 

 the water of a cranberry bog flooding to be maintained, it seems that, 



1 Mass. Agr. Expt. Sta., Bui. No. 180, 1917, p. 227. 

 ^ The arsenate and soap make a burning mixture. 



