142 MOSQUITO ERADICATION 



"The estimated requirements range from 90 to 600 lineal feet of 10 by 

 30 inch ditching, or its equivalent, per acre. As a matter of fact, only 

 rarely is the former figure practicable, and then under especially favor- 

 able conditions, and never on the New Jersey salt marshes has the latter 

 figure been reached. It seems probable that between 200 and 300 

 feet is the real average. To this must be added an amount of 

 hole filling and shallow spurring which will add about 10 per cent to 

 the acre cost." 



SALT MARSH DITCHING BY HAND 



The type of ditch just described is dug both by hand and by 

 machinery, the latter being considerably the cheaper. 



In hand ditching, the chief tools commonly used are patented 

 spades of various types, these having been found superior to 

 ordinary shovels. There are several different makes of these 

 spades on the market. 



In cutting the ditches by hand, it has been found best to remove 

 the sods in pieces about 10 inches wide by 6 to 8 inches thick by 

 30 inches long. These are heavy and not easily moved by the 

 tide; they can also easily be hauled away if desired. 



As a general rule, numerous small, shallow pools are found 

 scattered throughout the marsh; some of these will not drain 

 readily into the ditches, but are too small to merit drainage by 

 means of spurs. Such holes may be filled with sods from the 

 ditches and then smoothed over, in such manner as to prevent 

 formation of succeeding pools. In a year or so, the grass will 

 grow over the fill and the hole will be entirely obliterated as a 

 breeding-place. 



Sometimes, portions of the marsh are so shut in that opening 

 them to the ocean is impracticable. In these cases, the area may 

 be trenched with the usual ditches to concentrate the water 

 which should then be stocked with larva-destroying fish. 



Particular care should be taken in connection with the outlet 

 of the ditches. The greater the tide drop and the shorter the 

 ditch, the greater is its efficiency and its ability to keep clean. 

 According to Headlee, 1 every ditch should have a strong tidal 

 outlet, and no ditch depending on a single outlet should be more 

 than a quarter of a mile long. 



1 "Some Recent Advances in Knowledge of the Natural History and the 

 Control of Mosquitoes," New Jersey Agricultural Experiment Stations, 

 Bulletin 306, 1916. 



