18 FARMERS ^BULLETIN 868. 



The combined treatment advised bck)w includes Bordeaux mix- 

 ture for early-blight. 



ARSENICAL POISONING. 



The use of Paris green in water in large quantities results in a burn- 

 ing of the leaves, often in concentric spots centering at flea-beetle 

 punctures, somewhat rcsemblmg early-bhght. \Mien the arsenical is 

 combmcd with Bordeaux mixture, tliis injury is avoided. 



COMBINED TREATMENT FOR DISEASES AND INSECTS. 



Watch the young plants closely and spray with Bordeaux mixture 

 and arsenate of lead as soon as the first evidence of the Colorado 

 potato beetle or of flea-beetles is noted. 



Repeat this application every 10 to 14 days to keep all of the new 

 foliage protected. If no insects are present and the weather is dry, 

 the intervals between sprayings may be leagthened. 



As the late-blight season approaches, wliich in the North usually is 

 after the middle of July, a protective s])raybig should be given and 

 the weather watched more closely, for if contmuous showers occur, 

 with a mean tempsrature of 72° to 74° F., spraying every 5 to 7 

 days will be necessary, 



A system for reporting the appearance and progress of late-blight 

 should be organized in order that potato growers may be warned 

 when to increase their efforts. 



VALUE OF SPRAYING. 



Throughout the late-blight area shaded on the map (fig. 16) it 

 pays to spray potatoes with Bordeaux and arsenicals, whether blight 

 develops or not. With few exceptions, large gains in yield are due to 

 protection from flea-beetles, grasshoppers, early blight, ti])burn, etc. 



This fact has been established by extensive expc^rimeiits which 

 have been conducted in New York and Vermont. During a 10-year 

 period, at differeiit experiment stations hi N(>w York State, an average 

 gain of 60 bush(^ls per acre was secured. At the Vermont station, 

 during a 20-year period, wliich involved all possil)le seasonal varia- 

 tions, an average gain of 105 bushels per acr?, or 64 per cent over the 

 unsprayed, resulted. 



In addition, records taken from a business point of view on a series 

 of experiments of a nine-year duration, conducted by farmers under 

 the direction of the New York State Experiment Station, show large 

 gams. The average cost of spraying, including materials, labor, and 

 wear and tear on machinery, was $4.74 per acre. The nine-year 

 average increase in yield due to spraying was 361 bushels per acre, 

 making a net profit of $14.43 per acre. When these experiments 

 were conductcMl tlie cost of mat(^rials was less than at the time this 



