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Potato Scab. 



Potato scab, which is too well known to need description, can be 

 held in check by planting previously treated seed in clean land. As 

 it is very difficult to get this fungus out of the soil, great care should 

 be taken not to get it in. Soak the uncut seed potatoes one and one- 

 half hours in Formula 1, or two hours in Formula 2, and then spread 

 out to dry. After drying, the potatoes may be cut and planted in 

 the usual way, care being taken not to allow them to touch any box, 

 bag or bin where scabby potatoes have been kept. Treatment with 

 formalin is safer than corrosive sublimate, and on this account is pre- 

 ferred. All tubers treated with corrosive sublimate should be planted, 

 to avoid danger from the poison on them. For the larger grower or 

 seed dealer, disinfection by means of the formaldehyde gas method, 

 as described under Formula 10, is the most satisfactory procedure. 



Earhj Blight. 

 This cUsease (sometimes improperly called rust) seldom produces 

 so much damage in any one year as does late blight. Nevertheless, 

 it is widespread, and very destructive in that it attacks and weakens 

 the plant at a critical period, thus checking the development of the 

 tubers. It is confined to the foliage, and is not known to cause rot. 

 Early blight first appears as small brown spots scattered over the 

 older leaves. These slowly enlarge and frequently become somewhat 

 angular in shape, from the fact that they stop on reaching a leaf vein. 

 To control this disease, early, frequent and most thorough sprayings 

 with Bordeaux mixture (Formula 6) are necessary. 



Late Blight or Rot. 



This disease is caused by a fungus which attacks both the foliage 

 and the tubers. In this latitude it most freqviently becomes epidemic 

 during the damp, muggy weather of August and September; it does 

 little damage during hot, dry weather. Late blight may be well dis- 

 tributed over a field before it is noticed, except by a trained observer. 

 As a rule, it first appears on the lower and more shaded leaves, which 

 are hidden from view. Contrasted with early blight, it is more of a 

 leaf blotch than a spot disease. The diseased portions are brownish 

 or blackish areas, the leaf green fading out as it approaches the spot, 

 which rapidly enlarges and becomes moist and ill smelling. The 

 margins of the under sides of such spots show a delicate frost-like 

 mildew if examined on a moist, cloudy day or in the early morning. 

 This is the fruiting portion of the fungus, and on each spot are pro- 

 duced thousands of little fruiting bodies, each capable of causing 

 another spot. 



The washing of late bhght spores down into the soil is directly or 

 indirectly the cause of much of the loss from rot of the tubers both 

 in the field and in storage. The most common dry rot of the tuber 

 in Maine is caused by this fungus. Thorough spraying with Bordeaux 

 mixture (Formula 6) , beginning before the blight appears, and keeping 

 the foliage well coated till killed by frost or the crop is harvested, 

 will reduce the losses from this disease to a minimum. No tubers 

 showing dry rot should be planted. 



When to Spray and how to Spray. 

 Begin when the tops are 6 or 8 inches high, and spray every ten 

 days (every week, if the weather is very cloudy and rainy) until the 

 last of August or the first of September, or later if necessary. In any 



