The Coconino sun., 1918-03-01
THE PROPER TREATMENT
 OF SEED POTATOES
(By D. c. George, Plant Pathologist, Arizona Commission Agriculture and Horticulture.)

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 Potatoes are subject to number of diseases, the most important of which in Arizona are Rhiztoctonia and Scab. Of these two, the former is by far the more serious. In connection with the treatment and control measures rec commended the appearance of the dis ease upon the tubers and some other general characteristics are briefly con sidered
 The RhizOctOnia Disease.
 This disease appears upon the tu- bers as small, warty, dark-brown ele- Evations, resembling dirt patches that will not rub off. These structures are known as the sclerotia and are much more conspicuous when the tuber is wet. Frequently the disease causes slight corrosion or roughening of the skin to which the term "ruset-scab" has been applied. This stage is usu- ally associated with a deep, wide, crack or split very much roughened and corroded. Often slight pune ture or sunken spot in the skin re- veals beneath it deep pocket or pit resembling the work of some insect. The object of seed treatment is to kill all the sclerotia or any other part of the fungus that might be present upon the seed tubers.
 Potato Scab.
 Potato scab appears upon the tubers in crust spots, deeply cracked and furrowed. In serious cases these spots may join together, causing a general roughened appearance over the sur face of the tuber. Scab develops no , sclerotia or other structure upon the surface of the tuber and causes no pits or pockets as in the case of the Rhizoctonia disease.
 Similarities and Differences. The Rhizoctonia disease is caused by soil fungus common in many soils and supposed to be native to some. Scab is caused by soil bacterium, common in nearly all soils and espe- cially prevalent in soils with high humus content. Rhizoctonia is espe- cially favored by an acid soil, and scab by an alkaline soil. Rhizoctonia is lessened by the use of barnyard manure, while scab is increased by its use, especially if the manure is fresh It has recently been determined that the organism causing scab is very prevalent in humus material in the process of decomposition. Both dis eases develop best under high mois- ture conditions and when once estab- lished in the soil will remain there for indefinite periods. Both attack such crops as beets, turnips, mangels, ruta- bagas, etc, but have never been found causing injury to such crops as wheat, oats or barley, Rhizoctonia and. scab are both subject to the same seed treatment. Formaldehyde is effective against scab, but is very unsatisfac- tory against Rhizoctonia, while the corrosive sublimate solution is effect i've against both diseases. Control. In the control of these diseases the following system should be followed l. Use clean seed. 2. Rotate crops. 3. Select soil known to be unin- fected.-
 4. Treat Seed.
 The tratment recommended for both the Rhizoctonia disease and scab is as follows:
 Corrosive sublimate-4 oz.
 Water-30 gal. This strength makes a 1 to 1000 1 solution. The seed potatoes should be covered, by the solution from 11s to 2 hours.
 The following should be strictly ob- served:
 1. Treat all seed in wooden vessels such as candy pails or barrels, as the solution will corrode metal.
 2. Corrosive subIimate is deadly internal poison but is non-injurious to the skin and may be handled without danger.
 B. Use new solution to every 5 bushels of seed.
 4. Never feed treated potatoes to livestock.
 5. Treat all tubers before cutting.