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Show SELEGTGLfAN 5EE0 Most Important Precaution in Control of Potato Scab. Disinfection Treatment Is an Added Foresight Neither Will Be Ef- fecti"e If Soil Is Already ' Full of Disease. i (From the United States Department of . Agriculture.) ' The treatment of seed potatoes with formaldehyde or with corrosive sublimate sub-limate has been recommended for many years as a preventive of scab and other diseases carried on the tubers. tu-bers. Such treatment ls, on the whole, profitable, but has several limitations which should be clearly recognized to prevent disappointment, according to the specialists of the department. The object of disinfecting seed potatoes pota-toes is to destroy the germs of scab and other surface parasites which might otherwise be planted with the seed and infect the new crop. Only surface infections are reached by this method. It is only partially effective against deep pits of common scab. Formaldehyde is less effective than corrosive sublimate against the black sclerotia or resting bodies of rhizoc-tonia, rhizoc-tonia, or russet scab, and against powdery pow-dery scab. Neither chemical, as ordinarily or-dinarily used, will destroy silver scurf. Either one will kill surface infections of blackleg, but neither fusarium wilt nor late blight infection in potato tubers tu-bers can be reached by any seed treatment, treat-ment, nor can any of the nonparasitic diseases of potatoes, such as mosaic leaf roll, and curly dwarf, be prevented. prevent-ed. See Farmers' Bulletin 544 for description of these troubles. Clearly, therefore, the most important impor-tant precaution against these diseases is to select clean, disease-free seed potatoes from healtny, vigorous plants, as determined by field inspection during dur-ing the growing season and at harvest. Seed treatment should then be applied as an additional precaution. Soil Conditions and Potato Diseases. Soil conditions have an important relation re-lation to potattjfctuber diseases, and many of these are widely spread throughout the- country, perhaps na- ' ' -fij' jr- '''-:. v'i". -v-V r - '-!- I. - " i Potato Affected With Russet Scab, i Showing Russeting and Cracking Associated As-sociated With Rhizoctonia of Western West-ern Potato. tive to some soils. Common scab is favored by a neutral or slightly alkaline al-kaline soil, and seldom gives trouble in acid soils. It is therefore increased by liming and by fresh stable manure, wood ashes, and alkaline fertilizers, such as nitrate of soda and ground bone, while acid phosphate and sulphate sul-phate of ammonia tend to diminish scab. Rhizoctonia occurs to some extent in nearly all soils, but appears to attack at-tack potatoes most when the conditions condi-tions are unfavorable to the best development de-velopment of the potato plant. Bring the land to an ideal state of tilth to minimize loss from rhizoctonia. I Powdery scab Is worst on cold, wet, or poorly drained soils. Blackleg, on the other hand, 1b carried by infected infect-ed seed. No potatoes showing a deep brown discoloration at the stem end should be planted. Sulphur tends to prevent common scab. It is not a substitute for corrosive cor-rosive sublimate or formaldehyde, but is a good drier for cut seed. Applied lo scab-infected soils at the rate of 500 pounds per acre It reduces the scab, but such heavy applications cannot can-not be generally recommended as profitable. Preliminary experimental trials are advised. How to Disinfect Seed. The formaldehyde treatment consists con-sists of soaking the potatoes, before cutting, for two hours in a solution made by adding one pint of formal- Potato Affected With Common Scab. dehyde to 30 gallons of water. The solution can be used repeatedly. The gas treatment is no longer recommended. recom-mended. Corrosive sublimate is used at the rate of 1-1,000 for one and one-half to two hours. Dissolve two ounces of the salt in hot water and dilute to 15 gal lons. This is a deadly poison. Use with great care. It must also be kept in wood, porcelain, or glass vessels, as it attacks metal. It is more effective effec-tive than formaldehyde, particularly against rhizoctonia and powdery scab. Do not use the same solution more than three times, as the strength diminishes with each lot of potatoes soaked. To treat large quantities, set several sev-eral barrels on a slightly elevated platform. plat-form. Fit a plug in a hole in the bottom bot-tom of each barrel, fill with potatoes, cover with solution, let stand two hours, draw off solution, and pour into another barrel. Increase the number of barrels in proportion to the quantity quan-tity to be treated. Another method is to use a large wooden vat or trough, , into which the potatoes in sacks are ; lowered by a rope and pulley and later hauled out, drained, and dried on slatted slat-ted racks. Seed potatoes may be treated several sev-eral weeks before planting, provided they are not reinfected by storing in old containers or storage bins. Sprouted potatoes are injured by treatment, but will throw out new sprouts. In general, however, pota. toes will not be injured by following the above directions. Many growers believe germination is improved by treatment. |