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Summary: A preliminary field experiment was conducted to test the use of calomel as a dip treatment for potatoes in comparison with a hot mercuric chloride treatment and a Semesan Bel dip treatment. A laboratory test indicated complete killing of Rhizoctonia sclerotia with the hot mercuric chloride treatment and a nearly complete inhibition of growth of Rhizoctonia with the Semesan Bel and Calomel. Markedly and significantly better stands were secured on all of these treated plots as compared with the untreated. In this respect the hot mercuric chloride and Calomel dip treatments gave better average stands than Semesan Bel though the difference was hardly significant. All of these treatments also gave significant increase in yield over the untreated. These average increases varied from 22 to 37 bushels per acre. The higher yields were obtained with the hot mercuric chloride and Semesan Bel treatments though the differences between these yields and the yields of the calomel treated plots is not significant. The trial of less concentrated mixtures of calomel seems to be indicated.

Conclusions: For the past two years marked reduction in the percentages of potato scab have been obtained in certain fields by spraying potatoes with bordeaux mixture. Several ways in which spraying might cause such results are suggested. The delay in tuber-setting and enlargement caused by spraying, might throw these phenomena into a period when higher soil moisture prevails, thus reducing the amount of infection. Tubers from sprayed plants have a higher total nitrogen and copper content, either of which may have some influence on infection. Reduction in the population of flea-beetles may reduce inoculation. Sprayed plants wilt more in hot weather and this may bring about changes which make the tubers more scab-resistant.

Summary: The results both in upstate New York with Rural potatoes and un Long Island with Green Mountains seem to consistently favor a Bordeaux mixture with less lime than copper sulfate. In one experiment at Pittsford in which the amount applied was also varied, there seemed to be a clear indication that with mixture, not so much copper per acre is necessary to give maximum yields as with mixtures containing larger proportions of lime. So far as our experience goes in these three years in the three localities, it appears safe and desirable to reduce the lime in the mixture, either stone or hydrated, at least to half as much as the amount of copper sulfate.

Conclusions: In these rather simple exploratory tests, no reason was found for believing that lime has any effect on potato scab other than through its effect on the alkalinity of the soil. The general relation of acidity of the soil to scab was similar to that previously reported from a field survey.The amount of scab was reduced by extremely heavy applications of lime giving pH values of the soil (about 9.0) higher than those found on the survey (8.0–8.3) where scab was not troublesome.

Summary: Working with the Irish Cobbler, Rural Russet and Green Mountain varieties of potatoes at Pittsford, N. Y., it was found that all these varieties respond to copper treatments in the form of bordeaux mixture to approximately the same extent in final increases in yields. Using a Bordeaux mixture composed of the equivalent of half as much quick lime as copper sulfate, and applying most of the copper early in the season, there appeared to be no advantage in using more than a total of 60 pounds of copper sulfate per acre during the season. All copper-sprayed plants retained more tubers per plant than unsprayed plants of the same variety.All varieties showed evidence of a retardation in tuber development due to spraying. The retardation was less pronounced with the Cobblers and most pronounced with the Green Mountains. In the Green Mountains, the unsprayed plants yielded more than the sprayed until after September 21.

Summary: All data have been obtained from experiments in a region characterized by soils of rather alkaline reaction, usually at least pH 6.0. Formalin seed treatments have consistently given small reductions in potato scab when compared with the untreated check plots.Mercurial seed treatments have given small but significant increases in scab over the checks and formalin treatments.Mercurials added to the soil have, in all cases, increased scab.In Western New York tuber defects are markedly decreased by the use of sulfate of ammonia in the fertilizer.In limited trials tetrachloroethane and hexamethylenetetramine showed no promise of scab control.Netted Gem possesses a rather high degree of resistance to serious injury by potato scab.Slight differences in scab resistance apparently exist within the Smooth Rural group of varieties.White Blossom Cobbler is considerably more resistant than is the Irish Cobbler variety.

Summary: Maximum yields were obtained on Rural potatoes in upstate New York over a period of four years by spraying at 400 pounds pressure and using a total of 75 to 80 pounds of copper sulphate per acre per season in the form of Bordeaux. Apparently less copper sulphate per acre per season is required on Long Island to get the maximum yield. As the amount of lime in the Bordeaux was decreased better yields were obtained. A ratio of 5 pounds copper sulphate to 2 1/2 pounds of hydrated lime to 50 gallons of water is believed to be a safe recommendation.

Summary: MoreRhizoctonia occurred on potato tubers where potatoes were grown on the same plots for three successive years than during the longer rotations. On plots where potatoes were grown for three years in succession, the use of 1000 pounds of 5-10-5 fertilizer reduced the number of tubers showingRhizoctonia in the two locations where the rotations were such that this point was tested. The application of stable manure reduced the amount ofRhizoctonia on the tubers at all of the places. A rye cover crop also reduced the amount ofRhizoctonia in two of the three places. The best results in controllingRhizoctonia where potatoes were grown repeatedly on the same plots were obtained by combining all of these practices, that is the use of commercial fertilizer, stable manure and cover crops.

Summary: The results obtained in three rotation experiments in New York State in 1939, confirm the report made in 1938. They are as follows: More potato tubers bore sclerotia ofRhisoctonia where potatoes were grown continuously than where they were grown in longer rotations. Where potatoes were grown continuously, the largest percentage of tubers were affected withRhizoctonia where they were grown without commercial fertilizer, manure or cover crop. The addition of fertilizing material in any of these forms reduced the percentage of tubers affected, and the greatest reduction was secured on plots where all of these fertilizing materials Were used together. At the only location where the pH of the soil was such as to favor scab, the largest amount occurred on plots which received no fertilizer, manure or cover crop. At the other locations small increases in scab occurred on plots Which had been previously limed for clover. The largest increases were obtained on plots which received both manure and lime. Manure alone has caused a small increase at Malone.