ANNUAL REPORT, 1941 51 



abrupt, and since it was not accompanied with the usual amount of rainfall the 

 snow and frost disappeared rapidly and the soil dried quickly, furnishing excellent 

 ground conditions for early spring spra\'ing. Plant and animal life responded to the 

 unusualh- warm weather. Seasonal development began early and progressed 

 rapidly. In most orchards the period for delayed dormant application of oil 

 sprays was very brief so that many growers were unable to complete this appli- 

 cation before bud development progressed to the pre-pink stage. In the college 

 orchards the delayed dormant period was passed in 4 to 5 days, and some blocks 

 received the pre-pink spray 3 days after the delayed dormant. In the experimental 

 blocks the trees had received the dormant, delayed dormant, pre-pink, and pink 

 sprays by April 28 in contrast to 1940 when in the same blocks the delayed dor- 

 mant spray was applied April 29. Verj' few instances of damage to fruit buds or 

 foliage by oil sprays were obser\'cd or reported in spite of the unseasonable tem- 

 perature. This was probably due in large measure to the relative!}' small amount 

 of oil spraying done. 



In the cooperative project with the Dow Chemical Company on the investiga- 

 tion of DN .sprays, attention was focused on the relative tolerance of various types 

 of ornamentals (coniferous and deciduous) to dormant applications of DN-oil 

 sprays. In these tests different concentrations of dinitro-ortho-cyclo-hexylphenol 

 (DNOCHP) compounds were used. None of the common deciduous ornamentals 

 showed any ill effects from the application aside from a .slight retardation in some 

 cases. Moderate burning was noted on Irish juniper and more serious injury 

 resulted on rhododendron and laurel. 



In strictly dormant application on apples for the control of overwintering eggs 

 of European red mite, 2 dry-mix DN compositions containing 40 percent 

 DNOCHP and DNOC (dinitro-orthocresol) respectively were combined with 

 2 standard types of commercial oil sprays. Application of a DNOCHP — oil 

 solution of 7.9 pH caused no injury to fruit or leaf buds nor retardation in de- 

 velopment. A DNOCHP-oil solution of 6.6 pH caused noticeable retardation in 

 development but no actual killing of buds. The DNOC-cil solutions of 5.8 

 pH and 4.8 pH both caused marked retardation of bud development. The 

 combinations containing the DN compounds were somewhat less effective against 

 red mite eggs than were the oils alone. 



Counts of young mites on the test trees showed 1,660 mites per 100 spurs 

 following DNOCHP-oil emulsion; 675 following DNOC-oil emulsion; and 465 

 following the oil emulsion alone. Check trees showed 13,055 mites per 100 spurs. 

 Following DNOCHP-fmiscible oil, counts showed 20 mites, DNOC + miscible 

 oil, 80 mites; and miscible oil alone, 15 mites per 100 spurs. 



In applications at Waltham en April 8, 1941, no noticeable injury resulted to 

 bark or twigs from DN-oil mixtures having a pH value of 8.0, 7.45, or 6.75. 

 All of the mixtures retarded bud development slightly, and when trees were in 

 full bloom there was slightly more retardation on Mcintosh and Wealthy from 

 the alkaline mixture than from the more acid mixture. It was also observed that 

 a dinitro-orthocresol-oil mixture retarded bud development slightly less than 

 dinitro-ortho-cyclo-hexylphenol in combination with either alkaline or acid oil 

 emulsion. 



All of the sprays gave good control of the European red mite eggs and reduced 

 the average number of living mites per spur on April 30 by 90 percent or more. 

 No significant differences between the materials resulted, but the dinitro-ortho- 

 cresol-oil mixture, which is generally considered safer than the DNOCHP mix- 

 ture, gave very .satisfactory control of the red mite. 



At the college, incidental records on the overwintering eggs of aphids, includ- 

 ing heavy infestations on birch and pine and moderate infestations on several 

 ornamentals, showed practically perfect kill following the use of DN compounds. 



