16 X. H. Agri. Experiment Station [Bulletin 284 



Apple Scab Experiments 



In spraying experiments on Mcintosh apples the use of a secOfid cover 

 spray gave substantially twice the scab control obtained with one cover. 

 These results are in agreement with previous work. Two cover sprays are 

 required for the control of scab on Mcintosh. Experiments were made 

 during the year wnth cal-mo-sul (calcium monosulphide) lime-sulphur solu- 

 tion 1-50 followed by flotation sulphur beginning with the calyx application. 

 The scab infection on the check trees in the cal-mo-sul plot was light, and 

 the control obtained with this fungicide was as satisfactory as that given by 

 lime-sulphur solution ; but it should be noted that previous experience with 

 cal-mo-sul under conditions of heavy infestation has been extremely disap- 

 pointing. The use of flotation sulphur in lieu of lime-sulphur solution 1-50 

 beginning with the calyx application gave substantially the same control as 

 lime-sulphur solution 1-50 used throughout the season. 



In some of the plots lead arsenate was used in the lime-sulphur solution 

 when an arsenical was required; in others, calcium arsenate. No increase 

 in foliage injury resulted from the use of calcium arsenate, nor was there 

 any difference in the finish of the fruit. 



In experiments with Baldwins the results confirm previous findings tliat 

 the Baldwin is much less sensitive to scab tlian the Mcintosh. One cover 

 spray gave ample protection. The substitution of caldum arsenate for lead 

 arsenate in lime-sulphur solution was not found to significantly increase 

 ioliage injury. 



The ascospores were mature on April 24, but no discharge occurred in 

 -nature until Alay 10th. The delayed discharge was no doubt due to the 

 ..scantiness of the rainfall. The first rain after April 24 occurred on May 4 

  (.02 in.) and the next on May 9th (0.37 in.). The pre-pink spray w^s ap- 

 plied May 5. The data so far secured indicate that irrespective of the length 

 1 of the snow cover in winter, or the mean temperature of the winter, asco- 

 ; spores mature during the last ten days in April, and discharge occurs during 

 the first wetting rain following maturity. (O. Butler and S. Dunn, Hatch 

 iFund.) 



Contact Insecticides 



'The resiilts in two further phases of the studies in contact insecticides 

 have been completed and published during the year as Technical Bulletin 58, 

 entitled, "1. Alethods of Expressing Toxicity. 2. Toxicity of Nicotine, 

 Heptylic Acid and Caproic Acid to Mosquito Larvae Cidex pipions L." 



Substantial ])rogress was also made in an investigation of the perform- 

 ance of several familiar contact agents when applied to various leaf surfaces. 

 Such performance has a definite relationship to toxicity against insects- 

 While a contact insecticide is designed to kill an insect through contact with 

 that insect's body, the ability of such an insecticide to spread over leaf sur- 

 faces may also play a prominent part, because spread on a leaf may mean 

 that the in.secticide is the more readily able to reach the insect. Furthermore, 

 if a material spreads quickly and evenly over a leaf it may be safe, whereas 

 if it c(jllects in droplets it may be unsafe because the droplets on drying may 

 subject the leaf to undue concentrations of the spray. 



Several contact agents were included in these studies. Data were secured 

 as to the performance of sodium oleate, saponin, triethanclamine oleate, 

 potassium cocoanut oil soap, Gardinol, calcium caseinate, and monoamyla- 



