ANNUAL REPORT, 1936 49 



Washes of derris powder used at the rate of 2 pounds and 3 pounds in 50 

 gallons permitted 66 percent moderate or severe injury and were surprisingly 

 unsatisfactory. 



Derris and pyrethrum clay dusts diluted with inert clay were less effective 

 than the liquid sprays and left a very objectionable residue on the plants which 

 generally eliminates them from commercial use on snapdragons. 



Control of Cabbage Maggot with Mercury Compounds. The natural field 

 infestation of the cabbage maggot at Waltham was again very high and 82 to 

 94 percent of the untreated plants were killed or severely injured. Corrosive 

 sublimate, 1 ounce in 10 gallons of water, continued to give excellent protection. 

 One application when the eggs were first found (May 6) gave practical pro- 

 tection to 94 percent of the plants with a minimum of small or otherwise 

 unsalable heads. Later applications were not satisfactory, however, and 

 emphasized the importance of early treatment. 



Experimental treatments with calomel (mercurous chloride) both as a dust 

 and as a paste applied to the roots and stem of the seedlings when they were 

 transplanted gave promising results and reduced the labor of application. As 

 a dust, pure calomel shaken on the roots protected 88 percent of the plants 

 from moderate or severe injury and produced the most salable heads of the 

 experiment. When the powdered calomel was mixed in the proportion of 1:1 

 and 1:3 with inert clay the protection was reduced to 60 and 42 percent re- 

 spectively. 



As a wet treatment, calomel was mixed with various adhesive materials in 

 the proportions of 1:1, 1:3, and 1:9 and wet with sufficient water to make a 

 thick paste which covered the roots and lower stem with a thick coating. Mix- 

 tures with laundry starch, clay, and clay plus fish oil, gave 76 to 96 percent 

 protection and were the most satisfactory. The addition of fish oil did not 

 increase the effectiveness of the clay mixture. There was no significant differ- 

 ence between the 1:1 ratio and the 1:3 ratio, but the 1:9 ratio was generally 

 less effective in all of the mixtures. 



Mixtures of calomel and calcium caseinate, lead arsenate and sulfur (15-85), 

 and lead arsenate and lime (20-80) in paste form caused serious injury to the 

 cabbage seedlings and killed many of them. 



All of the paste mixtures slightly checked the growth of the seedlings by 

 sticking and matting the roots together. The plants dipped in the clay and 

 starch mixtures recovered quickly and formed new roots so that there was 

 little decrease in the size or earliness of head, but the mixture must be im- 

 proved to prevent this condition before the treatment can be considered 

 practical. 



Control of the Squash Vine Borer. In 1936 the field infestation of the squash 

 vine borer was much less than in previous years, and at Waltham the average 

 infestation in untreated Hubbard squash vines was 1.13 borers per vine. 



The most effective insecticidal treatment was a spray prepared from cube 

 powder at the rate of 5 pounds in 100 gallons of water, which was made wettable 

 with fish-oil soap at the rate of 1 quart in 100 gallons of spray. This reduced 

 the injury 74 percent. Spraying with nicotine sulfate 1-500 plus 1 percent of 

 summer oil was again more effective than nicotine sulfate 1-250. Dusts were 

 not so effective as in 1935 although they protected the vines from serious in- 

 jury and were applied much more quickly and easily than the sprays. Pyre- 

 thrum-clay dust 30-70 gave slightly better control than derris or cube dusts. 



The records in these studies are obtained by pulling up the roots and cutting 

 off and splitting approximately four feet of the vine stem. This is usually done 

 about August 20, and for the second year an excellent crop of squash has 



