32 CIRCULAR 867, U. S. DEPARTMENT OF AGRICULTURE 



Typical results obtained in tests using dinitro sprays for thinning 

 peaches in various fruit sections are summarized in table 9. In con- 

 sidering these data, it should be remembered that fruit-set records are 

 often confusing and fail to present a complete picture, because the 

 number of fruit buds borne per unit of shoot growth vary greatly 

 with different varieties as well as with the amount anof type of 

 growth made by the tree the previous season. Yield records, where 

 they are given, may also be somewhat misleading because of varia- 

 tions in tree size and vigor. Also, the total yield per tree in many 

 instances is not an indication of the monetary value of the crop. In 

 many areas and seasons the price differential between large and 

 small sizes may be as much as 50 to 100 percent. 



It may be seen from the data presented in table 9 that the same 

 range of concentration suggested for apples is effective in reducing 

 the set of peaches. While in most cases spray applications of 1 pint 

 of Elgetol per 100 gallons reduced fruit set, concentrations of V/ 2 

 and 2 pints were generally more effective. As with apples, the data 

 are too variable to permit definite recommendations as to concentra- 

 tion for any particular variety or environmental conditions. 



The flower buds of peaches develop earlier and more rapidly than 

 do the leaf buds. At full bloom there is very little exposed leaf sur- 

 face on peach trees, which may tend to minimize any indirect or 

 "shock" effect of a dinitro spray in reducing fruit set. Furthermore, 

 the stems of peach flowers are short and thick and for this reason 

 may be more protected from the caustic action of the spray than the 

 long, slender, highly exposed stems of plum, pear, and apple flowers. 



Bloom sprays for thinning peaches have usually given the most 

 satisfactory results when a rather constant and uninterrupted open- 

 ing of blossoms occurs over a 3- to 5-day period. For greatest effec- 

 tiveness generally the sprays should be applied when about 75 to 

 95 percent of the flowers are open. If the spray application is delayed 

 until all flowers are open the amount of thinning may be disappoint- 

 ing. 



More exact timing seems to be necessary with peaches than is the 

 case with apples. There are, however, a few reports of thinning re- 

 sulting from sprays applied after full bloom. Havis {17), in a well- 

 planned experiment with the Elberta variety, obtained more thinning 

 with a concentration of V/ 2 pints of Elgetol per 100 gallons 4 days 

 after full bloom than with the same concentration at the full bloom 

 stage. In contrast, Murneek and Hibbard (33) reported insufficient 

 thinning when Elgetol sprays at concentrations of 1 pint, 1 quart, 

 and 2 quarts per 100 gallons were applied to vigorous Elberta trees 

 3 to 4 days after full bloom. The strongest concentration resulted in 

 some thinning, but the trees still carried an overload of fruit. 



Under any given set of weather conditions different varieties may 

 vary considerably in the time required for them to reach the proper 

 stage of bloom development for the application of dinitro sprays. 

 Where several varieties are grown in the same orchard it will seldom 

 be possible to spray them all on the same day with equally satisfac- 

 tory results. Even in large blocks of a single variety, variations in 

 soil and exposure may cause enough difference in bloom development 



