With air-blast spray equipment , it is possible to apply the stop-drop 

 chemicals as "concentrate' sprays. With this equipnnent, concentrations 

 may be 4 to 6 times as strong as a dilute spray, and'Vie liquid per acre is 

 reduced accordingly. 



Timing 



How far ahead of harvest to apply a fruit -sticking spray depends on 

 the chemical chosen. 



Proper timing allows for a lag of some days after spraying, in which 

 period the chemical is taking effect. NAA requires about 3 days to become 

 effective; 2,4-D about 10 days; 2,4,5- T and 2,4,5- TP about a week. 



Since NAA is dependable for no more than 10 days or 2 weeks, a 

 preharvest NAA spray needs to be timed closely, to take effect just when 

 drop is expected to start. 



2,4-D and 2,4,5 -T and 2,4,5- TP may be applied 3 or 4 weeks before 

 harvest, which is often convenient timing for work management. 



Successful spray application is timed to keep within certain stages of 

 plant growth. Spray applied too early may increase a chemical's effect on 

 ripening, and fruit may be overripe when picked. A stop-drop spray is too 

 late and is wasted if applied after the abscission process is already under 

 way, because then the chemical cannot take effect. Spray is also too late to 

 give good effect if applied after foliage is old and faded from frost or other 

 cause. 



Combining Treatments 



Several varieties planted together can frequently be given drop pro- 

 tection by one preharvest spraying- -provided the same chennical and the 

 rate of application are suitable for all. 



A dual-purpose spray --in which a stop-drop chennical has been added 

 to material for plant disease or pest control--is often less satisfactory 

 than a stop-drop chemical sprayed separately, and especially so if the 

 other spray material contains lime. 



Climate Considerations 



Temperature makes some difference in results achieved with pre- 

 harvest sprays, and should be considered in planning their use. A rela- 

 tively warm temperature, 70° F. or higher, at spraying time is an 

 advantage, because the chemical will be absorbed more readily than when 

 weather is cool. At warm temperatures the chemical will also take effect 

 faster. Once a stop-drop chemical has become effective, temperature 

 changes do not further alter its potency to any extent. 



Considerable moisture from dew, fog, or rain is ordinarily an aid to 

 the potency of the chemicals. Lack of moisture, contrariwise, lowers their 

 efficiency. Occasionally, the unexpected happens, as when Mcintosh apple 

 trees in Northeast orchards dropped fruit badly in 1955, when the growing 

 season was rainy. Such situations are a reminder that, useful as the stop- 

 drop chemicals are, their action is not completely understood. 



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