USE OF STOP-DROP SPRAYS ON APPLES AND PEARS 



Chemical sprays that retard the drop of fruit from apple and pear 

 trees reduce fruit losses at harvest from suchhigh proportions as 20 per- 

 cent or more to only 5 or 6 percent and frequently less. 



The chennicals in these sprays --known as stop-drop sprays--so 

 tighten a tree's hold on its crop that the fruit is not likely to drop even 

 when jolted by ladders or shaken by the wind. 



Research is progressively adding to the number of chemicals that 

 can be used to stop the fruit from dropping, and is also determining more 

 specifically their effectiveness on particular varieties, solution strengths, 

 times of application, and such side effects as overripening and softening 

 of fruit and damage to foliage and buds. 



Loosening of fruit on a tree is natural in the maturing process. As 

 fruit nears maturity, a callous abscission (separation) layer forms where 

 the fruit stem joins the spur. The callous separates the cells holding 

 stem to spur, and from then on the weakly-held fruit may fall. 



Drop may be increased if trees are deficient in boron or magnesium, 

 or if they have too little moisture. Trees heavily fertilized with nitrogen 

 often drop more fruit than trees moderately fertilized. 



Growth -regulating chemicals that can retard the formation of the 

 abscission layer have been tried on some fruits besides apples and pears. 

 Thus far they have shown little value in protecting peaches from drop. 

 Some conripounds have prevented premature dropping of prunes and apricots, 

 if applied early--at the pit-hardening stage. On citrus fruits, preharvest 

 sprays have been effective under some conditions. However, the outstand- 

 ing success of preharvest sprays has been attained in saving apples and 

 pears --two fruits extensively damaged by drop. 



All varieties of apples and pears are subject to drop, some more 

 than others. Loss has been serious enough in apples to lead growers of 

 all commercial varieties to adopt preharvest spraying, except in the case 

 of early summer apples which are picked before they are eating ripe. 

 Among pears, Bartletts are most likely to drop, Bosc next. Other pear 

 varieties may not drop seriously enough to require a preharvest spray. 

 Protection against dropping by a preharvest spray may be gained at a 

 cost of around $4 an acre (a rough approximation) for cost of material 

 and application. 



Before fruit-sticking sprays were available, apple and pear growers 

 knew, and occasionally practiced, one drastic means of forestalling drop 

 loss. This was to pick early, even though fruit might not have attained its 

 best value in size, color, or storage quality. 



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