10 MASS. EXPERIMENT STATION BULLETIN 399 



disadvantage of both the grower and his orchard. In a good crop year, most 

 peach varieties need thinning, since the trees set more fruit than they can carry 

 to maturity and still develop good size. 



The principal reason for thinning is to obtain large peaches. A three-inch 

 peach has about three times the volume of a two-inch peach. With the increase 

 in size of the fruit there is a comparatively small increase in the size of the pit. 

 Therefore, one three-inch peach is worth more than three two-Inch peaches 

 because there is more flesh to eat and fewer pits for the tree to develop. 



The thinning should be done as soon as possible after the June drop. Early 

 thinning is essential, for it helps to preserve, but not to increase, the vigor of 

 the tree. It requires as much reserve material to develop the growing pit as to 

 develop the rest of the fruit. Early thinning decreases this heavy withdrawal of 

 food reserves by the developing fruits, leaving a larger portion for growth and 

 fruit-bud formation. 



This preservation of vigor by thinning helps to increase cold resistance, be- 

 cause, as has already been pointed out, cold resistance is correlated with the 

 presence of a large supply of reserve material within the tree. Experience shows 

 that where a tree has been exhausted by bearing a heavy crop, it is more suscep- 

 tible to injury by winter cold. 



Thin the fruit to a distance of six to eight inches, depending on the size of 

 the mature fruit of the variety. During the thinning operation, twist off the 

 fruit; never pull it ofT, because pulling results in many injured branches. 



In addition to increasing the size of the fruit and helping to preserve the vigor 

 of the tree, thinning improves the grade, quality, and color of the fruit, decreases 

 labor in harvesting the crop, and lessens the danger of broken limbs. 



Spraying 



The spra}- program to be followed for the peach, as for any other fruit, depends 

 on the insects and diseases present. Therefore, a knowledge of these troubles 

 is essential in order to follow a spray program intelligently. 



Insect Pests 



The following are the most important insect pests of the peach: 



The Peach Tree Borer is one of the worst pests of the peach. As a small 

 white larva it bores into the base of the tree trunk and eats the cambium and sap- 

 wood. Its presence can be detected by the gummy exudate from its burrows. 

 As it seldom burrows very deep, it can be dug out with a sharp knife in the early 

 fall or spring. The soil should be dug away from the base of the tree to a depth 

 of five or six inches to get any borers below the surface. 



In a large orchard, an easier way to dispose of borers is by using paradichloro- 

 benzene (Figure 5). This is a white crystalline solid which vaporizes slowly at 

 ordinary temperatures. It may be obtained under various trade names. The 

 gas is not poisonous to man but will kill insects on sufficient exposure. To apply 

 paradichlorobenzene : 



First — scrape away all sod, loose soil, sticks, large stones, or other debris from 

 around the trunk to a distance of about one foot, without disturbing the firm 

 soil beneath. Remove masses of gum present on the base of the tree. 



