14 MASS. EXPERIMENT STATION BULLETIN 422 



Spraying 



Experimental spraying was started in 1942 at Sandwich, Massachusetts. The 

 spray schedule recommended by Tomlinson (5) was used, since it had never been 

 tested experimentally to see whether adequate control was provided for all 

 insects and diseases. Although a crop failure prevented close checking of results, 

 observation indicated that (1) the plum gouger was poorly controlled, (2) a 

 gall-maker, which was very common on the leaves of unsprayed bushes, was 

 completely controlled, (3) plum pockets was not present in the sprayed area but 

 was abundant on older adjacent unsprayed bushes, (4) brown rot was only fairly 

 well controlled, some blossom blight being present on the sprayed plots in con- 

 trast to plenty of both blossom and twig blight in adjacent unsprayed areas. 

 It was evident that modifications in the spray program must be made if good 

 control of plum gouger and brown rot was to be obtained. 



On the basis of the work of 1942, the following changes in the spray program 

 were made: To control plum gouger — (1) Arsenate of lead was added to the 

 Pre-blossom spray because the gouger is supposed to start its work before the 

 blossoms open. In 1942, gougers were not found working until June 18 and in 

 1943 until June 17. (2) The amount of lead arsenate was increased from 3 to 4 

 pounds per hundred gallons whenever it was used. For better control of brown 

 rot a fifth spray, the Second Cover, was applied 21 days after the Shuck. The 

 lead arsenate in this spray should kill any gougers which might still be working 

 on the plums. 



In 1943, the experimental spraying was continued and expanded. A second 

 experiment was started in the beach plum planting near East Wareham where 

 the fertilizer work was done. Again in 1943 the crop was almost a total failure 

 at Sandwich. What few plums matured were badly stung by gougers. Since 

 there were so few plums, a very few gougers could have caused all the damage. 

 On the plot near East Wareham, it was estimated that not over 10 percent of the 

 fruit was stung by gougers. 



The control of brown rot at East Wareham was excellent. At Sandwich, 

 where control was not so good, brown rot was evident in the iorm of blossom 

 blight. The presence of many blighted blossoms on unsprayed bushes next to 

 the spray plot suggests that brown rot may be limiting the set of fruit by destroy- 

 ing the blossoms, thereby contributing in no small degree to the periodic crop 

 failures. The difference in control at these two locations was due to difference 

 in local conditions. The sprajed plot at Sandwich was surrounded on all sides 

 by unsprayed bushes, some of them old and heavily infested with the pests. 

 The plot near East Wareham was separated from the nearest unsprayed bushes 

 by some distance. Although a strip 20 feet wide was sprayed around the plots, 

 this was not wide enough at the Sandwich plot to keep pests from coming in 

 from the unsprayed bushes. This is particularly true with regard to the plum 

 gouger which is reported to be a verj' acti\'e flier. 



As a result of the two years' experience, one more spray has been added to the 

 1943 schedule. This is a Petal Fall spray to be applied when 90 percent of the 

 petals have fallen. It is intended to give better protection during the long period 

 between the Pre-Blossom and Shuck sprays when leaves and fruit are developing 

 very rapidly. 



