CONTROL OF THE GRAPE-BERRY MOTH. 3 



The extensive grape regions of Michigan have been the source of 

 very few complaints of loss due to the grape-berry moth. In the 

 summer of 1915 the writer visited many vineyards in the vicinity of 

 Benton Harbor, St. Joseph, Paw Paw, and Lawton, Mich., and found 

 the berry moth present in practically all of them, although usually 

 in small numbers. Its destructiveness in this region is obscured by 

 the greater and more consistent injury by the black-rot fungus, and 

 probably injury by the grape-berry moth is often attributed to the 

 black-rot fungus. In contrast to this, in the Ohio grape regions it 

 has been consistently destructive and the leading grape pest for years. 

 Even in a region where the grape-berry moth is a recognized pest 

 it is by no means consistent in occurrence, and may be erratic and 

 local even within a vineyard. In the vicinity of North East, Pa., 

 in the western part of the Erie-Chautauqua grape belt, in most sea- 

 sons fully half of the vineyards are practically free from it. In others 

 the outside rows, ends of rows, or irregular spots are heavily infested, 

 while the rest is practically free. Yet there are many vineyards that 

 annually sustain the loss of from one-fourth to one-half the crop. 



DESTRUCTIVENESS WITHIN A VINEYARD. 



The destructiveness of the grape-berry moth is underestimated 

 greatly even in vineyards where it is recognized as the chief pest, and 

 where the infestation is light it is usually ignored. This is due to the 

 fact that " wormy" grapes, unless very heavily infested, will bring 

 a price comparatively near the standard price, seldom with a reduc- 

 tion of more than 10 per cent. Even when the infestation approaches 

 total, the price may be much nearer to the standard for grapes than 

 the price for cider apples is to the standard price for a.pples. Because 

 of this the vineyardist is apt to consider the reduction in price as the 

 chief loss and largely disregard what may be a greater charge against 

 the berry moth — the reduction in weight. 



The berries infested by first-brood larvae (see PL II, fig. 1) are 

 totally lost, although if they are destroyed very early in the season 

 this loss may be partially offset by increased weight in the rest of 

 the cluster. Those infested by the second brood (see PI. II, fig. 2), 

 which the larvae have left or in which the larvae are well grown, lose 

 weight rapidly; by the end of the season they are little more than 

 dry shells and have but a fraction of their former weight (PL III, 

 fig. 1). This loss varies greatly, depending upon the time when the 

 berries are infested and upon the time of harvest. 



"Wormy" grapes are of course largely excluded from the market 

 for basket grapes, for unfermented juice, and for some wines, unless 

 all of the "wormy" berries are trimmed out. This exclusion from 

 certain markets may in certain years represent a considerable loss. 



