The Grape Rot. 223 



THE GRAPE EOT. 



BY PROF. WILLIAM TRELEASE, OF WISCONSIN. 



Of late years the attention of grape growers has been annually called to a 

 number of diseases of the berry, by which their vintage has been much les- 

 sened. As a rule these diseases are known as " the grape rot," and no little 

 anxiety has been felt as to the cause and probable duration of this rot. 



I shall try to bring together as briefly as possible the facts which have 

 come under my observation, through specimens and inquiries, from various 

 parts of Wisconsin. It is probable that there are other forms of the so-called 

 rot which are familiar to members of this Society, and the main object of 

 my paper is to direct their attention to the subject, with the hope of utiliz- 

 ing their observations in the further study of the diseases of the grape. 



Some berries show a discolored spot about an evident injury on the sur- 

 face, which most frequently appears as a minute puncture, suggesting at 

 once the idea of insect work. Occasionally such berries crack open, espe- 

 cially in wet weather, as a result of the osmotic imbibition of water by the 

 pulp cells near the puncture. 



An examination of grapes affected with this form of the disease shows that 

 they often contain small caterpillars. These larvae feed on their pulp and 

 seeds. From its resemblance to the larvte of the codling moth, this insect 

 (Eudemis botrana, SchifF.) has been called the Grape Codling, the Grape-fruit 

 Worm and the Grape-berry Moth. When grown the larvae deserts the fruit 

 and, as a rule, cuts a little flap from one of the nearest leaves, which it webs 

 over it, after the manner of the Tortricides or Leaf-rollers, to which group 

 of insects it belongs. In this retreat it changes into a pupa, from which the 

 small moth into which it transforms ultimately emerges. A very good ac- 

 count of its transformation m.ay be found in Prof. Riley's First Report on the 

 Insects of Missouri, pp. 133-6. 



The spring brood of larvse are said to eat the leaves of the grape. It has 

 also been shown* that they sometimes "feed on the tender shoots of the com- 

 mon Iron Weed ( Vernonia novehoiricensis), which they web together for 

 their better protection. When mature they desert these retreats and cut 

 little flaps from the larger leaves, which, folded over and fastened at the 

 edges, protect them during the pupa stage." The insect "has also been bred 

 from larvfe webbing the leaves of the Tulip Tree (Liriodendron), and of 

 the Lead Plant (Amorpha)," from which it will be seen that its food is sup- 

 plied by plants of the most diverse nature. 



A somewhat similar injury is caused by the Grape Curculio (Crapmius in- 

 xqucdis, Say), the larvte of which can be readily distinguished from the Cod- 

 ling by being footless, while the latter has three pairs of true legs and five 

 pairs of prop legs or abdominal legs. When mature the Curculio larvfe de- 



* Miss Murtfeldt: Psyche, 1881, III., p. 276. 



