380 



STATE BOARD OF AGRICULTURE. 



causing infection. Young shoots are also affected being soon killed by the 

 rapidly spreading mycelium which passes between the cells, into which short 

 sucker-liUe projections (haustoria) are sent. In this way the vines may be 

 much weakened. The berries are usually affected when only partly grown. On 

 these the fungus produces brownish spots which rapidly enlarge soon involving 

 the whole fruit, which may also be covered with downy patches of the fungus. 

 The brown color assumed by the fruit, when attacked, has also given the name 

 brown rot to this disease. 



Within the diseased tissues another form of spore is produced which serves 

 as a resting or winter spore. These are larger than the summer spores, possess 

 a heavy, dark colored outer coat, and hibernate in the tissues of the affected parts 

 which may be left in the vineyard. The downy mildew thrives best during moist 

 weather. It usually appears somewhat later in the season than the black rot 

 disease 



Treatment. When the black rot and downy mildew occur together, as is 

 quite common, no other treatment will be required than for the former. For 

 the mildew alone, sprayings with the ammoniacal copper solution have been 

 found efficacious. The standard Bordeaux mixture or the soda Bordeaux may be 

 substituted. 



Fig. 30. — Microscopic structure of the downy mildew fungus. A, small portion of the 

 mycelium from a disea.sed grape; b, a tuft of spore stalks, (conidiophores), which gives 

 the downy apiiearance to affected parts of the host plant; c, mature 'spores (conidia), 

 produced during summer; d, tliick walled, dark colored resting spore from diseased tissue 

 of grape, highly magnified; (d, after Viala, others original.) 



POWDEHY MILDEW. 



(Uncinula spiralis B. & C.) 



The powdery mildew is not apt to prove very troublesome to vineyardists in 

 this state except in graperies and upon European hybrids which are more sub- 

 ject to it than those of native origin. This disease is confined to the surface 



