This section is from the book "The Gardener's Monthly And Horticulturist V22", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
From an excellent article in Mr. Robinson's Gardening Illustrated, we have the following about mildew, which will be of service to some of our grape growers: "Before proceeding further, I would caution amateurs against the too free use of the syringe. It should be remembered that this instrument is merely a means provided for counteracting undue aridity in the atmosphere; therefore never employ it in dull, cloudy weather; and syringe early, so that every particle of moisture dries off by night. The syringe used with discrimination has great value; but in the hands of some it proves rather an enemy than a friend. Mildew, that worst of all enemies of the grape grower, will quickly make its appearance when excessive use is made of the syringe. This pest, unlike the red spider, only comes when a too damp, stagnant atmosphere is maintained it will, therefore, be seen that the vine grower must at all times seek to preserve a happy medium, avoiding the extremes of aridity and saturation. The mildew, however, makes its approach in such an insidious manner, and, when once in full possession, is so difficult to dislodge, that the inexperienced grower too frequently has to suffer great loss and vexation before he can destroy it.
The best way is to hinder its approach, which may easily be accomplished in the following manner: - As soon as the berries are as large as No. 1 shot, mix up some flowers of sulphur into a paste, and then, having stirred it into a pail of water, syringe the vines with it. It is not the great quantity of sulphur that is needed, but rather its equal distribution. A few grains on each leaf is enough. Be careful never to use black sulphur, the employment of which may cause the most disastrous consequences; and do not apply sulphur of any kind until the berries are fairly swelling. Many a crop of grapes has been ruined by dusting or syringing with sulphur before the skin of the berry has become thick enough to bear its application".