I’ve heard enough growers talking about high °Brix. The information received is that vegetables are more disease resistant if they have high °Brix. However, I cannot find any peer reviewed research publication to support this idea. °Brix is a measurement of the mass ratio of soluble solid (mostly sugar) to water in a liquid. A 15 °Brix solution roughly equals 15 grams of sugar dissolved in 85 grams of water. °Brix is the most important index in viticulture for harvesting. For most vegetables, however, no similar criteria have been developed although we know it is closely related to fruit quality in watermelon, melons and tomatoes.
Perhaps most growers get the idea of high °Brix from the Acres monthly magazine which is not a peer-reviewed journal. Acres claims itself "A Voice for Eco-Agriculture". Also, there is a website www.highbrixgardens.com that specifically sells high °Brix. However, I believe that they misconnected food quality to disease resistance in plants. It was wrong or at lease misleading to say “All disease is the results of a mineral deficiency”. I do not intentionally explain in detail here, but the take home message is that there is no scientific evidence for the high °Brix theory. I would recommend growers who have been doing foliage feeding of sugars, and perhaps calcium, to stop. Foliage feeding of sucrose to tomatoes doesn’t even raise the °Brix level in plants. Actually, I was only able to dig out two papers talking about the responses of tomato plants to foliage feeding of sugars, which were published in 1948 and 1960 respectively. Both papers don’t support foliage sugar feeding, at least for the raising °Brix purpose. The feeding might not hurt the plants significantly but most sugar will deposit on leaves, which encourages fungus growth and blocks light transmission that reduces photosynthesis.
REVISED: December 3, 2015