Example Problem One: Foliar blights (Late blight)
 
Consider foliar blights (often caused by Phytophthora for example). Common names for these problems are brown patch, foliar wilt, dollar spot, copper spot, etc. Two things related to the foodweb select for this condition. First, the plant is stressed and second, there is no protective biofilm on the leaves of the plant. There is a leaf-surface foodweb, just as there is a foodweb in the soil. To prevent foliar problems, or to at least reduce severity, you need to get the leaf-surface foodweb healthy as well. Stressed plants are generally the result of a lack of nutrients being made available to the plant in the right form, at the right rate and in the right places. This could be the result of any of a number of soil foodweb problems (but remember, it could be a soil chemistry problem too):
  • too low protozoa or bacterial-feeding nematodes (not enough N being made available to the plant)
  • high numbers of root-feeding nematodes (attacking and eating the roots),
  • a lack of the right fungi (low nutrient retention, lack of disease-protection)
  • too high fungal biomass (alters pH, wrong form of N, Ca not available, etc.)
  • the wrong fungi (disease-causing fungi un-challenged for possession of the root)
  • a lack of bacteria (no nutrient retention),
  • too many bacteria (all the N is in the bacteria, this is what happens if you apply too much sugar)
  • a lack of mycorrhizal fungi (lack of nutrients getting to the root, especially P, N, S, water, micronutrients)

Lots of possible causes, same result - a plant too stressed to be able to ward off disease. On the surface of the leaf, we want to occupy the space on the leaf surface so the disease-causing organisms can't find a place to live and can't find anything to eat because someone else has eaten it. So often normally occurring leaf-surface organisms are killed with pesticides and herbicides, and then we wonder why disease takes over. No inhibition, no competition and no predators left to control the disease-causing organism, and so, the disease takes over. When the biofilm of life that should be present on a leaf surface is there, disease will be reduced. What we don't have a good handle on yet is exactly what set of organisms are best on the leaf surface. While we don't know everything, at least we know we need to get the leaf surface occupied. We may not know their names yet, but maybe that isn't as important as having the spaces filled. Certainly there would be less guesswork if we knew their names, and who did what to whom, but that level of understanding is coming. And just because we don't know everything doesn't mean we can't take steps in the right direction.

 

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