A Plant’s Immune System is in the Soil


The $9 billion citrus industry if Florida was bought to its knees by a tiny little bacteria that by 2010 had destroyed most of the state's orange groves. The bacteria, referred to as HLB, causes citrus greening which prevents the fruit from ripening, causes fruit to drop prematurely and can eventually kill the host tree.

Given the size and economic cost of the disaster the proverbial kitchen sink was thrown at finding a solution. Over the years numerous remedies were tried, everything from GMOs to sniffer dogs and antibiotics. Indeed for 3 years in a row - with increased antibiotics resistance becoming such a problem - human grade antibiotics were applied to over 220 000 hectare of oranges, but all of it with no success.

Not surprisingly farmers started to give up on oranges and attempt to stay afloat with other crops. One such farms was Ed James who had already been having problems with citrus weevil and the HLB bacteria was the final straw. He decided he was going to rip out his trees with a digger and plant watermelons and other row crops. But after years of a monocrop of just oranges he had to start with planting cover crops to heal the soil. 

Ed James in his recovered orange orchard. Photo Frank Giles

He set about ripping out the tress and ripped until the digger broke. He decided that until the digger was fixed he would to carry on with the rest of his plan and plant the cover crops between the remaining trees. On the advice of University of Florida he planted a diverse cover crop with 5 families of plants represented - cereals, grasses, legumes, brassicas and broadleafs. That way he would have a really diverse system and build a diverse soil microbiology to heal his long neglected soils.

Ed had had given up on the oranges and he stopped applying any fertilizers to the orchard. But things began to change, the cover crops gradually bought renewed life back to the orchard. It was while he was tending to his cover crops that he noticed his orange trees were starting to recover, they looked a lot healthier and that season dropped a lot less fruit. Stopping the chemicals and growing the cover crops meant the soil biology was recovering and was able to give his orange trees what they needed to fight the disease. Despite the fact that they were still infected they managed to produce a crop.

Ten years later and Ed is still producing oranges. In his words "A plant's immune system is in the soil. Lots of my trees were sickly, and looked dead, but they're now transformed. Everything I've learned is about soil. Chemical fertilizers leave salts behind and kill soil microorganisms. ... Soil is a microbiome, much like the gut, and different varieties of plants supply different nutrients."

And if that wasn't enough there was a cherry, or should that be an orange, on the top "For years, the weeds managed me. I spent all my time as a caretaker fighting the weeds. Now, it is much more fun as I manage the cover crops."