The fungi that saved a farmer’s avocado orchards

Faced with wilting, unproductive avocado trees, Limpopo farmer Christa Rebel decided to replace them with another crop. In the meantime, however, she planted strawberries on the orchard floor. Then, serendipitously, she discovered nature’s remarkable ability to repair itself.

The fungi that saved a farmer’s avocado orchards
Strawberries have been planted under the trees in the foreground but not under the trees further back. Note the difference in leaf growth. Photo: Lindi Botha
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For a novice farmer, finding the best cultivation methods can be a costly, and lengthy, process of trial and error. Christa Rebel, who farms near Tzaneen in Limpopo, found herself at her wits’ end when trying to revive an avocado orchard.

“These Hass avocado orchards were on the farm when we bought it in 2016. They really weren’t in a good condition, as the previous owners were more lifestyle farmers and didn’t pay them much attention.

“I tried to revive them, but nothing seemed to work. I believe in an organic way of farming, which makes it tricky considering the lack of chemical assistance. But because I was struggling, I resorted to injecting the tree trunks with an ammonium sulphate solution. It was such a horrible process! Every time I tried to squirt the liquid into the tree, it would squirt back on me.”

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Christa Rebel revived her avocado trees by inadvertently introducing mycorrhizae fungi to the soil.

With the trees continuing to shed leaves and not bearing fruit, Rebel eventually gave up on the orchard and resolved to use the land for another crop. Constrained by cost and time, however, and not wanting to leave the soil bare, she decided to plant strawberries on the orchard floor as an interim measure.

Permaculture
“I follow a permaculture style of farming, where all the land is planted to crops or covered with mulch, and areas complement one another. The farm is therefore quite diversified, with a few dairy cattle whose manure is used for compost, flowers planted for bees, and chickens that roam around, fertilising the soil and taking care of insect pests.

“Since I started a permaculture approach on the farm, I can see how life has returned to the area. The soil was dead and the fauna was not particularly diverse before, but now I can see a variety of birds, insects and animals that have returned.”

Rebel chose strawberries for the orchard floor because they do well in partial shade and she also had access to plenty of plant material.

“Our farm is on a mountain slope and surrounded by indigenous forests, so only a small part of it gets full sun. What’s more, my cousin farms strawberries close by and they were multiplying quite quickly, so I decided to take the excess plants, grow them out and then sell the plants again.”

Perfect partners
Rebel planted the strawberries between the avocado rows and under the trees, and was
soon focused on tending the young plants.

A few months later, however, she saw to her amazement that the old avocado trees were coming back to life.

“The strawberries were hardly getting any sun because the trees had started putting out new shoots and the foliage was quite robust. Now, two years later, I’m getting an avocado yield of 16t/ha.”

When Rebel started investigating the mysterious rejuvenation of the trees, she discovered that by planting the strawberries in the orchard she had brought in valuable mycorrhizae fungi. Strawberry plants are good hosts for the fungi, which cling to the roots and then spread into the soil.

The mycorrhizal symbiosis has been credited as one of the most important of its type on earth. Approximately 80% of all known land plant species form mycorrhizal interactions with ever-present soil fungi.

The majority of these interactions are mutually beneficial as they create a two-way exchange of resources across the mycorrhizal area. The mycorrhizal fungi provide the host plant with nutrients, such as phosphate and nitrogen, and increase resistance to drought, salinity, heavy metals and diseases of the host plant. The fungus, on the other hand, feeds off sugars provided by the host plant.

“I didn’t treat the strawberries any differently from the avocados, so I know the new growth is not as a result of changing cultivation practices. We have a block of avocados where we haven’t planted strawberries, and you can certainly see the difference. I’m now in the process of planting strawberries there as well.

“The best part is that the strawberries reproduce very quickly, covering the soil completely. But there’s no need to slash them, as is the case with grass and weed cover crops. This is the foundation of permaculture: if you have the right, complementary systems in place that look after one other, it leaves you with very little work at the end of the day. And now I have strawberry plants and avocados that bring in an income.”

Because of the cooler climate on the mountain slope, Rebel’s avocado harvest starts only around August, but it runs right through to January. At this time of the year, traditional avocado production starts tapering off, so she can obtain a premium for her crop.

“Although we farm on a small scale and have only 1ha of avocados, the fact that I can get two crops from the land simultaneously is a big bonus.

“Moreover, the fact that I didn’t have to take out and replace the avocados has saved me time and money.”

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