Do your weeds love fungi?

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I was talking with one my farm forester friends, Doug. He had harvested an area of pines and was noticing weeds growing there that he had never seen on his farm before. Inkweed, woolly mullein and chamomiles. How did that happen?

Weeds get a lot of bad press, surely, they’re just there to annoy us, create work we don’t want and keep companies in business.  No, the purpose of a weed is to respond to soil signals and apply remedial action on behalf of nature. They’re not a sign of lack of herbicide, the same as a headache is not a sign of lack of aspirin. Weeds are evidence of repair taking place.

Soils are the result of  interactions between chemical, biological and physical factors. New or primitive soils are highly bacterial and can be dominated by moss, primitive grasses and small flat weeds. As soil builds, fungi begin to colonise, and healthy pastures will thrive at a 1:1 equal biomass of fungi to bacteria  (F:B). Orchards and gardens thrive in more fungal conditions ( 5:1 ) and mature forests are up to 1000:1 F:B. Hence the smell of a forest and the speed of decomposition of branches and whole trees is in large part attributed to high fungal levels. 

These forestry weeds are indicators of high fungal soils, not the natural biological conditions for pasture, which require more bacteria. Other examples of weeds indicating fungal conditions are below. 

To shift a forested area to pasture, it is essential to wake up these sleepy fungal soils. Grazing large mobs, if suitable, will achieve animal impact and trampling and evenly spread manure and urine.  Bacteria live on simple carbon foods – like manure, seaweed and sugars. Applying these can help achieve pasture suitable conditions. Fungi need more complex carbons – which may be provided by wood chips, trampled litter, straw and fish oils. The most important of these fungi in forestry or grassland establishment are the essential mycorrhizal fungi. Plants provide the fungus with its sole source of food (as liquid carbon sugars) and the fungus provides the plant with soil-derived nutrients.Around 10% of all plant species have ecto-mycorrhizal relationships, particularly seed producing forest trees. This group includes many hardwoods and conifers, such as alders, spruce, oak, chestnuts, eucalyptus, pine, poplar and willow. Grasses require endo-mycorrhizae, this can mean grasses struggle following tree removal. This is one of the times we advocate the use of an inoculum.

Mycorrhizal fungi will be damaged or destroyed by disturbance, as well as by the use of certain chemicals, all of which occur in intensive agriculture and forestry. Many foresters, farmers and ranchers are developing an awareness of the importance of looking after our underground livestock and low impact forestry techniques help to maintain the integrity of the soil.

So for Doug these weeds are his friend and employee. They’re ensuring continuation of the plant/fungal relationship. When re-planting reduce herbicide rates by one third to half and buffer with fulvic acid to reduce damage to your new fungal friends

And please think diversity, think beyond the monoculture that Pinus Radiata has become.

Other fungal indicating weeds :Blackberry (Rubus spp), wild rose (Rosa spp), Poison Oak (Toxicodendron diversilobum), hemlock (Conium maculatum), Foxglove (Digitalis), Hollyhock (Alcea rosea), Hawkweed (Hieracium), hemlock (Conium maculatum), Bloodroot (Sanguinaria canadensis), wormwood (Artemisia absinthium), mullein (Verbascum spp), St. Johnswort (Hypericum perforatum), houndstongue (Cynoglossum officinal), Matagouri (Discaria toumatou), bracken (Pteridium spp), gorse (Ulex), broom (Cytisus scoparius), rabbitbrush (Chrysothamnus spp), sagebrush (Artemisia spp), willow (Salix spp), sweet briar (Rosa spp), Leafy spurge, African Boxthorn (Lycium ferocissimum) or mesquite (Prosopis spp).

by Michael Cashmore

Michael is available for coaching to help you achieve your landscape regeneration goals and can be contacted by phoning +64 0272751112 or emailing