How to deal with post-fire weeds

Rapid post-fire growth of Bracken Fern

The devastating fires this season have had a massive effect across our own area, people, communities, and well beyond. I’ve written this article for those who may be struggling with the impact of post-fire weed growth. Now’s the time to act, and I hope this article can help you with that. I’d also encourage you to call me if you’d like to discuss anything to do with the weeds that may be invading your paddocks.

The effects of fire on weeds:

After a wildfire or other major soil disturbance, noxious and invasive weeds are often one of the first plant species you will find. These aggressive weeds use the opportunity to gain a foothold in the newly disturbed ground. Therefore, it is important to survey your property to locate noxious weeds, and create a treatment program as quickly as possible. 

Bushfires fall into 4 categories: Cool burn, moderate burn, hot burn and very hot burn. Many fires this summer fell into this latter category where all plant material and seeds are destroyed leaving an almost sterile soil surface.  Soil becomes ‘baked’ with reduced ability to absorb moisture and will repel water. 

Some perennial weeds, including Bracken, Blady Grass, Serrated Tussock, Coolatai, African Lovegrass, Chilean Needle Grass, Dock and Sorrel will survive the hottest of burns. Blady Grass, Bracken and Coolati Grass are actually germinated by fire. Blady grass is rhizomatous, so it spreads underground like running bamboo. Most of the other grasses are high in Silica which is largely indigestible for stock. Bracken is also highly toxic to animals. These weeds will grow out of control if given the opportunity. All these plants can rapidly regenerate or re-establish to dominate pastures weakened by fire and drought. 

Environmental effects:

Destructive weed species compete with desired native species for space and nutrients, as well as eliminating wild-life/livestock forage, and choking wildlife habit.  In addition to spreading by seed, some weed species can regenerate from roots and root fragments. Typically, most severe fires will only damage roots to a few inches below the soil, therefore noxious and invasive weeds, often with deep root systems have an excellent chance of surviving and the roots can actually be stimulated to produce more plant material. 

Goals of weed management:

A combination of control methods, soil treatment and re-seeding as necessary, makes for a well-rounded and integrated weed management program. The primary goals of weed control in burned areas is to keep weeds from spreading from road shoulders into the recently disturbed soil, keep “new invader” species from gaining a foothold in the burned area and to keep previously known weed infestations from spreading. Funding may be available to assist via federal, state and local grants. So, it is worth exploring these options.

Taking action:

Firstly, assess your property to identify the weeds to be treated

Secondly decide on the method/s of treatment – chemical or natural

Create an Integrated weed management program by yourself or in consultation, beginning with immediate actions and prioritising worst affected areas

Longer term, consider arranging soil testing and soil remediation to restore the health of your pastures, which ultimately will assist to reduce the amount of weed growth

Noxious and invasive weeds, and their continued expansion, are recognized as one of the greatest threats to the integrity of native plant communities so it is essential to take quick action on post-fire weed control, particularly when you see a species that has not been there before. 

For assistance in identifying, assessing and controlling noxious weeds on your property, or creating a weed management program, please call 0402 830 770 for further information or to arrange a consultation.

Greg Burch, 

Weed Warrior, 

Dyers Crossing NSW     

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