Plan for weeds after drought
When a drought breaks, sometimes there is an increase in new and existing weeds on a property. These weeds can impact the production of a farm and cause economic loss. As part of your drought management plan, you should think about planning for and preventing the spread of weeds after a dry period.
Under the Biosecurity Act 2015, producers in NSW must have a biosecurity plan for their property. Biosecurity planning is a shared responsibility. It protects our environment, economy and community from biosecurity threats like weeds, pests and disease.
Your farm biosecurity plan is an important tool to help combat the threat of invasive weeds, especially after a drought. To minimise weeds on your farm, combine your plan with integrated weed management, sustainable grazing and agriculture practises.
Why weeds thrive after drought
Drought can kill existing vegetation, removing competition for light, nutrients and moisture. This creates the perfect conditions for weeds to establish themselves after the dry period ends.
Drought creates dry soil conditions that prolong the viability of weed seeds. The fungi and bacteria that break seeds down need moisture to function. In dry soil, weed seeds do not break down, and remain completely viable. Weeds will germinate from the seed bank immediately after rain occurs. Drought also causes mineralisation of nitrogen in the soil, newly germinated weeds take advantage of these nutrients.
After a drought, existing weeds on a property may spread to new areas, weed densities can increase, and new weed species may appear.
How weeds get onto your property
Weeds can get onto your property in many ways. Knowing how they arrive can help you take steps to prevent their spread.
Supplementary feed
Drought often results in the importation of fodder and grain from both local and international suppliers. This can bring new weeds onto a property.
The following weeds are most likely to cause concern:
- Common heliotrope (Heliotropium europaeum)
- Summer burrs – Bathurst and Noogoora burrs (Xanthium spp.)
- Amaranthus spp.
- Caltrops (Tribulus terrestris)
- Thistles
- Panic grasses (Panicum spp.)
- Mintweed (Salvia reflexa)
- Johnson grass (Sorghum halepense)
- Wireweed (Polygonum aviculare)
Other weeds of significance include:
- Parthenium weed (Parthenium hysterophorus) from Queensland
- Bifora (Bifora testiculata) and bedstraw/cleavers (Galium tricornutum) from South Australia (both widespread in the South Australian wheat belt)
- Silverleaf nightshade, wild radish (Raphanus raphanistrum) and spiny emex (Emex australis).
An important component of a farm biosecurity plan is recordkeeping. This includes the completion of the Introduced Livestock Feed Register and Commodity Vendor Declarations. You can request these declarations from growers and vendors with all purchases of introduced grain and fodder.
When you are bringing feed and fodder on to your property, try to:
- get as much detail as possible about the source and quality of the fodder or grain
- if it is possible, complete a visual assessment for weed contaminants.
Fodder and grain from interstate and overseas pose the greatest risks of introducing new weeds on-farm. If supplementary feed is not well made, it can include other items that can cause animal health issues. For example, green cestrum and young sorghum could cause poisoning if it is in hay. Animal carcasses that are accidentally incorporated into bales of hay can cause botulism. You can learn more about weeds in hay and feeding stock during drought.
Livestock movements
As herd numbers increase as part of your restocking program or when returning from agistment, they can bring new weeds with them.
Weed seeds can pass through the digestive systems of livestock and remain viable. Under your farm biosecurity plan, you should quarantine introduced or returning livestock.
You should restrict stock movement across your property for at least 2 weeks. Check your holding paddocks for weeds germinating so you can control them.
Contaminated seed and machinery
Contaminated seed and machinery used during sowing can be a source of weeds.
To avoid weed contamination, you should:
- source seed from certified suppliers
- have a weed hygiene procedure with designated washdown areas.
This will help to reduce the risks of weeds spreading to your pastures and cropping land.
Herbicide resistant weed seed
Some contaminated fodder and grain can contain herbicide resistant weed seeds. For example, annual ryegrass. Herbicide resistance is more common in northern and central NSW. It is widespread in the grain belts of South Australia and Western Australia, so take care when bringing in fodder and grain from these regions.
The impact of weeds after drought
After drought, weed outbreaks can harm your livestock and farm productivity. Plan ahead to reduce risks and act quickly if weeds appear.
Livestock poisoning
After a drought breaks and there is significant rainfall, there can be an increase in livestock poisoning from weeds.
Stock loss can be from direct plant poisoning and photosensitisation.
Weeds of significant importance are:
- Panic species and St Johns Wort (causing photosensitisation)
- Amaranthus species (causing nitrate poisoning and kidney failure)
- Rock fern (causing blood in urine and sudden death)
- Green cestrum (causing sudden death)
- Marshmallow weed (staggers and possible death)
- Thistles (causing nitrate poisoning).
Crops, pastures and weeds grown during drought times can have nitrate levels above safe limits, resulting in livestock poisoning. For example, Kikuyu pastures are sometimes toxic after rapid growth post drought.
Bringing in hay or silage with higher nitrate levels than animals usually consume can cause nitrate toxicity. Producers should request feed tests on hay and silage before feeding to identify risk levels and guide safe feeding strategies.
New feeds should always be introduced to livestock gradually.
Vaccination (5 in 1) to prevent the major clostridial diseases is recommended.
Increased weed susceptibility on fallow cropping areas
In cropping areas, the immediate problem is fallow weeds, which quickly mine the soil of both valuable nutrients and moisture. Control fallow weeds with a combination of mechanical and chemical practices.
In pastoral and rangeland areas, weeds of greatest significance are:
- Fireweed (senecio madagascariensis)
- Blackberry (Rubus fruiticosus species aggregate)
- Giant parramatta grass (Sporobolus fertilis)
- Blue heliotrope (Heliotropium amplexicaule)
- Nodding thistle (Carduus nutans)
- Scotch thistle (Onopordum species)
- St John’s wort (Hypericum perforatum).
How to reduce weed impacts after drought
Weeds can contribute to the financial impact of drought in both production decline and the cost of weed control. This can be a short and long term issue. It is important to be vigilant so that weeds do not become a threat to your drought recovery. Make sure you have an accurate assessment of the situation so you can form an effective weed control program after drought.
Restriction and monitoring of feedout areas and access roads
Keep detailed livestock feeding records by paddock and mob. Consider where to feed the grain and fodder. Restrict feed-out areas to 1 or 2 “sacrifice paddocks.” These paddocks should be near where you can make regular checks after each rain event for up to two years after a drought. Flat, arable areas will allow easy access for integrated weed control. This can include mechanical, chemical, biological or grazing management.
When considering herbicide resistance, it is best to avoid feeding in or near cropping paddocks. Take care not to feed livestock in catchment areas for farm dams as manure and weed seeds can contaminate water storages.
All farm biosecurity plans should control farm access by vehicles and farm machinery. This includes the having designated wash down areas to reduce the chance of weed seeds and plant fragments coming on to the farm. You should also monitor road frontages for weeds.
Monitor riparian areas and water points
Native and feral animals may also access livestock feed and stock water. This can increase the chance of weed spread via both manure and through water flows. Monitor water points and riparian zones for two years after a drought.
Control weeds after germination
When rain occurs and weeds have germinated, you must identify and control them as soon as possible, before they are able to set seed. If possible, delay sowing crops for up to a week to allow the first germination of weeds to be fully controlled. Be aware that you also need to control the vegetative parts of perennial weeds, such as silverleaf nightshade and blue heliotrope.
Identify any new plants
Early detection and identification are key to controlling newly introduced weeds. Watch for unknown plants and identify them as soon as possible, don’t let them establish and set seed.
Need help identifying potential weeds? You can Local Land Services, your local agronomist, or local council weeds officer for advice and help. You can also use the WeedWise website and app. WeedWise is a resource with individual weed profiles and herbicides registered for control.
Integrated weed management during and following drought
Integrated weed management uses a combination of chemical, physical, biological and management options to control problem weeds. This helps in minimising costs to the farm enterprise and maximising environmental outcomes.
Start planning for weed management before the rain arrives.
Effective drought recovery plans may include:
- expert advice
- grazing strategies
- herbicide use
- biosecurity planning and record keeping.
Sustainable pasture and agricultural management
To stop weeds from taking hold on non-arable grazing country, it is important to maintain good groundcover. This will help minimise the risk of weeds. Sustainable pasture and land management can reduce land degradation. For example, rotational grazing systems can help improve your pastures. Pasture and ground cover measurements
Use pasture and ground cover measurements to guide livestock movement or de-stocking. This can improve production, increase profits and protect the environment.
On arable country, one of the best weed control methods is to out-compete target weeds. You can do this with equally aggressive crop or pasture species with matching growing seasons. For example, a post-drought pasture plan may include a tropical grass system. Once established, it will out compete the aggressive weeds like blue heliotrope.
Successful management of persistent weeds like blue heliotrope needs an integrated approach. Starting with timely chemical control, followed up with the provision of a competitor with a matching growing season. A boost in soil nutrition can then give the pasture a head start over the weed, assisted by rotational grazing and ground cover management.
Contact Local Land Services NSW
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