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Weed Control Using Goats

• Peter Holst, NSW Dept. of Agriculture, Cowra, NSW
• Helen Simmonds, "Rowan Park", NSW

Weeds in pasture greatly reduce the short and long term profitability of the pasture. The traditional methods of weed control in pastures are cultural, biological, chemical, mechanical or grazing. Not all are necessarily effective or desirable.

Preferential selection (palatability) of plants by animals is affected by plant and animal based factors.

Animal-based factors may be categorised into five classes:

• the senses
• species and breeds
• individual variation
• previous experience
• physiological condition

The actual ability of goats to utilise a variety of vegetation types is attributed to their dexterity, narrower mouth, mobile upper lip, prehensile tongue and a propensity to stretch upward on the hind legs to reach forage.

Plant-based factors include:

• species
• intra specific variation
• chemical composition
• morphology or physical traits
• succulence or maturation

All animals have dietary preferences. This can be observed in horse paddocks, or on adjacent sheep or cattle properties, where the weed problems are different to where goats are run. Goats eat a variety of undesirable plants and shrubs that sheep and cattle avoid, and often the nutritive value of these species is quite high.

Goats are efficient browsers and grazers of uncontrolled plants in rocky outcrops. They will also eat any weeds that germinated too early or too late to be affected by herbicides. Similarly, degraded non-arable country with woody and other weeds may be reclaimed by goat grazing.

The major control process is ecological, as the weed is placed at a comparative disadvantage in the presence of vigorous clover. This is because clover is not highly sought by goats.

In Australia we have both fibre and meat type goats that are suitable for weed control. In general the bush goat (derived from ferals), cashmeres (not off-shears), and boer X goats can be used.

The principle roll of the goat as a weed controller is to place the weed at a competitive disadvantage to the surrounding pasture. They preferentially graze the weed, preventing it from flowering and setting seed, reduce the plants stored energy reserves, and finally, ringbark and trample small bushes.

Advantages of using goats include the savings in the cost of chemicals, time, labour and machinery, also a sustained and efficient level of control. The returns from the "spin-off" profits make utilising goats plain common sense.

Assessing Pasture and Weeds

Before you can devise a stocking strategy you need to assess pasture quality and quantity and the degree of weed infestation. This is best judged in the weed"s late vegetative stage, before flowering. Simply estimate the percentage ground cover of the weed in a square (0.5m x 0.5m). Walk over the entire paddock and repeat the assessment in about 30 random positions.

For larger woody weeds (blackberry, broom, gorse) estimate the proportion of the paddock taken up by the weed.

From these assessments, and with the knowledge of weed palatability (see Table 1), you can devise a stocking strategy.

Preparation

Any necessary improvements must be made before goats arrive on a property. These include fences, water points, and yards.

Goats test the lower portion of fences: any drains, low areas and diagonal stays etc. will need to be attended to, to ensure there are no escapees. Electric fencing is a reliable and inexpensive method of upgrading existing fences. As a general rule, any fence that will contain crossbred ewes will contain goats.

For localised woody weed infestations, it may be best to isolate the infestation with fencing. This has two benefits. It confines your goats to the infested area, so that fewer goats may be required for the job of controlling the weed; and it preserves the remaining pasture for your sheep or cattle.

In dense infestations of woody weeds such as blackberry, scotch broom or gorse, slash paths through the infestation to allow greater access for goats.

Goats will ringbark some mature trees, particularly over the late winter/spring period. Soft-barked gums are most at risk and so may require protection from goats. You may need to take protective action if your goats begin to chew the tree bark. Even within the same species, individual trees will have a different attractiveness to goats. A trace element salt lick is always useful and often negates the need to attack trees.

Wire mesh wrapped twice around the trunk to a height of 2 metres will prevent damage. Exposed roots may also need covering.

Control or Eradicate

Control is achieved by stopping the annual replenishment of seed reserves in the soil, and eradication is achieved after the exhaustion or effective suppression of these seed reserves. Therefore, eradication of a weed depends on several years of continuous control.

Efficient control is achieved by goat grazing, even though the goats are consuming seedheads of weeds. Research has shown that very few of the seeds ingested by goats remain viable.

"Set" or "Strategic" Stocking?

Knowing how palatability varies at each stage of plant growth allows you the flexibility of either set stocking or strategic stocking.

Set stocking with goats can be an advantage in the first year of a weed control program. It allows you to "quarantine" the new animals, a good management strategy in case the animals are affected by lice or other health problems. It also reduces the cost of upgrading fences, as only one paddock will require upgrading.

However, after the quarantine period, it is advisable to integrate other livestock. This ensures peak production from the herbage in the paddock.

The strategic grazing option requires goats to graze alongside other stock at the "strategic" time - for example when the weeds are most palatable to the goats (as when thistles are flowering) so that competition with other livestock for feed is greatly reduced. Because strategic grazing, by definition, is only used at particular times there must be alternate grazing and holding areas for the goats. This means you will have to fence both the weedy paddock and the other holding paddocks.

Conclusion

The integration of goats on a farm can be ecologically and economically significant. These comments on management are intended to be positive and allow sound management of the animals. The few hours per month involved in sound management are negligible to that involved in traditional weed control.

Table 1. The potential toxicity, and palatability, of some Australian plants to goats.

palatability^* where:

Flower	= Eaten at flowering
High	= High palatability
Low	= Low palatability
Medium	= Moderate palatability
Nil	= Not eaten
Physical	= Physical damage caused by goats
Recent	= Recent growth, regrowth
Toxic	= Toxic

Grazing impact is a result of plant selection (palatability or aversion) rather than plant availability so that Table 1 directly assists grazing management while the genera listing helps our understanding of palatability, toxicity, and the theory of aversion (Provenza, 1996).

These are indications of potential toxicity only, and not all of these are applicable to goats,who have a remarkable digestive system. Many plants are found as garden refuse, and fed to livestock as a "treat", while others are found naturally in grazing areas.

For further information see: "The Potential Palatability and Toxicity of Australian Weeds to Goats". Simmonds, Holst and Bourke. This also includes new information on palatability to goats of many more weeds.

© 2000 ACGA