Tips for managing pasture dieback

MLA coordinates a range of activities to investigate potential pasture dieback causes and management options. Following recent trials in Queensland, Pasture Dieback Update has compiled some key suggestions for the management of the disease.

• Sow forage crops

For producers who need to feed stock, growing forage species such as sorghum, oats, barley, wheat or millets (if the property is suitable and if it fits your business model) is recommended.

Indicative seed costs for forage crops are as follows:

• sorghum ($3.20–$8/kg)
• millet ($3.40/kg)
• winter oats ($1.10–$1.65/kg).

Seeding rates are:

• forage sorghum 2–6kg/ha
• millet 7–12kg/ha
• oats 25–35kg/ha.

Sowing rates may vary depending on region and sowing method. Sowing and establishment costs also need to be considered, as well as animal health in terms of grazing of some of these crops at certain times/densities – consult your agronomist.

• Re-sow pasture or legumes

Consideration could also be given to sowing legumes and/or pasture species such as Callide Rhodes or mixes. Legumes do not appear to be affected by dieback.

Re-sown pasture (e.g. Callide Rhodes) has established well in pasture trials and will give an initial stand of biomass which can be grazed. Callide Rhodes grass is known to quickly establish; however, other pasture species may take months or up to one year to fully establish. Re-sown pasture may also subsequently succumb to mealybug and may not establish permanently.

Indicative seed costs for pasture crops are as follows:

• Rhodes grass ($11–$17/Kg)
• green Panic ($18–$25/Kg)
• buffel ($14–$20/kg).

Seeding rates for pasture are about 8–12kg/ha depending on region and sowing method.

Sowing and establishment costs need to be considered, as well as the risk that mealybugs may reinfest the new pasture. It’s recommended to consult your agronomist before re-sowing pastures into dieback-affected areas.

• Increase pasture diversity

Many Queensland pastures have become monocultures and are lacking diversity. The greater the diversity in the pasture, the greater the number of beneficial micro-organisms there are within the soil to help fend of attack from pathogens.

Consider increasing pasture diversity using legumes; forage crops and other species such as other monocots (Monocotyledon: basically grasses) and dicot (or Dicotyledon: legumes, shrubs, plants flowers etc) as well.

• Incorporate intensive/cell grazing

Findings from MLA’s pasture dieback trials suggest that incorporating intensive/cell grazing may limit dieback by reducing biomass in affected paddocks.

Consideration should be given to modification of grazing practices, with reference to local conditions/environments. See Reference 1 below.

• Monitor leucaena

There are reports that pasture between rows of leucaena are more susceptible to dieback and do not recover. This could be a set of compounding issues such as moisture/nutrient competition; row spacing; leucaena height, multiple insect effects including mealybug and scale. Advice should be sought from QDAF and local agronomist service providers.

• Burning

Burning is often used as a management tool within a grazing operation. When mealybugs are present, and visible on the leaf, stalk and ground, burning will reduce their numbers. However, mealybugs will generally return since there will be many mealybugs under the ground not affected by the fire.

• Avoid straight nitrogen fertiliser

It’s been demonstrated that high levels of added nitrogen can increase mealybug size, growth rate and egg production (see References 2 and 3). As a result, it is not recommended to apply straight nitrogenous fertiliser (e.g. urea) to dieback-affected pasture monocultures as it may encourage mealybugs.

• Minimise pesticides and insecticides

There are no insecticides that are legally approved for spraying on pastures in Queensland. Integrated Pest Management strategies, including the combination of control methods and grazing practices, aim to limit the insect populations to a manageable level without reliance on pesticide.

As well as being illegal and of little benefit, broad spectrum insecticide can have a negative impact on beneficial insects and may lead to an increase in mealybug populations over time.

• Insecticide in seed coatings

Consider using registered systemic insecticide products such as Poncho™ (BASF) or Gaucho™ (Bayer) in seed coatings when re-sowing forage or pasture crops as per label directions.  Advice on the use of these products should be sought from your agronomist or seed supplier.

References

1. “Towards sustainable grazing – A professional producer’s guide” by Warren Mason, Lisa Warn and Greg Cahill. ABN: 39 081 678 364 and ISBN 174036 351 5.
2. Effect of Nitrogen Fertility on Reproduction and Development of Citrus Mealybug, Planococcus citri Risso (Homoptera: Pseudococcidae), Feeding on Two Colors of Coleus, Solenostemon scutellarioides L. Codd; BRIAN K. HOGENDORP, RAYMOND A. CLOYD,1 AND JOHN M. SWIADERDepartment of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL (2006).
3. Effects of Nitrogen Fertilization on the Life History of the Madeira Mealybug (Phenacoccus madeirensis) and the Molecular Composition of its Host Plant. Stephanie Alliene Rhodes, Clemson University 12-2015

More information:

Cameron Allan
MLA Program Manager – Sustainable Feedbase Resources
Ph: 0419469246
E: callan@mla.com.au