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Every few years Australia experiences mice plagues that threaten to ruin crops in the areas in which they occur.

This page documents the early stages of a mice plague, and predicts its evolution. It will be updated periodically to reflect the events as they occur.

• A case study in progress
• Trends for winter and spring
• MOUSEOFF^© ZP Bait availability
• BULKA bags: Bulk supply
• Bait efficacy after long term storage
• Mice and locusts
• More information

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Mouse problems in Australia

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Mouse biology

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Monitoring mice and assessing crop risk

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For an update on the situation in 2011 see PestFacts Special Issue 4 May 2011 (407KB PDF)

 

Dealing with mice plagues

Mouse Plague: June 2010

Case study based on the experience with a mice plague in Autumn 2010

Following high mouse infestations in late 2009 there were increasing mouse problems that threatened newly sown cereal and pulse crops in South Australia and Western Australia this autumn, reaching a peak in March 2010.

Since March, the areas affected by mouse infestation In South Australia and in Western Australia have not changed, though the type of problem being experienced has changed from seed loss to cotyledon chewing as the crops emerge. A wide area of the Victoria Wimmera and the SA regions of the upper York Peninsula and lower mid north around Saddleworth, the western Eyre Peninsula in SA and the areas around Geraldton/Northampton and Esperance to Ravensthorpe in WA, remain on high alert through winter and spring. However in WA for recent weeks activity has been a little quieter than expected.

Other areas have remained relatively quiet and no new “hot spots” have been identified by June.

The DPI in Victoria have done a sample survey, about three weeks ago just before planting, of mouse infestations that have indicated common estimates of 1000 to 5000 mice per hectare at many sites and situations.  These are rough estimates based on counting active holes and allowing 2 mice per hole.  The number of mice in an active hole can be anywhere from 0 to 40 (a single mouse can use more than one hole so sometimes there is no-one “at home” when an active hole is excavated). Numbers of 5 to 15 mice per active hole are not uncommon, so the estimate of “2 mice on average” is conservative. We realise that this information is not directly applicable everywhere, but it does give an indication on the range of habitats in which mice are found in Victoria this season.

Trends for mice over winter and spring:

Seasonal breeding should be in decline right now so we do not expect major increases in mouse numbers. Nevertheless, since in many situations those surviving autumn have now been “fed” with a newly planted crop, it is likely that high mouse densities will persist in many affected areas. These pose a serious risk for the emerging crops and developing stages.

This mouse infestation is progressing to what we consider to be a “normal process”. Early recognition of an emerging problem then appropriately delayed action to hope for a natural crash before treatment is needed.   This is followed by some pre-treatment at sowing, then a “lull” while sowing is progressing and until emerging crops are treated after the damage is recognised. SA crops are ahead of the other states (earlier sowing due to better rains) and they are now seeing crop damage – especially in canola and pea crops. We anticipate the concern about mouse damage will shortly increase in WA and Victoria, since their crops are a few weeks behind much of SA.

Wheat and barley damage should not be great after emergence, though we have received reports of hungry mice “grazing” the young seedlings. The greater danger for cereals is when mice preferentially attack the tillering crops at the nodes and again at the milky stage when nutrition accumulates for the seed head. Later damage in canola crops will be at podding so farmers should not be complacent about seeing a field of yellow flowers at fence height then assume all is well down the stem.  NSW had a massive experience of canola pod losses in 1999, when relatively few mice appeared to be present. THE RISKS THIS YEAR ARE VERY HIGH AND CROPS MUST BE CHECKED.

We lack information on whether many mouse populations crashed naturally, especially in WA.  We suspect not, and there has not been sufficient rain anywhere to flood them out either. In 1997 the situation was very similar to this season and farmers ceased buying bait on the 30^th June. We called this the “financial year mouse plague” where buying patterns were only partly influenced by the mouse numbers. Many farmers brought forward their purchase to maximise the tax deduction for the current year.   This may not happen this year, given the enormous financial pressures on all farms these days.  But it showed us that, even with big problems at sowing and emergence, it is NOT certain that the mice will survive to do the damage later in the crop. Last year in Geraldton this DID happen, whereas in 1997 in Victoria it did NOT happen. I wish we could be more predictive but we do not fully understand all the possible dynamics here.

Hence, our strong recommendation to help your clients is to keep a close watch. This does not cost much but could save a fortune whether treatment is, or is not required. Be wary of wilting in wheat that can be misinterpreted as moisture stress or root problems. Look closely at stems to check for nodes being eaten and react fast if this is seen on any scale.  Likewise be careful to thoroughly check canola crops for pod loss in a couple of month's time.

Mouseoff ZP Bait is READILY AVAILABLE from ACTA

We have received some queries as to whether MOUSEOFF^© bait is running out because of the high demand in these mouse plague conditions. We want to stress that we have taken early action to be ready for this emergency. We have air and sea freighted chemical and streamlined our supply chain so that we have production working smoothly, with no interruptions to supply at any time.  We continue to maintain a substantial stockpile of packaged bait so there is bait available to cover any short term spike in requirements. We can further increase production if needed, so there is no need for anyone to panic or “stockpile” to avoid a shortage. There is no shortage and we expect to be able to buffer the supply side to help everyone manage the in store stock issue.

At the end of a big mouse problem, while we cannot take back, we do always try to smooth out any excess stocks, if asked. ACTA will not dump bait into any area if we know that any merchant has bait that he wishes to relocate.  It is obviously difficult to do this perfectly but we will do our best to help where possible. Cooperation between merchants is also helpful here.

New BULKA bags available:

We are pleased to announce that we can now supply MOUSEOFF^© Zinc Phosphide Bait in 500kg bulka bags, under APVMA permit. The emergency permit does not allow long-term storage in the bags and all bait thus packaged must be used by the end of the permit (within 6 months). THUS THE BAGS WILL BE FILLED AND SUPPLIED ONLY TO ORDER. Please allow an extra day or two for delivery of bulka bags as we can only retain stocks of product in permanent packaging. The bags come as one per pallet and cannot be reused.

We envisage that this initiative will make it easier for large areas to be treated, if needed, and will facilitate faster aircraft turnaround if treatment of developed crops becomes necessary.

We are also pleased to advise that the savings of bulka bags, compared to drum packaging, will be fully passed on with a wholesale price reduction to our customers, with a saving of $302 per 500kg bag pallet. We expect that this will be passed on in full to landowners. Also we have received some criticism of bait pricing at the retail level. We have a recommended retail of 10 to 15 percent above wholesale and we are freighting free to capital cities. As the bait goes through stock very fast we would expect that most merchants will help us to keep prices for critical crop protection as low as possible while we are in crop saving mode. We have absorbed all consequences of declining exchange rates and air freight costs at this time.

Ordering procedure for bulka bags is the same as for the 15kg pails and 125 kg drums (i.e. simply fax your order to 03 9308 9688). Remember to allow at least one extra day as we do not hold large stockpiles of the bulka bags, due to the limited nature of the APVMA permit.

MOUSEOFF ZP Bait Efficacy after storage

As mentioned previously in some states, our rodent research team has taken the opportunity of high mouse numbers to check whether old MOUSEOFF^© bait works satisfactorily. In a replicated block design we tested bait that had been freshly made this month (June 2010) against bait that had been stored for 8 (2002) or 13 years (we had retained samples from as far back as 1997 to enable these tests).

Mouse numbers averaged 849/ha at the first test site and 516/ha at the second site.

The good news is that control within two days of treatment was good at one kg/ha regardless of how old the bait was (no statistical differences between fresh or stored bait). At trial site #1, the stored baits achieved 87 percent control and the fresh bait 98 percent and at site #2 all three bait ages achieved 98percent control. These data were by capture-recapture population estimates and were confirmed by tracking boards and canola census cards.  The lower figure of 87 percent was partly due to a decline in control plots due, probably, to some mice being killed in adjacent treated areas.

An interesting finding was that after four days post baiting, some new adult mice were caught in the trapping grids at site #1 (see green arrow).  The trap grids were centrally placed in 25Ha treatment plots so these adults would have moved about 150 meters from adjacent untreated areas that were known to also be infested.   Whether the new mice were moving down a concentration gradient after the residents were killed, or seeking out the bait itself with alternative feed being short, or entering the treated sites to scavenge the carcasses of mice killed by baiting, is unknown.  However, it does cause us to be slightly more cautious about edge effects.  The infiltrating numbers were very small and all were new mice but it is a factor to be cautious about.

Mice and locusts:

There is no solid science to link the occurrence of mice and locusts, but in 15 years of intensive mouse management we are surprised how often mice and locusts are mentioned to be problems simultaneously.  Of course there are many areas with one pest and not the other, but this year we wonder whether the locusts, or other insect larvae, are assisting to trigger an early breeding season for mice.

We do not have the confidence to predict cause and effect here – it may be just a coincidence, but it may be worth keeping an eye on this for future years, IF locusts are an early predictor of mouse activity

Information and further support:

We still have MOUSEOFF^© 32-page booklets, fliers, and MOUSEOFF^© technical DVD's available if you or your clients need them. These are all free and were cosponsored by GRDC some years ago. The advice has been reviewed by a panel of 20 of Australia's most knowledgeable mouse managers, so you can rely on it as the best advice available.

Or you can simply explore this web site: Mice problems in Australia; Mouse Biology; and Monitoring mice and assessing crop risk.

Call Kym in our office (03 9308 9688) or Fax 03 9308 9622, if you need additional supplies of anything. Once again we hope that these comments are of assistance.

If you would like any of our team to visit to assist with workshops or field days, please also call me to see if we can be there to assist you and your clients.

Use our web site at www.animalcontrol.com.au for additional information about any of our products.