REDLEGGED EARTH MITE
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Photo: Andrew Weeks, CESAR Consultants
Spring spray keeps mites under wraps
Catriona Nicholls KONDININ GROUP
As spring approaches the time is right to keep redlegged earth mite (RLEM) numbers in check. This month Farming Ahead outlines the key factors producers need to keep in mind to keep on top of this voracious predator. As the weather starts to warm up, the WPSBDJPVT QBTUVSF BOE DSPQ QFTU UIF SFEMFHHFE FBSUI NJUF 3-&. XJMM TUBSU UP emerge from its winter diapause. 3FTFBSDIIBTTIPXOUIBUBUJNFMZTQSJOH spray is the most effective way to combat mite numbers and protect annual pastures and crop seedlings next autumn.
Invasion: As the weather gets warmer redlegged earth mites, aptly named Halotydeus destructor, will start to emerge from their winter diapause, ready to wreak havoc on pastures and crops.
At a glance Spraying for redlegged earth mites (RLEM) during spring will hit mite populations when they are at their most vulnerable. Online decision-support tool — Timerite — will determine the best date to spray for optimum RLEM control. Non-chemical options such as pasture choice, grazing management and natural predators also can be used to control RLEM.
Pest profile Pest species: Redlegged earth mite (Halotydeus destructor) Appearance: Adults — one millimetre long and 0.6mm wide. Red legs with black, velvety bodies. Newly-hatched mites are pinkish/orange with six legs, are only 0.2mm long and are not generally visible to the naked eye. The nymphal stages have eight legs and resemble the adult mite, but are smaller. Often confused with the blue oat mite. Location: Estimated coverage of 20 million hectares across southern Australia Host plants: Clover, plantain, wheat, oats, canola, ox-tongue and capeweed. Seedlings are particularly susceptible to attack. WARNING — do not confuse RLEM with blue oat mites (BOM), which are similar in appearance. Management options for RLEM may not control BOM. When looking for RLEM in the field ensure mites have a completely black velvety body — BOM have a blue-black body and a red mark on their back.
Devastating damage 3-&.GFFEPOQMBOUTCZNBLJOHIPMFTJO the cells on the upper surface of leaves and sucking up the discharged sap. This causes a silvering of the leaves, which can look like frost. Seedlings are particularly vulnerable although attack can also suppress adult plant growth, reducing pasture dry matter production, palatability and digestibility for stock. 3-&.BMTPDBOJNQBDUUIFBNPVOUPGTFFE set, which is important in self-regenerating annual pastures.
A mite population of 12,000 mites per square metre can use as much energy as one dry sheep equivalent (DSE) per hectare. Mite densities well in excess of this are recorded frequently in pastures, which can lead to a high level of competition with sheep for the pasture resource.
Timely control $POUSPM PQUJPOT GPS 3-&. JODMVEF spring and autumn spraying, selection of mite-tolerant pasture species, grazing management and the use of predator species. Farming Ahead August 2010 No. 223 www.farmingahead.com.au
CROPPING REDLEGGED EARTH MITE
3FTFBSDIIBTTIPXOUIBUBUJNFMZTQSJOH spray is by far the most effective control NFBTVSF BT JU UBSHFUT 3-&. BU B TUBHF JO their life cycle when there are the maximum number of live mites and a minimum number of mite eggs, which are impervious to sprays.
New pasture varieties set to survive mite attack The development of two new clover
varieties is set to give livestock producers an additional weapon in their toolkit against redlegged earth mite.
Photo: Catriona Nicholls
The recently released sub-clover varieties — Bindoon and Rosabrook have proven to suffer less damage from redlegged earth mites than existing varieties under low to moderate RLEM pressure. This amounts to a potential increase in winter pasture production and seedling regeneration in tolerant subclover pastures. However, this advantage is less apparent under high RLEM densities, so consider chemical control of mites at sowing, to guarantee successful pasture establishment, and at times of high infestations. Bindoon replaces cultivars Seaton Park and York, with the additional advantage of resistance to race 1 of clover scorch. It is
best suited to areas of southern Australia where the growing season extends to late October, corresponding to an average annual rainfall of about 425–625 mm (depending on location). PGG Wrightson Seeds holds the license to produce and market seed of Bindoon. Limited quantities of certified seed will be available for sowing during 2010, with larger quantities available during 2011. Rosabrook will replace Denmark and is best suited to areas where the growing season extends to late November and corresponding to a minimum annual rainfall of about 650mm (depending on location). Seed Force Pty Ltd holds the license to produce and market seed of Rosabrook. Limited quantities of certified seed should be available during 2011. Provisional Plant Breeders Rights have been obtained for both cultivars.
Controlling RLEM during spring leaves a minimum number of eggs to hatch the following autumn. Getting it right $4*30 XJUI GVOEJOH GSPN "VTUSBMJBO Wool Innovation (AWI), developed a model to predict the optimal date for spraying EVSJOH TQSJOH UIJT NPEFM JT DBMMFE Timerite®. Timerite targets the time at which a minimum of both winter and diapause eggs are present, ensuring optimal control of adult mites. This date is exactly two weeks before the date at which 90 per cent of eggs are diapause. These dates are similar at any given site each year, but vary between sites (the onset of diapause seems to be correlated with a change in day-length and a correction for long-term length of growing season). Spraying on this date is critical. Spraying too early means too many winter eggs
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76 Farming Ahead August 2010 No. 223 www.farmingahead.com.au
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CROPPING REDLEGGED EARTH MITE
will still be present and survive the spray to go on and hatch and produce diapause eggs. Spraying too late means diapause eggs will already be present and can emerge from diapause the following autumn to attack pastures and crops. But before heading for the spray rig, it is important to understand the potential level of risk of attack and to check for mite populations to minimise the risk of pesticide resistance. To check mite numbers in the field, first determine the ideal spray date for your property by accessing Timerite online. Input the latitude and longitude of your farm or paddock in degrees and minutes. An example of this is 31°21’S and 115°41’E to determine. Use a GPS to find the latitude and longitude in degrees and minutes or visit the Geoscience website (www.ga.gov. au/map/names). Check for mites before the ideal spray date. If no mites are observed, non-chemical control may be a better option. If mites are observed, use the Timerite spray date for optimal control. MORE INFORMATION To better understand the potential risk of mite attack and for more information on RLEM control go to: www.timerite.com.au.
Benefits of control Between 1997 and 2003, 60 trial sites were set up in New South Wales, Victoria, South Australia, Tasmania and Western Australia to quantify the benefits of spraying mites on the predicted Timerite® date. The trials were set up using a paired paddock design where half of the paddock was sprayed on the calculated date and the other half was not sprayed. Mite numbers — spraying on the Timerite date reduced RLEM numbers by 97 per cent on 20 farms in WA the following autumn. Unsprayed paddocks had an average of 21,569 mites per square metre whereas paddocks sprayed on the calculated date only had an average of 550 mites/m2. In eastern Australia the following autumn there were an average of 8000 mites/m2 in the unsprayed plots, while those that were sprayed had 919 mites/m2 — a reduction of 88% across 38 farms. Sub-clover seedling density — the autumn following spraying on yielded a 97% increase in sub-clover densities across the WA sites. The unsprayed paddocks had an average of 697 sub-clover seedlings/m2 and the
sprayed paddocks had an average of 1371 seedlings/m2. In eastern Australia there was a 13% increase in sub-clover seedlings. The unsprayed paddocks had 566 sub-clover seedlings/m2 and the sprayed paddocks had 640 sub-clover seedlings/m2. Increase in sub-clover seed yield — sub clover seed yields at sites in WA increased by 34% due to spraying on the Timerite date. Unsprayed plots yielded 464 kilograms per hectare, whereas sprayed plots yielded 621kg/ha. In eastern Australia the seed yield increased by 51% from 285kg/ha in unsprayed plots to 430kg/ha in sprayed plots. With average sub-clover seed prices at $5/kg, the additional seed produced in the sprayed plots is valued at $785/ha in WA and $725/ha in eastern Australia. The size of benefits varied considerably between sites. This reflected the fact that many factors other than RLEM are important in determining seed yield. At half the sites the benefit was more than 100kg/ha.
Eastern State Dealers Required
Farming Ahead August 2010 No. 223 www.farmingahead.com.au
Published on Aug 25, 2010
As the weather starts to warm up, the Invasion: As the weather gets warmer redlegged earth mites (RLEM), aptly named Halotydeus destructor,...