Tasmania worms, flies and lice update - November 2018

Perth: Paul Nilon, Nilon Farm Health (pandonilon@bigpond.com)

Our season is hanging on in many areas, although while attacking the lawns t’other day, I was surprised to see large cracks in the soil hidden by the green mat. Rain is forecast for the next few days (20–24 November).

Marking is just about complete, and the earlier lambers are weaning (or should be). Be prepared to wean as soon as possible unless there is substantial rain in the next week to rejuvenate the spring. Now, the weaning drench is the first summer drench for those with a strategic programme. If cross-bred ewes are being sent to Jenny Craig paddocks, it is unlikely they will need a drench. Those remaining on perennial pastures should be drenched along with the lambs. The weaning/first summer drench is the most important of the year, so make sure you use a drench that works: use your DrenchTest information or one of the new products (Startect^® (abamectin and derquantel) or Zolvix Plus (abamectin plus Monepantel)—but watch the export slaughter interval (ESI) of 84 days with the latter).

Mainland lambs are arriving in large numbers. On the whole we expect drench resistance to be worse than it is here. Use a potent quarantine drench with at least 4 actives, including one or both of the newer actives: monepantel or derquantel. Also beware of the potential for importing lice and footrot (see comments below on lice biosecurity).

Pasture Grubs: Attached is a picture of grub predation on a ryegrass pasture. It’s drawing a long bow to write about them in a sheep worm missive, but as my mainland colleagues are ignorant of these things it may be instructional. The culprits were black-headed cockchafers, which are treatable, unlike their red-headed cousins.

Figure 1: Ryegrass pasture with areas of grub predation. Source: Paul Nilon.

Lice Biosecurity: The high wool prices (and perhaps a return to Merino sheep) rejuvenates concerns about preventing lice. Losses due to lice infestation are found in this article, and you can do the sums on what current losses may be. Remember that fine and superfine clips will be absolutely crucified by even modest lice infestations.

Cynical Paul sometimes contends that biosecurity plans have little day-to-day utility. This is not the case with lice biosecurity: if you understand and act diligently on the risks (whether you have a written plan or not) you may well save yourself a packet. Jenny Cotter has written a great article on this, but it’s important to highlight a few actions you can take to have a workable approach to lice prevention:

• Boundary security: It’s glib to say keep your place secure. The large Midlands properties with extensive bush runs have little chance of keeping trees off the fence-line. Do what you can, but as importantly, quarantine mobs exposed to foreign sheep and do an inspection 3 months after any known incursions. Talk to your neighbours and ask what their status is. Use the LiceBoss tools to help decide the advisability of treatment.
• Sheep purchases: Ask for a sheep health statement and use it as a risk gauge. The story books tell us that you should quarantine for 3 months or more. This is difficult, but do what you can and inspect the sheep before exposing others to them. If there is any doubt about the status of new rams, shear and treat them. Lamb traders have special needs. It must be presumed that they will introduce lice with some regularity. Shearing may be on the cards, but efficient finishers will not be happy to extend finishing times with lice treatment withholds. Moreover, you have an obligation to protect your neighbour’s flocks. Keep imported prime lambs away from your breeding flock (including replacements that may also be grazing high growth rate pastures), and preferably away from boundary fences.
• Active surveillance: Take the time to inspect all mobs twice a year, and also 3 months after any challenges. Inspect sheep with rub and pulled wool. The experts differ a bit in numbers to inspect, but I suggest 20 sheep with 15–20 partings per sheep.
• Risk management: Be risk averse, particularly if you run Merinos. When all is said and done, the other causes of rub are rare in Tasmania. The Greens may well go in to bat for itchmite since ivermectin made them an endangered species. Grass seed worry is less of an issue here than the mainland, and dermo not all that prevalent. So, if you see rub and cannot find lice, either keep looking or look at your treatment options.