The summer drench is a bit of a vague term, but there is some strategy behind drenching in the drier part of the year. This article breaks down the complexity of the summer drench and gives you what you need to know to successfully control worms.
This information is predominantly relevant to winter rainfall areas of southern Australia, where Barber’s Pole worm is around, but not the main/only concern. If you would like information about how to control Barber’s Pole over summer, refer to the Barber’s Pole article by clicking here.
Goal of Summer Drenching
The aim of a summer drench strategy is to kill off as many worms as possible at a time of year when larval development is stunted. Meaning that:
- all of the worms in the sheep are controlled with a chemical drench, and
- all, or most, existing larvae in dung/on the pasture can’t survive the hot, dry conditions either.
Ultimately, this provides the greatest ‘cycle-breaking’ parasite control effort for the year.
Getting a good natural and chemical parasite cull will set you up for success in the year to come. This is because when the autumn break hits, worm loads will be significantly lower. Lower worm burdens in autumn usually translate through to winter and spring as well.
Best Time for Summer Drenching
The timing of the summer drench varies by region and the type of season. Some properties do one summer drench, and some might do a second summer drench.
In moderate to high rainfall areas, the first summer drench is usually given in November or December. This coincides with the grass drying off and dung pellets hardening. Drier feed leads to more formed dung, which in turn holds moisture better and increases larval survival rates. To ensure worm-egg output is lowered, the best way is to remove worms in the sheep by drenching with an effective drench. That way, the chance of large numbers of larvae surviving in their favourite dung pellets is reduced.
The second summer drench is timed when pastures dry off completely, or sheep are put into stubbles. This is often in January or February. The aim of the second summer drench is to kill any worms remaining in the sheep, on the premise that it’s too hot and dry for larval survival in the environment. In Western Australia and other dryland regions, this might be the only summer drench required. Also, if the first summer drench was given in November/December, a second summer drench may not be required and may only be done so in response to high worm counts from a worm test.
What drench to use
To achieve the desired outcome of a summer drench, a highly effective drench must be used. Ideally 98-100% of worms should be killed off with the drench, as proven by a drench check. As a general rule, a triple active drench (e.g., Vetmec LV and Vetmec Dual together), or a drench with new actives (e.g., Startect or Zolvix) given in combination with other actives, would be the best options.
Using a highly effective drench over the summer is extremely important because, at this time, virtually all the existing worms are in the sheep. So, any worms that are left in the sheep after drenching (i.e., survive the drench) are resistant to the drench used. These will be the ones that breed into the major part of the worm population when the season breaks. Using a drench with low or failing efficacy over this period will super-charge the development of resistance on your property.
Drench efficacy will vary between properties, so if you already know which drenches are working on your property, that’s great! If you don’t already have that data, now’s the time to start collecting it. This year, take a worm test before, and 10 days after, your summer drench to find out if it worked.
For any further questions or enquiries about summer drenching, don’t hesitate to give us a call on 1800 243 683.
References
Summer drenching of sheep | DPIRD WA
Best practice first summer drenching strategies | Agriculture Victoria
Management of Worms | Making More from Sheep
Weaner Worm Control & Summer Drenching | Paraboss