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No Rain, Still Worms: The Summer Sheep Drenching Solution + Double Points in December on Tridectin*

1st December 2023


“No Rain, Still Worms: The Summer Sheep Drenching Solution”

All indications are that we’ll likely experience a drier Summer this year that will greatly assist us in our management of worms. The worms in the animals are still producing eggs and these will hatch when conditions such as moisture and heat are right. It is really important to keep monitoring the sheep’s worm burdens by doing regular worm egg counts (WECs) and treating them when required.


Why a Summer Drench?

The summer drench is a strategic drench which aims to reduce the worm population using the dry summer heat. Summer drenching is a common practice in regions which have uniform or winter rainfall - such as Victoria, Tasmania, much of New South Wales, the southern parts of South Australia and Western Australia. The goal is to lower the amount of worms that are present in the following Autumn and Winter, as the dry hot weather reduces the amount of viable worm eggs and larvae on the pasture. 

One of the dangers associated with this practice, if not done correctly, is the selection for drench resistant worms. Any worms that survive the summer drench, can be carried by the sheep over the summer period into the Autumn where they contaminate the pasture with drench resistant worm eggs that then develop into infective larvae.


Drench Considerations

It is really important then to use an effective drench (ideally greater than 98% effective). In many cases this would be a combination drench like Tridectin, containing three broad spectrum actives and the only three way drench that contains moxidectin. Its export slaughter interval (ESI) of only 17 days provides flexibility if destocking is required. Always consider doing a worm egg count 10 to 14 days after drenching (Drench check) to monitor the efficacy of the drench used.

The timing of the summer drench is not a set date or management event like other strategic drenches such as the pre-lambing drench and the weaning drench. Drenching occurs when the weather conditions are no longer suitable for worm egg development and larvae survival. This is when the days become consistently hotter, the humidity drops and the pasture begins to hay off. For many areas, this can start as early as the first week of November.


The Final Word on Summer Drenching

Nature doesn’t closely follow a script though. Should conditions favour the development of infective larvae (rain and heat) the flocks should be monitored by doing worm egg counts (WECs), starting about 3 weeks after the rain event. Should a second Summer drench be required, consider a different combination drench to the one used as the first Summer drench.

To ensure continued profitability over the next few seasons, the summer drench is a critical consideration for any sheep producer. If you would like to learn more about when and how to incorporate the summer drench into your operation, you can do so by contacting your local Virbac representative. 


Special Offer

Purchase your Tridectin during the month of December and receive double points!*


Want more information about the drenches that are still working on your farm? Head to for more information. 


*The Virbac Tridectin Double Points promotion is valid nationally to Nutrien Rewards Members. To be eligible for the double points offer, the Nutrien Rewards member must purchase Virbac Tridectin from any Nutrien Ag Solutions store that is part of the Nutrien Rewards Program between 1 December and 31 December 2023 (inclusive) using their Nutrien Account. Points will be applied to the Member’s Nutrien Rewards account the following month. Please see Nutrien Rewards Terms and Conditions for more details.


The information provided in this article is intended as a guide only. Information contained in this article has been provided by the manufacturer/ You should not rely on the information in this article, and it should not be considered advice. You should seek professional advice regarding relevant factors specific to your situation. This article does not take into account variable conditions that may impact performance. Always read and follow label directions before using any product in this article. To the maximum extent permitted by law, Nutrien Ag Solutions Limited and its related associated entities will not be liable for any loss or damage suffered by any person arising out of any reliance on any information contained in this article.