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South Australia worms, flies and lice update - February 2016

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides


Adelaide: Colin Trengove, Sheep Health Lecturer (UA Roseworthy campus) (trengovet@icloud.com)

After a protracted dry spell across SA since late spring, rainfall of 20–100 mm fell across most of the state in early February leading to a significant green pick. While this pick is essentially of moisture-sapping nuisance value as well as a summer weed conundrum for croppers, it does provide a welcome protein and energy boost for livestock. It can also lead to an emergence of worm larvae ready to infest unsuspecting livestock nipping at the short green pick. However, subsequent dry conditions have more likely minimised the risk of larval pick up, as the green pick and larval survival will have been short lived in most environments.

Recent monitoring has indicated continuance of the typical wide variation seen over summer with most adult sheep maintaining low to negligible worm burdens. In contrast, lamb to hogget stage animals still to acquire immunity to worms have displayed worm egg counts up to 500 eggs per gram. Similarly, some old ewes have had significant worm burdens, possibly indicative of waning immunity. Significant worm burdens (>100 epg) in young and old alike should be addressed to limit the carryover of worm infestations to the following winter. The choice of drench will depend on the level and spread of drench resistance in particular flocks; pay special attention to avoid using the same chemical(s) used in late spring/early summer, in the same sheep.

The rainfall, spread over two episodes a week or more apart in February, also contributed to isolated flystrike incidents highlighting the need to be especially vigilant during unseasonal weather patterns. The reported flystrike cases were mainly the more difficult to detect body strike form, making careful observation even more critical to avoid losses.

Late summer worm monitoring is especially important 3–4 weeks after summer rainfall exceeding 20 mm, as worm larval emergence and pick up can be unpredictable—especially where there is a risk of Haemonchosis (barber’s pole worm infestation). Worm egg monitoring should be a routine procedure in February across several mobs to assess and minimise the risk of winter worm burdens in the lead up the autumn break. The unseasonal rain has placed even greater emphasis on this preventative management strategy.