Prevention and control of grass seeds
Grass seed most typically affects sheep during summer and autumn. In WA, we most often notice sheep that have issues with grass seed contamination when we see that their eyes are inflamed, closed or they are having trouble running freely since they can’t see properly. They may also scratch because the seeds are penetrating their skins.
Strategies to reduce the impact of grass seed contamination of sheep and their wool include pasture management, breed selection, animal management and fleece preparation.
Pasture management
Producers should be familiar with the grass seed problem grasses and be able to identify them easily. This is easier when the plants are seeding. To keep pastures healthy and prevent grass seed problem grasses from flourishing, stocking rate can be manipulated and pastures can be spelled or grazed with other species.
Burning
The results from burning are often not consistent, as it can have diverse effects upon species composition and subsequent growth of vegetation depending on the season, amount of herbage, frequency of burning and intensity of the burn.
Mechanical treatment
Slashing tracks through tall seed-bearing plants to allow safe access to water from grazing areas or enable animals to move further into grass-seed-infected areas is useful.
Herbicides
Probably the most widespread control of grass seed set has been through chemical control. Since these grasses are usually the earliest to set seed, they can be sprayed out early in the season with little damage to clovers and other legumes. They can also be sprayed out later in the season (spring) to reduce seed set for next year. For more information on chemical control, contact your local agent.
Breed selection
Sheep and goats without wool or dense hair are rarely affected by grass seed and hence are recommended in seed prevalent country. For sheep, this includes Dorpers, White Dorpers, East Friesians and Damaras. Merino and Merino crosses with these breeds will be more prone to seed damage.
Animal management
Shearing
Shearing sheep before grass seed matures will often reduce wool vegetable matter faults and seed damage to skins. Late summer and early autumn shorn wools typically have higher vegetable matter and may be discounted accordingly. Spring and early summer shearing will minimise seed contamination and usually set weaner sheep up for a happier, healthier summer season.
Stocking rate
Strategic short-term heavy stocking including cell grazing and rotational grazing may reduce infestations of problem grasses. Long-term set stocking is undesirable. It is important to match grazing and rest periods with the growth and reproduction of the pasture species in conjunction with seasonal conditions. Changes in the pasture would also depend on favourable seasons, influence of rainfall and the conditions of the pasture.
Varying stocking rates can be achieved by taking on agistment or dealer livestock for short terms through anticipated spring growth periods and destocking them before summer and winter.
Cross-grazing
If grass seed problem grasses dominate the property then a change in stock species or ratios is suggested so that the animals can assist the change back towards a summer grass pasture. Cattle are virtually immune to grass seeds. They eat large quantities of tall fibrous material and trample seeds and tall growth; this clears access to short feed for sheep. They are kinder on summer perennials during drought times and are often destocked for sale sooner than sheep. Take care to use enough cattle to reduce the density of seed-bearing plants but not so many that the paddock is eaten out.
Horses will similarly do the job or goats as they eat the wiregrass tussocks and woody regrowth more readily than sheep. Goats are less susceptible to grass seeds due to the fall or lay of their hair coat.
Merino breeding and selection
Select Merino sheep with little face cover or open faces and few body wrinkles. Run wethers and adult sheep which are less likely to be affected by grass seed rather than lambs and weaners.