What is the best timing for seed set control?

The pattern of seed head emergence has a major impact on the choice and effectiveness of silage, hay or cutting as a weed control option.

The timing of seed head emergence is influenced by a combination of the species present, environmental conditions and grazing history.

Common pasture grasses have different maturity patterns (Figure 3).

While this general pattern holds, plants will also respond to different climatic conditions. A short spring will result in earlier seed head production, whereas a long, cool finish will contribute to later, more staggered seed head formation.

The finish to the season will also affect the dormancy within the seed set. As a general rule, a ‘hard’ finish to a season will result in less dormancy and a ‘soft’ finish will lead to a more staggered level of dormancy in the carryover seed.

Grazing will delay maturity and the later the grazing, the later seed emergence will be. If a pasture is unevenly grazed, some plants will reach maturity before others. This staggered seed emergence results in uneven formation of viable seed, with some seed surviving when cutting occurs.

Even grazing of the pasture before livestock are removed is essential to achieve synchronous seed head emergence. This improves the chances of getting more effective weed seed control. Even grazing can be achieved by running heavy stocking rates in winter and early spring.

Figure 3. The timing of seed head emergence of common grasses (example for south-west Victoria).

Even seed head emergence (left) and uneven seed head emergence (right) from selective, or patch, grazing.

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