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Dormancy in grass weeds

HGCA PROJECT REPORT 498 
Dormancy in grass weeds


by
Sarah K Cook and Denise Ginsburg

ADAS Boxworth, Boxworth, Cambridgeshire CB23 4NN

Abstract

Innate or primary dormancy is a natural condition that develops as the seed matures. It prevents premature germination of the seed whilst it is still attached to the plant or just after shedding and allows for dispersal of the seed from the parent plant.

A range of controlled environment and small plot experiments were done between 2007 and 2010 to provide the farming industry with an annual forecast of dormancy in black-grass, Italian rye-grass, barren, meadow, rye and soft brome and to understand the implications of dormancy on emergence patterns. Results from the dormancy testing were released to the press annually in late August. These contained specific management principles so that farmers and agronomists could adjust cultivation method and timing, drilling date and herbicide programmes to accommodate the effect dormancy would have on black-grass emergence.

Seed of black-grass, Italian ryegrass, barren and meadow brome were collected from winter wheat fields in July when 10-30% of seeds had already been shed. Germination tests were done on the seed according to a strict protocol. A population was termed more dormant or as having high dormancy when, given the ideal growing conditions a low percentage of seeds germinated. Conversely, a population was termed less-dormant or with low dormancy when a high percentage of seeds germinated in the test. The dormancy level of black-grass seed was low when June and July had been warm and dry and high when this period was cold and wet. Dormancy in Italian ryegrass, meadow brome and barren brome was unaffected by weather conditions during seed ripening.

In black-grass, emergence of high dormancy seed was delayed when compared to seed of low dormancy. The knowledge of changes in emergence patterns can be used to adapt the management strategies adopted by growers to improve black-grass control. The emergence patterns of Italian rye-grass, meadow brome and barren brome were unaffected by dormancy level; all species emerged rapidly during the autumn.

To reduce the cost of annual dormancy forecasting, nine years of black-grass dormancy results from 367 sites were collated. A weather data for each site was created and a window pane analysis was done. This type of analysis looks for the period of weather that has the greatest effect on dormancy. Black-grass dormancy was affected by both average temperature 20-39 days after flowering, and rainfall 4-12 days after flowering. Only 31% of the variation was accounted for and this indicated that there was a strong level of genetic control in addition to the weather affects. The correlation can be used to give an indication of the level of dormancy expected for the season but some field sampling will be necessary.

HGCA Project Number: 3336

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