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Effects of Paclobutrazol treatment on the growth and seed yield’ of phalaris

K. J. Morthorpea and G. L. Stewartb

a NSW Agriculture & Fisheries, Trangie, NSW 2823
NSW Agriculture and Fisheries, Albury, NSW 2640

The tallness of phalaris seed crops interferes with crop management and can markedly reduce yields through lodging and seed shattering. In addition, culm length and lodging severity are increased when nitrogen is applied to maximize seed yield. Paclobutrazol is a growth retardant which has shown promise for lodging control and yield enhancement in grass seed crops (1). However, the results vary widely between site, season and species. This paper reports a preliminary field study to evaluate paclobutrazol treatment on Sirosa phalaris in south western NSW.


Treatments were applied to an established stand of dryland phalaris at Holbrook, NSW in 1986 and 1987. The crop had lodged severely in 1985. Plants were treated with paclobutrazol at rates of 0, 0.5, 0.75. 1.0 and 2.0 1/ha a.i. at floral initiation in a replicated randomized complete block design. Nitrogen fertilizer totalling 120 kg N/ha was applied to all plots. Rainfall for one month after application was 77 mm in 1986 and 28 mm in 1987.

Results and discussion

Table 1. The effect of paclobutrazol on phalaris

Applications of paclobutrazol at floral initiation significantly reduced the culm length of fully emerged phalaris fertile tillers in 1986 (Table 1). Stems did not lodge and so the effects of lodging on tiller mortality and seed filling were not evident. Seed yields are significantly lower as a result of treatment. This may be attributed to less fertile tillers per unit area and a reduction in seed head length at high rates. The discrepancy in the effect of paclobutrazol application on culm length between the 1986 and 1987 seasons illustrates the unpredictable element in growth regulator studies resulting from seasonal differences. Activation of paclobutrazol is known to be increased by soil moisture (2). More consistent results are likely under irrigation and application at different growth stages should be examined.

1. Albeke, D.W., Chilcote, D.O. and Youngberg, H.W. (1983). J. Appl. Seed Production 1, 39-42.

2. Hampton, J.G. and Hebblethwaite, P.D. (1985). Grass and Forage Sci. 40, 93-101.

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