What factors lead to poor pasture persistence and weed ingress?

In an ideal pasture, sown species would persist indefinitely and there would be no weeds. 'Poor persistence' occurs when the desirable species are replaced by weedy, undesirable species. Unfortunately, poor persistence of sown pasture plants is the reality that most farmers experience. In this paper we review the literature on three key factors leading to poor persistence and weed ingress: 1) inter-specific competition; 2) sward disturbance; and 3) propagule pressure. We reveal that grazing and other management decisions, pasture insect pests, nutrients, climate and the composition of the sown species mix have a critical influence on these factors, and hence over the replacement of sown pasture plants by weeds. The key practical message from this review is that farm practices that improve the vigour of sown species, reduce pasture gaps and minimise weed propagule pressure will improve the persistence of sown species and minimise weed ingress. An outstanding deficiency is our lack of knowledge of the economic impacts, and hence weed status, of most of the ca 187 volunteer plant species that may invade and replace sown plants in New Zealand's pastures.

Effects of atrazine treatment of sorghum on growth of a subsequent rice crop

In an experiment at Yanco Agricultural Research Centre in the Murrumbidgee Irrigation Area, rice was grown on land that had been cropped with sorghum for the preceding 1, 2 or 3 years, and had received applications of atrazine at rates of 0, 2, 5 and 10 kg ha-1 on each sorghum crop. Rice yield was not adversely affected by previous herbicide applications, and growth was often more vigorous on plots receiving atrazine in previous years. The removal of volunteer plant growth by cultivation or non-residual herbicides during the winter fallow periods had no consistent effect on subsequent rice growth.

Observations on Feeding Habits of First-instar Larvae of the Pale Western Cutworm, Agrotis orthogonia Morr. (Lepidoptera: Phalaenidae)

The pale western cutworm, Agrotis orthogonia Morr., has been a major pest of cereals in the prairie region of Western Canada since 1911. Present control measures consist of (a) cultural measures that inhibit oviposition in fields being summer-fallowed and (b) starvation of the young larvae by destroying the volunteer plant growth by means of cultivation at a critical period. Cultural operations to minimize oviposition in fields being summer-fallowed have become accepted procedure throughout the area. Control by starvation is practised during outbreak years in fields that have-been “stubbled in” or in those tilled during the moth flight. This procedure has been recommended generally throughout potentially infested areas, but more precise methods of evaluating larval numbers are required so that control may be used only where critical populations are present.