Survey of weeds and diseases in cereal crops in the southern wheat belt of New South Wales

Abstract

A field survey of weeds in 86 cereal crops in southern New South Wales was conducted in spring 1993 to determine weed and disease distributions, and their levels of infestation. Fifty weed species from 19 families were identified. The most widespread species were Arctotheca calendula (capeweed) in 76% of fields, Avena spp. (wild oats) in 72%, Trifolium subterraneum (subterranean clover) in 69%, Lolium rigidum (annual ryegrass) in 69%, Vulpia spp. (silvergrass) in 63%, Juncus bufonius (toad rush) in 62%, Crassula spp. (stonecrop) in 37%, Polygonum aviculare (wireweed) in 37%, Fumaria spp. (fumitory) in 36%, Chondrilla juncea (skeleton weed) in 36%, Rumex acetosella (sorrel) in 28% and Hordeum spp. (barley grass) in 26%. Some species were associated with region and previous crop. Levels of weed infestation, based on a visual assessment of the relative weed-crop ground cover, plant density and height, were surprisingly high. A questionnaire completed by 181 farmers and 30 agronomists, to determine their perceptions of the most abundant weeds, showed close agreement with the field survey. Current weeds were generally considered difficult to control and expected to be a continuing problem. The exception was Raphanus raphanistrum (wild radish) which had a low incidence, but was expected to become more serious. The root disease, take-all (Gaeumannomyces graminis var. tritici), was recorded in 32% of the 56 wheat crops examined. It was associated with a previous pasture, lupin or cereal crop, but was absent when the previous crop was canola. Another root disease, rhizoctonia bare patch, was found in only one wheat crop. Common foliar diseases were ring spot (Pyrenophora semeniperda) in 57% of wheat crops, septoria tritici blotch (Mycosphaerella graminicola) in 23%, yellow spot (Pyrenophora tritici-repentis) in 2 1 %, stripe rust (Puccinia striiformis) in 3%, and septoria nodorum blotch (Phaeosphaeria nodorum) in 2%. These diseases were generally present on less than 5% of crop leaf area.