ISHS Acta Horticulturae 415: VIII International Asparagus Symposium
SUCCESSION OF WEED FLORA IN SOME NEW ZEALAND ASPARAGUS CROPS |
| Authors: | A. Rahman, P. Sanders |
| Abstract:
The weed flora of most New Zealand asparagus crops has changed rapidly due in part to cultural practices but largely due to repeated use of herbicides. The weed composition in early establishment phase of most asparagus crops consisted of many annual broadleaf and grass weed species, of which only five or six broadleaf and two or three grass weeds dominated. The spectrum of weeds varied with both climatic and soil (mainly texture) differences and the numbers reached several million seedlings/ha in some cases. As these common weeds were removed by cultivation, or more often by herbicides, the composition shifted to warm-zone perennial grasses e.g. Paspalum spp., Cynodon dactylon. Broadleaf weeds that emerged as specific problems were Gnaphalium luteoalbum in fields where uracil or triazine herbicides were used repeatedly, and triazine-resistant Chenopodium album and Polygonum persicaria as a result of reliance on triazine herbicides. Other particularly troublesome weeds to appear in many fields included Cirsium arvense, Calystegia silvatica, and Convolvulus arvensis, as their growth habits are somewhat similar to asparagus and herbicides do not provide adequate long term control. Ranunculus repens, a weed of pastures and orchards, has also encroached into some fields, and recently Cyperus rotundus has also appeared in some crops and may prove a difficult problem in future. Research has kept pace in developing control strategies, which are discussed in the paper. It is strongly recommended to rotate herbicides (belonging to different chemical families) in the weed control programme to slow down the shift in weed composition and limit development of herbicide resistance. | |
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