Evaluation of new herbicides for capsicums and chillies

Evaluation of new herbicides for capsicums and chillies
Serve-Ag Research, PO Box 690, Devonport, Tasmania 7310, Australia
Summary Effective weed management strategies are
300 kPa. In all data presented here, oxadiargyl, limited for capsicum and chilli producers. Current weed pendimethalin and clomazone were applied pre management practices include the use of plastic mulch, transplant, within two days of transplanting. Plot sizes selective grass herbicides, handweeding or tillage. were between 10 and 30 m2. Assessments were There are currently no herbicides registered for conducted as whole plot subjective ratings using the broadleaf weed control in capsicums or chillies. European Weed Research System (EWRS) scales for Potential new herbicides were screened and weed control efficacy (1 = total weed control, 9 = no efficacy, crop safety and residue data was generated. A effect on weeds) and crop tolerance (1 = healthy plant, 9 total of 13 trials were conducted over three seasons = crop killed) (Puntener, 1981). Weed density counts throughout major Australian production regions. The were conducted using randomly placed quadrats and most effective herbicides identified from this work were results presented as percent control compared to the pendimethalin, clomazone and oxadiargyl, which all untreated control. Crop yield measurements were gave best results when applied pre crop transplanting. conducted by harvesting 10 plants per plot and All three products provided effective pre emergent classifying fruit into marketable and non-marketable control of a range of common broadleaf and grass weeds categories, based on factors such as size and colour. Clomazone, oxadiargyl and pendimethalin applied at double the proposed use rates, on soils with very low levels of organic carbon and clay, did not cause any crop phytotoxicity. Yield and quality of capsicum and chillies was also not affected by these herbicides. Keywords capsicum, chilli, oxadiargyl, pendimethalin,
Capsicums and chillies are grown from transplants commercially throughout Australia, although most of the production is in Queensland. Effective weed management strategies are limited for capsicum and chilli producers. Current weed management practices include the use of plastic mulch, selective grass herbicides, handweeding or tillage. There are currently no herbicides registered for broadleaf weed control in capsicums or chillies. The development of effective broadleaf weed herbicides, to be used as part of an integrated weed management program in capsicum and chilli production in Australia, is essential. A total of 13 replicated small plot trials were conducted over three seasons throughout major Australian production regions. Trials were conducted in North West Tasmania, Perth (Western Australia), Atherton (North Queensland) and Bowen (North Queensland). Small plot trials were sprayed with flat fan nozzles, generally applying water rates of between 200 and 300 litres/ha at an application pressure of between 200 and (crowsfoot grass) control but was not as effective as pendimethalin and clomazone on these weeds (Table 4). Oxadiargyl at 400 g a.i. ha-1 was generally more effective than clomazone at 480 g a.i. ha-1 and pendimethalin at 990 g a.i. ha-1 for controlling broadleaf weeds (Tables 5 & 6), although all products provided weeds AMACH Amaranthus hybridus (green amaranth), CHEAL Chenopodium album (fat hen) and POROL 9.8 Portulaca oleracea (pigweed). Crop safety The three herbicides oxadiargyl,
pendimethalin and clomazone, applied pre transplant showed high crop safety over a number of sites with average EWRS crop ratings of 1.1, 1.4 and 1.1 respectively (Table 2). Yield data from a trial in Bowen showed these herbicides had no affect on marketable yield of either capsicum (cv Blister) (Table 2) or Chilli (cv. Warlock) (Table 3). This trial was conducted on a light textured soil with a cation exchange capacity of 5.9 Sulfentrazone, flumioxazine, carfentrazone, oxyfluorfen, metribuzin, isoxaflutole and imazamox were also weeds SOLNI (Solanum nigrum, black nightshade), screened, but they were not further evaluated due to SONOL (Sonchus oleraceus, sow thistle) and TRBTE weeds ELEIN (Eleusine indica, crowsfoot grass) and DIGAD (Digitaria ciliaris, summer grass). Herbicide residues in fruit Analysis of clomazone
and pendimethalin residues in capsicum fruit showed that when applied pre transplant, these herbicides were Weed efficacy The three herbicides pendimethalin,
not detected at a limit of quantification of 0.01 mg/kg at clomazone and oxadiargyl all showed activity on two sites. common grass and broadleaf weeds in capsicum and chilli crops. Both clomazone at 480 g a.i./ha and pendimethalin at 990 g a.i. ha –1 provided near complete Trial data at 13 sites over three seasons has shown control of Eleusine indica (crowsfoot grass) and clomazone, pendimethalin and oxadiargyl provide Digitaria ciliaris (summer grass). Oxadiargyl at 400 g control of a number of problem weeds while being safe a.i. ha –1 provided 91% (summer grass) and 84% to capsicum and chilli crops. A variety tolerance trial was conducted at Bowen in North Queensland on a light textured soil with a cation exchange capacity of 5.9 cmol kg-1. This site presented a worst case scenario for crop safety with soil applied herbicides and the herbicide rates used in this trial were approximately double those required for control of susceptible weeds. Despite this, the products showed high crop safety with no effect on marketable yield of capsicum or chilli. Clomazone, pendimethalin and oxadiargyl can potentially be used to manage weeds under plastic mulch, in inter-rows between plastic mulch or within rows in crops grown without plastic mulch. Effective herbicide options may even assist growers to reduce their reliance on plastic mulch in capsicum and chilli crops in some situations. These products can not be used in commercial crops until permits or registrations are obtained from the Australian Pesticides and Veterinary Medicines Association. The information generated from this project maybe used to support these applications. Funding supported by National Vegetable Research & Development Levy and Commonwealth Government through Horticulture Australia Ltd. We thank all growers who kindly provided trial sites. We also thank all researchers who undertook trials as part of this project. Researchers included, Mark Sumner, Chris Monsour, Keith Lewis and David Kilpatrick. Frost P and Hingston T (2004). Weed Management in Capsicums and Chillies. Horticulture Australia Ltd Final Report. Puntener W (1981). Manual for Field Trials in Plant Protection. Second Edition. Ciba-Geigy Limited, Basle, Switzerland. Thomson W (1997). Agricultural Chemicals Book II Herbicides. Thomson Publications, California.

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