Biology and management of dodder a new threat to the canola industry Abul Hashem Department of Agriculture and Food Western Australia Centre for Cropping Systems P.O. Box 483, Northam WA 641, Australia ABSTRACT Seed dormancy release, host species preference, the effect of parasitisation on pods or burrs of canola and other broadleaf crop/pasture species, and control of dodder (Cuscuta spp) by selective herbicides were investigated in a series of experiments under laboratory and glasshouse conditions in 5 at Northam, WA. About 88% of untreated seeds of dodder were dormant but soaking seeds in concentrated sulphuric acid for 1 minutes improved seed germination from 12 to 45%. Treated seeds of dodder germinated over a range of temperature regimes. This weed species successfully parasitised lupin, lentil, field pea, faba bean, chickpea, sub-clover and canola plants in order of decreasing preference. Dodder parasitisation reduced pods or burrs per plant by 1% in canola, % in lentil, 5% in faba bean, field pea 58%, 6% in lupin, 75% in chickpea, and 1% in sub-clover. Herbicides such as trifluralin, atrazine, simazine, and propyzamide controlled 1% of dodder plants. Key words: dormancy, host preference, parasitic effect, herbicide control, time of sowing. INTRODUCTION Cuscuta spp (dodder) is widely distributed in Mediterranean and central Asia but it has been introduced in many other countries (Parker and Riches 1993). It is known to attack lucerne and clovers (Al-Menoufi and Hassan 1976) and some species of dodder are mildly toxic to animals (Movesian and Azaria 1971). Plants of dodder was found in a canola crop in the Northern Agricultural region of WA in 1, the first time for any reported infection of canola. This was identified as Cuscuta planiflora (red dodder) but it did not appear to be so in subsequent studies. The presence of dodder in paddocks and the potential for contamination of produce by dodder may exclude that produce from some markets where there is a zero tolerance for dodder seed. Very little information is available on the biology and management of this parasitic weed under WA wheatbelt conditions. The aims of this study were to investigate dodder seed dormancy release, crop host preference, effect of parasitisation on host plants, and control options for dodder under Western Australia conditions. MATERIALS AND METHODS A series of experiments were conducted in a completely randomized design with 5 seeds petri dish -1 or pot -1 replicated 3-5 times under laboratory and glasshouse conditions at Northam, WA in 5. An untreated control was maintained in each experiment. Release of dodder seed dormancy Seeds were treated with concentrated sulphuric acid for 1 minutes and then allowed to germinate at three temperature regimes (5/15, 1/, and 15/3 C night/day) with or without prior chilling. Germination of seeds was recorded either daily or every alternate day for 3-6 weeks. Host preference for dodder plants Treated seeds of dodder were sown with seven species of crops and pastures (canola, chickpea, faba bean, field pea, lentil, lupin, and subclover) in 1-L pots with three replications. An untreated set of three pots species -1 was maintained without dodder seeds. Emergence and survival of dodder plants were recorded for up to 7 weeks after sowing. Effect of dodder parasitisation on the growth of host plant species Treated seeds of dodder were sown on the surface of pots and covered with a thin layer of sandy soil. In the pots where natural parasitisation did not occur, artificial parasitisation was performed by
wrapping an 8 cm long fragment of dodder shoot on to the stem of the target host plant. Pods produced by host crop plants both in the absence and presence of dodder were counted. Effect of time of sowing on dodder emergence and survival Treated dodder seeds were sown in pots four times at weekly intervals. Emergence and survival of dodder plants were recorded for each time of sowing (TOS) up to 31 days after sowing. Dodder control by herbicides Selected pre-sowing herbicides recommended for each host species were sprayed on the surface of pots and covered with a thin layer of sandy soil. Emergence and mortality of dodder plants were recorded for 7 weeks after sowing. Selected post-emergence herbicides recommended for each host plant species were sprayed at label rate and at the recommended growth stage of each host plant species. Density and mortality of dodder plants were recorded 4 weeks after spraying. Dodder control results by herbicides that can be selectively used in canola are presented. RESULTS Release of dodder seed dormancy About 88% untreated seeds of dodder were dormant. Soaking seeds in concentrated sulphuric acid for 1 minutes (followed by rinsing with distilled water) increased germination from 12% to 45% (Figure 1). Chilling after acid treatment reduced germination of dodder compared to acid + no chilling treatment while chilling without acid treatment did not affect its germination. Temperature regimes (5/15, 1/, and 15/3 o C night/day) did not affect germination of treated dodder seed under growth cabinet conditions. Cumulative germination (%) 5 45 4 35 3 25 15 1 5 no acid, no chill Acid + no chill No acid + chill Acid + chill 3 6 9 12 15 18 21 Days after sowing dodder seeds Figure 1. Effect of concentrated sulphuric acid and chilling treatments on the germination of Cuscuta spp under laboratory conditions. Host preference for dodder plants Germination of treated dodder seeds sown with various host crop and pasture species started 5 days after sowing (DAS) in lupin and 7 DAS in other plant species (Figure 2). Regardless of species, the highest number of surviving dodder plants (5-3 pot -1 ) was found at 8-22 DAS (except in canola) where after the number of surviving dodder plants gradually decreased. The number of surviving dodder plants at 44 DAS was reduced to 3-6 plants pot -1 regardless of species. In canola, the highest number of surviving dodder plants was 5 pot -1 observed at 26 DAS. Although the number of surviving dodder plants did not vary greatly at 44 DAS, based on the highest observed number of surviving dodder plants the host species may be ranked in the order of decreasing preference by dodder as lupin>lentil>field pea>faba bean>chickpea>subclover>canola (data for field pea and sub-clover not shown). Parasitisation of dodder in canola remained at a very low level although number of final surviving plants was similar to those in lupin (Figure 2).
Surviving dodder plants pot -1 35 3 25 15 1 5 Canola Chickpea Faba bean Lentil Lupin 4 8 12 16 24 28 32 36 4 44 48 Days after sowing dodder seeds Figure 2. Emergence and survival of Cuscuta spp plants in association with various host crop plants under glasshouse conditions. Effect dodder on the pods or burr of host plant species The production of pods or burr per surviving host plant was greatly affected by dodder in all host species (Figure 3) except in canola where the number of surviving dodder plants was also lower than in the other species (Figure 2). The presence of dodder reduced pods or burr plant -1 by 1% in canola, % in lentil, 5% in faba bean, field pea 58%, 6% in lupin, 75% in chickpea, and 1% in subclover (Figure 3). Dodder reduced canola pods by 1% only but it reduced canola dry biomass by 6%. Reproductive output (pods/plant) 1 1 8 6 4 Canola Lentil Faba bean Field pea Lupin Chickpea Sub-clover Figure 3. Effect of Cuscuta spp parasitisation on the production of pods by canola and other crops under glasshouse conditions. Effect of time of sowing on dodder emergence and survival Time of sowing experiment showed that delaying the sowing time of lupins can substantially reduce the number of surviving dodder plants, but a delay of at least two weeks after dodder germination is necessary (Figure 4).
35 Surviving dodder plants/pot 3 25 15 1 5 Dodder sown July 1st lupin sowing July 19 TOS1 TOS2 TOS3 TOS4 3 6 9 12 15 18 21 24 27 3 33 Days after sowing dodder Figure 4. Effect of time of sowing of lupin crop seeds on the survival of Cuscuta spp plants under glasshouse conditions. Dodder control by pre-sowing and post-emergent herbicides Pre-sowing herbicides controlled 1% of dodder plants (Table 1). No emergence of dodder plants was observed in pots sprayed with propyzamide while a few plants emerged in the pots sprayed with trifluralin. Dodder in simazine treatments emerged normally and then slowly died. As post-emergent application, atrazine controlled 1% of dodder plants and Lontrel controlled 5%. Table 1 Effect of different pre-sowing and post-emergent herbicides on the control of dodder plants in legume crop and pasture plants. Herbicides Atrazine Lontrel Simazine Propyzamide Trifluralin Dodder control (%) 1 5 1 1 1 DISCUSSION The proportion of hard seeds in dodder was 88%. Hutchinson and Ashton (198) reported that the proportion of hard seeds in Cuscuta campestris was up to 95% in USA. Acid treatment greatly improved germination percentage of dodder although chilling after acid treatment reduced its germination. Lower temperature is known to reduce germination of small-seeded dodder (Allred and Tingey 1964). Dodder seeds germinated well across all the three temperature regimes used in this study suggesting that dodder may germinate in crop at any time during the growing season. Unlike Striga and Orobanche, the seeds of Cuscuta spp have no specialized germination requirements of temperature (Parker and Riches 1993). Dodder successfully infested all crop and pasture species (canola, chickpea, faba bean, field pea, lentil, lupin and sub-clover) and reduced their pod or burr production by 1-1% although only lucerne and clovers were the known hosts (Al-Menoufi and Hassan 1976). Pre-emergent herbicides such as simazine, propyzamide and trifluralin controlled dodder by %. Post-emergent herbicides atrazine controlled dodder by 1% and Lontrel by 5%. Dodder plants are completely dependent on their own roots for minerals and water uptake for the first 8 days of their life cycles (Sitkin 1976). As such dodder is more likely to be controlled more effectively by pre-sowing herbicides than post-emergence herbicides. The postemergence herbicides that can translocate within host plant are also likely to effectively kill odder plants. Delaying crop sowing by 2-3 weeks effectively reduced density of dodder plants. Since a dodder plant must contact a suitable host plant within eight days, a delay in the sowing of crop up to two weeks and killing all existing weed plants by a knockdown herbicide might help in reducing the density of dodder.
ACKNOWLEDGMENTS We are grateful to GRDC for funding this project (DAW28). Thanks are due to DAFWA Biosecurity Team, Dr. Clinton Revell and Dr. Terry Piper. REFERENCES Allred, K.R. and Tingey, D.C. (1964). Germination and spring emergence of dodder as influenced by temperatures. Weeds 12, 45-48. Al-Menoufi, A.O. and Hassan, M.T. (1976). Studies on the parasitism of Cuscuta spp. And their hosts in Noubreya Region (El Tahrir Province). Egyptian J. Phyto-pathol 8,25-29. Hutchinson, J.M. and Ashton, F.M. (198). Germination of filed dodder (Cuscuta campestris). Weed Science 28, 33-333. Movesian, T.B. and Azarian. K.A. (1971). Pathological changes in cattle poisoned by dodder Cuscuta campestris Yuncker. Biologichskii Zhurnal Armenii 24(7), 67-7. Parker, C. and Riches, C.R. (1993). Parasitic weeds of the world (Cab International, Wallingford, Oxon OX1 8DE, UK). Sitkin, R.S. (1976). Parasite-host interactions of field dodder (Cuscuta campestris). (MSc Thesis, Cornell University, USA).