Ground Cover Supplement : GC Supplement - Root and crown diseases
HOSTS AND ROTATIONS How long Results from trials by Dr Hollaway support other findings that the length of break required depends on the conditions during the break year. This is because residue breakdown is driven by soil moisture, so in dry years breakdown is slower. His trials in 2004 at Birchip found that a single year of field peas reduced a high crown rot level from 1231pg DNA per gram of soil to 211pg DNA/g soil (medium risk). In 2005, a single year of field peas reduced the crown rot level from 3041pg DNA/g soil to 58pg DNA/g soil (low risk). Dr Hollaway concluded that in general a two-year break from cereals is required to control crown rot, but in some seasons a one-year break may be adequate. The length of break is also determined by the level of inoculum in the soil. Dr Evans has shown that the frequency of cereals in the rotation and the choice of cereal affect the inoculum level. Monitoring changes in inoculum in rotations that had two durum crops followed by a break crop and back to a third durum, she found inoculum levels increased rapidly in systems with a single year of break crops. In trials comparing choice of cereals, oats resulted in a soil inoculum level of nearly 1000pg DNA/g, compared to the bread wheat Kukri A that resulted in soil inoculum levels of less than 100pg DNA/g. Although rotation remains an important control tool for crown rot, these trials show results can be highly variable. Monitoring soil inoculum levels before seeding should be considered to help growers make informed rotation decisions. GRDC Research Codes DAV00062, DAS00032 More information: Dr Grant Hollaway, 03 5362 2111, email@example.com; Dr Margaret Evans, 08 8303 9379, firstname.lastname@example.org .gov.au 1600 1000 1400 1200 600 800 400 200 0 Canola Pre-treatment crown rot level Crown rot risk level for durum wheat Peas Vetch Medic Fallow FIGURE 1 EFFECT OF BREAKS FROM CEREALS ON SOIL LEVELS OF FUSARIUM PSEUDOGRAMINEARUM AT CAMBRAI, SOUTH AUSTRALIA, 2003–06 Fungal DNA (picograms per gram) 2004 soil levels after a range of breaks from cereal in 2003 2005 soil levels after canola cv Outback 2006 soil levels after durum wheat cv Tamaroi in 2005 HIGH test was actually recording was extreme numbers of P. penetrans, an RLN able to multiply and survive on the roots of lupin, field peas and cereal crops. While P. neglectus levels were in fact reduced by the rotation, P. penetrans numbers had subsequently increased. The ability of eight varieties of field peas to host P. neglectus and P. penetrans was tested in field trials. The average multiplication of P. penetrans across the eight varieties was eight times that of P. neglectus. Multiplication of P. neglectus was negligible. Multiplication rates varied between the field peas varieties tested. A seven-fold increase in P. penetrans was recorded under Sturt A compared to a rate of less than one under Cooke A and Parafield (Table 1). Crops that are resistant to P. neglectus but susceptible to P. penetrans include narrow-leafed lupin, faba bean and field peas (as illustrated above). Crops that are especially susceptible to P. penetrans are wheat, narrow-leafed lupin and chickpeas (these crops giving a six to 13-fold multiplication). Canola and barley produced the lowest rates of P. penetrans multiplication in pot trials, and it is anticipated that varieties of these crops may offer rotational management options for this species of RLN. Cereal crops are the weakest link in the management of mixed populations of nematodes and where P. teres dominates. Under wheat, oat or barley a six-fold increase in P. teres was recorded, compared to a multiplication rate of less than two under a lupin crop. Oat and barley are moderately susceptible and wheat susceptible to P. neglectus, and all three cereals are susceptible to P. penetrans. It is important that rotations are tailored to the predominant species of RLN present. Growers are encouraged to regularly use soil and plant tests to monitor the populations and species of RLN. The importance of controlling susceptible volunteers and weeds must not be overlooked, otherwise the benefits of resistant crops can be negated. Our research has highlighted that nematodes other than RLN, especially burrowing nematode (Radopholus), may also play a part in crop damage in WA. Investigation into the ability of crop species and varieties to host different nematode species is continuing, to enable production of rotational and varietal recommendations for implementation where nematodes have been identified at damaging levels. GRDC Research Code DAW00124 More information: Dr Vivien Vanstone, 08 9368 3141, 0418 810 711, email@example.com ROOT & CROWN DISEASES GROUND COVER 13 Field peas are a valuable break crop for P. neglectus but not for P. penetrans, a species of nematode recently identified as a problem in WA.
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