Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 Page 53 Page 54 Page 55 Page 56 Page 57 Page 58 Page 59 Page 60 Page 61 Page 62 Page 63 Page 64 Page 65 Page 66 Page 67 Page 68 Page 69 Page 70 Page 71 Page 72 Page 73 Page 74 Page 75 Page 7631 IREC Farmers' Newsletter No. 195 ­ – Rice R&D 2016 only small numbers of crops affected. In recent years armyworm problems have become more widespread, and also more consistent from one season to the next. The reasons for this are unclear, however a new research project on armyworms in rice — the first one ever in Australia — started in July 2016. What we do know is that the adult armyworm moths (Figure 3) migrate over large distances, and affect a number of crops other than rice, particularly winter cereals. There doesn’t seem to be a difference between ‘new’ and repeat crops or between aerial and drill sown crops in terms of susceptibility of rice crops to armyworms attack, but evidence is mounting to suggest that mid-season drained crops and possibly those receiving delayed permanent water may suffer higher levels of armyworm damage. This may be because the lack of standing water is altering the microclimate in the crop in a way that damages the parasitic wasp and fly populations that help to regulate armyworm densities, but the most likely cause involves chemical ‘signaling’ by the plants. Water-stressed rice plants may be emitting a different blend of natural volatile compounds than non-stressed plants, allowing female moths to identify the stressed crops and target them for egg laying. Armyworms are often heavily parasitised by other insects and initial work suggests this is also the case within rice crops. A single collection of mature armyworm from a crop near Jerilderie last season had 72% parasitism, with a further 11% dying from unknown causes and only 17% of larvae developing into adult moths. Most were parasitised by wasps, which finish development after the host dies (Figure 4), with one armyworm cadaver producing an astonishing 1094 individual wasps. At present the rice industry relies on broad- spectrum insecticides like chlorpyrifos for armyworm control, so there could be considerable benefit in developing newer selective chemicals that kill armyworms but have little or no impact on their parasitoids. Stem rot In 2014, a farm in northern Victoria experienced yield losses of around 2 t/ha due to a heavy infection of stem rot. This was the first recorded incidence of a significant yield penalty associated with this disease in southern Australia. DNA sequence comparisons were made between the Victorian isolate of the fungus and an isolate from the MIA collected in 1995, and there was more than 99% similarity between the isolates for the genes sequenced. This indicates the Victorian isolate is not a new strain of the fungus — it is largely identical to the MIA strain. The yield loss at the Victorian property has been attributed to three factors working in conjunction: a previous history of the disease, repeat cropping and poor stubble management. Stem rot is a disease that produces sclerotia (small dark-coloured propagules) that remain infective within the crop stubble within the plant stems (Figure 5). If stubble is not effectively managed through burning, incorporation or removal, these sclerotia will be released when the next crop is flooded and infect the young plants. Increased repeat cropping makes effective stubble management harder to achieve, and together with potential restrictions on stubble burning it is more difficult for growers to ensure that damaging levels of stem rot do not persist from season to season. Stem rot can cause rice plants to lodge, so any unexplained instances of crop lodging should be investigated, particularly as this disease may go unnoticed for several seasons until the density of sclerotia build up to the point where crop yield is affected. Pathogenicity tests have shown that none of the commercial rice varieties grown in southern Australia have any appreciable resistance to stem rot. RIRDC Project PRJ-07773 Improving pest and disease biosecurity in the Australian rice industry Further information Pests — Mark Stevens T: 02 6951 2644 E: [email protected] Diseases — Andrew Watson T: 02 6951 2647 E: [email protected] l Figure 5. Rice stem rot lesions at waterline level. INSET: Sclerotia of the stem rot fungus that persist in stubble between repeat crops.