Ground Cover Supplement : GC Supplement - Integrated pest management
11 INTEGRATED PEST MANAGEMENT GROUND COVER CULTURAL CONTROLS FOR CANOLA PESTS Manipulating the environment of pest or beneficial species and the use of resistant varieties are two cultural-control options Dr Hainan Gu has been testing for canola REDLEGGED EARTH MITE (RLEM) and diamondback moth (DBM) are two common pests of Australian canola crops. While RLEM tend to be resident in the paddock and threaten establishing crops, DBM are considered to fly in and the larvae cause damage to leaves and pods of more mature plants. Dr Hainan Gu, from CSIRO, has worked on improving our understanding of both of these pests. In the glasshouse, outdoor cages and field trials, Dr Gu has established that varieties differ in their resistance to and tolerance of RLEM. This finding may offer an opportunity to plant breeders to use more resistant and tolerant material in future breeding programs. Dr Gu looked at the impact of three densities of RLEM on up to 28 commercial canola varieties. Seedlings were grown in pots and 0, 10, 20 or 30 RLEM were introduced into each pot, located in the glasshouse or in outdoor cages, during winter 2006 and 2007. In the field trial, the randomised plots were allowed to be naturally infested with RLEM. Plants were scored for visual damage symptoms. In the pot trials, plants were harvested when they had grown four to five true leaves and dry matter was measured. In the field trials, some plants for each variety were harvested at the four to five true-leaf stage, while others were taken to maturity, so that seed yield could be evaluated. The trial established that damage to cotyledons and true leaves of canola seedlings caused by RLEM, and the impact of the mite infestation on seedling growth, differed significantly between canola varieties. Mite damage and impact also tended to increase with the mite density per plant. At a density of 10 mites per pot, damage was not sufficient to affect dry matter production. Another important point is that the impact of mite infestation on seed production was not correlated with the impact of RLEM on seedling growth in some varieties. The result illustrates that the relationship between seedling damage and seed production varies, depending on the variety concerned. In relation to DBM, Dr Gu has looked at whether the moths are able to overwinter in south-eastern Australia. Traditionally, it has been thought that DBM overwinter in milder areas, away from germinating canola crops. In field surveys around Griffith, NSW, and Horsham, Victoria, Dr Gu and his colleagues found DBM at all life stages -- larvae, pupae and adults -- on volunteer canola and wild turnip plants throughout a winter season. Observations of DBM populations caged outdoors in Canberra showed that all the life stages are able to develop and/or reproduce on Brassica plants through winter. Therefore, this study provides further evidence that the diapause-type dormancy (a period of inactivity in the insect's lifecycle) does not occur at any life stage of DBM. The laboratory tests showed that DBM is able to survive temperatures of --5°C, and that the ability to survive sub-zero temperatures increases from the larva to adult stage. The adult moths that had been exposed to --5°C for 20 days could still successfully reproduce without supplemental food. These findings indicate that the DBM populations show tolerance to sub-zero temperatures allowing the insect to survive the winter coldness in most parts of south-eastern Australia. DBM is a specialist herbivore that feeds on Brassicas. The greater the presence of Brassica plants, the greater the potential for survival and early migration into canola crops. Wild radish, wild turnip and volunteer canola plants initiated by early- autumn rainfall all provide suitable hosts for DBM. Late summer/early autumn rain and above-average winter temperatures have been considered triggers to previous outbreaks of DBM. Dr Gu considers that these factors do influence DBM populations, but indirectly, by providing suitable conditions for the growth of Brassica weeds and canola volunteers. □ GRDC Research Code CSE00029 More information: Dr Hainan Gu, research scientist, CSIRO Entomology, 02 6246 4432, firstname.lastname@example.org SOFTER OPTIONS The identification of differences in resistance to, and tolerance of, redlegged earth mite in commercial canola varieties offers plant breeders the opportunity to target this trait in future breeding material.
GC Supplement - Foliar fungal diseases
GC Supplement - Spray application technology