An integrated approach to nutgrass control : SRDC final report NFS002
Date
2010Metadata
Show full item recordAbstract
This project aimed to formulate and promote an integrated approach to nutgrass control in
sugarcane cropping systems. The project was a Grower Group Research Project
undertaken from July 2007 to June 2010 by the NSW Farming Systems Group Inc. and
BSES Limited extension officers in NSW. Trials evaluating the effect of nutgrass on plant-cane yield, ratoon biomass and soybean
biomass were undertaken. These trials showed cane yield losses of around 30% in both
plant and ratoon cane where nutgrass was allowed to grow without any control. Even
allowing nutgrass to grow for 4-8 weeks after planting or ratooning resulted in a reduction in
cane growth. Quantification of nutrient uptake and removal of soil moisture by nutgrass
provided reasons for the large effect of nutgrass on cane yield. In moderate to heavy
infestations, nutgrass tops took up 25-45 kg N/ha that would otherwise be available to the
cane crop. Similarly, nutgrass tops took up 45-50 kg K/ha (equivalent to the K applied in
many planting mixes). A thick sward of nutgrass removed the equivalent of 11-12 mm rain
from the plough layer in 4-8 days. The key to long-term control of nutgrass is to reduce the number of viable tubers and the
literature clearly shows the effect of gylphosate in reducing the number of viable tubers.
However, the effect of other nutgrass-specific herbicides registered for cane on tuber viability
had not been evaluated. A large-plot, replicated trial assessed Hero®, Krismat®, Sempra®,
and ‘double-knock’ treatments of 2,4-D followed 2-4 weeks later by one of the former
nutgrass-specific herbicides for their effect on nutgrass tuber viability. All herbicide
treatments improved cane growth by reducing nutgrass density and all significantly
decreased tuber viability. Trials were established to evaluate some ‘best-bet’ options for nutgrass control. These trials
aimed to assess ‘packages’ of successive treatments all aimed at reducing the viability of
nutgrass tubers. Results from these trials were used to extend options for long-term
nutgrass control to cane producers. The trial work undertaken and associated economic analysis showed that it is highly
economic to control nutgrass in cane. Total control of nutgrass resulted in large dollar
benefits ($350-450/ha) and trials evaluating ‘one-off’ herbicide treatments for nutgrass also
showed net benefits of $200-400/ha. This indicates that, even where nutgrass is patchy,
growers could outlay $60-100/ha for nutgrass control and still obtain a substantial net
benefit. A factsheet/decision support package titled ‘Managing nutgrass in cane’ was produced and
circulated throughout the Australian sugarcane industry. This factsheet emphasises that
nutgrass can only be managed using a long-term integrated approach aimed at reducing the
number of viable tubers. No single ‘one off’ treatment will control nutgrass and repeated
treatments are the only sure way of controlling nutgrass. A single ‘one off’ treatment will
reduce nutgrass competition in the short term but, because of its ability to rapidly propagate
under suitable conditions, repeated treatments are imperative. The factsheet provides
options for nutgrass control at various stages in the cane crop cycle