Check soilborne pathogens before sowing winter crops
From the edition of Agriculture Today.
Most farmers have been or are about to start making solid decisions about their winter cropping programs for next autumn.
They are weighing up different crop types, weed burdens and input requirements for different paddocks.
While over the last four years it has been difficult to maintain productive and profitable winter crop rotations, those who persisted with broad leaf crops are reaping the benefits.
Stripe rust is the most obvious disease limitation in cereal systems at the moment.
Many growers are fed up with investing in fungicides to protect crops that have low commodity value.
While it would be great to switch to more resistant varieties in the short term, the reality is that stripe rust will need managing again in 2006.
However, don’t overlook some of the most common factors limiting yield potential in cereal rotations, such as root and crown diseases.
Take-all is likely to be a serious problem when wheat crops will follow a wheat or barley crop, a grassy pasture or a broad leaf crop with a high level of grass weeds.
There are three variants of take-all pathogens, all of which survive over summer in crown and roots of wheat, barley, triticale or grasses. Gaeumannomyces graminisvar. tritici or Ggt is the most common, attacking wheat, but not normally oats. G. graminisvar. avenae or Gga can attack both wheat and oats.
Symptoms of take-all are not always obvious. The disease blocks the root core preventing movement of water and nutrients, and makes the plant very susceptible during periods of moisture stress.
One option to assess the level of inoculum is through the use of DNA testing developed by CSIRO Entomology, SARDI and C-Qentec Diagnostics. The service called PreDicta B has been designed to determine which soilborne pathogens pose a significant risk before crops are sown.
PreDicta B currently includes tests to measure inoculum levels of take-all, cereal cyst nematode, rhizoctonia, crown rot, root lesion nematodes (Pratylenchusneglectus and P. thornei), and blackspot of field peas.
The Predicta B service is a valuable tool for repeat cereal paddocks in 2006. The tests will also help make decisions about seed treatments for stripe rust control. If a paddock has high take-all inoculum levels detected via a DNA test, the likelihood of effective suppression by fluquinconazoles (Jockey®, Quantum® etc) or flutriafol (Impact®, Jubilee® etc) may be easier to justify.
These tests are conducted by accredited local agronomists.
This column appears in Agriculture Today.