Take the pressure off the crop with good weed control, judicious use of fertilisers and moderate sowing rates.
LET'S HOPE the drought breaks in time for a good farming season in 2003 but, even if it does, our worst season in years will still have a bite. According to Gordon Murray of the Wagga Wagga Agricultural Institute, this drought has turned disease management strategies on their head and rotations that were expected to deliver disease breaks for wheat and canola may not have worked.
Dr Murray also fears that 2003 has the potential to be a bad year for take-all and crown rot in wheat and blackleg in canola.
"If you follow a canola crop with a cereal, anticipating that this year provided a break from take-all, you may be disappointed. The soil has been so dry that there has been little if any breakdown of take-all innoculum and canola may not have provided the looked-for break crop advantage. "
On top of this, a series of dry springs has seen a build-up in the level of crown rot in southern NSW, a disease more usually associated with northern NSW and Queensland. Dr Murray said he had examples of some quite heavy infestations last year.
"In some cases they've gone unnoticed by farmers and agronomists but, unless we get a good wet year next season, this disease could be a real problem.
"The best defence against crown rot is two-fold: rotation with broadleaf crops to keep the level of inoculum down, aided by the sowing of resistant varieties.
Unfortunately because it's more usually associated with northern areas, we don't have much information about the level of resistance afforded by our southern varieties.
"This is a disease that survives on grass and crop residues for two years and while stubble burning provides some measure of control, it's not completely effective.
"Take the pressure off the crop with good weed control, judicious use of fertilisers and moderate sowing rates. It's also advisable to make certain that the crop isn't subjected to trace element deficiencies. Unfortunately there's no test currently available for the level of crown rot inoculum in the soil and farmers will have to rely on paddock history to gauge their level of risk. "
Test soil for take-all
Dr Murray says that "as far as take-all is concerned, 2003 will be the year to test your soil before sowing to gauge the level of inoculum present. If that shows up moderate levels of take-all, the best advice might be to sow late and accept the attendant yield penalty.
"This might also be one of those rare occasions where a wheat-on-wheat crop is acceptable in the rotation, " says Dr Murray. "If you had a good clean canola crop in 2001, you won't have had a buildup of take-all in 2002's cereal crop and provided there's no problem with crown rot, wheat-on-wheat could be the way to go"
Avoid canola on canola
However, canola-on-canola might be a very dangerous proposition in 2003.
"If last season's canola crop failed, growers might be tempted to sow again in the same paddock next time, " says Dr Murray. "That could be very dangerous. We've seen a surprising amount of blackleg stem canker this season and unless the canola crop failed completely in the seedling stage, I'd treat any 2002 canola paddock with caution. "
The GRDC has provided support for a plant pathologist to continue working on an early warning system for Sclerotinia with the goal of a disease prediction model by next year.
"The season hasn't had much effect on the amount of inoculum present. There may be a little less and there certainly hasn't been the build-up that we have been experiencing over the last couple of seasons. That said, we've seen examples of Sclerotinia occurring at the stem base of canola plants in 2002 with the infection coming directly from the sclerates in the soil rather than airborne spores. "
Program 3 Contact: Dr Gordon Murray 02 6938 1879 Ms Tamrika Hind-Lanoiselet 02 6938 1608