Top Crop Manager

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Say ‘node’ to ascochyta in chickpeas

Spray by node number to reap harvest and quality benefits.


November 26, 2007
By Top Crop Manager

Topics

Bigger, more consistent chickpea crops are fast approaching, thanks to innovative
new cropping strategies being devised by Canadian researchers. For growers who
want to optimize their chickpea production, however, these same scientists are
urging they first adopt research-based recommendations on ascochyta control.

Without effective ascochyta control, chickpea crops will flop despite the best
agronomy in every other area, but there is a plus side too. Their new by-the-number
approach to timing foliar spraying is providing producers with a tool to control
ascochyta more efficiently and more economically.

"Nodes are our best application guides," says Dr. Yantai Gan, alternate
crops scientist for Agriculture and Agri-Food Canada at Swift Current, Saskatchewan.
"You need to get out into the field and kneel down to see the emerging
plants, but counting them is quick and simple and the benefits more than make
up for the effort."

Nodes provide keen insight into the day-by-day crop risk, says Gan, who is
working toward producing a detailed spray model for the crop. Based on two years
of his own trials plus extensive public and private research here and in Australia,
Gan has re-confirmed the linchpin of any successful ascochyta program. "It
must be timing," Gan says. "Early is essential. Being successful with
chickpeas depends on getting ahead and staying ahead of ascochyta symptoms visibly
seen."

Looking at his company's multi-year on-farm and research station trials, BASF
technical specialist, Mark Kuchuran also advises a node-count approach to spray
timing. "I'm convinced. It pays to walk your crops and track the node number,"
Kuchuran says. "It's become my number one recommendation to any chickpea
grower."

Gan's research is also confirming that node counting works both for unifoliate
and fern-leaf varieties, despite their differences in ascochyta risk. Overall,
unifoliate varieties such as Sanford, Dwelley and CDC Diva are much more susceptible
than fern-leaf varieties. In Swift Current trials, Gan has found on average
that unifoliates are hit twice as severely by ascochyta as the fern-leafs.

 16a
Counting nodes on chickpea plants is key to determining timing for
fungicide application.

However, Gan cautions there is a reason ascochyta is often called the most
aggressive crop disease in Canada. Even the best unifoliate varieties need ascochyta
help and some fern-leaf varieties, such as CDC ChiChi, are also as vulnerable
as some unifoliates. They all need ascochyta vigilance, Gan says, and they all
need a grower who gets ahead and keeps ahead of the disease, using a node-count
approach.

Alternatives such as spraying by calendar date or by a set number of days after
planting or emergence are unrealistic, Gan says. Unless the year is normal,
which never seems to happen, calendar rules such as these can mean a grower
is wasting money by spraying too early, or losing money by spraying too late.

What is important is crop development, Gan says, because what the crop really
needs is to be protected from ascochyta before it begins flowering. Depending
on growing conditions in any given year, the crop can flower earlier in the
summer or later, but it always starts at about the time when the plants achieve
14 to 15 nodes.

By counting nodes, growers can time their fungicide applications, thereby ensuring
the field is protected at the beginning of flowering. Then growers can monitor
infection conditions and follow their fungicide recommendations for follow-up
applications.

"Pay special attention to unifoliates," adds Kuchuran. "We recommend
spraying unifoliates at eight to 10 nodes and if you detect any of ascochyta's
black pinpoint lesions, starting as early as six to eight nodes, it's time to
treat immediately.

"Once you see symptoms, you're playing not just with fire, but with wildfire,"
Kuchuran says. Gan agrees, "Lesions mean the disease has already colonized
the crop and is ready to take over."

Like other pulses, chickpea plants develop nodes on their main stem at the
points where leaf stems will branch off. Typically the bottom two nodes are
underground or at the soil surface and are simple scales. The first leaves develop
at the third nodes and then the plant adds a new node every three or four days
under normal temperature conditions, and somewhat more slowly when it is cool.

Kuchuran recommends growers start with a strobilurin such as Headline. Then
watch field conditions for the timing of follow-up applications. Conditions
such as rainfall or high relative humidity heighten the risk of infection and
therefore mean growers need to spray sooner for effective protection. "Monitor
your unifoliates very closely," Gan says. "You don't have to be quite
as quick to spray your fern-leafs, but you definitely still need to be on top
of what's going on in the field."

Kuchuran advises growers to stick with Headline for their second early-season
application. Once the crop is aggressively flowering, however, he recommends
switching to the anilid-family fungicide Lance. In addition to providing continued
control of ascochyta, Lance picks up other diseases such as sclerotinia and
botrytis grey mould. As well, the rotation of strobilurin and anilid products
is a wise stewardship practice, reducing the risk of fungicide resistant ascochyta.

With an effective ascochyta program in place, growers can benefit from new
research into the management of crop fertility and maturity, Gan says.

As one example, research shows that supplying a carefully calculated 28 to
56 pounds of nitrogen per acre at planting can help the crop get off to a faster
start compared to waiting until nodulation kicks in at about the 12 node stage.

Ironically, this at-planting application leads the crop to run out of nitrogen
sooner in its late-podding stage. The applied nitrogen not only encourages the
crop to soak up more early season nitrogen and develop more vegetative growth,
it also curbs the crop's appetite for atmospheric nitrogen obtained via fixation
in the nodules.

The result, Gan says, is that nitrogen and water stress during the late-podding
stage will force the plants to shut down as much as two weeks before non-fertilized
plots, paving the way for earlier harvests and improved crop quality.

"Ascochyta control must be part of the package," Gan stresses. "By
following the node-count approach for fungicide timing, you can be confident
of growing a crop that can benefit from these other strategies. Without ascochyta
control, everything is left to chance."