Top Crop Manager

Features Fungicides Seed & Chemical
Managing ascochyta blight in chickpeas

Determine a field's risk factors and act accordingly.


November 15, 2007
By Lorne McClinton

Topics

Are you planning to grow a large seed, kabuli style chickpea variety this year?
If you are, be prepared to apply a preventative foliar fungicide application,
whether ascochyta symptoms are visible or not. Saskatchewan Agriculture, Food
and Rural Revitalization's (SAFRR) latest guidelines for chickpea production
now advocate preventative fungicide treatments for managing ascochyta in particularly
susceptible varieties.

Managing ascochyta blight in chickpeas has never been easy. Under the right
conditions this disease, caused by the ascochyta rubiei fungus, can cause over
70 percent yield loss. Guidelines for ascochyta control in chickpeas have been
evolving steadily as researchers learn more about the disease.

Controlling ascochyta starts by selecting the right seed varieties and the
right fields. Producers should select a variety with as much resistance as possible,
use disease-free seed and limit rotations to just one in four years to keep
initial infection levels to a minimum. As with all crops, good seeding and fertilizer
practices also get the crop off to a good healthy start.

SAFRR publishes a new set of chickpea best management practices each year on
its web site. Since many producers only have access to dial up internet, and
the amount of information is growing so rapidly, the guidelines are now published
on a CD-ROM titled Management of Ascochyta Blight in Chickpeas.

Scouting
"The guidelines outline a step-by-step process to help determine whether
or not you should spray a fungicide," says SAFRR's crops specialist, Ray
McVicar. "Begin scouting your chickpeas two to three weeks after planting,
when the plants are still in the seedling stage and continue through to the
late pod stage. What you do next depends on what you find. Do you or don't you
have symptoms? What is the weather doing? What varieties and types of chickpeas
are you growing? The guidelines treat kabulis different than desis. This has
to do with economics and disease susceptibility."

How often a field should be scouted depends on weather conditions and whether
or not you have applied a fungicide. The guidelines suggest scouting within
seven days if a fungicide has been used, or within three to five days if one
has not been used. Walk in an 'M' pattern while watching for discoloured plants
or spots on the leaves. Pin flags that mark specific sites make week-to-week
comparison simpler. Avoid scouting when the canopy is wet to prevent spreading
disease throughout the field.

Calculate your risk rating
Since it is usually not practical to scout all fields all the time, concentrate
on fields at greatest risk. A zero to 7 risk rating scale is included in the
guidelines to help with risk assessment. With this scale, a field planted with
disease-free seed, showing no signs of disease, and dry weather conditions at
the time of rating would receive a zero-risk rating. On the other extreme a
heavily infected field, one almost completely destroyed by ascochyta, drought
or hail, would receive a 7 risk rating.

The guidelines suggest very careful monitoring of fields planted with infected
seed and to varieties with poor and very poor disease ratings, or planted in
a tight chickpea rotation. Other high-risk factors include fields planted close
to chickpea stubble, low spots sensitive to flooding, or areas where the crops
have been subjected to stress.

"If you go out into the field a week after your last fungicide application,
don't see any symptoms, and the weather's been hot and dry, then don't spray,"
McVicar says. "But if it's been three weeks since the last application
and there's rain in the forecast, then perhaps it's time that you put on another
application."

Selecting the right fungicide
"We now have four foliar fungicides registered on chickpeas: Bravo, Quadris,
Headline and Lance," McVicar says. "Three of them have only been added
in the last couple of years. The labels for all of them are included on the
CD. It provides information on how each fungicide works and when that fungicide
should be applied."

All are protectant fungicides. They work best by forming a protective barrier
to prevent the disease from entering the leaves. Headline, Quadris and Lance
also have a limited curative effect and a small amount of systemic activity.
Application has to be made within 36 hours of rainfall for these fungicides
to have a curative effect. None will repair tissue already damaged by disease.

The guidelines recommend considering the use of Bravo as an early preventative
application when the disease risk rating is still low, zero to 1, or Headline,
Quadris or Lance if the disease risk is a 4 to 5. Since both Quadris and Headline
are from the strobilurin fungicide group, rotate their use with either Bravo
or Lance to help delay the onset of strobilurin-resistant ascochyta. Lance is
also a good choice if sclerotinia and botrytis are problems.

When to quit spraying
"The guidelines also recommend when to stop spraying fungicides,"
McVicar says. "There's a certain time period when it doesn't really pay
to continue putting on a fungicide unless you're a pedigree seed grower. We've
found that applying much past the seventh or 10th of August gives you a nice
green crop, but doesn't give you any more grain. It all comes down to economics.
You can't just keep spraying product until you use up all your money. At the
end of the day, you still want to get enough crop to pay for what you put into
it." -30-

New CD makes growing chickpeas easier

Deciding whether or not to spray fungicides to control ascochyta blight in
chickpeas may soon be a lot easier for prairie producers. Growers can now have
all the latest chickpea best management practices available on their home computer.
Researchers from the University of Saskatchewan, Agriculture and Agri-Food Canada,
Saskatchewan Agriculture, Food and Rural Revitalization (SAFRR) and North Dakota
have made all the latest information available on one new interactive CD, Management
of Aschochyta Blight in Chickpeas in Saskatchewan.

"A CD is just such a better method to give producers information to take
home," says Ray McVicar, a crops specialist with SAFRR in Regina. "All
the photos and everything they need is right there, and the colour and quality
is excellent. It has the best management practices, labels for fungicides and
some really nice photos to help ID disease. It provides a lot of very involved
material that will help with scouting and diagnosing disease. With this CD,
they won't have to sit at their computers trying to download it off the web.
It provides a lot of valuable information whether you are growing chickpeas
for the first time, or if you have been growing them for six to eight years."

Since best management practices are still evolving, the CD, like other continually
changing government documents, will be updated annually to reflect the latest
research. McVicar recommends getting a copy of the latest version well before
the growing season starts. The CD is available at no cost from the SAFRR head
office in Regina, 3085 Albert St. Regina, Saskatchewan S4S 0B1 (306) 787-5140.
-30-