Features Agronomy Other Crops
Scoring system simplifies use of fungicides in peas

Deciding whether it is necessary to spray a fungicide on field peas may have
become a lot simpler. A new rating system, developed in 2003 by Ken Lopetinsky
and Sherri Strydhorst with Alberta Agriculture's Crop Diversification Centre
North in Barrhead, can predict a potential disease outbreak based on plant density,
humidity, the weather forecast and the presence or level of disease. In 2005,
tests using the system with Headline fungicide were very promising. Producers
taking part in Lopetinsky's trial recorded yield increases ranging from 14 to
36 percent (10 to 27 bushels).

"If you have good yield potential, if disease is present and you spray
at the proper time, our data from 2005 shows that the prediction system worked
and that the fungicide Headline gave a very high yield advantage and return
on investment," Lopetinsky says. "We had significant yield increase
at all five locations and also found a significant difference in the thousand
kernel weights at harvest in several locations. Ascochyta appears to reduce
the yield partly by preventing the seeds from growing properly and reducing
the seed size."

Figure 1. Percent yield increase associated with Headline fungicide application over five sites in research conducted by K. Lopetinsky, J. Kaufmann and M. Olson of Alberta Agriculture, Food and Rural Development in 2005.

Lopetinsky wanted to develop a simple, easy-to-use system that farmers could
utilize to determine if they need to spray fungicides on their peas. He says
that systems developed by the University of Saskatchewan and Syngenta were available
but most farmers found them too complicated to be useful. "Sherri Strydhorst
and I developed what we called a modified system," Lopetinsky says. "It
looks strictly at four factors – crop canopy density, leaf wetness at noon
which provides a measure of humidity, percentage of the crops showing ascochyta
symptoms and the five day weather forecast. We put a higher emphasis on leaf
wetness and the percentage of plants showing ascochyta symptoms. If the crop
had a score of 65 or more and ascochyta is present, you spray."

"We are hoping this research will help us answer questions that we get
every year from field pea growers in Saskatchewan, Alberta and Manitoba,"
Mark Kuchuran, technical specialist with BASF says. "Producers often ask
us when is the optimum time to apply a fungicide and whether it's worth the
investment. We believe that using a fungicide, like Headline, in a preventative
manner can go a long way in helping to control the onset of disease symptoms."
The system that Lopetinsky and Strydhorst have developed is an excellent tool
that should help growers to maximize the contribution of fungicides to disease
management.

The scoring system is heavily dependent on scouting. It requires growers to
check their fields in several different locations, twice a week from the onset
of first flower. Special care should be taken not to destroy the canopy during
scouting to preserve the micro-climate.

Not disturbing the plant stand is critical to judging plant density and maintaining
the micro-environment underneath, says Wes Latimer, a farmer near Westlock,
Alberta, one of the farmers who took part in Lopetinsky's study in 2005. "I
carefully took about three steps into the crop along a sprayer track and then
another step off it. I would very gently move the crop and look down at the
bottom leaves of 10 plants. I'd return to the same spot each time and try not
to tear the tentacles apart or lay down the crop. It wasn't easy but you could
do it. Looking at the same leaves again and again allows you to observe the
changes."

Latimer started scouting his crop on June 28, 2005. He had a moderate crop
canopy which scored a 10. Leaf wetness in the afternoon was so high that just
scouting soaked his pants and shoes – that scored 40. The five day weather
forecast was for showers – that scored 15 for a total score of 65. However,
at that time, none of the plants showed any disease symptoms so he held off
spraying.

Three days later, on July 1, he scouted the field again. The crop canopy was
still rated moderate (score of 10), the leaves were not quite as wet (score
of 30) and the weather forecast was for unsettled weather (score of 10). The
crop still had no signs of disease so once again he held off spraying. Disease
started to show up when he scouted the third time on July 4. This time the risk
factors score still did not add up to 65, so once again he held off spraying.
On the fourth scouting trip, July 7, he rated the crop canopy as moderate/heavy
(score of 15), leaf wetness was moderate (score of 20), the plants showed disease
symptoms (score of 20) and showers were predicted for the next five days (score
of 15). Since the score totaled 65+ and disease was present, he sprayed Headline.

"The system is simple," says Clifford Cyre, another Westlock farmer
who took part in the study. The only uncertainty in it is the five day weather
forecast. "I thought it was very easy to follow. Make sure that the field
has a good plant count, seven plants per square foot, and is clean of weeds.
Assess crop density and the humidity at noon. Once you identify that you have
some disease and if your numbers add up to 65, start spraying."

"The twice a week scouting schedule was fairly rigid," Latimer says.
"But that's good because you can get so busy that you tend not to scout
and then it's too late. The nice thing is when you score that number (65 or
more) you spray, you don't have to think about it. The decision is taken out
of your hands. I was just supposed to spray the test plots but I thought that
it was a good idea, so I sprayed the whole field." With a 36 bushel yield
gain Latimer was very happy he did.

Lopetinsky credits the high yield gains his fungicide study recorded to selecting
only fields with high yield potential to begin with. "People blame disease
for all of their yield problems," Lopetinsky says. "We eliminated
one field because it had too low a plant population and if we'd had weed problems
we'd have thrown out another field. If a crop doesn't have the capacity to yield
well then I would question the use of a fungicide. If weeds or a lack of plants
have already taken away the yield then using a fungicide will not make up for
it."

Using Headline really paid off in fields under heavy disease pressure in Lopetinsky's
study. "A lot of farmers in this area had a 60 to 70+ bushel crop without
spraying and were happy with it. They could have got another 10 or 20 bushels
with spraying."

Lopetinsky and Strydhorst's system worked very well in 2005, but Lopetinsky
admits it was a perfect year for doing ascochyta research in the Parkland area
of Alberta, north of Edmonton. The weather conditions were ideal for both peas
and disease. It has yet to be determined if it would work as well under drier
conditions. He plans to test his system for two more years under a range of
growing conditions.