News
Using 2,4-D to enhance colour pigmentation

For years it has been talked about in hushed tones, grumbled about at grower
meetings: 2,4-D can allegedly enhance the skin colour of red potatoes. Is it
one part fact, another part rural legend? US potato growers have had access
to the product for years, but can it work for Canadian producers?

Researchers on this side of the border are working to find the answer, testing
the use of a low volatile ester of 2,4-D to enhance the colour of red-skinned
potatoes.

Ontario Ministry of Agriculture, Food and Rural Affairs potato specialist,
Eugenia Banks is among them. Her first trial was conducted in 2002 at a research
plot near Alliston, Ontario, using the variety Chieftain in a twin row system.
The 2,4-D ester was applied twice to the treated plots at a rate of two ounces
per acre. The first application was at bud initiation, the second two weeks
later. At harvest, 100 potatoes were randomly chosen from both the treated and
untreated plots and placed into storage. After a month in storage, the tubers
were then rated for their colour quality: brownish red (BR) or enhanced red
(ER).

The results showed that all of the tubers selected from the 2,4-D treatments
displayed enhanced colour qualities (see Table 1), even after they were returned
to storage and kept for a total of six months. The potatoes from the untreated
plots were the typical colour of the Chieftain variety after being placed in
storage, brownish red. Despite the colour differences, there were no significant
differences in yield or tuber size between the treated and untreated plots,
although Banks did comment that the 2,4-D treated plants did produce more seed
bolls, most likely as a response to plant stress.

Samples of the treated potatoes were also sent to the University of Guelph's
pesticide laboratory to be analyzed for 2,4-D residues. None were found.

Banks decided to repeat her trial in 2006 using a few of the newer potato varieties
that have pinkish, netted skin. "There was no colour enhancement,"
she reports. "This suggests that varieties with netted skin do not respond
the same way as smooth-skinned varieties."

But other trials she conducted during the 2006 season proved the product had
some kind of effect on red colour enhancement. Banks also tested the effect
of 2,4-D on two yellow-fleshed varieties, Yukon Gold and Keuka Gold. While the
Keuka Gold plot showed no visible differences between the treated and untreated
tubers, the Yukon Gold samples treated with 2,4-D exhibited enhanced pinkish
colouring around the eyes, while the untreated samples displayed the typical
slight pink colouration normally seen on the variety.

"It did have an impact," says Banks, adding the resulting Yukon Gold
potatoes were very similar to gourmet potato varieties currently being sold
in high-end markets. "It really did show an effect."

She hopes to continue her trial work with 2,4-D in 2007, this time using the
white skinned variety, Atlantic, which is known for its flaking skin. "I
was told 2,4-D could make the flaky skin smooth. We'll see what effect it has."

Dr. Doug Waterer, an associate professor in the Department of Plant Sciences
within the College of Agriculture at the University of Saskatchewan, and research
assistant Jackie Bantle have also studied the effect of low dosage, foliar applied
2,4-D on the skin colour of red potatoes during trials in the late 1990s. "I've
not been overwhelmed with it," says Waterer. "It's not the magic bullet
for colour that it's been made out to be."

During his and Bantle's trials, "Foliar application of low rates of 2,4-D
produced little change in yields or skin colour of Norland potatoes, either
at harvest or following storage," they report. This may have been due to
improper timing of the application.

In their trials, which were conducted from 1996 to 1998, two rates of 2,4-D
ester were applied: 28 grams of active ingredient per acre and 60 grams of active
ingredient per acre, both mixed with 80 litres per hectare of water. The rates
and timing of the application, which was tuber set, were based on the recommendations
of crop specialists at the University of Minnesota. The plots were harvested
and graded in early October and 50 tubers were randomly picked from each treatment
plot for evaluation of skin colour. The samples were also evaluated after a
period of storage.

According to Waterer and Bantle's observations, after harvest in 1996, some
of the tubers from the 2,4-D treated plots were "obviously darker, with
a smoother, shinier skin than tubers from the control rows. However, this difference
was not consistent."

Results from the 1997 trial showed poor colour. "We suspect because of
the hot conditions prevailing through July and August," the pair reports.
After six months of storage at four degrees C and 80 percent relative humidity,
the 2,4-D treated potatoes were "significantly darker." The 1998 trial
results showed better skin colour at harvest compared to 1997 but there was
"no significant effect of the 2,4-D treatment on skin colour at harvest."

Bantle and Waterer also examined yield and tuber size after treatment with
2,4-D (see Table 2). In 1996 and 1997, the trials showed no symptoms of phytotoxicity,
canopy or leaf shape changes after the 2,4-D treatment. In 1998, the researchers
observed 'fiddleheading' symptoms, which they say is normally associated with
2,4-D exposure. "These symptoms could be detected for several weeks but
they did not appear to slow crop growth," they report.

Following the 1998 trials, there had been plans to continue the work during
the following season, examining multiple application timings. The work was dropped.
"We ran into regulatory problems," Waterer explains, adding it became
questionable whether there was actual interest in having the product registered
in Canada. "The initiative stopped."

Unfortunately, colour quality issues attached to the production of red skinned
potatoes have not. Saskatchewan growers are not immune to the problem, he says,
and the 2006 season had its fair share of colour concerns. "Growers are
very interested in anything that can help with colour," Waterer says, adding
there has been a return in interest in registering the product. "If our
regulatory industry can pull the trigger, I'd be interested in working with
it."

The use of 2,4-D to enhance potato skin colour is common practice in the US,
where the ester is registered for use on the crop. A fact sheet distributed
by Michigan State University Extension recommends applying 2,4-D L.V.4 (Riverdale)
ester at a rate of 2.3 fluid ounces per acre at the pre-bud stage and 10 to
14 days later as a way of enhancing skin colour on the Michigan Purple potato
variety. Wisconsin and New York State potato advisors also recommend the use
of the 2,4-D Riverdale ester, which is marketed by the Riverdale Chemical Company
of Illinois. -30-