February 2019 - 17

was a weakness that caused the rapid
deterioration.
Location matters
" The location, not the crops, determines
the amount of degradation, " Miles said.
" You really need to test these products on
your farm to see which of these products
works for you. Having enough mulch intact
through the length of the growing season is
very important for weed control. "
Solid results on comparisons of weed
control were difficult to come by. " There was
a mixed response on weed control because
weed pressures are different at different sites, "
Miles said. " There are more issues affecting
weed control than just mulch. "
Yield is a more consistent message. " The
site is what's really going to determine yield, "
Miles said. " All of the black, biodegradable
plastic mulches had comparable yields to
black, polyethylene mulch. "
WSU has been testing the products
BioAgri, Exp.PLA/PHA (an experimental
film), Naturecycle, Organix (black), Organix
Clr (clear), standard polyethylene and
WeedGuardPlus.
did stick to the pumpkins. In a new study,
Miles found the mulch fragments could
be wiped off the fruit if the fruit was
slightly damp when it was picked due to
humidity, dew or irrigation and the fruit
was wiped immediately. " If you have a
food grade product going out of your
field, you're not going to want to take
the time to try to wash it off, " Miles said.
" Consider biodegradable plastic mulch
carefully if you're in this situation. "
WeedGuardPlus in the study was found
to have a cooling effect on the soil, which
had a negative effect in Washington's cool
climate. In warmer parts of the country, the
cooling effect could be a positive.
WeedGuardPlus also had the ability
to control yellow nutsedge. " It controlled
yellow nutsedge every year in the trial, "
Miles said. " We feel this is very important
for growers who have that problem. There
are no postemergence herbicides labeled for
pumpkins so weed control is a real issue. "
Deterioration vs. degradation
When assessing biodegradable mulches,
it's important to understand the difference
between deterioration and degradation.
Degradation is actual decomposition.
Deterioration is weather damage or rips and
tears from improper handling.
" If the mulch is drawn too tight over the
crop it tends to pull apart, " Miles said. " The
key is to alleviate any tension on your mulch. "
Tips on collecting and measuring mulch
fragments from the soil - to assess how well
a product works for you - are available at
www.biodegradablemulch.org. The site is a
partnership of the University of Tennessee,
WSU and Montana State University.
" You have to do your due diligence when
collecting and measuring these samples, "
Miles said. " Mulches are going to perform
differently at each site. "
Oxo- or photo-degradable plastic mulch
is a serious issue in the discussions on
biodegradable plastic mulch.
" It's being marketed as a biodegradable
plastic and it's not, " Miles said. " What you're
going to end up with is plastic pollution in
your field. It won't decompose and will be
there for 300 years like polyethylene mulch.
You can't pick it up; it just crumbles apart. "
A guidance document on oxo- or photodegradable
plastic mulch is available at
www.biodegradablemulch.org. VGN
Carol Miles, professor in vegetable
horticulture at Washington State
University said all of the black,
biodegradable plastic mulches yield
comparably to black, polyethylene
mulch. Photo: Dean Peterson
Stokes Seeds Trial Evaluation
Researching the best for our customers since 1881.
The products vary in their bio-based
percentage. BioAgri is 20 to 25 percent
bio-based, Exp.PLA/PHA is 86 percent biobased
and Naturecycle is equal to or greater
than 20 percent bio-based. Organix and
Organix Clr are 10 percent bio-based while
polyethylene is less than one percent biobased
and WeedGuardPlus is 100 percent
bio-based. WeedGuardPlus is paper, 100
percent biodegradable, and allowable for use
in certified organic production.
The percentage of bio-based composition
is not the determining factor in product
quality or time of degradation because the
mulches can be made in many ways.
Biodegradable plastics can be derived
from corn starch or other plant starches
or from the bacterial fermentation of
plant sugars or lipids. The biodegradable
polymers can also be made from synthetic
products containing ester bonds which are
readily broken down by microorganisms,
sunlight and water.
A sticky situation
Biodegradable plastic mulch has a
reputation of sticking to heavy fruit and
causing problems with visible appearance.
The WSU study used pumpkins in the trials
to assess that problem.
The problem did emerge and the mulch
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VGN | FEBRUARY 2019 | 17
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http://www.biodegradablemulch.org http://www.biodegradablemulch.org http://www.StokeSeeds.com
February 2019

Table of Contents for the Digital Edition of February 2019
