technically speaking
Height Control
for Vegetable
Transplants
By Erik Runkle
A recent supplemental labeling of Sumagic for use on vegetable transplants
has made height control less complicated. There are a few other methods
that may be helpful, too.
C
ompared with ornamentals, controlling T h i s st rateg y i s ef fe c t ive, but whe n t a ke n to a n ext r e me,
plant height of vegetables can be diffi cult. it inhibits photosynthesis and limits plant growth. By
That challenge has been reduced with the providing a low, constant rate of the nitrate form of
labeling of Sumagic (Valent Professional nitrogen (no ammoniacal nitrogen) and limiting the
Products) on tomato, pepper, eggplant, ground- amount of phosphorus, stem extension can be sup-
cherry, pepino and tomatillo during the young plant pressed with little effect on other growth attributes.
stage. This article discusses guidelines for use of
Sumagic on these crops, as well as alternative height Negative DIF and Drop
control strategies. Providing a negative DIF (a cooler day than night)
is effective technique in inhibiting stem extension of
Sumagic Sprays most crops, including vegetables. A temperature drop
Sumagic (uniconazole) is the only plant growth during the fi rst two to three hours of the day, begin-
retardant that can legally be used as a foliar spray ning about 30 minutes before sunrise, is similarly
on young tomato, pepper, eggplant, groundcherry, or slightly less effective. In both techniques, plant
pepino and tomatillo plants. The recommended response increases as the value of the DIF or drop
label rate is 2-10 ppm at a volume of 2 quarts per 100 increases. For example, plants grown with a 68/72° F
square feet of crop. Based on experiments performed day/night (-4° F DIF) will be taller than those grown
at Michigan State University, University of Florida at a 64/76° F day/night (-12° F DIF). If you use a DIF or
drop, be sure to maintain your desired average daily
temperature and use Virtual Grower to estimate the
impacts on energy costs for heating.
For decades, growers have grown vegetable
transplants with as little water and fertilizer as
Brushing
An effective — though not widely used — strategy
possible. When taken to an extreme, this strategy
is to brush plants repeatedly throughout the day. The
goal is to slightly bend plants without tearing leaves or
inhibits photosynthesis and limits plant growth.
breaking stems. This can be accomplished by hanging
plastic or some other material from irrigation booms
and operating the booms frequently (10 or 20 times
per day). For more information on brushing, read
and University of Kentucky, a suggested starting rate my article from February 2009, “Brushing Plants for
for tomato is 1.0-2.5 ppm applied very early in pro- Height Control” (www.gpnmag.com/article10047).
duction. Perform small-scale trials to determine
appropriate rates for your growing conditions and Supplemental Lighting
desired responses. When the daily light integral is low, the addition
According to the supplemental label, the cumula- of light from high-pressure sodium (HPS) lamps can
tive amount of Sumagic may not exceed 10 ppm. In suppress stem elongation. HPS lamps emit a high
addition, the fi nal application may not occur later than amount of red light relative to far-red light, which
14 days after the two to four true leaf stage. Currently, inhibits stem extension, particularly when applied
Sumagic is registered for use on vegetable transplants during sunset.
GPN
in all states except New York (label is pending there).
Erik Runkle is associate professor and fl oriculture
Limiting Water and Nutrients extension specialist in Michigan State University’s
For decades, growers have grown vegetable trans- department of horticulture. He can be reached at
plants with as little water and fertilizer as possible. runkleer@msu.edu or (517) 355-5191 ext. 1350.
50 GPN February 2010 www.gpnmag.com
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