Edinburg, Texas
February 17, 2009
Color infrared photography has
potential for large-scale use in greenhouses
 Greenhouses
are an integral part of U.S. agriculture. Nearly $200 million of
food is produced in domestic greenhouses each year, and the
facilities play a vital role in producing seeds and
transplantable vegetation. Understanding how to keep greenhouse
plants healthy can translate to increased revenue for producers.
Kenneth R. Summy of the University of Texas-Pan American and
Christopher R. Little of Kansas State University (Manhattan) led
a study examining the stresses of a variety of greenhouse
plants. The study, published in the August 2008 issue of
HortScience, used color infrared (CIR) photography.
CIR images are divided into wavebands. Ratios are created
comparing the NIR wavebands to red wavebands. High NIR and low
red values are typical of healthy vegetation because light is
being reflected in the proper proportion. Ratios of colors
accentuate even slight differences in light reflection, which
can indicate disease.
Trifoliate orange, 'Valencia' orange, sour orange, grapefruit,
'Bo' tree, and muskmelon were infested with sooty mold, insects,
and pathogens; all are common ailments in greenhouses. Leaves
exhibiting a range of symptoms were chosen to compare with
healthy leaves of the same species and photographed using CIR.
Certain diseases such as powdery mildew give the leaf surface a
powdery finish. Another disease, sooty mold, appears on the leaf
as tan, brown, or even black spots. This image analysis allows
for detection of these diseases early on. Color ratio was also
affected by the age of the leaf in some cases. The ratios for
sour orange leaves that were 10 and 35 days old were
significantly different. However, there was no difference
between 20- and 35-day-old trifoliate orange leaves. This could
affect the efficiency of this method when used on whole-plant
foliage.
The study also showed a variation in the accumulation patterns
of a particular disease on the two trees in the study.
"'Valencia' orange leaves were coated very evenly with insect
honeydew, whereas honeydew deposits on 'Bo' leaves were very
spotty," reported the researchers. Insect honeydew can
contribute to sooty mold growth. As mold infestations increased,
the ratio decreased into the unhealthy proportion for all sample
plants.
The study points out that this image analysis technology has
potential for large-scale use in greenhouses. However, to be
most beneficial, the application must be effective in
distinguishing the health of plants, cost-effective enough for
the purchase of CIR cameras and equipment, and user-friendly so
that on-site software processing of data can be completed
easily.
The complete study and abstract are available on the ASHS
HortScience electronic journal web site:
http://hortsci.ashspublications.org/cgi/content/abstract/43/5/1485
Founded in 1903, the American Society for Horticultural
Science (ASHS) is the largest organization dedicated to
advancing all facets of horticultural research, education, and
application. More information at
www.ashs.org
Photo by Chris Little |
|
