EDINBURG, TXGreenhouses 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. "'Valenc
|Contact: Michael W. Neff|
American Society for Horticultural Science