Recently I purchased a VT02 Visual IR Thermometer for use on grapes and grapevines. This instrument has been used in various studies, mainly those addressing irrigation scheduling, stomatal conductance, and other water-related issues. I have used a similar instrument previously in Oklahoma and blogged about it here: okgrapes.wordpress.com/?s=infrared.
Yesterday, I went to the vineyard and looked at some of the few bunches left on vines that bird had not carried off or destroyed. I took IR readings on two different cultivars, ‘Lake Emerald’ and ‘Rubaiyat’. ‘Lake Emerald’ is a white-skinned grape. It was released by the University of Florida in 1954 and resulted from a cross of ‘Pixiola’ and ‘Golden Muscat’. This is the first year it has produced fruit (2nd leaf) and the clusters have not fully ripened yet, but is getting close. You can read more about ‘Lake Emerald’ here: http://mrec.ifas.ufl.edu/grapes/cultivarbulletins/Lake%20Emerald%20circularS-68%201954.pdf. ‘Rubaiyat’ is a cross of ‘Bailey’ and Seibel 5437. It has red skin and red flesh. It was released by Oklahoma State University in the 1970s. You can read more about ‘Rubaiyat’ here: http://www.grapes.okstate.edu/PDFs/2006/Rubaiyat.pdf
Below are the images I took of the clusters during mid-day. Ambient air temperature was around 35 C. As you can see, cluster temperature was greater than air temperature.
The temperature difference is nominal, just 0.7 C higher for Rubaiyat (the red grape). Rubaiyat was also ripe, or past ripe. The “cooler” tones around the bunch are leaves and air (or other objects). I still need to work with the instrument to optimize its use. While outside I also looked at leaves that had problems (disease, nutrient deficiency, etc.) vs. normal, healthy leaves. The problem leaves invariably had slightly higher temperatures. I attribute this to reduced transpiration from damage to the leaves. I also tested some blueberry plants. I saw some differences in canopy temperature among cultivars, but not sure what to attribute it to — could be water stress, leaf age, or some other factor.