This basil had been growing in a greenhouse system of 12 foot channels and 4 inch offsets with water-flow, similar to a hydroponic operation; however the root plugs of the plants appeared to be encased in a soil mixture. These growers had first experienced problems 4 weeks ago. Luckily, this submitter had included information with his plant sample that provided some much needed clues as to the demise of their sweet basil.
As routine, I try to rule out problems on ALL parts of the plant, even if they don't appear to be an issue at first glance. I scanned some of the plant parts under the dissecting scope and checked for bacterial ooze under the microscope. There were no signs of bacterial disease.
Downy mildew wants to ruin your summer
Downy mildew poses a threat to Illinois basil crop
Luckily, we found no sign of any fungal diseases, such as Downy mildew, on this sample. Dr. Babadoost and I agreed that the sample had signs of abiotic injury (most likely cold injury) as well as some insect and possible virus symptoms. The plants had also been without water for about 15 hours and the heat was turned up to 80 degrees F (I assume to warm the greenhouse). These factors could have also caused some plant stress symptoms.
My next stop was the office of Dr. Weinzierl, U of I Extension, Fruit and Vegetable Entomologist. He looked at the sample and found a few leaves with possible thrip feeding. When these leaves were examined under the scope, there were still a few thrips present. By the way, thrips are very, small and can be very, tricky to find! Dr. Weinzerl said that he did not recommend any treatment, as the thrip injury to the basil did not appear to be threatening the crop at this time. Thrips can be one of those pests you don't want to have in the greenhouse, because infestations can be very, difficult to control.
|The small, tan circles on leaves are thrip feeding. The darker areas are suspected cold injury.|
impatiens necrotic spot virus). The recommendation was to rogue all of the plants that appeared to have viral symptoms immediately. But, guess the insect vector of INSV? THRIPS! This may change the previous recommendation of no treatment for thrips.
The moral of the story is there could be multiple problems with a sample. Many questions come to my mind. How long were some of these plants infected with INSV? Did the cold, heat, or water stress bring on the virus symptoms? The fact of the matter is that these plants should "grow out of abiotic injury"; however, if they do not, it is possible that the plants may face further complications from the virus infection or other possible factors not seen in the sample submitted.