Botrytis, Meet Calcium

By: JC Chong, Clemson University
We pack our carts with the best crop of bedding plants ever, or our boxes with the best cut roses, only to receive a call from our customers rejecting the shipment because of gray mold. Botrytis meltdown is a huge problem during shipment because high humidity in sealed shipping carts or containers is just what Botrytis needs to cause an outbreak.
With funding from AFE, Jim Faust and his graduate student Kathie Bennett (Clemson University) studied the potential of reducing Botrytis meltdown on petunia flowers with pre-shipment sprays of calcium chloride. Kathie sprayed four concentrations of calcium chloride (at 0, 400, 800 and 1,200 ppm) over two weeks before the expected shipping date. She infected the flowers with a fludioxonil-resistant Botrytis strain and kept the flowers in sealed boxes to simulate the high humidity of sealed shipping containers. She then compared the disease incidence score of these calcium-treated petunia flowers with those treated with one application of Palladium.
The picture tells the tale: Flowers in the inoculated control (i.e. infected with the pathogen, but not treated) and the fungicide treatment didn’t fare well. Flowers treated with 800 and 1,200 ppm calcium chloride looked good, although they had some blemishes.

Petunia flowers treated with calcium at 800 and 1,200 ppm suffered from less botrytis meltdown than untreated and fungicide-treated inoculated control. (Photo credit: Kathie Bennet, Clemson University)

Pre-shipment sprays of calcium chloride at 800 or 1,200 ppm can reduce Botrytis meltdown during shipment, even against fungicide-resistant strains. Some of us are already using calcium spray to prevent calcium deficiency or bract edge burn in poinsettia. As shown in this study, calcium spray can also help with Botrytis suppression, reducing fungicide application frequency and cost.
It’s still very important to practice good cultural and sanitation practices, e.g., remove and properly discard plant debris before and during production, provide proper plant spacing, lower air temperature, and reduce humidity level.
Jim and Kathie are conducting follow-up studies to select the most efficacious calcium source.

JC Chong is currently being funded by AFE to look at calcium effects on thrips infestations.
*This article was originally published in the first issue of PestTalks, a new newsletter from Ball Publishing that provides research and news on the latest pest management techniques.