Many growers face Botrytis early in the season as plant materials are densely packed in plug-and-liner trays, shipped, and held in conditions that favor the development of this omnipresent disease. Botrytis is also commonly called gray mold. This fungal pathogen affects virtually all greenhouse and nursery crops with the potential to cause an infection at any point in the season. Botrytis can persist in the greenhouse on plant debris under benches as well as actively growing plant tissues which makes sanitation and scouting key in the management of this disease. Botrytis symptoms can vary in appearance due to several factors including where on the plant it occurs and the current environmental conditions. Symptoms range from leaf spots and stem cankers to petal blight. As the pathogen grows, fuzzy gray spores develop which eventually invade the affected plant area causing decay.
Figure 1: Botrytis sporulation on Petunia plug tray
Managing Botrytis needs to be addressed by evaluating the greenhouse environment. Begin by supplying adequate air circulation to reduce the relative humidity in the greenhouse. Allow as much space between plants as is economically possible. Do not be tempted to open vents on rainy days. If it is raining or foggy outside, keep the greenhouse closed and supply some heat. During periods of damp weather, set the thermostats so that the heat runs occasionally throughout the night. Reduced Botrytis pressure can quickly pay back the energy costs.
Figure 2: Botrytis development at the crown on Lavender
The timing of irrigation is also important. Growers should limit overhead watering to the morning hours to allow adequate drying time during the day. Horizontal airflow (HAF) fans mix the air effectively, which helps to eliminate pockets of high humidity that develop in the plant canopy and production space, further reducing the potential for condensation. The prompt removal and disposal of infected tissue from the greenhouse also helps to reduce disease pressure.
The ideal environment for Botrytis development is 75-82°F and 80% humidity, however, it will tolerate temperatures down to 32°F. As little as two to three hours of leaf wetness allows the spores to germinate and make penetration into healthy plant tissue. Excess nitrogen can make plant tissue more prone to foliar disease, so work with GGSPro to make sure that you are not feeding crops at higher rates than are needed for ideal growth. Current research and grower feedback have shown that foliar sprays of calcium chloride dihydrate help decrease Botrytis outbreaks by increasing tissue and flower calcium concentration1. Not only does calcium bind with pectin forming Ca-pectate, which is important for strengthening cell walls, but it also has a direct effect on Botrytis hyphal growth2. GGSPro recommends 1/2 oz per 3 gal or 1 lb. per 100 gal calcium chloride dihydrate (approximately 324 ppm calcium) as a starting rate for most situations.
Summary of Scouting Tips and Cultural Management Tools for Botrytis:
Figure 3: Botrytis stem canker on Zinnia
Even with the best cultural methods, fungicide sprays are often still necessary. Fungicide application tactics differ depending on the location of the Botrytis infection. For example, with Botrytis stem rot or blight the best application approach is a “sprench” which is a heavy wet spray that ensures contact with the stems and canopy penetration. If the infection is present on the leaves, a typical foliar spray is sufficient. Below is a list of products that have shown good efficacy on Botrytis either as a preventative or curative foliar spray:
*Some edible crops on the label
**Other sizes available
1 The power of calcium – Greenhouse Management (greenhousemag.com) https://www.greenhousemag.com/article/the-power-of-calcium-jim-faust-clemson-university/
2 Calcium Application Method Impacts Botrytis Blight Severity on Petunia Flowers: HortScience, https://doi.org/10.21273/HORTSCII4419-19
Note, not all products are registered in all states. Some pesticides are restricted use in some states or regions and not others. It is the responsibility of the applicator to read and follow all label directions, remembering that labels may change. Other products may be safe and effective. Rates, application methods, and edible status are detailed in our GGSPro Insecticide & Fungicide Guides. Griffin also offers the 5th Edition GGSPro Technical Reference Guide in both English and now Spanish versions. This valuable resource outlines a wide range of pest control options and information on pollinator safety, BCA’s, scouting, weed management, plant lighting, nutrition, water quality and more!
Figure 1: Botrytis sporulation on Petunia plug tray
Managing Botrytis needs to be addressed by evaluating the greenhouse environment. Begin by supplying adequate air circulation to reduce the relative humidity in the greenhouse. Allow as much space between plants as is economically possible. Do not be tempted to open vents on rainy days. If it is raining or foggy outside, keep the greenhouse closed and supply some heat. During periods of damp weather, set the thermostats so that the heat runs occasionally throughout the night. Reduced Botrytis pressure can quickly pay back the energy costs.
Figure 2: Botrytis development at the crown on Lavender
The timing of irrigation is also important. Growers should limit overhead watering to the morning hours to allow adequate drying time during the day. Horizontal airflow (HAF) fans mix the air effectively, which helps to eliminate pockets of high humidity that develop in the plant canopy and production space, further reducing the potential for condensation. The prompt removal and disposal of infected tissue from the greenhouse also helps to reduce disease pressure.
The ideal environment for Botrytis development is 75-82°F and 80% humidity, however, it will tolerate temperatures down to 32°F. As little as two to three hours of leaf wetness allows the spores to germinate and make penetration into healthy plant tissue. Excess nitrogen can make plant tissue more prone to foliar disease, so work with GGSPro to make sure that you are not feeding crops at higher rates than are needed for ideal growth. Current research and grower feedback have shown that foliar sprays of calcium chloride dihydrate help decrease Botrytis outbreaks by increasing tissue and flower calcium concentration1. Not only does calcium bind with pectin forming Ca-pectate, which is important for strengthening cell walls, but it also has a direct effect on Botrytis hyphal growth2. GGSPro recommends 1/2 oz per 3 gal or 1 lb. per 100 gal calcium chloride dihydrate (approximately 324 ppm calcium) as a starting rate for most situations.
Summary of Scouting Tips and Cultural Management Tools for Botrytis:
- Inspect all cuttings, plugs, and liners upon receipt from the propagator for any signs of blighted leaves or decaying tissue
- Weekly scouting of mature plants for signs of blighted foliage, water-soaked leaf spots on flowers or leaves, and stem lesions or cankers
- Maintain good air movement with Horizontal airflow (HAF) fans
- Space plants to avoid overcrowding
- Remove all plant litter, debris, and diseased tissue from the production area
- Clean and disinfest production areas before introducing crops
Figure 3: Botrytis stem canker on Zinnia
Even with the best cultural methods, fungicide sprays are often still necessary. Fungicide application tactics differ depending on the location of the Botrytis infection. For example, with Botrytis stem rot or blight the best application approach is a “sprench” which is a heavy wet spray that ensures contact with the stems and canopy penetration. If the infection is present on the leaves, a typical foliar spray is sufficient. Below is a list of products that have shown good efficacy on Botrytis either as a preventative or curative foliar spray:
| Fungicide | MOA | Item Number | Size |
|---|---|---|---|
| Affirm* | 19 | 71-1131 | 2.4 lb. |
| Astun | 7 | 71-1190 | 1 qt. |
| BotryStop* | NC | 71-12601 | 12 lb.** |
| Broadform* | 7 & 11 | 71-1290 | 12 fl. oz. |
| Cease* | BM02 | 71-13301 | 1 gal.** |
| Medallion | 12 | 71-16502 | 8 oz. |
| Mural* | 7 & 11 | 71-1690 | 1 lb. |
| Orkestra Intrinsic | 7 & 11 | 71-2200 | 16 fl. oz.** |
| Pageant Intrinsic* | 7 & 11 | 71-26801 | 1 lb.** |
| Pageant Intrinsic TR | 7 & 11 | 71-2683 | 12/3 oz. cans |
| Palladium | 9 & 12 | 71-2685 | 2 lb. |
| Postiva* | 3 & 7 | 71-2400 | 28 fl. oz. |
| Regalia CG* | P5 | 71-2841 | 1 qt.** |
| Sil-Matrix* | UN | 71-2939 | 2.5 gal. |
| Spirato GHN* | 12 | 71-2948 | 1 pt. |
| Stargus* | BM02 | 71-2950 | 2.5 gal. |
| Triathlon BA* | BM02 | 71-3040 | 1 gal. |
| Zerotol 2.0* | NC | 71-35501 | 2.5 gal.** |
| Secondary Nutrient | |||
| Calcium Chloride Dihydrate | 35315 | 1 lb.** | |
*Some edible crops on the label
**Other sizes available
1 The power of calcium – Greenhouse Management (greenhousemag.com) https://www.greenhousemag.com/article/the-power-of-calcium-jim-faust-clemson-university/
2 Calcium Application Method Impacts Botrytis Blight Severity on Petunia Flowers: HortScience, https://doi.org/10.21273/HORTSCII4419-19
Note, not all products are registered in all states. Some pesticides are restricted use in some states or regions and not others. It is the responsibility of the applicator to read and follow all label directions, remembering that labels may change. Other products may be safe and effective. Rates, application methods, and edible status are detailed in our GGSPro Insecticide & Fungicide Guides. Griffin also offers the 5th Edition GGSPro Technical Reference Guide in both English and now Spanish versions. This valuable resource outlines a wide range of pest control options and information on pollinator safety, BCA’s, scouting, weed management, plant lighting, nutrition, water quality and more!