Zamir K. Punja from Simon Fraser University presented at the Canadian Greenhouse Conference this October where he discussed powdery mildew management on greenhouse crops. Cucumbers and cannabis were the focus of this presentation as they are both high value crops grown in a large portion of Canada’s greenhouses. In addition, both these crops are susceptible to powdery mildew infection and management tends to be tricky.
How does Powdery Mildew Spread?
Spores spread in the air by workers of by infected plants, and they can survive for up to a week. In humid conditions (70%) the spore then germinates producing a germ tube and haustoria. The mycelium then develops, and eventually more spores are produced. This happens within 5 to seven days. Overall mildew development is favored by warm dry conditions.
Powdery mildew management using Bacillus species as a biocontrol agent
Bacillus spp. reduces powdery mildew development in a variety of ways which include:
- Inhibiting fungal growth by producing lipopeptides
- Produces endospores
- Display broad-spectrum activity against fungi
- Produces lytic enzymes that can destroy fungal cell walls
There are currently no synthetic fungicides registered for cannabis. To minimize damage cause by powdery mildew growers, apply vaporized sulphur (except organic), hydrogen peroxide (Zerotol) and potassium bicarbonate (MilStop). In addition, Regalia may induce resistance to powdery mildew. Other practices include using UV-C light and a physical means of control.
Figure 1. Effect of treatments on Powdery mildew in cannabis after weekly applications were made for 4 weeks. Photo taken from Zamir K. Punja’s presentation at the Canadian Greenhouse Conference.
In this trial Rhapsody (Bacillus subtilis), Regalia Maxx, and MilStop were applied prior to viable mildew infection and were tested for 4 weeks. Both MilStop and Regalia provided good control of powdery mildew, with Zerotol and Rhapsody providing less control. MilStop and Regalia application resulted in the collapse of mycelium in the infected leaves.
In addition to evaluating the efficacy of registered biological controls on the market, Zamir wanted to experiment with the use of UV-C light for controlling powdery mildew. In this Trial CleanLight Pro Unit UV-C Light was used for 3-5 seconds daily at approximately 3-6 mJ/cm2. UV-C radiation reduced mildew development but can be difficult to implement in a commercial setting.
For the complete slide deck from Zamir's presentation, click here.
Posted by: Talia Plaskett