submitted by Dr. Mohyuddin Mirza (July 2011)

In late May and early June I was called by a Basil grower to come to the greenhouse and check leaf scorching on potted and leaf Basil. What I mean to say is that we grow two types of Basil. Potted basil, in 4, 6 and 10 inches pots for direct sales and basil leaves and stems for sale through farmers markets and commercial wholesale channels. Here it is how the symptoms looked like:

 

The upper side of leaf looked as if it has been scorched, loss of green color and when you check the underside one can see brown, black dirt like deposit. It will stain your fingers as well. This is a fungus commonly called Downy Mildew and the botanical name is Perenospora belbahrii. Then I checked the young seedlings and found that they are also showing the same symptoms. I investigated more and found out that this fungus is seed borne and it has come from Europe to USA and then it has come to Canada as well through purchase of seeds from US sources.

What do we know about this disease?

To keep it simple, one thing we know that is a seed borne disease and high humidty and poor air circulation in the crop will encourage its development. The symptoms were more visible when cloudy and rainy weather was prevalent. Understanding these two facts will help to control or reduce the incidence of the disease. Also we know that this group of mildews are specific to their hosts and don't move to other crops. So there was no danger that the disease will spread to bedding plants or tomatoes.

What actions were recommended to the growers?

It was suggested to contact the seed supplier and bring to their attention the fact about the seed borne nature of this disease. The response from one source was " we did not know about it and nobody else has reported this problem". That is a typical "legal" response. I encouraged the growers to check out sources in Europe and see if they are aware of the problem and if they can supply disease free seeds.

The grower installed circulation fans and also a humidity meter was purchased. Heavily infected crops were removed from the greenhouse.

What about the use of any fungicide?

No fungicide was registered for use on Downy Mildew of Basil. I contacted Dr. Ron Howard and learned that Ontario has this problem with the field grown Basil (did not realize that crop is worth close to $ 8.0 milion) and were thinking of submitting a minor use requisition of two fungicides. Alberta growers were also interested in acquiring these two fungicides and worked on developing the proposal together. The Alberta Greenhouse Growers Association paid the fee, Dr. Ron Howard, Jim Broatch from Alberta Agriculture and growers worked together to make the submission. Growers provided the background information. I learned that we do grow close to $250,000 worth of potted and commercial basil.

So finally we got the approval of two plant protectant products which will be good till the end of the year. One is called CONFINE fungicide. It is a Mono and Di Potassium salt of Phosphorus Acid, 45.8% and the other is REVUS fungicide. The details can be found in links at the end of this article, for your information.

This is a good model of cooperation and highlights advantages of being members of an association, in this case of course I am talking about the Alberta Greenhouse Growers Association.

Confine fungicide information
Revus fungicide information