Powdery Mildew
 

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Control Powdery Mildew    

              

The Van Dyke Zinnia Way


Michigan and the Midwest enjoyed a particularly long and warm growing season in 1998. Credit El Niño if you like, but the longer than usual string of warm autumn days and night time temperatures falling below 60°F after a warm fall day set up ideal conditions for powdery mildew in the zinnia beds and on lilac bushes around the Farm. High humidity exacerbates the problem, but the moisture at the leaf's surface from the overnight temperature change is all that's needed to give powdery mildew a foothold in your zinnia beds during early autumn or late spring. And if that isn't bad enough, it doesn't go away after the first hard frost of autumn, rather it may over-winter in the bed and come back with a vengeance the next season, particularly if you've grown your zinnias alongside perennial hosts of the fungus or beside plants that are conducive to this phenomenon (lilacs).

The words "powdery mildew" send chills up any sensible grower's spine. We get letters at Redbud Farms from people asking us for advice to help them get rid of mildew and fungus. They report leaves with "white stuff" on them, and buds or blooms turning black and dying before they bloom. Environmentally unsafe chemicals are used little or not at all at the Farm, the owners preferring instead to make use of natural pest and disease control mechanisms. This, then, is the recommendation we make when customers write to us with the problem.

We've read articles by others who have had excellent results from using bicarbonates and horticultural oils for controlling mildew on plants. (R.K. Horst, "Powdery and Downy Mildews"; National Gardening May/June '92, pp.18-21) One of our favorite remedies is to use one tablespoon of baking soda to one gallon of water and spray it directly on the leaves and other parts of the affected plant. Weekly spraying thereafter, as long as weather and climate conditions prevail, should keep your zinnias mildew free! Cultivating where and in a way the stems, leaves and blooms get plenty of air and direct sunlight help prevent the problem as well. This solution won't hurt the bees or birds or frogs that do their work or make their home in your gardens!

The summer of '99 was especially hot and humid in mid-Michigan.  The threat of powdery mildew and rust infection came very early in the season.  If you are unable to control the environment with the more natural methods mentioned above, you may want to buy IMMUNOX multipurpose fungicide spray concentrate by Spectracide.  We've found it to be immediately effective when used according to label instructions.  You can only use it a total of six times, once every two weeks, for 12 weeks, and the warning on the label stated it could be harmful to fish; so avoid using the product around back yard ponds or other natural waterways  So begin treatment early if symptoms appear and you seem unable to stem the fungus tide in the garden by these other means.

The following letter to one of our customers continues the discussion about powdery mildew and rust.  Information on other zinnia varieties with good disease resistance is part of this conversation:  

January 2000

.....I am always delighted when our customers take such a profound interest in resolving problems we ourselves face as growers of these wonderful flowers.  Our affection for their simple loveliness, cheerful colors, and many intriguing varieties is overshadowed by the threat of disease.  Yet this does not deter us from growing them year after year, and working hard to get the environment just right, as we watch for signs to heed to preserve them throughout the season. 

I saw some interesting observations on the mildew problem and other topics as I read your letter, and so I wanted to add my 2 cents worth to the discussion, if I may. 

Classic (white) angustifolia:  know that we have them, just not in the quantities I’d feel comfortable about, advertising widely through our web site or catalog.  We try to buy or grow enough stock that we may positively respond to any discriminating customer who asks if perhaps we have such and such or know where to get it.  If you’d like some of these, know they are $2.50/pack for from 50-70 seeds.  Just write it in on your catalog order form should you place an order with us.  This is true of anything you cannot find elsewhere.  We have very many sources and know the best ones from our experience.

Bluepoint formula mix (Benary’s Giant):  We actually have these ready to add to our Supreme Variety mix.  Again, we don’t advertise to sell them separately unless a customer specifically requests it.  We were successful in finding these in an array of colors from a couple of good vendors:  Stokes 2000 Growers Guide and from Johnny’s Selected Seeds 2000 Commercial Catalog.  Let us know if you’d like us to send you some.  Again, the price per pack is $2.50, and you may write them in on the catalog order form.

Immunox by Spectracide:  because I am not a biologist, I cannot evaluate the statements made on the instructions that came with the product, but I think it is a good idea to put a stronger caution statement with my advice to my customers.  Thanks for the suggestion!  Oh!  I can tell you we used only 3 applications of it this past summer when the humidity soared early and stayed long.  We never saw a powdery white spot!  And my husband says to tell you he usually dilutes it by half of what the instructions recommend.  It worked for us.  Have never tried Bayleton and hope we don’t have to.

Purchase seed from southern seed companies:  I cannot see the scientific logic behind this statement.  If we want to buy a used car up north, we often advise people to go south where the rust isn’t so pervasive and as much of a problem.  We believe the cars will last longer because they aren’t polluted when we buy them.  Why would flower cultivation be any different?  I would be more afraid to buy seed from a southern grower.  (p.s. Most of our seed not grown at the farm comes from Stokes in Buffalo, NY and Johnny’s or in Albion, Maine. Another favorite is Pinetree Seed in New Glouster, Maine.) 

The small varieties are less prone to diseases:  NOT TRUE.  We see very different evidence. Think about it. These little guys hug the ground.  Where does the dampness lay but near the ground, less disturbed by air currents in the fields.  Our taller varieties have much less problem than our shorter ones.  And note it’s the Profusion and Pinwheel mixes (we call these “minis”) that were bred and most successful at resisting fungal  disease. 

Stagger planting times:  I am not at all sure this is a relevant approach.  What if the microorganisms are in the soil?  What then?  We will plant all at once then pull any that appear to exhibit the potential for problems. 

Final point to consider – plant east-west instead of north-south rows:  For Michigan, this is excellent advice, as the prevailing winds are west to east most of the summer here.  We noticed to our chagrin that the east-west rows had very little problem with fungal disease as opposed to our north-south rows.  Even the Profusion and Pinwheel mixes had some problems with rust in the north-south rows.  Not so our east-west rows.  Aside from the prevailing winds, I do not have a scientific explanation.  I just know we will plant all rows east-west each season and will advise others to determine the direction of their prevailing winds and plant rows to “line up with them” as opposed to lining up against them. 

I agree with every other bit of advice given by your experts on avoiding diseases in zinnias! [this advice appears on our planting/watering tips page]

I’ll close by saying I am in many ways just a novice when it comes to predicting or knowing much about Mother Nature.  One of our more interesting problems is how to grow more beautiful zinnias through natural selection, while still taking advantage of the new varieties made possible by the hybrids. I sense we have not even begun to understand all the possibilities through this process.  And success is slower this way; so we have to be more patient. As evidence of the Mystery, I leave you with a picture in your mind of a zinnia one of our customers grew in South Africa.  She wrote just this week, saying, “I have to say that there was one rather surprising flower, part rose, part apricot, and part lemon.  And on the same plant, the same base stem in fact, a flower which was just lemon.”  That one would have been a sight to see!  I told her I hoped I’d get one like it someday in our gardens! 

Kindest regards,

Sharon Baller

 

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From time to time, we will offer web-only specials and publish short stories about the Farm Dogs or the grandkids, and inspirations from life on the Farm in mid-Michigan, the American heartland.  Seasonally, we will write to help Gardeners grow beautiful Zinnias, learn how to make a stunning bouquet, or how to collect precious seed when harvest is here.  Let us know if you would like to receive them.  We have moved our web to a new server and resized all photos for faster load times.  As we approach another winter, I hope you visit us often to see our pretty pictures and read about the simple things we love most here.  Thanks for being a customer!  -Sharon Baller, President

 

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