What’s Happening Here?
I’d like to start the newsletter off with an all too familiar diagnostic challenge. As a past consultant and current grower, it’s an issue or topic that comes up nearly every spring or summer. Having said that, I think this challenge should be fairly simple. Take a look:
The image above should be all you need to diagnose this problem. However, if you need a couple of clues that should solidify your answer, here they are. The plant is asclepias and the spot on the leaf is smaller than what you’d usually expect. I’m afraid that if I say much more, I’ll be giving away the answer if I haven’t already done so. With that being said, the time has come for me to ask, ‘What’s happening here?’
Stay tuned, I’ll reveal the answer after you enjoy these next few articles.
Triple Crown of Horticulture
Perhaps for the first time in the history of horticulture, a plant will be promoted in unison by three major industry non-profit organizations. This phenomenon is being referred to as the “Triple Crown of Horticulture.” Which plant has this distinct honor? It’s the ever so popular and well deserving Rudbeckia.
Rudbeckia American Goldrush
In no particular order, the three accolades, or crowns, rudbeckia received are:
There you have it; rudbeckia is the first horticulture triple crown winner. Sure, I love rudbeckia and have a few in the landscape, but more importantly I wanted to share this with you so you could position your product offering accordingly and take advantage of all the additional press, aka free advertising, rudbeckia will be receiving in the upcoming year.
More Royalty
After talking about the first ever prestigious triple crown of horticulture above, I remembered another royal plant I wanted to pass along.
Agastache Royal Raspberry is a recent Proven Winners introduction. With its colorful flowers, great garden performance and cold hardiness (to Zone 5), this great new hummingbird mint, aka anise hyssop, is definitely a worthy candidate for growers, garden centers and landscapers. Royal Raspberry has rosy purple flowers with burgundy calyxes that easily cover the top two-thirds of the plant. It’s super easy to grow and invites lots of pollinators, including butterflies and hummingbirds, into the garden. It would be a great honor to grow and sell Royal Raspberry.
The Answer Is…
I shared this image at the top of the newsletter and asked you to put your diagnostic skills to the test. I only gave two clues, but they should have given away the answer. They were: 1) the plant is asclepias and 2) the spot on the leaf is smaller than what you’d usually expect. Were these clues helpful and were you able to diagnose this issue? Before I reveal the answer, why don’t I show you how this problem usually appears?
Aha, there it is. I just imagined many of you locking in your final answer. If you answered aphids, you correctly solved the challenged and earned yourself a gold star. If you answered oleander aphids (Aphis nerii) you earned two gold stars.
I hope I have enough, grab your stars before you move on.
Management Options
Masses of Monarch butterflies form after they migrate to their overwintering locations in Mexico each year.
The main concern with managing aphids on asclepias is to do it in such a manner that it doesn’t have a negative impact on Monarch butterfly (
Danaus plexippus) caterpillars. As I’m sure you’re already aware, Monarch butterflies who make an incredible migration to their overwintering locations in Mexico and back again in the spring are now classified as “Endangered” by the
International Union for Conservation of Nature (IUCN). Milkweeds (asclepias) are the only food source of the monarchs’ distinctively striped larvae (caterpillars).
A monarch caterpillar feeds on common milkweed, Asclepias syriaca. Milkweed plants, primarily from the genus Asclepias, are the only food source of monarch caterpillars. Photo by Peggy Greb.
To aid with the preservation and survival of monarchs for future generations to enjoy, I urge you to avoid the temptation to control any pests (aphids, thrips and mites) on asclepias using traditional chemistries that may harm them. This includes avoiding the use of systemic neonicotinoids often used by growers to control aphids.
Consider using biological control agents (BCAs) for controlling insects or mites when possible. Aphidius and Aphidoletes for controlling aphids. Amblyseius (Neoseiulus) cucumeris, A. swirskii, Steinernema feltiae, Atheta (Dalotia) coriaria, Hypoaspis mites and Orius insidiosus for controlling thrips and Amblyseius cucumeris and Phytoseilus persimilis for controlling spider mites. Biopesticides such as those containing Beauveria bassiana and Paecilomyces can be used to control aphids and thrips.
I recommend avoiding the use of broad spectrum insecticides and miticides on asclepias altogether, particularly if they control lepidopterans (butterfly and moth larvae). There are several insecticides that are specific to aphids and other soft bodied insects that are perfectly safe and do not harm monarch butterfly larvae. They are Altus, Aria, Endeavor, Kontos and Ventigra. Each of these products will provide several weeks of aphid control when applied as sprays (best when applied preventatively).
Thanks for reading this edition of Perennial Pulse. My email is paul@opelgrowers.com if you have any comments, article suggestions or if you'd just like to say hello.
Paul Pilon
Editor-at-Large—Perennial Pulse
Director of Growing—Opel Growers
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