July 5, 2015
The Garden Chronicles
A monthly newsletter from the California School of Garden Design

ISSUE
No. 29






Green Leaf Volatiles
How a Plant Deals with Pests 


 

I was recently visiting a new design project I'm working on in the Sacramento area when I noticed a familiar plant growing wild amidst star thistle and some sparse grasses.  The flowers were just closing - this is typically a night-blooming species - but the tubular flowers are quite distinctive and that's what caught my eye.

 

I took a few photos and gathered some seed from ripe pods and went on with my work for the morning. 

 

I knew the plant was in the genus Nicotiana and once back at the office it didn't take long to identify which species it was.  What I stumbled on was Nicotiana attenuata, the common name being coyote tobacco.  A sparse, glandular (sticky) herb growing up to 3 feet tall or taller, it is native throughout western North America from Mexico to British Columbia.

 

It's not a particularly showy plant, still it has some interesting attributes and is a master at IPM - Integrated Pest Management.  

 

And thus, the story begins....

 

Like all plants that depend on insects and other animals for pollination there is the need to be able to protect yourself from being eaten by herbivores - after all, being a plant you can't run away!  In many cases these herbivores are insect larvae - caterpillars - that are interested in munching your leaves and stems.  In the case of coyote tobacco the problem is compounded since the main pollinator is also the adult version of the main predator!  

 

Most plants, in the pursuit of survival, are in some manner or way poisonous. And  

Nicotiana is poisonous - nicotine (that nasty stuff in cigarettes) is a potent alkaloid that affects muscles and is found in the nightshade family (neonicatinoids are thought to be at least partially responsible for Colony Collapse Disorder in bees - thank Bayer for this!)). Nicotine is made in the roots and is transported and accumulates in the leaves of the plant. In the case of Nicotiana attenuata, the concentration can be up to three times the value found in common tobacco, Nicotiana tabacum, and it is so efficient in paralyzing or killing insects that it was once widely used as an insecticide.  In this way, coyote tobacco keeps a lot potential predators away. But not all of them ...  

 

Enter the moth (stage left)  

 

Nicotiana blooms at night when there aren't many other pollinators around, so this is a perfect host for two species of hawkmoth that act as the main pollinators.  These two moths, Manduca quinquemaculata and Manduca sexta (the tomato hawkmoth and the tobacco hawkmoth, respectively) ensure the survival of the species.  However, as any of us who grow tomatoes knows, the tomato hornworm caterpillar  is a voracious feeder and can do a lot of damage in a short amount of time.  

 

 

And so it does to our coyote tobacco.  So, what's a plant to do?

 

Like all plants when under attack by herbivores, Nicotiana emits volatile compounds into the air known as green leaf volatiles.  These act as warning signals to other plants nearby - "Hey - I'm being eaten here!  Save yourselves!"  But they also act as a mayday signal -  

 

"Hey - I'm being eaten here - Would Somebody Help Me?!"   to insects that have learned to read these compounds as a dinner bell.

 

 

 

When tobacco hornworm caterpillars start munching on coyote tobacco, their saliva interacts with the green leaf volatiles and this causes a chemical change in these compounds. This new compound attracts bugs of the genus Geocoris, popularly known as big-eyed bugs, which prey on tomato and tobacco hornworm eggs and larvae.   

 

The parasitic wasp, of the genus Cotesia, has also learned to interpret these altered green leaf volatiles emitted by coyote tobacco as a sign for food for its own larvae. The Cotesia wasp lays her eggs in the bodies of hornworms. The wasp larvae feed internally (ouch!), and emerge from the body to spin their cocoons. Thereby, further damage to coyote plants is thus prevented by the predatory actions of these insects.

 

 

 

However, the predators may not be always nearby and ready to respond and when you consider that one single female hawkmoth can lay as many as 200 eggs and then multiply this by some dozens of nectar-addicted hawkmoths and you have doomsday for coyote tobacco plants. So to protect themselves even more, what if the plant was able to make the tobacco worms even yummier? Coyote tobacco is a hairy plant and some of those hairs, called trichomes, specialize in producing nectar. Now nectar is irresistible to most insects and tobacco worms are no exception. As with the fruit of the apple tree in the garden of Eden, this nectar comes with a price, smell. As tobacco worms feed on nectar they smell like nectar. So, for all of those predators that have not noticed the previous call, this one comes truly with flavor, a sweet and irresistible flavor of pure nectar. In the insect world these tobacco worms are walking desserts and therefore, hard to resist....

 

But there is one more arsenal for Nicotiana - what if all this is just not doing the job?  You're still getting eaten right and left?  The next trick in it's IPM bag of tricks is to stop the pollinators in their tracks by changing the bloom time of the Nicotiana flowers.  Yes, coyote tobacco will shift from being a moth-pollinated night blooming plant to being a hummingbird-pollinated day-blooming plant.  No moths, no caterpillars, no munching! What's really fascinating is that coyote tobacco takes all these measures and changes in only one year.  I think this is IPM at its best! Or at least a pretty good show!!

 

Our Lesson - encourage IPM.  Don't use insecticides (spray, systemic, etc.) that will kill off the parasitic good guys (insecticides don't care who they kill - insects, pets, children...). If you find a problem insect look at the conditions your plants are growing in - stress (lack of water, nutrients, good soil - all sorts of things cause stress, look at our own lives) and work to correct it.

 

Be a good steward of the land. 

 NEW!!

VIDEO LESSON OF THE MONTH

Starting this month I'll be presenting a series of videos on how to deal with different situations in the garden, covering many different topics.  None longer than 10 minutes and hopefully to the point.  I hope you enjoy them.

 

Have a comment or a topic you'd like covered?  Let me know and I'll do my best.

 

Replacing a Defective Irrigation Valve

 

 

 

 

 

 SUMMER FARE WITH FLAIR


 

It's mid-summer and either you're harvesting loads of zucchini squash or people are sneaking over and leaving it on your doorstep at night.  Either way, this is a great, easy summer recipe that will use squash and you'll have a flavorful, light dinner.  

 

 

 


 

Zucchini and Sun-dried Tomato Quiche

In summer we are always looking for ways to use up zucchini. Even if

you don't grow it, you can end up being given quite a bit by

other desperate gardeners. This quiche recipe is from a British cookbook called

"Easy Summer Food" (with a couple of my own tweaks), and it is delicious and very simple to prepare. It is a little bit different, in that it does not call for any cheese. You can make your own crust if you like, but we tend more often to purchase an organic frozen pie shell.

 

 


 


 

Ingredients:

 

1 deep dish pie shell, either made or from frozen

2 medium or 3 small zucchini, sliced diagonally (don't peel)

1 medium shallot, peeled and sliced fine

1-1/3 cup crème fraîche (or use sour cream)

2 whole eggs plus 2 egg yolks (Note: we sometimes use just 3 whole eggs)

Scattering of chopped sun-dried tomatoes in olive oil ( approx ¼ cup)

Olive oil for frying

Sea salt and freshly ground black pepper


 

 

Method:

 

Preheat oven and blind-bake the pie shell according to package instructions or if making

own pastry, preheat oven to 400̊ F and blind-bake for 10 minutes or until just cooked. Remove shell from oven and set aside. Reduce oven temp to 350̊ F.


 


 

 

Heat a little olive oil in a skillet and when hot, add the shallot and zucchini, in batches if necessary so that the squash cooks golden and does not simply steam in the pan. Stir and sauté as it cooks until tender. Meanwhile, in a metal or glass mixing bowl combine the crème fraîche or sour cream and the eggs and beat to mix. Season with salt and pepper.

 

When the shallot and zucchini are tender, put them directly into the pie shell and make sure they are distributed evenly in the shell. Scatter over the sun-dried tomato pieces, then pour over the egg mixture. Smooth with a spatula to spread it evenly.

 

Bake in the preheated oven for 30-35 minutes or until golden on top and set.

Serve it hot, warm or cold. It is quite nice for a brunch or picnic. We usually have it with an arugula salad on the side.

For something different, you can also add some chopped fresh basil to the quiche before adding the egg mixture.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What I'm Still Working On... 

 

I've been working steadily on my first book, "A Field Guide to the Conifers and Shrubs of Placer County, California

Ok, I'm way behind getting this out there, but I'm contracted with Booknook.biz to produce this.  Now it's up to me to finish. Anyone who's ever written a book will appreciate the efforts - this is my first book and boy, am I appreciating the efforts!  Still, I'm pushing forward. 

 

 

" Conifers of the Sierra Nevada Mountains - Interstate 80 - Applegate to Donner Summit" where you'll learn to identify the major species of pine, fir, hemlock, yew, juniper and California nutmeg along with major shrub species that are associated with them by taking a video tour, starting at 2,000 ft. elevation and finishing on top of Castle Peak at about 9,000 ft. elevation.  

 

 


And don't forget


Fundamentals of Garden Design is in the works and I hope to have this out by September.


So, as always, stay tuned and... 

 

 Thanks for reading!

Rob 

 

  rob@csgd.net

 





FOR THOSE IN THE AUBURN/SACRAMENTO AREA
(or those willing to travel!)


Saturday, July 18 is the annual Colfax Garden Club Garden Tour.    Seven private gardens will be open to the public and they all look wonderful, inspiring and well worth visiting on this self-guided tour.   Cost is $20 for adults, 12 and under free.
 For tickets and more information email 
ColfaxGardens@gmail.com
or call
Zee Baird at 530 - 389 - 7065