Question
QUESTION: My petunias get small black spots on the leaves and the stems and leaves get very sticky.   I have the same problem every year.   What is it and how do I get rid of it?   Many thanks for your help.

ANSWER: Time again for the Annual Black Spots On The Petunias question.  

As you may have guessed, this is a common problem with several possible causes.

1. Hornworm Caterpillar Moth Larvae are WILD about Petunia leaves and flowers.  If those 'black dots' don't move, they might be the droppings of said caterpiller.  Female Moths follow the night fragrance of Petunias, then lay eggs over the leaves.  The eggs are pale green or yellow, and very small.

2. Tiny black insects called 'Potato Flea Beetles' ('Epitrix cucumeris' to botanists) may be another cause.  How big are these 'spots'?  Epitrix can measure anywhere from the size of the period at the end of this sentence to a 1/8th inch at maturity.

They hop from leaf to leaf, plant to plant, using their superpowered back legs.  Days are spent chewing holes in the leaves of Tomatoes, Petunias and other garden plants.  

TINY Beetle. BIG appetite.

Adult female Beetles deposit eggs in the Soil at the base of the plant around now.  The larvae hatch in 10 days, and commence their work of devouring the plant roots.  When July comes along, they turn into adult Beetles.  There is a week's worth of information about this insect on the Connecticut Cooperative Extension website, which posts a cheat sheet on Petunias:

www.ct.gov/caes/cwp/view.asp?a=2823&q=377880

and on Potato Flea Beetles:

www.ct.gov/caes/cwp/view.asp?a=2815&q=376696

as well as some lovely photographs of damage to potato and tomato leaves suitable for framing at IPM Images:

www.ipmimages.org/browse/subimages.cfm?SUB=7477

Think you've got problems?  This bug drives potato and eggplant farmers CRAZY.  If you're growing Tomatoes this year, they're next.

University of California posts a closeup of one of these bugs, which they describe as measuring a mere '.065 inch' -- that's .65 HUNDREDTHS of an inch big.  Around the size of the period at the end of this sentence.

Although the Cornell University position suggests that this insect can be controlled by natural predators, the North Carolina State authorities maintain, 'There are no natural predators or parasites that can effectively control flea beetle populations.'

Any organic insecticidal soap will give these bugs a stomach ache they'll never forget.  Safer has a great line.  You can buy it at many garden centers and discounters.

Don't let this one go.  If this is those Beetles, they'll be back next year, bigger, stronger and hungrier.

THE LONG ISLAND GARDENER

---------- FOLLOW-UP ----------

QUESTION: From your response, I think I have the Hornworm Catapillar MOth as these black little balls do not move and they do NOT eat the leaves, but the petunias become very sticky.   Does the insecticidal soap work on the Moths as well as on the beetles or is something else needed for them?    regular flower insecticides do not work.  I have tried them.

Answer
The problem with bug killers -- and this includes organic bug killers -- is that they work on ALL bugs. The good, the bad, the ugly, none are spared.

But this is a judgment call and you do what you gotta do.  Insecticidal soap gets everything.  It won't kill birds, which is nice, and it won't give you any weird diseases, which is very nice, and it won't sicken your dog if s/he tastes a Petunia.

It won't hurt to expand your repertoire of earth-friendly bug killers.  So here's some home-made concoctions that are hazardous to Hornworms, collected by a Tomato grower who like you has had it up to here with the winged wildebeasts:

www.ehow.com/how_5086628_make-worm-repellants-tomato-plants.html

And here's a little bedside reading about your Hornworm, courtesy U Mass at Amherst's Coop Extension website:

www.umassvegetable.org/soil_crop_pest_mgt/insect_mgt/tomato_hornworm.html

The U Mass people point out, 'The moths are commonly seen at dusk, hovering hummingbird-like over beds of Petunias and other flowers with long corollas. Nectar is extracted through their long, coiled, tube-like mouthparts.'

Tonight, as the sun goes down, head over to the Petunia Patch and see if you can catch any of them red-handed.  Then get back to me.

Now, given that I am anti-insecticide, generally, you might wonder what I would do instead.  After all, even the U Mass people recommend you take it easy with the bug killer: 'Use a selective material that will conserve beneficial insects, because those predators and parasites are very likely keeping your aphid populations under control.'  The wrong bug killer can do more harm than good, facilitating an epidemic of aphids, for instance, that will make you WISH you had only the Hornworms to deal with.

This is where IPM -- integrated pest management -- comes in.  Fighting fire with fire. Good Bugs.

U Mass recommends Bacillus thuringiensis (Bt), but you must use the kurstaki or aizawi strain (sold as 'Dipel DF', Agree' and  'Xen Tari', among other brands, they note), indoxycarb (aka 'Avaunt' tebufenozide ('Confirm 2F')or spinosad ('pinTor 2SC'or 'ntrust').  Not all these bug killers are registered for use in all states, so you will have to find out the one(s) you can obtain locally.  (If you had supplied a location, I would have been able to give you better information.)  Valent, which makes Xen Tari, posts a zipcode box for identifying retailers near you:

www.valent.com/agriculture/products/xentari/index.cfm

Bt is VERY earth friendly, and so easy to use.  Be the first on your block.

Thanks for writing.  Keep me posted,

THE LONG ISLAND GARDENER