Question
QUESTION: Our pear tree's leaves are rolling up.  Our neighbor says it is a bug.  They have been curled for a while and now there is a few holes in the side edges of the leaves.  Is there any way to kill the bugs without chemicals?.  I thought some tangle foot around the trunk might help keep bugs from going into soil for the winter.  Any ideas would be greatly appreciated.  You have helped me out before.   Jo Anne

ANSWER: Leaf curl has a number of causes, but the holes point to insects -- mostly likely "Apple Aphids".

Dysaphis plantaginea -- 'Rosy Apple Aphids' -- are common beasts around Pears and other ornamental trees all over the world.  France's INRA, an agricultural research organization, posts a page about it:

www.inra.fr/internet/Produits/HYPPZ/RAVAGEUR/6dyspla.htm

Summers are spent munching on the leaves of English Plantain, Plantago lanceolata.  According to INRA scientists, adults lay eggs during fall on branches or snuggled under layers of bark.  Eggs hatch, and out swarm hundreds of hungry parasites ready to gorge themselves.  By the time Summer rolls around, populations can grow out of control, completing an entire life cycle in just 7 days.  The curling leaves protect the Aphids.  They are dispersed by the wind.

Besides curling leaves, enzymes in their saliva corrode developing cells, make branches twist and contort; they interfere with fruit development, and eventually destroy the entire tree.

By July. they descend on the unlucky Plaintains, where they spend the rest of the season.

Broad spectrum pesticides -- even those that are organic -- may do more harm than good because they elminate natural predators from the scene.  Once the Aphids have recovered, they return, unchecked.

The Utah State University extension posts everything you need to know that isn't posted by the French about this nasty little bug:

extension.usu.edu/files/publications/Insects%2013%20apple%20aphids.pdf

Pay close attention to the timing of any horticultural oils you apply.  As they point out, you don't want to end up wiping out beneficial insects at their height of activity.  But you'll do that if you spray right now.

I can tell you that Aphids are a favorite food of Ladybugs and various other easy-to-buy beneficial insects.  Diligent treatment is quite effective, in my opinion, often more effective than pesticides that tend to kill everything and everyone.

It is a little more of a challenge, intellectually.  You have to think.  Many people have a problem with that.  We've gotten so used to the Spray-and-Wash, Nice-n-Easy lifestyle that the thought of having to calculate the application of a non-toxic Aphid killer can be overwhelming.  Don't let that scare you.  This is easier than installing Microsoft Word for your computer.

But it depends on where you live.  My answer to you in Maine would be different from my answer to you in Texas, or Turin, or Buenas Aires.

That said, keep these under control.  Just don't go crazy.

L.I.G.








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

QUESTION: L.I.G.  Thank you for your reply.  I forgot to mention in my question that I did not see any bugs.  The leaves have been rolled all summer, bug holes appeared recently, only a few holes.  We picked off small catapillars in the spring.  I think your answer still applies, but just in case additional information is needed.  I will send for ladybugs at any rate.  JoAnne

Answer
Full grown adult Dysaphis plantaginea is a wee 2.5 millimeters long -- that's just under one-tenth of an inch.  You can see them, but you have to look hard.  These are not caterpiller size.  They're a little smaller than one of those little notches on the side of a ruler.

Holes in the leaves are insects out for dinner.  It does not sound like you have a serious problem, to be honest, but it could develop into one if you do the wrong thing -- or if you do nothing.  Damage control is the answer.

See any of these out in the yard?

www.discoverlife.org/mp/20q?search=Plantago+lanceolata

That's their second most favorite item on the menu, Plantago lanceolata.  These September days, the grownup insects that have been Summering around Plantago are busy closing shop, putting on a set of wings, and heading over to the nearest apple or pear tree.  Once there, say INRA experts, they'll lay eggs:

"Winter eggs are deposited in Autumn at the base of [tree] buds or under bark.  Each hatches when buds swell to produce a fundatrix which gives birth parthenogenetically to about 70 apterous virginoparae.  Dense colonies develop on the underside of leaves or on twigs..."

The "dense colonies" are easier to see than random specks less than a tenth of an inch long.  Watch for them in the spring.  Here's how they describe it (in clearer English) at the Atlantic Canadian Organic Regional Network (AcornOrganic):

'Female rosy apple aphids lay oval shaped black eggs on the bark of apple trees in the fall. The eggs hatch in the spring at around the same time that tree buds begin to open. The emerging pink and purple nymphs will feed on the buds and leaves...'

More where that came from:

www.acornorganic.org/cgi-bin/organopedia/insectdisplay?389

To control these pests: 'Syrphids, Lady Beetles and Lacewings are the primary predators...  Syrphids in particular will kill 20 or more aphids per day.'

What are Syrphids?  Here's one:

bugyou.blogspot.com/2006/05/syrphids.html

And we should give credit to Vanessa Cardui in California.  Vanessa describes the Syrphids' work:

'...These plants were literally dripping with Aphids which were dropping off wholesale in response to my messing with their flower stalk.  I always wonder how long it takes 'em to climb back to the top where they like to feed.  Anyway, it's the smell of a happy, productive aphid colony that guides the female Syrphid Fly to good Aphidy spots to lay her eggs...'

I just love the way Mother Nature works.

L.I.G.