milkweed leaf ozone damage

[deunson]

When milkweed leave display damage of ground-level ozone (black spots on the upper surface of leaves), do the leaves become inedible to monarch caterpillars? (I'm working on an environmental curriculum for elementary school students.)

[Pat]

Just curious: ground-level ozone, where does that come from? How much does it take to damage a plant? I only notice ozone in the air when there are thunderstorms or if my laser printer's been working overtime, but I've never noticed black spots on the plants I keep indoors near the printer. Also isn't ozone a pretty strong oxidant, wouldn't it bleach a spot instead of turning it black?

I get black spots on some of my leaves but they seem to be caused by a mold, it's been hopelessly humid here this summer. In general my cats eat around the less-than-delectable spots no matter what the cause of the damage, or they move to a newer leaf. I have noticed that the females will lay eggs on some really crummy leaves even when relatively perfect ones are available nearby, though.

[deunson]

The following website will give you some information about ozone damage to milkweed leaves. Ground level ozone is caused by auto emissions, factory pollution and other human activities and it is harmful to animals (incl humans) and plants.

http://www.dnr.state.wi.us/org/caer/ce/ ... windex.htm

[Keith Petrosky]

Yeah almost all of the milkweed by me get that way when almost full grown. And with all the plowing and garbage being dupmed here, that could explain why I see little or no caterpillars.

[Pat]

Hmmm... I don't recognize that type of black spotty look; I guess we don't have much of that kind of damage here. But we're on a small, little-used street. I can't imagine my caterpillars eating that stuff, though, although I wouldn't feed a leaf that looked like that to them anyway.

Keith, are they spraying for West Nile in your area? I've heard that parts of LI are getting sprayed practically every day. I'd be surprised if all the mosquito spraying wasn't affecting the other insect life as well. I thought our season was going to be pretty lousy since we had practically no monarchs in May or June, but in the last couple of weeks things have picked up nicely and I've been getting a dozen or more eggs a day (finally!).

Pat

[Keith Petrosky]

Yeah every year they do spray for it. I guess the chemicals affect the milkweed which in turn affects the monarchs.