after 6 weeks of drought.. my lilacs were droopy ... are you watering them properly .. how long have they been planted??? dig a small hole near the plant.. and insure that water is making it to the root zone.. if not.. they are thirsty ...

webs is not enough info for a good idea of what is happening to them .. its spider time in august ... no need to do anything about those ...

NEVER spray a plant unless you see damage on the plant.. white flies could be from your soil or mulch and have nothing to do with the rubeckia .... please limit your spraying to problems that need it.. rubeckia are near bullet proof and i have never done anything with mine ... are you sure there really was a problem ...???

i wouldn't go digging stuff up in august for quarantine ... most likely the shock will kill it due to high summer heat ..

relax.. lilac and rubeckia are not plants that should need all that much care ...

good luck

and understand.. you aren't a true gardener.. until you have killed each plant three times .... both will probably be fine without anything other than good watering in august.. ken

Most likely the webbing you are seeing is from spider mites and hot, dry weather is to their benefit. The simplest means of control is to mist the lilac several times a day, or spray with an insecticidal soap every 5 to 7 days although that is not as effective as misting, simply increasing the humidity around the plant.

but do only mist them at a time that allows enough time to dry before darkness ... to avoid powdery mildew ... ken

Webbing could also be from plain old spiders. We need a picture or detailed description to sort out what sort of webbing you have.

Free water on plant leaves does not cause Powdery Mildew to appear or grow. But even knowing that most plant pathologists will tell you not to spray in the evening so your plants leaves will not be wet overnight. Over many years I have not seen any problem with plant diseases if there is rain in the evening and my plants leaves are wet from that rain overnight, but I have seen PM develop when there has been no rain (like now) in months.

Thank You for the follow up postings. The local garden store concurred: spider mites. (The leaves were actually pasted together by the cocoons) so I am treating the lilacs with insecticidal soap which has unstuck the leaves and halted the damage. Thank You to Ken for telling me to expect a few plant casualties along the way.

Still, it is not good news that rudbeckia are practicially indestructible because they are not thriving as I have seen them thrive in other gardens.

you didnt mention if the rubeckia was new this year ...

if so .. the plant could have brought the bugs with it ... ergo ... the plant may have been in a weakened state since you got it ...

though perennials give some instant gratification ... their beauty is they get better every year ... or die.. lol ... ergo .. i dont expect all that much the first year.. they are growing roots.. to live through winter.. to prosper next year ... and for years after ...

in the year of transplant.. everything BUT ANNUALS will NOT be what i call vigorous ...

and kimm .. of course the water doe NOT CAUSE the PM ... it provides a place for the floating spores to latch on ... if spores is the correct term ... as dylan [i think] said.. 'the PM is blowin in the wind' .... lol .. that is why there is a second suggestion of trying to increase air movement ... let them blow right on by.. instead of having some dead air and wet leaves to settle on ...

i mean really .. if you dont want a bunch of college drunks on your lawn .. dont leave the keg out there ....

by knowing the things that can cause the problem.. you can TRY to avoid the problem .. because we all know.. an ounce of prevention, is worth a pound of cure.. ok .. enough cliches for this post ...

good luck

ken

You wrote:
"The local garden store concurred: spider mites. (The leaves were actually pasted together by the cocoons) ..."

Sorry, but you need to find a more informed garden store. At the very least, please tell them the facts.

Mites don't paste leaves together with webs/cocoons.

Spiders will roll leaves with webs. And leafrollers will do the same, later pupating (cocoon) within that webbing.