It’s that time of the year–although in the garden, as soon as there is green, any time of the year is time for insects.
One thing I am always sure to talk about when I lecture is insect life cycle. Many insects in my part of the country can simply be ignored. This may not be possible in warmer parts of the country where ignoring an infestation just permits continuing infestations.
But in my cold climate, most insects only have the ability to have one life cycle–or one chance to breed, reproduce, chew and die.
If I had to worry about repeated infestations, I would surely have to be more proactive.
So when I see these rose sawfly larva on my rose leaves, I know that they are going to disfigure the leaves and then they will pupate and become the tiny wasp-like insects that they turn into and fly away and that will be that.
You can see the little larva here on the leaf. While it looks like a caterpillar, it’s not: it’s a sawfly larva. Why am I making this distinction? Because I could spray bT all day on this and it would have no effect. BT only affects caterpillars. Know your insects.
It’s the same with the hydrangea leaftier. Most years they are so minor that I just ignore them completely. If an infestation seems to be getting out of hand, I cut them off, bag them up and they’re gone. That solves the problem for several years. The moth that this caterpillar becomes is an unremarkable tan and brown–nothing worth writing home about and certainly nothing worth poisoning a plant or the earth over!
But the point about both of these insects is that their caterpillar stages are relatively short-lived. True, the rose sawfly can cause quite a lot of leaf disfigurement in a short period of time, particularly if you can’t tolerate that look.
But I will repeat: is it worth poisoning your earth, your plants and possibly yourself over? Catch it early and the sawflies succumb nicely to being sprayed off with a hose. If you need something stronger, some insecticidal soap or a great OMRI registered product called Rose Pharm works.
But I’d never resort to anything stronger than that. And even then, because those products will affect the pollinators, I would be extremely careful with them.
Gardendaze 
Although I have no problem using (most) synthetic pesticides, I find that it is only rarely necessary. We must maintain many acres of landscape here, but have not used any pesticides in years. We needed to trap wasps, only because they were a problem in an area with significant traffic. Thrip damages foliage on the rhododendrons, but only because they had been so overgrown. Now that they are thinned out and groomed, I expect thrip to be less of a problem. No one mind that they are there, as long as they do not become a problem.
I am so glad to hear you say that. I had a California master gardener insist to me once that not only did she HAVE to use chemicals to battle aphids, but that I had no idea what I was talking about because I didn’t live in her climate. No, I didn’t. And while I really didn’t want to get into an argument in a social setting, that sounded fairly ridiculous even then.
Karla
I was in the park yesterday. I looked up at the oak leaves. They were like swiss cheese and the tree was just fine. Now this is not always the case. Some infestations do harm the plants. It takes some experience and judgement knowing when to treat and how to treat. And sometimes how to treat means planting for beneficial insects.
You’ll notice that I said very clearly in my post ” know your insects. ” Of course there are bad insects that harm plants. But it is still worth knowing the insect and the life cycle.
After all, just because a tomato hornworm is a caterpillar, and most caterpillars are benign where I live, don’t think that I will just let it chomp my tomato plantings into oblivion.
But luckily, those I can still hand pick. The “swiss cheese ” issue on the oak tree would not have been like that.
Karla