The time to start controlling most caterpillars is during the winter by locating and destroying the egg cases that you can find, each insect has an egg case someplace. Then at leaf break when the eggs start to hatch apply Bacillus thuringiensis - Kurstaki sprays since it is only effective in the early stage of the larvas life. Later you will need more potent stuff maybe like Neem oil products.

Chantel, you can't get rid of aphids. Every garden has aphids. As long as you break up the heavy concentrations with soap spray or frequent squirts from the garden hose, they do no harm at all. Later in the season they will practically disappear.

The bacterial product mentioned by kimmsr is commonly known as BT and sold as DiPel or Thuricide. In my experience, it works on caterpillars of all sizes. It is harmless to everything but caterpillars. That's what you need.

Chantel asked this question a few years back, but I'm encountering the same problem now, and I'm also in Massachusetts.

Those pesky green worms have skeletonized all of my roses. I applied BT two nights ago, but it is raining now. Should I re-apply? Would too much of it hurt the rose bush?

Thanks!
TS

BTK is the insecticide of choice for such things as the Eastern, or Western, Tentworm Caterpillar and the Gypsy Moth Larva, both of which are around right now. It is too early for Japanese Beetle adults yet. If after you spray the BTK on your trees it rains you will need to spray again since the rain will wash it right off.

I realize this is a month late, but good to plan ahead for next year. The green worms were almost certainly winter moth larvae, which were out in full force in MA this year. This year I used Monterey Garden Spray, a spinosad product which is also organic but supposedly works better than Bt, and works even after it rains. I only applied it once via hose-end attachment, but my roses did so much better than last year--hardly any damage.

UMass has a good fact sheet on their website. Note the warning about dangers to honeybees. If you have a lot of early-flowering trees/plants nearby you should probably stick with Bt.
http://www.umassgreeninfo.org/

You are not only a month late but in reality about 5 years late on this.
The folks that review material for the Organic Materials Review Institute (OMRI) have serious reservations about Spinosad and do not believe it is a good substitute for any of the current, acceptable organic pesticides.

Here is a link that might be useful: OMRI on Spinosad

tulipsmiles....you need to identify your pest properly. There ARE green caterpillars that can be found munching on roses, but the most common culprit is the rose sawfly larvae. They cause the skeletonizing you mention.

Bt will have absolutely no effect on the sawfly larvae, and shouldn't be applied unless you have a targeted pest.

Kimmsr, the link you keep posting does not really support the intent of your statement. The OMRI board DOES support the use of Spinosad with organic practices and believes that it has a place in organic agriculture. However, there is still much research to be done regarding various USES.

It may turn out that spinosad loses some labeling for some uses, but maintains labeling for others. In the meantime, when used according to existing label directions, and with some plain common sense, it is a pretty good tool to have in the organic closet.