Horticultural oil

8 years ago

Has anyone used this before and can give me advice? Last year, I had some bug, probably sawfly, eating the leaves of one of my roses. I was wondering if I can spray them now before they leaf out using this oil. I've never used it before. Any advice is appreciated.

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rifis (zone 6b-7a NJ)

8 years ago

From Missouri Botanical Garden:

Sawfly larvae feed on the surface of leaves of their respective host plant, removing the soft tissue leaving behind the papery, translucent surface and veins. Heavy defoliation gives plants a brown scorched appearance. In general, light to moderate infestations are cosmetic in nature and rarely harm the host plant. Heavier attacks, however, can weaken plants when leaf loss stresses them to the point of vulnerability to other insect and disease attacks

Rose sawfly: Adult sawflies emerge in early spring and lay their eggs on the underside of host plant leaves. Larvae appear several weeks later, feed on soft leaf tissue for about a month, and then drop into the soil to pupate. European roseslug sawfly (Endelomyia aethiops) produces only one generation per year, but another related species, the bristly roseslug sawfly (Cladius difformis), can produce two to six generations per year. A third species, the curled roseslug sawfly (Allantus cinctus) generally produces two generations per year. The three species are all similar in color (light green), but are easily distinguished: bristly roseslug sawflies have bristle-like hairs covering the body, and curled roseslug sawflies curl up the body when at rest.

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Comments (6)

gardengal48 (PNW Z8/9)
8 years ago
It is not a preventative for insect control....it is only effective when the insects (or their eggs/larvae) are present.
bella rosa
Original Author
8 years ago
Oh, ok. Thanks.
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Vaporvac Z6-OhioRiverValley
8 years ago
Since I have bare landscape fabric for midge in place, I'm anxious to see if this will prevent the terrible sawfly infestation I had last year.
rifis (zone 6b-7a NJ)
8 years ago
vaporvac: I'm interested to hear how the fabric does for midge (and sawfly). Please let us know. I realize it may be later this summer before you can conclude anything about midge.
Vaporvac Z6-OhioRiverValley
8 years ago
last modified: 8 years ago
rifs, sorry for the late reply. I already know that this works for midge as I tried it last year and experimented with it on different beds and potted plants. I also used plastic, but hope to "upgrade" it all to fabric.

During the heat of summer the effect was almost immediate as their life-cycle is so short then. There was no abatement in the beds I left bare, but again, very quick cessation once I put it there. I tried someone's suggestion of bare soil and that didn't work at all. Some people felt it did, but it was late in the season when they take three weeks vs. three days to complete their life-cycle, so I think that is really what was being seen, although they do seem to prefer wet soil. The potted roses I kept on the tile patio with their soil covered in fabric showed only 1 burnt tip all summer out of 15+ pots, whereas those I placed in the beds were just as infested as those already planted.

This is not 100% effective, as some must land on grass or out of the barrier to pupate and those can infect. However, over time the infection rate was effectively "0". I also read they can pupate IN THE ROSE, but I now wonder about that. My goal this year, after I apply manure, mulch, etc. is to get the fabric on everything to stop them emerging when the buds start. Granted, it's not the most attractive look, but only I see my roses and NOTHING thus far, was as bad as seeing zero roses as I had already missed the spring flush being out of town. I hope this year, I can remove the fabric if I see NO symptoms after the first flush. We'll see.

P.S. black plastic also worked and still let in sufficient water surprisingly. I didn't notice any baking of the soil, but mine was placed over mulch so that may be why.

P.S.S. I noticed the same thing with sawfly, but not to the same degree as they can actually fly further. We seem to get them all year so I'm hoping since everything will be covered from the get-go, I'll have better results. I was hand picking them, but that's not tenable with so many roses now.