leaf-rolling caterpillars on my apple trees - UPDATE

[patandchickens]

My turn to ask for advice.

We have these 3 pathetic little apple trees we planted a few years ago. Every year they get horribly infested by leaf-rolling caterpillars (anyhow I am assuming they're caterpillars not sawfly larvae?) to the point of losing many of their leaves by September. The critters are pale green-bodied with a dark head, from 'tiny' to <1" long, and they fold/roll leaves longitudinally, secured with a light webbing of silk.

In past years I have tried manually removing (squishing) the bugs on every single darn leaf on each tree (ok the trees are shorter than I am so it was not THAT mammoth a task) but you know what they just come right back in a few weeks. Dunno whether it's from small ones that are missed, or ones that drop down to the ground then crawl back up, or new eggs hatching, but they do not stay gone despite my best efforts.

Needless to say these trees are not growing well and have not yet bloomed at all, but, what can I say, I have been busy doing other things, like having kids and chickens and repairing fences and so forth

So anyhow. The damned things are baaaaaaack, already tucked into the newly sprouting leaves. In LARGE numbers I have GOT to start doing something about this (or just give up on apples entirely). A quick google suggests that a Bt product is recommended (I will have to check and see if anything like that is even sold around here -- not everything in the US is available in Canada).

But, does anyone else have any suggestions, or experience to share?

Thanks,

Pat

 

[OaklandCityFarmer]

Judging from the description I would say it's the Fruittree leafroller Archips argyrospila something we have a big problem with here in California as well. The fact that you have this species (I'm hoping) and not one of the others is good because they only produce one to two generations per year, whereas, the Omnivorous leafroller can produce up to six! So I guess that would be a good question, do you notice them all year? I'm guessing in your climate they wouldn't have a chance really for more than one or two generations anyway.

Bt is probably the best route as far as sprays to go, however it's best applied when they are still in their larval stage and is only truly effective on the ones smaller than 1/2 inch. The caterpillars won't eat after the get bigger than that because they are beginning to get to the next stage. Also, it usually takes about 2-3 applications to really get rid of all the caterpillars.

A step for next year, leafrollers overwinter their eggs so this gives you some time to try and combat them before the emerge. Oil sprays (Neem, etc) seem to work really well on controlling egg populations normally you'd want to spray when the trees go dormant. Although this doesn't always work for a major infestation this does tend to level out the playing field when the larvae emerge. Then, you go back to the Bt applications.

Leafrollers do have some natural predators that tend to help in the battle as well. tachinid flies (specifically Erynnia tortricis) prey on the larvae and eggs of leafrollers. Anthemis tinctoria Golden marguerite, Melissa officinalis Lemon balm, Mentha pulegium Pennyroyal, Petroselinum crispum Parsley all work well in attracting tachinid flies. Lacewings also help. I'm not sure on you local population or if you can purchase them commercially but they are another step we take in Southern California. They usually help make more of a dent in their populations.

Leafrollers are really pesky and really mess up a lot of our trees if not controlled in time. Since they've already started to go into their next developmental stage they are much harder to get rid of. Be sure though to kill the newly laid eggs from the emerging moths. This will help control a lot more of the next infestation and the overwintering eggs.

Hope this helps.

-Carlos

 

[patandchickens]

Woooo! Thank you very much, Carlos! Couple followup questions:

So I guess that would be a good question, do you notice them all year? I'm guessing in your climate they wouldn't have a chance really for more than one or two generations anyway.

Yeah, 'all year' here means from mid may til mid september But yes, they're out there now, albeit quite tiny (considerably less than a centimeter) and they'll still be out there when the leaves start to drop in the fall.

Bt is probably the best route as far as sprays to go, however it's best applied when they are still in their larval stage and is only truly effective on the ones smaller than 1/2 inch. The caterpillars won't eat after the get bigger than that because they are beginning to get to the next stage. Also, it usually takes about 2-3 applications to really get rid of all the caterpillars.

So since mine are still <1/2", it probably is worth spraying, every week and a half or so maybe? I will be stopping at The Great Big Garden Center on monday (my fee for driving DH to airport for business trip <g>) and surely if anywhere in Ontario has Bt sprays, they will. Does it have to be labelled for fruit trees, or would it just be a generic plant spray thing? (Only Bt I've ever used is for mosquitoes)

A step for next year, leafrollers overwinter their eggs so this gives you some time to try and combat them before the emerge. Oil sprays (Neem, etc) seem to work really well on controlling egg populations normally you'd want to spray when the trees go dormant.

In the fall, you mean? Or like a early spring dormant-oil application?

Anthemis tinctoria Golden marguerite,

Hah, half my property is landscaped with Anthemis, seems like. I like it cuz it grows fast, blooms long and you can't kill it with a stick I am glad it may have some practical use.

Be sure though to kill the newly laid eggs from the emerging moths. This will help control a lot more of the next infestation and the overwintering eggs.

Okay, stupid question, where are the eggs laid, how do I recognize them, and what do I do to kill them? (And, is that the stage in which they overwinter? Are they overwintering on the trees, or in the debris on the ground, or what?)

Thanks VERY much,

Pat

 

[OaklandCityFarmer]

Pat, you've helped plenty folks on here, it's my pleasure to let you in on some of my own insight. If however confusing it can be sometimes.

So since mine are still <1/2", it probably is worth spraying, every week and a half or so maybe? I will be stopping at The Great Big Garden Center on monday (my fee for driving DH to airport for business trip <g>) and surely if anywhere in Ontario has Bt sprays, they will. Does it have to be labelled for fruit trees, or would it just be a generic plant spray thing? (Only Bt I've ever used is for mosquitoes)

Yes, I would think every 7-10 days would be fine. Bt var. kurstaki is the best recommended type for caterpillars. I think Safer actually sells one names Caterpillar Killer or something like that. They may have a brand of type that is meant for fruit trees, mainly you want to ensure that it is going to target caterpillars, which shouldn't be a problem since Bt generally only targets, mosquito larvae, caterpillars and beetle larvae.

In the fall, you mean? Or like a early spring dormant-oil application?

Yes, like an early spring dormant-oil application. Sorry for being confusing on that one.

Hah, half my property is landscaped with Anthemis, seems like. I like it cuz it grows fast, blooms long and you can't kill it with a stick smile I am glad it may have some practical use.

Wow, I'm picturing it now. Have you noticed any tachinid fly populations? Unfortunately, they're not available commercially or at least not from anywhere I know of. Lacewings are available commercially and do help a lot.

Okay, stupid question, where are the eggs laid, how do I recognize them, and what do I do to kill them? (And, is that the stage in which they overwinter? Are they overwintering on the trees, or in the debris on the ground, or what?)

Eggs are usually laid on the trees, mainly in the crotch areas. They are very tiny egg masses usually oval shaped and covered in a silky webbing. Yes, they overwinter in the egg stage. Usually after the moths emerge from the nicely rolled leaves, they fly around, lay more eggs and the process starts all over again. Usually by the second generation the eggs have to overwinter and emerge when temps start to rise again. The oil sprays in the spring usually do a good job of taking care of a lot of eggs and decrease the number of emerging caterpillars.

 

[Tutter]

I don't have this pest, and have not looked it up, but it seems to me that you could take a couple more precautions as well, which wouldn't hurt.

For example, could you rake and burn the litter from under the trees this year?

Also, what about something sticky for adult emergence. I'd have to read up on them, but I'd think yellow or white paper, or a ball. Even non-eating moths tend to get themselves stuck.

Too, you could wrap the base of the tree with a wide sticky-dealy. Some might fall and try to climb back up. I watch caterpillars fall from trees all through the early season, and they just go right back to what they were doing, as soon as they can.

Those, with your steps, might really make a difference, especially being this isn't a grove of large trees.

Just some thoughts...

 

[OaklandCityFarmer]

Tutter does make a good point as far as falling larvae and sticky traps, even though you may have a larger problem than the amount of sticky traps you could get. Controlling leaves and debris from around the trees wouldn't hurt although the leafrollers entire life is spent in the tree.

Another note to add, Bt is more effective when used in the evening because it breaksdown in sunlight more rapidly.

 

[patandchickens]

Carlos, I took your advice and got a BTK spray (after having to go thru several garden-center employees til I could find one who knew what I was talkinga bout, grrr, and point me to the last little bottle they had of it, cleverly hidden behind some mosquito fogging stuff )

I know it's supposed to take multiple sprays to get good control, and I *will* do that, but I wanted to report that a week after spraying (liberally) there are LOT fewer of the leafrolling caterpillars on the trees. Woo hoo! Thank you very much.

I have to be careful spraying one of the trees, though, because about 10' away is a big patch of Anaphalis (I forget the common name - pearly everlasting maybe?) that used to be in my flowerbeds til I discovered that its main role in life was to ranch up gazillions of Painted Lady Butterfly caterpillars. I moved it out to where I don't have to look at the carnage So I have to make sure the spray doesn't drift over there. Actually next time I should just throw a bedsheet over the anaphalis, that'd be simpler

So, thanks for putting me on the right track,

Pat

 

[OaklandCityFarmer]

Wow, that's great news!

Anaphalis is very pretty, I haven't seen much of it up here but when I used to live on the Central California Coast there was tons of it. I'm sure the caterpillars will be fine. Maybe a gentle spray of water to wash away any Bt that drifted over? Bedsheet would work fine I would think.

At least you've leveled the playing field now.

Pat 1 - Leaf Rollers 1

 

[Tutter]

I'm so glad to hear that you're getting somewhere with them. I hope that it continues to get better!