Questions not deserving of a whole thread


Hi Olpea,

I just bought a scale to measure small weights, i will actually measure the amount and see what it equates to volume wise.

The University of Kentucky recommends a lower dose:

Doesn’t mean the university is right.

I always mix a fresh batch, I am paranoid about spills, leakage. As far as resistance goes this is my first year spraying Imidan, so i don’t think I would be the culprit, unless resistance can happen after 3 to 4 sprays. There are no orchards close by, some of my neighbors have fruit trees but I seriously doubt they are spraying anything not available at Lowes or HomeDepot.

Thanks - Olpea!



They show a rate of 2.5 tablespoons of Imidan per gallon and you are using less than half that. Plus they are assuming 400 gal. per acre for a full dilute spray.

400 gal./acre is fine if you are spraying 25’+ tall apple trees, but for peach trees that’s waaaay too much for a full dilute. If I tried spraying peach trees with that much spray per acre, I’d have pesticide running down the terraces.

You’ll get all kinds of answers of how much it takes to spray to the point of run-off (full dilute) depending on tree size, but for peaches about 200 gal./acre is full dilute. I spray at 100 gal./acre and it gets the trees pretty wet.

If you are using a 200 gal.acre for full dilute, you would double the amount of pesticide per gallon (since you are spraying 1/2 the amount of spray per acre.

I’m not saying to double what the U of K shows, I haven’t run their calculations, but I would at least use what their table shows, 2.5 Tablespoons per gallon.


thanks Stan!


Hi Olpea,

I went back and reread the UKY doc again, it says 2.5 TSP - isn’t TSP Teaspoon? I have no problem using more, just want to make sure we are seeing the same thing :slight_smile: .



Oh yeah. I saw the capital T and thought they were talking about Tablespoons.

Let me look at their calculations and see how they arrive at that. I suspect they are low because they are using such high gallon rates.

If you think about it at a traditional 100 peach tree per acre planting, you’d have to spray each tree with 4 gallons at the 400 gallon/acre rate. That would be extremely wasteful. After the first two gallons, the rest would be just running on the ground.

I really think they are using old apple orchard numbers.

Of course you can always figure the square footage of your tree’s footprints and calculate that way, vs. gallonage/acre extrapolations, but they should be about the same.


Has anyone here ever grown peanut butter fruit? Ran across mention in a “weird fruit explorer” episode and piqued my interest. Bunchiosa argentea, native to South America, supposed to taste like pb&j. Found one at Logees and ordered it on a pure impulse buy, wondering if anybody has seen, tasted or grown this thing.



The labeled rate of Imidan 70W for peaches is 4.25 lbs/ac or 68 ounces/ac.

If you are using an equivalent of 200 gal./acre as a spray (if you are using a couple gallons of spray for a full sized peach tree, that’s probably the rate you are looking at) that equates to 0.34 ounces of Imidan/gal of spray.

According to U of K, a tsp of Imidan weighs 2.43 grams, which equates to 0.08571573 ounces/tsp. 0.34 ounces Imidan/gal divided by 0.08571573 ounces of imidan/tsp = 3.96 tsp/gal. of Imidan

Since you were using a Tablespoon/gal, that’s about 25% less. I don’t know if that would explain the total failure but it might.

Other than that, I’ve run out of ideas. I agree PC resistance is unlikely if there are no commercial orchards around. You might try the extra tsp of Imidan and see if that makes a difference.

I’m sure sorry you are having such a time with this. I know you have worked hard to get this fruit. Hate to hear it’s getting ruined.


@Olpea and @SpudDaddy I really enjoyed reading your exchange. Richard and I are in almost exactly the same boat and pretty much all of his answers could have been mine. One difference- and this could be a big one- is that I let 11 days pass between my sprays, and we had a pretty hard rain for a few hours during that time. So from what Mark said, my problem is probably caused by that simple explanation??? I had never heard you (Olpea) say that you spray every 7 days in the beginning. My goal has always been 10 day intervals, so it sounds like I need to do it more often, especially if it rains.

Like Richard, I always mix my imidan right before I use it, I always use a sticker (pinene II), I always use an acidifier (vinegar so far but planning to go to citric acid), and I use 1 Tablespoon per gallon- so it sounds like that could be an issue also. I got that right off Scott’s reference page, so it sounds like we really should change that?

Mark, i was a little surprised to hear you speculate that the problem could be resistance, even though later you said it was unlikely. I thought you have long felt that the chances of an insect population in a backayrd orchard developing a resistance to a spray was almost 0? But I guess in the case of me and Spud you are having to look for the unlikely since since he and I are otherwise pretty much doing the “right things”

Also, my problem is with my plums. I spray plums and peach at the same time with the same mixture. Only my white peaches and plums got hit hard, which is strange. Thanks for the help.



I think it’s nearly impossible for a backyard grower to cause a resistant strain of some insect population (like PC) simply because the numbers aren’t there. Someone spraying 100 acres of peach trees is 1000 times more likely to develop resistance than someone with a backyard orchard of 10 peach trees.

But, it’s possible for pockets of resistance to develop where there are commercial growers, and for those pockets to move (especially for flying insects, which are built for mobility). This has happened on a widespread scale with glyphosate resistant weeds (and weed seeds don’t fly as far as insects) and Topsin M resistant M. fructicola (brown rot fungus).

Spud mentioned there are no commercial orchards in his area, so PC resistance to Imidan seems less likely.

Really, you guys situation has me scratching my head. As I’ve mentioned, I’ve personally talked with several commercial growers who have used Imidan with good success (and we have plenty high PC pressure here).

Additionally, all the literature states it’s highly effective for PC. These would be controlled university field studies.

So, it’s really puzzling when I read that it’s being sprayed every seven days, water acidified, sticker, thorough coverage, and still not working for PC. I can’t put it all together, unless the rate is a bit low, which is having an effect, or there are some resistance issues. That’s my thought process anyway.

In terms of the rate, if someone were spraying large backyard apple trees, the rate U of K uses would be about right (if extrapolated to an old commercial apple orchard). But again, for peaches, I think it’s a little low.

The most accurate way to figure the rate would be to determine the size of your planting footprint and then back that down from the per acreage rates on the label (i.e. if your planting is 1/10th of an acre, use 1/10th of the per acre amount of pesticide).

Sometimes that’s a little difficult to do for backyard growers who don’t have all their fruit tree plantings together. In that case the next best method is to figure it from gallonage/acre calculations, which I did above for peaches. It’s going to be different for stone fruits and pome fruits, since the labeled rates are going to be different. It’s also going to be different for the size of the trees (i.e. a 25’ tall apple tree is naturally going to take more spray over it’s footprint than an 8’ tall peach tree, so the apple tree wouldn’t receive as much of the pesticide per gallon in the spray mix).

When the EPA comes up with spray rates, a big part of the methodology is how much of the pesticide lands on a given land area. They are concerned about this for the obvious reasons of leaching, potential runoff, and other environmental issues. They are of course also interested in residue limits for the consumer, worker exposure, etc., which issues can be mostly addressed through PHI and REI.

So the most accurate way to stay true to the label would be to calculate the area of the backyard planting (if possible) then use the per acre rates to figure the amount of pesticide to use on the backyard planting. Beyond that, there are different rates for pomes and stones, and it gets a little dicey trying to account for the tree size variable, so it might be best as a general rule to stick with something close to the U of K rate because it would be difficult to account for individual tree sizes, figuring off gallonage/acre rates.

If you are interested in some of the EPA methodology of phosmet (Imidan) labeling here is a final decision on the re-registration of it. It discusses some the EPA’s “thinking” in how they come to labeling.

I’ve sort of forgotten all the particulars, but as I recall the EPA required re-registration of a lot of the old pesticides because these compounds were registered under “easier” restrictions with less testing. Phosmet was one of these, and so required to be re-registered under more testing.

Here is a more detailed paper on EPA methodology on the re-registration of phosmet, if interested.


Spider mites may be another story. Mine seem to select out for resistance in a matter of 1-2 yrs. I never spray the same material more than one yr. Then I rotate to other classes of pesticide for two yrs.


PC scars could have been there before you sprayed and began to show as the fruit got bigger and the scar healed, becoming more visible. Keep spraying Imidan and you won’t have worms, the scars will heal over.



I have thought about what could be wrong. The Brandt’s ph balancer could be the culprit. You are supposed to add the balancer until the water turns pink. It doesn’t take much, so i cannot exactly stop when it turns pick. Is it possible I am getting the PH to low (low number) by adding to much PH balancer?

I sprayed again today, first dry day since I have been home. Its hit and miss on the PC damage. The pattern seems to be that the larger peaches were spared. The hardest hit was the Elberta which again is so odd because I drenched it right before I left. But it is not a 100% hit rate on the PC, plus maybe i will get lucky and Imidan will catch the larvae in time to save the peach. So far no peaches have dropped.

I tried the higher dose today. I am hoping I am at the end of PC season, @scottfsmith mentioned that he stops spraying at the end of May, Scott is same zone but further North… My first peach will be Desiree and that should come in around June 24th (per an orchard 30 miles NW of me that has that variety). I think you have to stop spraying 14 days before picking and I will play it safe so June 1st will be my last spray on that tree. Likely will wind down on the other trees at the same time unless I start seeing more hits.

Thanks Olpea and everyone else for the help.


I made an observation that when peaches have a heavy load and the branches are stressed, that after harvest the tree seems to need time to repair it’s branches, and has very little new wood growth, thus the next year peaches are light as the new wood growth was stunted from the damage of carrying a heavy load.They only produce on new wood (meaning 1 year wood) So thin correctly, and you can avoid this biannual thing on peaches. Take note of new wood growth. Don’t prune it all out either! Don’t prune late in season, do your pruning after harvest. If late harvest prune before harvest.



I don’t think it’s likely you are getting the pH too low. Everything I read about phosmet suggests the more acidic the water the longer the half life. Perhaps at some point the pH could become so low acid hydrolysis could occur, but I think at that point you’d burn the foliage off the trees. Note that some pesticides are subject to acid hydrolysis, but phosmet doesn’t appear to be one of them.

If you look at this link and scroll down toward the bottom on Table 4, you can see the curve of hydrolytic behavior of phosmet. It’s more stable the lower the pH, even down to 2 pH.


Do you think there’s time for a tree to grow new fruiting wood for the next year after harvest?


In some cases no. I still need more experience. It seems when a tree is growing fine and not stressed it produces plenty of new wood no matter when you prune. If you leave 1/3 and you should do that, it still has wood to fruit on. Peaches are a challenge to me as I don’t want to keep letting the tree get bigger and bigger so renewal pruning is essential for new fruiting wood, and to keep tree at a reasonable height. The trees tend to lose buds on older wood. I have been grafting a lot of cultivars on my tree, and my goal is for these grafts to become new scaffolds, and I’ll cut the old ones slowly out. So I may have a year where I have little fruit waiting for the grafts to get bigger. that should though renew the tree very well.


Those are the sorts of problems I’ve been having with my Flavor Delight - Alan suggested I need to cut out lower branches that aren’t producing, but I’m wondering if there’s time to do this after harvest [FD bears early] and still get new bearing wood.


It looks like I missed most of this discussion … one thing I would add is I often had problems of damage from BEFORE I even put on my first spray. By the time the fruit are yellowing and dropping you are 2-3 weeks from the original egg laying event. The kickback is much less if its raining a lot, so you need to be putting it down just before optimal egg laying – kill them just as they start to get into the canopy. Anyway, this may not be your problem but it is easy to under-estimate how long ago the damage occurred. For this reason I am constantly monitoring for PC bites and dating their freshness based on how healed over the crescent is.

This year I was super good on hitting the apricots and plums right after petal fall and I have almost no PC damage on any of them. The apples it rained too much during their somewhat later petal fall and I got some damage. This is with Surround.


This discussion about the failure of my imidan (and Spud’s) has been interesting. I think mine may be less perplexing than Richard’s, though. I think I went 12 days without spraying and we had a pretty good amount of rain during that period.

I am 90% sure, however, that my PC damage wasn’t pre-spray because I added imidan to all my sprays- even my late oil and copper spray at bud swell. I also check my fruit religiously and feel I would have seen the scars within a day or so of appearing.

thanks everyone.


Scott, What you described - fruit dropping before you spray was me last year. Last year I did not know what PC was. This year I sprayed right after I saw the first strikes. I admire the fact that you use Surround and are successful with it - I will eventually get there (trying Surround). I have 50lbs sitting in my basement that I had intended to try on some of my trees this year, but that didn’t happen. Thanks for all of the help.

Spud - AKA Richard S…