Spray effectiveness vs time to rain ?

garedneckJuly 10, 2011

Here is a list of insecticides and fungicides i have seen discussed here which are also readily available and wanted to get your input on how much time before it rains should these chemicals be applied to say be at least 90% effective? Also, if they should be applied in full sunlight or not? I generally spray early morning when the winds are calm.








lime sulfer

liquid copper

dormant oil

any other chemicals?

I assume every morning there is dew on the plants so if you spray in a day there is no rain then it should be 100% effective?

I guess it would be helpful to eventually put together a chart which outlines how effective these have been at manufacturers recommended concentration for fighting various pests and also spray regiments.

PS- anyone ever try just putting out those electric bug zappers instead of spray?

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Scott F Smith(6B/7A MD)

You are not asking a simple question. If the chemical is a protectant and you have no sticker and it is easily washed off, then even though it completely dries if it rains not long after it will not be effective -- your trees have no protectant from the moment the rain washed the chemical off. So, the first thing is to distinguish whether the spray is a protectant or an eradicant (or some of both). Dormant oil for example is an eradicant. The dormant oils used today usually completely vanish in a few days, so as long as it doesn't rain in a few days you get 100% effectiveness of the spray. Most of the effectiveness probably occurs in the first six hours since that will probably be enough time to smother any egg, so maybe even six hours is all that is needed for oil. Another dimension is whether it is systemic or not. Systemics are absorbed into the plant flesh and so they will still be effective after a rain. Also it depends on whether you use a sticker or not to hold the chemical onto the tree. When I lay down a protectant I almost always use some nufilm-17 which will triple or more how long some chemicals (sulphur and copper in particular) will stay on the tree and be effective. Surround is a protectant which sticks pretty well so you need a lot of rain to wash it all off. There is also a bit of a paradox that many disease protectants should be put on before it rains -- even though some will wash off, the rainy period is when diseases are likely to bloom and after the rain is over and things have dried up the disease can be cranking out badness and its too late. My guideline on those is I don't put them on right before a big downpour is forecast since an inch of rain will wash it all off. But in smaller amounts of rain it is best to put them on before the rain. Lime-sulphur penetrates the flesh so is partly systemic, and for that reason can eradicate some pre-existing diseases. It also has some activity as a protectant, but does not do as well as sulphur does for that. I don't use the other chemicals you list so I don't know the details of their behavior. Many chemicals do some of both protect and eradicate: any bug poison will eradicate what is there now, and as long as there is enough chemical still there it will sicken future visitors. But each poison varies greatly in how long it will be effective.

In terms of how long it takes for the chemical to completely dry, if it is not oil-based and it is sunny it can dry in as little as a few minutes. Oil-based sprays take somewhat longer to dry, but given how dilute they are I cannot imagine they would not be dry on a sunny day in a few hours (assuming there is no dew and not too high humidity). Note that "dry" is not like oil paint, its like those water-based paints your kids use: rain will cause them to un-dry, and all you can do is mitigate that a bit with a sticker.

Jellyman used to use bug zappers and I think Ace was also using them and also adding pheromone for a double attractant. My impression is they can help but will not solve the problem alone. Don took his down at some point, he said why but I forget.


    Bookmark   July 10, 2011 at 9:58AM
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alan haigh

That's a great answer Scott.

I would also say that significant rain is about 1". I sprayed several sites this season when it was drizzling a bit but was supposed to clear up. Instead it drizzled most of the day and then an evening downpour occurred. In total we got between a quarter and half an inch.

I consulted with a commercial grower I know and he said that even without setting that much rain shouldn't be a problem - as far as I can tell it wasn't. It was an Imidan, Captan, "Immunox" spray. I don't see how anything could have set as there was always water on the trees till the following day.

There is some literature on this subject but not much about how much things need to set before rain and how much rain washes off unset spray. For instance an inch of rain is supposed to wash off 50% of an Imidan application after set. If it's been a week since you spray this would probably mean inadequate protection but it is still affective with 50% removal shortly after application.

I've always considered an hour of good drying conditions enough for most chemicals- at least the fungicides and insecticides that are poison.

Hopefully Olpea will chime in as he has the links for some studies on the subject- I'm working from memory.

    Bookmark   July 10, 2011 at 10:59AM
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olpea(zone 6 KS)

As Hman mentioned, there's a lot more info. that has come out in the last few years regarding wash-off potential of pesticides.

The link below discusses rainfastness of several insecticides after they have dried.

In a nutshell, effectiveness of a pesticide after a rain depends on:

1. As Scott mentions, the penetrative ability of the pesticide.

2. The lethality index of the pesticide to the target pest. Imidan washes off easily, but is highly lethal to target pests, so is still effective after significant rain, even though there may be a significant reduction in residue left on the plant surfaces.

3. The compounds residual life under field conditions. This reason was omitted in the linked article, but a recent article in a trade magazine addressed it. According to the article, "UV degradation of surface residues and plant metabolism will gradually reduce the activity of insecticides. Rainfall events occurring near the end of a compound's residual life will be at greater risk to plant protection than if occurring in the first days after a spray. (emphasis added)"

4. The amount of rain received from a precipitation event.

As to your specific pesticides, only Imidan, Triazicide, and Malathion are on the list below.

You can look at the charts to see where they fall. Triazicide is a pyrethroid. Malathion is an organophosphate like Imidan. However, Malathion is much less toxic to target pests than Imidan, plus it breaks down faster, so would need reapplication sooner.

All this research is based on applying the compounds without a sticker. As Scott mentions, a sticker helps considerably against wash-off, and can help against UV degradation (i.e. Nufilm).

Regarding your Captan, I once read that field tests showed Captan applied before a heavy rain >1" would still protect against apple scab, even though almost all the fungicide had been washed off. Apparently despite the fact the compound was removed because of rain, it did it's intended job (protecting fruit and foliage) in the process.

The only thing I would add in terms of recommended drying time of an insecticide is that some systemic compounds continue to penetrate plant tissue even after they are dry, so supposedly they continue to benefit from longer drying times, even though the compound is already dry.

For some compounds (i.e. Imidan, Captan, Surround) the spray solution leaves a visible film on the plant surfaces, so you can somewhat gauge the amount of pesticide residue after a rain.

Here is a link that might be useful: Rainfast characteristics of insecticides

    Bookmark   July 10, 2011 at 10:26PM
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alan haigh

These are the kinds of discussions that I find so rewarding here. Scott and Olpea, have you encountered any info about the specific advantages of spreader stickers as tested after rainfall? Or their actual affect on breakdown from sun?

When I began this business I asked my trusty 2nd generation commercial grower if he used them and he said "only when the label calls for it".

In spite of this, in recent years I always mix a generous amount of Nufilm in every spray but wonder if I'm wasting time and money. The only material I use that the label calls for a spreader-sticker is Indar and I'm not even sure if the new label and formulation calls for an SS.

Michael Phillips touts them for sticking sulfur but what about Rally, Imidan and other synthetic formulations?

If a spreader sticker made a measurable difference wouldn't Cornell guidelines recommend their use? Greater efficacy would mean the need to use less pesticide which is the whole point of IPM. Indar is the only substance where I've read of them recommending an SS.

    Bookmark   July 11, 2011 at 6:30AM
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Scott F Smith(6B/7A MD)

I am also not sure when the sticker helps. One of my oil labels (Stylet oil) recommends not to use Nufilm with it so I generally do not use a sticker with oil. I also put oil in a lot of sprays, for example this time of year spinosad/oil is my standard anti-moth spray, and since there is oil I do not add a sticker to that. I do know that for dormant copper a big blob of nufilm keeps that blue look on the trees for months and I like that a lot. The whole idea is to let a little come off in each rain. Similarly, I can smell the sulphur weeks later sometimes if I used a lot of Nufilm. You ask a good question about their effectiveness vs UV degradation. I just looked and found two studies, both of which showed Nufilm had zero (!) effect on improving lifetime. Hmm. Look at the 4th and 7th hits from this search.

Olpea, you add two other dimensions I forgot to list, UV and lethality. If you put together the dimensions of rainfastness, lethality on each pest, residual life (UV degradation), degree of systemic action, and the preventative vs eradicative you can get a pretty good profile of the each chemical. I personally spend a lot of time working on refining this "chart" in my head. For example I rely a lot on spinosad for my moth control, but it is supposedly highly UV-sensitive. So, this year I was watching how it did in really hot sunny periods, and I found it (plus oil) did amazingly well, pretty much wiping out all moth activity. So, while it may degrade it is somehow getting around that, for example the spray that is on the permanently shady parts of the tree/fruit. Or maybe the virus is getting into the tissue somehow. On the other hand I have found it very sensitive to rain and so I want a nice long dry spell before putting it on.


    Bookmark   July 11, 2011 at 8:52AM
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alan haigh


OK, I'm getting interested now. Here's a study that shows that in certain situations latex based SS's are far superior to terpentine based ones like nu-film 17. Inspired me to order a gallon of Tactic for upcoming fungicide sprays. Sucks because it requires much more ingredient and costs about the same a gallon.

I picked this up in 5 minutes but have to go back to work. I'm going to look into it further tonight.

    Bookmark   July 11, 2011 at 10:53AM
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I spoke to a spectracide rep 1 800-917-5438 (need to give product id number located at barcode) today:
immunox will not wash off once it dries.
triacide needs 24 hours before rain.

So glad everyone contributes giving meaningful advice and thorough answers!

    Bookmark   July 11, 2011 at 10:53AM
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olpea(zone 6 KS)

Scott and Hman,

Your info. was an eye opener. I had always assumed Nufilm offered superior UV resistance. That's their big marketing point. Interesting to learn it's just a marketing gimmic. Ed Fackler claimed superior UV performance with NuFilm, but I guess he was taken in by the marketing, just as I was.

Hman's link suggests Nufilm doesn't even offer very good rainfastness.

Although the link compared organo-silicone stickers to terpene stickers, I'd be interested in any studies comparing organo-silicone stickers to traditional non-ionic surfactants. I've been using Latron B 1956 (non-ionic spreader/sticker) The only info. I could find comparing silicone vs. traditional non-ionic surfactants was a passing reference in the link below.

Quote, "The organosilicone-based materials are another group of surfactants more recently introduced. These surfactants are used in place of or in addition to more traditional nonionic surfactants. Proponents of these surfactants stress low surface tension, greater rain fastness, and possible stomatal penetration characteristics."

From that passing reference and Hman's link, I gather organosilicone surfactants are newer technology and may offer a step up in rainfastness.

Here is a link that might be useful: Penn State Agronomy facts 37

    Bookmark   July 12, 2011 at 10:50AM
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Jim_9999(NE PA Zone 5)

Very interesting topic. Like many of you I've also been a user of Nu-Film. After reading these posts and reading the links I'm starting to wonder if Nu-Film is as good as I've always thought it was. Hman you mention the Loveland product Tactic. I read the product label and was wondering what your mixture rate is. You say that you have to use much more Tactic than Nu-Film. I forget what my calculations for Nu-Film are but I know that I use 1/4tsp Nu-Film per 1 gallon water, and that is probably about 2x what my calculations suggest (I think I calculated .016 oz per gallon but not positive). By my calculation of Tactic at the high application rate of 32oz Tactic per acre per 100 gallons = .32oz per gallon of water, which is app 1/2 oz per gallon. Am I close with this calculation? Yes, it is a lot more product than Nu-Film but as a home orchardist that mixes 30 gallons to do the orchard it isn't that bad providing it works.

This is a very interesting topic! I for one am going to look into these new organosilicone products. I'm going to try to locate Tactic and see how it works. I've been searching the web and haven't been able to lacate any as of yet, any suggestions on who stocks it?

    Bookmark   July 12, 2011 at 6:08PM
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alan haigh

CPS (Crop Production Systems) carries it and when I asked their guide in my area what spreader sticker to use many years ago he suggested Tactic. Maybe I should have "stuck" with it. Michael Phillip's rave revue got me thinking that Nu Film was probably about as good.

CPS is a national chain so if you google it and follow with a comma and your area you should come up with your source. They UPS product so they'll be no problem getting a gallon. Mine arrived today- 24 hours after ordering it.

    Bookmark   July 12, 2011 at 8:32PM
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alan haigh

Jim, as I recall, I use a cup of Tactic for 25 gallons of spray which is about 4X what NuFilm calls for. I'll probably go through 4 gallons of it next season if I don't find another similar but cheaper product. It's the only latex based SS the CPS here carries.

    Bookmark   July 12, 2011 at 8:42PM
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Scott F Smith(6B/7A MD)

Note that in the study hman cited the bad results with nufilm were only on cabbage, which is a very hard surface to stick to. It wasn't all that much worse on the non-cabbage case. So while it did show nufilm was not the best, it didn't point to grossly inferior results on sticking to fruit trees, which are generally not too hard to stick to (plum fruitlets being the main exception). The UV results on the other hand were pretty strongly negative.


    Bookmark   July 12, 2011 at 9:22PM
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olpea(zone 6 KS)


I would say apples also have a fairly non-stick surface because of the wax they produce.

The researchers in the study did not test organo-silicone stickers on the easy wet bean foliage.

It seems to me the results were significant enough to conclude there are much better products out there than Nufilm. Even on the bean foliage, Nufilm's best performance was 64%, but that was at twice the rate of Bond X-tra and Rainmaster. Rainmaster had 86% retention on the hard to stick cabbage. It's possible, and perhaps probable, X-tra and Rainmaster would perform even better on the "stickier" bean leaves, if care was taken, as the author's suggest, not to overuse the sticker.

I had planned to start using Nufilm at some point, but unless some new information surfaces, this discussion has turned me in the other direction.

    Bookmark   July 12, 2011 at 10:23PM
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alan haigh

My guess is that it isn't just about the surface of the fruit, but also the adhesion qualities of the spray material. Indar is very bad at attaching to fruit on it's own and even the label suggests using an SS with it. Fruitletts are smooth and waxy- with the exception of peaches.

These materials are not poison and yet most are not approved for organic production- Nu Film 17 is an exception so maybe that's why its performance has been over hyped.

    Bookmark   July 13, 2011 at 5:39AM
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alan haigh


Here's a pretty informative article about wash-off. I'm experimenting with Avaunt on Jap Beetles this season and only hope it provides adequate control. I have a site where Sevin caused a mite outbreak trying to control the SOB's.

    Bookmark   July 13, 2011 at 5:57AM
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Jim_9999(NE PA Zone 5)

One thing to remember is that this is only one study, not saying that the results aren't correct, I would like to see more studies done before I draw any conclusions.

Hman...thanks for the info about where to get Tactical, I'll contact them today. I'm having problems getting chemicals of any sort lately from local suppliers. Even though I have my Private Applicators License the local suppliers are very hesitant about ordering chemicals. Not sure the reason for this, guess they are starting to feel pressure from the EPA and figure the liability isn't worth the small profit. My suppliers don't come right out and say they can't/wont get a chemical, they just always have a reason for not being able to order it. (This might be a good topic for another thread).

    Bookmark   July 13, 2011 at 6:08AM
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Jim_9999(NE PA Zone 5)
    Bookmark   July 13, 2011 at 7:13AM
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olpea(zone 6 KS)

"Even though I have my Private Applicators License the local suppliers are very hesitant about ordering chemicals. Not sure the reason for this, guess they are starting to feel pressure from the EPA and figure the liability isn't worth the small profit."

It's possible your local suppliers cater their business to row crops, or landscaping. In that case they may do very little business in crop protectants for fruit and consider them specialty products.

Depending on the dealer, some pesticides don't sell enough volume, so they don't want to order them. Suppliers generally have to order pesticides in case lots. It doesn't make sense for them to order a case of something when a customer needs only a bottle. They end up with the remainder of the case sitting in the warehouse for a long time. It's strictly an economic issue (i.e. money tied up in unwanted inventory, storage space occupied, product can get old).

    Bookmark   July 13, 2011 at 10:32AM
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alan haigh

I think a study of rainfastness is pretty straight forward and any carefully done one should bear universally accurate results (at least with the plant material used). There's not many things I could say that about.

    Bookmark   July 13, 2011 at 5:22PM
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Jim_9999(NE PA Zone 5)

olpea, what you say makes 100% sense. Now that you mention it I do remember on several occasions my chemical supplier offhandidly mentioning that my order comes from the specialty section. I never put much thought into it until reading your post.

hman...first I want to thank you for bringing CPS to my attention. Opened an account with them today. 2 gallons of Tactic was my account opening order.

Second....regarding studies and reports...I've worked for a major govt agency for 30+ years and have been involved in more studies than I can remember. Most studies are done by universities (this is what makes a study impressive and believable). Studies are very time consuming and expensive, this is where the govt comes in, the govt provides funding. The funding doesn't come out of thin air, it has to be approved or paid for by a senator or congressman (they have pork barrel slush fund accounts accounts for this), part of the funding usually is provided by a large business or business entity that has an interest in the reports outcome. As the report is being written it is sent to the reports sponsor for review, most likely the political sponsor doesn't have any knowledge of the subject matter so it is passed on to the business entity for their review and comments. At this point data is manipulated and wording is changed to favor the expected outcome. The report is then sent down the chain to the originating university where the appropriate changes are made. At this point the university has the option of rewriting the report as the reports political sponsor would like it to read or they can not change anything. Not changing anything can assure the university of not receiving any future govt funding. The report is almost 100% of the time rewritten with a specific outcome in mind. The, actual report/sponsor procedure is actually much harder to follow, I made it seem easy, it is purposely made difficult to follow.

I'm telling you this from experience. Been there, done that. I didn't go back and reread the initial report mentioned here but I do remember looking at a reference on the bottom of the page that it was written by a university (Michigan??). I take university reports with a jaded grain of salt. Look at political polls and statistical studies, these are always geared toward a specific outcome by whomever is sponsoring (paying for) the poll....the way the question is asked, whom is asked, the way the numbers are presented etc...

Look at the report, it took a product (Nu-Film 17) which had a good reputation but is produced by a relatively small chemical company (Miller) and basically said that Nu-Film didn't work but Tactic (a Loveland product, huge company) works much better. It would be interesting to see who was the reports sponsor...follow the money. I try to keep an open but jaded mind when it comes to reports and studies.

From my own experience I have used Nu-Film for several years and can actually see it working as advertised, not saying that Tactic is better or worse just saying I'm keeping my mind open. I did purchase Tactic and will use it when I receive it. I don't have the money, time or resources to conduct a scientific study of Tactic but I will use it on about 50% of my orchard (30 trees) and do my own comparison.

    Bookmark   July 13, 2011 at 6:51PM
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Scott F Smith(6B/7A MD)

Jim, you have a good point about sponsors. Its something to always check for and I didn't on that one. The paper with the negative wetting results was sponsored by the company selling the product with the best results (Du-Wett), Elliott Chemical, so there is a serious conflict of interest here. So I would notch down the meaning of that paper by several notches.

For me these studies don't change my spray program, I use nufilm for copper and sulphur and UV is not an issue there and as long as I am not spraying on plums I get good enough sticking with it. I use about double what the label recommends and have never seen any phytotoxicity. That said, I do agree that these other stickers will probably work better on some things and if I had a cabbage farm for example I would be changing stickers.


    Bookmark   July 13, 2011 at 8:24PM
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alan haigh

I talked to Michael Fargione, a Cornell fruit production advisor, about stickers and he mentioned that the commercial growers around here use Tactic and Nufilm is mostly used by the landscape guys. My hunch is the commercial guys wouldn't spend the extra money unless they were pretty sure it was well spent. Landscape guys don't have the same opportunity to compare results.

As far as the study's legitimacy, I find it unlikely that such a simple study as this would get twisted. You simply measure the amount of material left after a rinse. There's no interpretation involved- it's simply straight ahead measurements. To twist results would require out and out lying (and that doesn't wash). Even a small company is capable of mounting a very large lawsuit if this was the circumstance.

    Bookmark   July 13, 2011 at 8:59PM
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Jim_9999(NE PA Zone 5)

I want to apologize to hman & everyone else for me saying that Tactic was the surfactant recommended in the article. Hman spent time, did research & recommended a product that he is going to switch to which is Tactic. Hman. olpea, scottfsmith know way more than I will ever know about this stuff, I just like to put my 2 cents in now & then.

I read the articles this morning before work and wrote my post about sponsors when I got home from work without rereading the articles to refresh my memory. I was hung-up on Tactic because I spent a good portion of the day reading about Tactic and purchasing some for myself. My mind isn't as sharp as it used to be....comes with old age.

    Bookmark   July 13, 2011 at 9:05PM
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dethride(7a / 6b GA)

(sound of clicking, cutting and pasting)

This is why I love this forum.

Thanks to all of you for taking the time to put down your experiences and thoughts.

I would like to suggest something: As the conditions arise, I wish people would tell what and why they sprayed or pruned. I know everything is local, but certain times of the year warrant particular actions and it could prompt many of us semi-dummies into action.

And maybe WHY those actions were taken at that time. I like to know all the why's behind what I do. Helps it stick in my mind. Hmm? Oral NuFilm?


(sound of more clicking and ordering of NuFilm 17)

    Bookmark   July 14, 2011 at 9:02AM
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alan haigh

I just finished reading the Tactic label and it's not really as pricey as I thought. I had thought I was using a quart per 100 gallons, but that's double the highest rate recommended. My notes suggest that I used to use 6 ounces in a 25 gallon mix so I may have been using too much or recommendations (formula?) changed in the last several years.

Herbert, I'm putting down fungicide on stone fruit for brown rot. If I see any J beetles some insecticide (probably Sevin) will go in the mix.

    Bookmark   July 14, 2011 at 4:53PM
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alan haigh

Forgot to mention that Tactic label only calls for a 30 minute interval preceding rain!

    Bookmark   July 14, 2011 at 5:07PM
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