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Rainfastness Characteristics of Fruit Insecticides

Posted by olpea zone 6 KS (My Page) on
Tue, Jun 4, 13 at 23:05

Every year there are questions on the forum about the affect of rain on sprays.

MSU posts the relevant information linked below about this time every year.

This year they included new information (at least I don't recall reading it before) about how much drying time is needed before the spray is "set".

They are saying 2-6 hours for most sprays and 24 hrs. for neonics.

Here is a link that might be useful: Rainfastness of Insecticides


Follow-Up Postings:

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RE: Rainfastness Characteristics of Fruit Insecticides

1 hour for roundup with a good surfactant. Most have their own surfactant added.

4 hours is pretty standard for everything else in the commercial ag chemical world.

Of couse overcast foggy weather, cool weather, and even too temperatures too hot can decrease the effectiveness. The best time to spray is when the plant is dry and actively growing.


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RE: Rainfastness Characteristics of Fruit Insecticides

I don't find this information convincing at all, based on my long experience of two sprays 10 to 14 days apart using various materials. I have never come back to sites to respray in the many years I've used this schedule- there is almost always very significant rain between sprays. I've always considered an hour of good drying conditions adequate and have depended on this calculation many times.

This year 4" of rain fell shortly after my first insecticide application and at many sites there was no respray for up to 13 days after the rain but I did not find any significant damage at any of the sixty or so sites I spray. I've enjoyed such results year after year- also at another 40 or so others sprayed to my schedule.

This article suggests a spreader-sticker penetrant helps, but doesn't mention how much. These days I use a latex based one. I haven't used organophosphates for the last two years and primarily rely on a pyrethroid.

If the insecticides are losing their effectiveness it must not matter, perhaps because it's usually adequate just to kill the pests already in the trees. I don't want everyone here thinking they have to run out and respray after every significant rain- I'm pretty sure they don't need to.

My original mentor is a second generation commercial apple grower who produces pristine fruit- he never considers respray necessary when unexpected rain comes immediately after spray if its not well over a half inch, even when it's already drizzling when he puts it down, . He likes some drizzle while he sprays to spread around the Cap.

The problem with following conservative advice is you never find out if its necessary. Of course, not following it contains the risk of finding out it is. If you are only protecting your own small orchards, hopefully you can rely on careful monitoring and go with less spray.


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RE: Rainfastness Characteristics of Fruit Insecticides

I am still very much a novice at this insect control procedure. Dealing with the "good bug" - "bad bug" thing when spraying has me even more confused.

It has become a real issue this year. The majority of my blueberries are just now going into full bloom. With all of the wet and cold weather, there hasn't been a bee in sight anywhere. I'm afraid to spray because of the chance of killing off any insect that might help with cross pollination.

How does one balance this out?

Northern MN


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RE: Rainfastness Characteristics of Fruit Insecticides

I agree with northernmn. I'm even farther out with years before I need to really worry about pests, except for cherry trees. I have one tree that is fairly mature at 4 years, another at 2 years, the rest of my stone fruits were planted this year. Even though you guys have mentioned your routines before, it would be nice to have a thread with your schedules, and the products you use. So we can try and find similar products and not have to reinvent the wheel via the school of hard knocks. Fruitnut has been the most helpful to me as far as caring for stone fruits. But his location and such are way different from mine. Still I learned the basics from him, and am grateful for his willingness to teach us all. You guys are near me and deal with in ground trees in my area. Olpea has gone over the products he uses recently, but not really when he uses them.
Also nuances like how to avoid exposure to bees, by products used, and timing.
I must say I have seen few bees this year too. But it has been cold, and such. I saw more this week than any other, so a good sign. Anyway if you have time sometime, please teach us, or at least let us see how you handle and manage the trees under your care. I'll have to buy you a beer sometime!


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RE: Rainfastness Characteristics of Fruit Insecticides

North, here's my advice.

You use safest effective compounds and you eliminate all flowering weeds by scalping with a whacker where spray will fall or cover flowering plants with a tarp and you spray early in the morning- preferably a cool one.

To insure a heavy population of pollinators you try to always have plants in bloom on your property they find nourishing from earliest spring (crocus are great) to latest fall, but never grow plants near fruit trees that flower at the time insecticide must be routinely applied.

My home is surrounded by sprayed plants but I have the richest most vigorous group of pollinators I see anywhere.

Wish I had even a single species interested in my kiwis. They are in fragrant and profuse bloom right now and all my mason bees, bumble bees, serphid flies, carpenter bees, etc treat them like the ugliest girl at the dance.


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RE: Rainfastness Characteristics of Fruit Insecticides

Thanks Hman.

I will start planting "pollinator attractor" plants.

The weeds that bloom have been about 95% eliminated from around my fruit plants, so collateral damage from overspray has been pretty well eliminated.

I like to spray early morning. Do you wait for the dew to be gone?

I've been looking at the posting times on some of your replies on the forum. Do you ever sleep?


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RE: Rainfastness Characteristics of Fruit Insecticides

I'm in my '60's now and sleep seems to come in relatively short intervals these days. Sometimes if I can't fall right back I go to the computer. If something I write seems unintelligible this could be the reason.


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RE: Rainfastness Characteristics of Fruit Insecticides

Forgot to mention, I don't wait for dew to dry, just mix a little hot.


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RE: Rainfastness Characteristics of Fruit Insecticides

  • Posted by olpea zone 6 KS (My Page) on
    Wed, Jun 5, 13 at 18:45

"I don't find this information convincing at all, based on my long experience of two sprays 10 to 14 days apart using various materials."

I wouldn't suggest home orchardists use the decision chart. That wasn't why I posted it. It's not necessary for home orchardists (or some commercial orchardists) to maintain insect lethal residues on fruit at all times.

The relative rainfastness of the materials can be helpful, but the part I found most interesting was the amount of drying time suggested for insecticides to set. Of course it's dependent upon the material sprayed, temp. and humidity but I was surprised the amount of drying time required for neonics.


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RE: Rainfastness Characteristics of Fruit Insecticides

Don't get me wrong, I find the chart of great interest, I'm just glad I didn't have it when I started out this business or during spray season I'd probably have to be spraying 24 hours a day- except when there was any rain in the near forecast.

University advice always seems to suggest a lot more coverage is needed than what seems to be the reality.


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