Spray temps?

When is the best time of day and what is ideal ambient temperature for spraying fungicides and insecticides? Should I refrain from spraying in hot sunny conditions?

Generally (with the exception of oil) hot sunny conditions are good because the spray dries fast. Oil can supposedly cause phytotoxicity if sprayed when too hot (or too cool causing extremely slow drying conditions).

The warnings for something potentially phytotoxic like Captan are to avoid extremely slow drying conditions, although I’ve never experienced Captan burn under any conditions.

Sometimes people will avoid spraying under really hot sunny conditions with airblast sprayers because the spray particles are so small they can evaporate some before they hit the tree, but this would not be an issue with wand sprayers where the droplet size is generally larger.

I try to spray my large orchard at night because there is little wind. I try to spray my backyard orchard (with a wand sprayer) in the daytime because I can’t see at night.

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Thank you Olpea. That’s very helpful. Today would’ve been great but I was afraid I was going to fry them. I was going to use immunox, triazicide, and a sticker.

I guess an addition to this question would be how much time should I spray before rain. I miscalculated the forecast. I sprayed immunox and triazicide with sticker today around 5pm. I thought it wasn’t supposed to rain until tomorrow. I just looked at the radar and now it looks like it is going to rain tonight around 11pm. Is 6 hours enough time? It was pretty hot at the time of spray so I’m certain the trees are dry. In fact, I just looked at them and I can’t even tell I sprayed them.

Will I be okay?

It protects against rainy weather diseases right? So you want it on before the rain not after. If it’s dried you should be OK.

When spring temps are very wet and apple foliage is tender form a lack of much sun, Captan can burn apple foliage (not sure what else), but generally not anything that creates any problems beyond the cosmetics.

Here we’ve had nothing but heat and sun for the last couple weeks since things began blooming. It has created the shortest, most condensed blooming period in memory. Spring started late but caught up in a hurry so I will begin petal fall spray at the normal time- by May 15th.

Things are setting up for a very heavy crop as long as adequate rainfall starts to show up. It’s been the driest spring in memory.

Just going from what I have read about using synthetic pyrethroids such as triazicide, cooler weather is favored because the active ingredient breaks down quickly in the heat. I think weather that stays under 75 degrees F was ideal but I am not absolutely certain.


As Fruitnut indicated, for most sprays, you just need the spray dry before the rain comes.

For pesticides which translocate, it’s best to have a little more time before rain. Some pesticides, like the herbicide glyphosate, or insecticide imidacloprid translocate throughout the plant tissues. Others, like Immunox, are locally systemic (in other words they won’t travel throughout the plant but will travel throughout the individual leaf tissues- i.e. if a drop lands on a leaf, the fungicide will travel throughout that leaf)

For something like Triazicide, which is not systemic but only a contact insecticide (stays on the surface of the leaves) once it’s dry, it is at it’s maximum rainfast state. For pesticides which are completely systemic, or locally systemic, the longer the pesticide stays on the foliage, the more is absorbed, so they benefit from extended drying intervals in order to resist rainfall. Once the pesticide is absorbed in the foliage it is completely rainfast.

I’ve not read the optimum drying time for systemic fungicides, but John Wise has done a lot of research in this area for insecticides. He claims a locally systemic neonic needs 24 hrs. drying time for optimum penetration. I would assume a locally systemic fungicide like Immunox would require the same drying times for max. absorption.

That said, I wouldn’t worry too much about your spray not having enough drying time. Any spores your Immunox comes in contact with are going to die, whether the spray has dried or not.

Likewise with your insecticide. Even if your insecticide was washed off immediately after it was applied, it will still kill any eggs laid on the surface of the fruit/leaves (assuming good coverage) or any adults which come in direct contact with the spray. That’s going to do some good even if there is no protectant residue left on the tree.


Olpea is always a sound source of researched information he himself has applied- carefully. I can add something to his experience because I spray so many sites that I sometimes I can’t help but spray an orchard preceding an unexpected thunder shower once or twice every season.

I’ve had up to a half inch of rain come down shortly after making an application on numerous occasions over the years- I used to return to recover the trees but a 2nd generation commercial grower I know assured me that it wouldn’t be enough to matter unless it was nearly an inch.

On the few occasions where I’ve let his reassurance guide me I’ve not paid a penalty for whatever that’s worth. My number of applications is already at the minimal level for the pest pressure in my region.

The man my chemical supplier hires to guide commercial growers puts a lot of faith in Tactic, a latex based sticker-spreader. It works so well that it increases the PHI on some pesticides if it is in the mix.

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Once the triazicide (or any other synthetic pyrethroid) has done it’s initial work after being applied, it could be argued that it does not matter what the temperatures are that follow. But that would ignore the repellancy capabilities of this class of insecticide. I am not claiming to be an expert on this subject, but rather trying to be a point of entry to further investigation of this topic. Real world application of these materials always begins by reviewing the research, product labels, and dictates of law. Consequently, there are white papers out there on the internet particularly describing these materials and their application.


I’m using Tactic for the first time this year. I’ve noticed the look of it is almost like a thin latex paint. I’ve not seen any sticker like it before.

I’d like to have some way to test the efficacy of some of these stickers, so I could rely some on my own experience as well as the research, but I don’t know how an individual could do that. I know Nufilm seems really sticky on my hands and on the measuring cup, but I know that probably has little correlation with what is sprayed on the trees. Tactic’s paint attributes are probably why the research suggests it has superior rainfastness. Paint isn’t all that sticky on ones hands but of course stays on a painted surface really well.

I hadn’t heard Tactic increases the PHI of some pesticides. I don’t recall seeing that on the label. Is this on the label of some pesticides themselves (i.e. If this product is used with the surfactant Tactic the PHI increases to X.)?

I used Bonide Turbo Spreader Sticker simply because it was the only thing available at my local ag shop. I’m sure it’s not up to par with Tactic or other products used by commercial growers.

I’m sorry, Olpea, you will just have to take my word on that, which is risky, of course. I can’t find where I read about that. Apparently it has not yet become a legal issue.

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Swamps, I fear you completely misconstrued my last statement and I’ve no idea why you just made that statement here. It is certainly not something within the rules of this forum, but the fact that you’ve made this statement after a completely innocent comment baffles me. I was certainly in no way belittling my friend Olpea, who knows has my highest respect.

There is the ability on this forum to address people privately with statements like yours. You are doing what you accuse me of, so why not keep it private.

This yesr im switching things up a bit and instead of doing fungicide /pesticide im going to do a prebloom copper. I’m still undecided on the antibiotic spray for fb. The weather has a lot to do with my spray decisions. If i see heat with no humidity im not concerned but if i see humidity/moisture at 65% and hanging 65 degree weather thats bad. Fireblight will certainly be a problem. In Kansas wind is a friend and enemy depending on if you want things to be wet or dry.

I guess you get no university help on this because fruit growing is not big business in KS. Here, Cornell sends me FB warnings when conducive weather conditions are eminent. I never respond to the warnings beyond clenching my jaw a bit- the consequences here don’t match the effort of control- In all the orchards I manage I don’t even lose a tree a year, although I’ve lost several in the last two.

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Kstate is interested in forestery, wind breaks etc but are more focused on livestock, prairie, and row crops. They are very helpful but there are a few orchards in the entire state. We definitely do not get fireblight alerts. I’m still doing pear tests since we do not have a pear orchard in the state. Olpea is the only peach orchard in the state.

I think you are wrong about Olpea’s Kansas peach orchard being unique. He frequently mentions things he learns from bigger growers nearby.

I may stand corrected then but stone fruit is not grown here a lot. The nearby state of missouri has some excellent apple growing pockets that are second to none. One of my uncles is a commercial grower there and the cllmate is ideal. I would think those commercial peach growers would be on the Missouri side based on climate differences.