Hey chem folks: question about chemical halflife

[FeltchWyzard]

Hello!

I couldn't find the info in a search, but I figured maybe others would like to know the answer to this as well.

In regards to chemical half-life, do pesticides continue to break down after harvest? Does this differ between root treatment and foliar? Say I have 14 days til harvest and a chemical that has a 21 day half life and I wait at least 7 days after harvesting to consume, am I in the clear? What kinds of things do pesticides break down into?

Now say I accidentally sprayed something that has a 50 day half-life onto a plant I'm just about to harvest? Could I just cure for 2 months and be in the clear?

Thanks in advance, I actually haven't had any issues & always play it safe but just been thinking and realizing I don't know enough about this subject. I'm just looking for a bit more info about how these things work.

Wyz

 

[Picarus]

Half-life (t1⁄2) is the amount of time required for the amount of something to fall to half its initial value.

 

[bench warmer]

The plant needs to metabolize anything it is exposed to. It won't be able to transport much of a toxic substance out of itself after it stops living.

 

[Mikell]

Ima go out on the limb here and say this isn't a hypothetical question.

Without more information it's impossible to give the response you're looking for.

 

[FeltchWyzard]

Well that limb just broke! It is indeed hypothetical. I only use bio agents and organic oils in flower, but I recently have had a bad go with both root aphids and broad mites(insanely good luck!) and I guess I would like to know the maximum I can stretch my pesticide efforts and still be safe.

What prompted me to think about it, though, was I used a chemical in soil about 30 days before harvest and someone at a local grow store told me that was not good, even though the label said it was fine for edibles within 14 days. He said I need to know the half-life values or actual breakdown period before I sprayed. I did some research and found that the chemical breaks down within 14 days so I should be more than fine, but it just got my brain churning on wondering how the process works of chemicals breaking down.

benchwarmer was onto what I was getting at, but I am just wondering whether even systemic chemicals will continue to break down in the plant material and eventually be harmless even if unmetabolized or whether the unmetabolized chemical will continue to cause harm past its typical point of breaking down because it is trapped in the plant tissues. Maybe what Mikell is getting at is it depends on a lot of different factors, is that right? Just wondering whether there are any other rules of thumb.

 

[Mikell]

Not the first time I've fallen out of a tree onto my ass

I believe benchwarmer is on the right track and that was what I was implying. Concentration, frequency of application, pesticide type, application site (soil, foliage, surface), environment (heat, light, water, microbial activity, etc) are just some of the factors.

What did you apply? I'm not here to judge. Half lives are useful but not good as a thumb ruler. Some products, myclobutanil (Nova, Eagle20) for example, have relatively short half lives but total breakdown can exceed 12 monthes under specific circumstances.

 

[FeltchWyzard]

well, originally, I had used acephate to eradicate root aphids(it worked great!) I am currently more concerned with imidacloprid, though. I use Bonide annual tree that just has the imid, which everyone says is great to use in veg, though I see that it can chemically last over 200 days! That definitely doesn't jive, but it's so effective as a systemic preventative. I can use other things to prevent, but overhead gets costly with bio agents. Thanks for the responses y'all!

 

[FeltchWyzard]

I do want to mention, this is indoors. I love bees and I love nature and I like to keep my horticultural experiments as isolated as possible.

 

[Granger2]

If you will re-read Picarus' post, you will see that half life means only half of the toxin will break down. The other half is still there. I've read that imid breaks down into more toxic substances. Everybody who says imid is OK in veg is wrong. The half life is too long for it not to still be active at harvest. And way worse, it is a systemic. Acephate has a pretty short half life. Good luck. -granger

 

[FeltchWyzard]

Granger, yes I guess I meant total breakdown. I had those two confused initially because when I was talking to a dude at the store and had questions about breakdown and the label and what-not, he said I need to find the chemical half-life because it could be much longer than the label states.

I'm realizing in my ignorance that this is a complicated issue with a lot of variables and maybe it's best just to get info from manufacturers themselves.

I have heard mixed things about both imid and acephate, with some people switching around which lasts longer or is more likely to cause issues. I got some good info straight from an acephate tech specialist.

She turned me over this:

http://pmep.cce.cornell.edu/profiles/extoxnet/24d-captan/acephate-ext.html

Great news! Not specifically about cannabis, but the range of plant tissues should basically cover what we do. Looks like acephate is pretty damn harmless up to halfway thru flower as long as you are careful applying it. Fingers crosses, I have had NOTHING on my sticky traps in over a month (I had HUNDREDS of RA fliers and was losing branches DAILY!) and my plants are bouncing back with the help of Z7, roots excel, and foliar instant karma. I did a lot of treatments, like limonene lemongrass rosemary oil, nukem, pyrethrin bombs, SNS, and in veg hit them with fluoramite and spectracide and waited about a week then hit everything with MET52 to be sure anything remaining would be a zombie for any others.

Honestly, Granger, reading about what you have had to say over the years, I was so scared when I ID'd these fucks. I know they had caused you insane damage and I had broad mites ruin me last year, so I couldn't afford another fall-apart. I am still treating just in case and have stopped my perpetual so I can heat-treat my flower room and sanitize all the lights and ducting and equipment. I do gotta say, though, I started with Acephate as my initial chemical blast and my soil and fresh sticky traps have been COMPLETELY silent since then(soil was crawling hours before). I hope some folks get some good info about it because a lot of people seem to trust imidacloprid as a sure-thing way to keep from having root aphids, which I am sure it is, but to what health costs? I think maybe my regime will be hitting with acephate late in veg and then just do a single OGBW or MET52 application in flower. What do you think of PFR-97? I heard Isaria fumosorosea, the spores in PFR, were in caps bennies but it isn't on the label of OGBW :/ Same with the MET52 stuff... I thought it was initially in caps, but no longer in OGBW.

I respect your opinion and surfed your posts when I was in my initial battle-mode and I found things you said to be very very helpful. It's funny, a lot of growers I know look down on me because I have had some serious bug issues(first broad mites, now RA), but it was just because I had never had to battle with them before. You don't become educated on things that aren't a practical issue. Some of the growers in my area that have been successful for years tell me like "Sometimes I use Neem oil, have you tried Neem oil? I had spider mites once, they're the worst!" They get clones from various sources and never do any quarantine or initial spray-down when they take them in, so I guess they're just lucky. For now.

Anyway, thanks again!

 

[DocTim420]

Hmmm, I think one must determine how a particular insecticide actually moves through the plant. Contact, Systemic and Translaminar are different terms. Most "cides" are contact, few are systemic or translaminar, and very few are all three (like imidacloprid).

Contact "cides" only work if the pest comes in contact with the active ingredient. Other than surface residue, expect very little of the active ingredient to actually enter the plant. UV (sun) will usually speed up the degradation process of the active ingredient.

Systemic "cides" enter the plant and move slowly UP the plant (not down) and will eventually move to new shoots, but if the toxic material has not yet moved to the new growth then expect very little pest control. Woodier the plant, the slower the active ingredient will move and expect to see higher residue levels.

Translaminar "cides" do not remain on the plant surface, but move into the leaf where the active ingredient is stored and remains there for a certain period of time. The active ingredient moves a very short distance and but does not move throughout the plant. Hence the instructions to spray a plant until it is "dripping" to obtain full coverage.

I think the underlying question is, how much chems are in my bud at harvest (new growth) if I sprayed it 10 weeks ago when it was in veg? As you can see, it depends on what you are analyzing--new growth or old growth, active ingredient, and type of cide: contact, systemic or translaminar.

Then we have the unknown variable called "inert ingredients" and it's half-life. Go here for a sampling of EPA allowed "inert ingredients".
https://www.epa.gov/sites/production/files/2016-07/documents/section25b_inerts.pdf