Yellowing is not neccessarily a lack of N.

[Microbeman]

Grapeman, don't mind Mr. Fista, he's a crotchity eccentric just like me, just not so old. I have observed that variances in senescense can be due to environmental factors which trigger the plant to rush to seed production if it senses one form or another of impending doom, like drought, flood, disease, pest attack or cold. I've mentioned previously that I've cut down thistles which were not yet flowered, laid them on the ground and one to three days later have seen seeds blowing from the 'dead' plant....amazing!

 

[MrFista]

I agree environmental factors play a role in the severity and rate of senescence.

The initial senescence control is via the plants circadian rhythym and recognition of night length (which we wrongly called day length and it stuck). You can't interrupt the night length in a plant and get away with it, only the day length.

The circadian rhythm in plants is a feedback mechanism involving phytochrome (red light) and blue light receptors. Two isomers (two forms of one molecule with change in structure but not composition) of phytochrome: Pr (phytochrome red) and Pfr (phytochrome far red) convert to each other according to levels of the light they recieve. The switches between the two molecules and resultant levels present of these molecules control varied light induced plant reactions including their role in circadian rhythm and senescence.

Sunlight contains both red and far red light, but the conversion to Pfr is faster than the conversion to Pr. So over the day the level of Pfr builds up and during night it goes down. The increase in Pfr each dawn resets the biological clock (blue light receptors also involved somehow). Position of leaf organs will create microenvironments where Pr and Pfr levels differ, like on the lower leaves that go first during senescence.

Senescence is the programmed death of certain cells or organs or the entire plant. At the molecular aand cellular level genes code new enzymes that break down chlorophyll (containing N), DNA (N), RNA (N), proteins (N), and lipids. Many of the breakdown products are salvaged. Ethylene is almost always associated with the programmed destruction of cells, organs or the plant entire.

Leaves detect changes in photoperiod and produce signal molecules that cue buds to develop into flowers. Exposure of just one leaf on an entire plant to differing photoperiods induces changes in the plant. For over 70 years a possible hormone involved in flowering has eluded science. It is hypothetically called Florigen. Most of the problem seems to stem from looking for a micromolecule involved. It may be a macromolecule.

In flowering arabidopsis (model research plant), the CONSTANS gene is expressed and the protein it synthesises can move via plasmodesmata (cell junctions) on the symplastic route. More recent research suggests CONSTANS turns on another gene FLOWERING LOCUS T (FT) and this protein travels to the shoot apical meristem and induces flowering.

Senescence is genetically programmed to occur. But some environmental factors can alter the genes expression which in turn may be noticed as changes in rate and severity of senescence. Genes in many plants differ, as do phytochrome production levels and resultant reactions to photoperiod... The variation is natures way of surviving long term. Plant seed falls wherever it may. Variation in the gene pool helps some to survive in what might be adverse conditions for the other. As the environment changes the better genetically adapted plant thrives via making it to reproduction (even if it involves flowering early and stripping all it's veg growth) while other lines will die out.

Jeepers, time for a smoke.

 

[MrFista]

Always remember when looking at man made rules about nature and how it works, that nature is capable of breaking the rules.

Senescence in weed is tied to photoperiod. Weed is annual and is genetically programmed to die. The end goal of this genetic programme is to make more copies of the genes via seed production. The strategy that annuals adopt is an all or nothing strategy, a race to the finish and produce as many seeds as is possible.

But some weed plants in temperate-tropical areas will continue to grow season after season. We know revegging works, albeit the plants look like shit for a bit but they do recover.

The plants upon making seeds and fruit put out smells to attract animals to eat them and distribute their seeds. Ethylene seems to attract insect predators to foliage as well. Grazing foliage and fruits (flowers) off a revegging annual greatly increases it's chances of surviving in reasonable conditions.

The decrease of vegetation causes a decrease in auxins, this occurs during senescence and after a plant being grazed. This in turn slows or halts root production by altering auxin/cytokinin levels in the root system which balances out the root:shoot ratio eventually.

Hypothetically:

If one were to reveg plants in their climate (where permissable) year after year selecting out the successful reveg every time a 'perennial' strain should result. To save a lot of time try a bunch of strains first and get the best survivors then breed them. For outdoor growers this merely involves leaving the base and a few popcorn buds and leaves on plants in the ground and if you return next year and it's alive - yay! Clone it, take em home and seed it, or seed it on site.

 

[MrFista]

While I'm dishing out dubious advice on breeding...

The writings on the wall with global warming. We need to be selecting outdoor strains specifically for their ability to cope with heat. Keep a close eye on plants in the hottest days and mark which one's are coping. Clone then breed...

 

[staff11]

Heres a plant that refuses to green up after my normal mix(fish, sea kelp and DG Pro tekt) so everyone who see's it calls it an N deficiency and say i should hop on it with some more nutes. i think shes doing wonderful and she's just gonna be an early finisher. I never look at yellowing in flower as a bad thing, i just think the plants use up their energy reserves they've built for themselves.

You can see the plant next to is dark green and is the same age just the sativa leaning pheno of Ultra Sonja(cheese x tang-tang=blockhead sativa male). Their at about 4/5weeks(?). The sativa takes it all in and the Bubba kush which isnt pictured would burn even if i gave it a drop of my mix..

I get the same exact thing about 6 weeks in (over half way of a 65 day strain) and there is nothing I can do about it, yet it yeilds well and smokes even better. I have tried top dressing more, adding more to the containers, bigger containers and anything else. Another strain I run almost looks immaculate the whole way through and only fade when it hits around 12 weeks... no matter what i do.

The plant tells me when it's done in the short time I have tried the organic method. And I do it more basic then most.

 

[MrFista]

Yeah it's definately genetic, so most of what we see is pre-programmed. Environment however can make so many variations of clones... Difficult to follow anything as soon as changes in genes climate substrate etc come into play.

There are several things that influence the model plant Arabidopsis in flowering - daylength, plant development level, exposure to cold, and giberellin levels. Different plants do differnt things though.

What we do know on hormones: Auxins play a part in phototropic response including flowering and senescence. Auxins influence ethylene production and this in turn influences leaf senescence and fruit and leaf drop. Cytokinins are antagonistic to Auxins and can delay senescence for increased yield. Cytokinins do this by inducing auxin repressors and slowing down the gene responsible for Auxin transport (PIN). They can also release lateral buds from dominance. Giberellins are responsible for the stretch (hyperelongation, or bolting). They stimulate long day flowering (not weed) and biennials flowering (not weed). Abscisic Acid stimulates leaves to send photosynthates to developing seeds so may be involved in leaf breakdown too.

 

[grapeman]

Yeah it's definately genetic, so most of what we see is pre-programmed. Environment however can make so many variations of clones... Difficult to follow anything as soon as changes in genes climate substrate etc come into play.

There are several things that influence the model plant Arabidopsis in flowering - daylength, plant development level, exposure to cold, and giberellin levels. Different plants do differnt things though.

What we do know on hormones: Auxins play a part in phototropic response including flowering and senescence. Auxins influence ethylene production and this in turn influences leaf senescence and fruit and leaf drop. Cytokinins are antagonistic to Auxins and can delay senescence for increased yield. Cytokinins do this by inducing auxin repressors and slowing down the gene responsible for Auxin transport (PIN). They can also release lateral buds from dominance. Giberellins are responsible for the stretch (hyperelongation, or bolting). They stimulate long day flowering (not weed) and biennials flowering (not weed). Abscisic Acid stimulates leaves to send photosynthates to developing seeds so may be involved in leaf breakdown too.

whoa - and the above is why over the years I have pretty much given up on trying to control senescence. I use all of the above materials (with the exception of aba) on a regular basis on our crops.

There are so many variables involved that I went nuts trying to figure it out. Then over the years I observed no net decrease in crop so I gave up.

Especially when growing outside, you add a whole other layer of variables that can never be controlled.

My first crop here in this hobby was hydro and successful. All plants showed signs of senescence and I posted up the senescence question with pics just because I didn't know for sure on this crop.

But I can say that since I have been playing with organic soils and stopped pushing these plants to their limits, senescence rarely appears. So there are probably stress factors that trigger senescence also.

 

[MrFista]

I think there must be a feedback mechanism with senescence possibly to do with various solute concentrations.

There's a few minor players probably involved too. A burning question for me is if flowering triggers/influences onset of senescence. So far, with the strains that behave like clockwork, I think it does.

Plants that overexpress cytokinin will delay senescence. A larger root mass:shoot ratio likely directly affects levels of senescence by producing more cytokinin. So those boys trimming all their leaves off in another forum are delaying senescence by elevating cytokinin:auxin ratio. Don't try it with sativas unless you want seeds!

 

[Scrappy4]

I looked up senesence and found this:

•Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to that of the whole organism. ...


What I wonder is, if early onset yellowing (say 2-3 weeks in flower) is considered early aging, due to whatever, or if it should be considered new problem. Or put another way when is it lockout, and when is it aging? scrappy

 

[VerdantGreen]

scrappy, if the plant is yellowing at 2-3 weeks then there is a good chance that it's down to a nutrient deficiency.although you may lose the bottom couple of sets of leaves around this point and thats nothing much to worry about. just because yellowing isnt necessarily a lack of N doesnt mean it isnt a lack of N.

there is probably a less clumsy way of saying that but i just smoked some Lemon Thai

 

[MrFista]

That's about it.

If you got a bunch of seeds in the same mix and one is yellow before it's kin chances are it is genetic - but - a pest or disease or airflow or something unthought of can't be ruled out.

If a known performer that's been cloned is not performing so well then it's probably environmental.

 

[Microbeman]

if the plant is yellowing at 2-3 weeks then there is a good chance that it's down to a nutrient deficiency

or calcium deficiency, or root sucking nematodes, or other bugs, or water barrier/captive walls or lighting or some weird quirk that made the plant race or.........diagnosis is a bitch

 

[guest2012y]

or calcium deficiency, or root sucking nematodes, or other bugs, or water barrier/captive walls or lighting or some weird quirk that made the plant race or.........diagnosis is a bitch

I've recently identified some nematodes in my soil....was wondering if they may be the root suckers. White,about 1/4 inch long,fast,plentuful............have a couple pots fitting the description of a problem with them. How would I know without a microscope?
Take the plant apart at the roots after harvest and look close?

 

[guest2012y]

Double post...

 

[schwagg]

can you see a nematode with the bare eye?

 

[guest2012y]

can you see a nematode with the bare eye?

Yes...they flush out the bottom of one of my couple early yellowing plants and other pots when I water. I'm not sure if it's the cause of the early yellowing because those plants are also rootbound.
I was looking around and found this.......maybe good huh?
http://www.redwormcomposting.com/worm-composting/ive-got-white-worms/

 

[!!!]

I've had plants that dropped almost all their fan leaves starting 3-4 weeks in flower. Not a lack of anything.. just genetics. Light not going to an area also causes the plant to defoliate itself in that area sometimes. No point sending nutes where there's no energy and no potential for seeds to thrive.

 

[Dignan]

or calcium deficiency

Several years ago I had plants in 5-gal buckets indoors in a pretty rich soil mix that were yellowing at week 3-4. A very experienced old grower friend helped me correct the issue and I don't recall the actual explanation behind it all but he was positive that the yellowing was a Ca deficiency caused by repeated partial waterings. IOW I was watering but not well enough and the roots were directing the water down and around "dry zones" and somehow those dry zones caused a chemical reaction that prevented the uptake of Ca. ?

 

[Scrappy4]

or calcium deficiency, or root sucking nematodes, or other bugs, or water barrier/captive walls or lighting or some weird quirk that made the plant race or.........diagnosis is a bitch

__________________

In my case I think it's lockout due to too much nutes and possibly too much lime. My run off has been 7, even with the starting water at 5.5ph. But like your sig says anyone can be wrong about anything......scrappy

 

[Microbeman]

I've recently identified some nematodes in my soil....was wondering if they may be the root suckers. White,about 1/4 inch long,fast,plentuful............have a couple pots fitting the description of a problem with them. How would I know without a microscope?
Take the plant apart at the roots after harvest and look close?

Most nematodes I look at are much smaller than that and I require a scope to see them. I can barely see some of the largest by naked eye. The bacterial feeders I see usually range from a 300 microns to 2500 microns long. By naked eye it is easy to confuse nematodes with other types of worms.