Light sensitivity late flower

Fordprefect42

Fordprefect42

Well-Known Member
I’ve been growing for a couple years now so I have some degree of experience under my belt, but I wouldn’t call myself exceedingly knowledgeable.

What I have noticed is my plants tend to start showing increasing photosensitivity late in flower starting say about 6 weeks post light flip, and I invariably have to raise the lights to avoid frying them.

Does anyone else see the same behavior? As with most things weed you can ask 5 different people and get 7 different answers. If this is generally normal I’ll keep doing what I’m doing. If not I’ll be looking for what I’m doing wrong. I’m not having yield issues or quality problems. I just want to maximize my harvest.

I’ve noticed this behavior in both my soil and hydro grows, and across strains. Typically there is nothing unusual about my environment. I have plenty of circulation. Temps tend to run high 70’s under lcd’s with humidity mid 50’s during flower.

Appreciate those 7 opinions if I can get 5 people to respond :)
 
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Phytoplankton

Well-Known Member
This isn’t going to help much, but it depends on what you mean by light sensitivity. Are the leaves closest to the light bleaching, or are they turning yellow from the bottom up and eventually dying? The first could be light sensitivity, the latter, deficiency or senescence.
 
Fordprefect42

Fordprefect42

Well-Known Member
Phytoplankton said:
This isn’t going to help much, but it depends on what you mean by light sensitivity. Are the leaves closest to the light bleaching, or are they turning yellow from the bottom up and eventually dying? The first could be light sensitivity, the latter, deficiency or senescence.
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No it’s definitely light burn. I get the difference between the yellowing at the bottom of the plant late in life, and bleaching. In my case it’s a mix of bleaching and burn spots mostly at the top of the plant, but also effects some lower large fan leaves. It’s one of those things where I started looking around and have seen claims that this is “normal”. It does seem normal for me. I’m not really looking for a solution to a problem. It’s more seeing if there is any consensus on if this is weird or not.
 
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Phytoplankton

Well-Known Member
What you’re describing (pics would be very helpful) sounds more like a deficiency than light burn, but it could be a combination of the two. Usually light burn is more bleaching and leaf edges curling, actual brown spots on the leaves is usually something else. I recently got a new HLG light, and I get some bleaching, my current grow has some bleaching because I let them veg a little too long and with the stretch they are too close to the lights, and I can’t safely raise the lights any higher.
 
Fordprefect42

Fordprefect42

Well-Known Member
Phytoplankton said:
What you’re describing (pics would be very helpful) sounds more like a deficiency than light burn,
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I’ll leave the bleached examples out, but this is what I mean by scorched. I don’t think these are deficiencies, but certainly open to another take. My biggest reason for that conclusion is raising the lights halts progress and the problem is concentrated at the top among the leaves that are most light exposed. The inner canopy is fine which I think you can kind of see.

At one point in a different grow I thought it was calcium which made sense using RO water in hydro, and with top of canopy issues, but this is soil, and I’m seeing that similar problems tend to crop up at about the same time. Also adding calcium made no difference.

In this case I left this plant largely unattended for a few days, and didn’t catch the issue quickly enough. Should still be fine, but I’m sure I did my yield no favors.
 

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Phytoplankton

Well-Known Member
Fordprefect42 said:
I’ll leave the bleached examples out, but this is what I mean by scorched. I don’t think these are deficiencies, but certainly open to another take. My biggest reason for that conclusion is raising the lights halts progress and the problem is concentrated at the top among the leaves that are most light exposed. The inner canopy is fine which I think you can kind of see.

At one point in a different grow I thought it was calcium which made sense using RO water in hydro, and with top of canopy issues, but this is soil, and I’m seeing that similar problems tend to crop up at about the same time. Also adding calcium made no difference.

In this case I left this plant largely unattended for a few days, and didn’t catch the issue quickly enough. Should still be fine, but I’m sure I did my yield no favors.
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I’m still 50/50 on whether that’s burn, let’s get some more opinions. Do you have a picture of the top of the upper buds?
 
Billy the Mountain

Billy the Mountain

Well-Known Member
Fordprefect42 said:
I’m skeptical especially given the only effective solution is consistently to raise the lights, but can you elaborate?
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You're likely conflating a nute issue with light stress. Could be insufficient or unavailable as @Thundercat mentioned.

It's definitely not light stress/burn.

The reason raising the lights may alleviate the problem is that the nutritional requirements are less with decreasing light intensity.
 
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Phytoplankton

Well-Known Member
Fordprefect42 said:
This is the top. Btw guessing you are a no on plants getting more sensitive late?
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Honestly, looks like a deficiency or lockout. The top of the bud doesn’t look burned, and the leaves look nice and purple, light burn would affect the buds/upper leaves first. Most leaf issues occur in flower, as/after the plant is going from vegetative growth to flower production and its nutrient/micro nutrient needs change rapidly, so in that respect, yes, they get more sensitive, not necessarily to light.
 
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ALPHA.GanjaGuy

Well-Known Member
what is your watering routine like? I used to see something like this and I found I was apparently letting my girls dryback too much.. now I try to water them a day earlier than I would have and I do not get this.. I also aim for less more often instead of more less often when watering

fme it is a result of ph/nute issues caused by allowing the soil to dryback which affects your soil ph which in turn locks out certain nutes
 
Thundercat

Thundercat

Well-Known Member
Fordprefect42 said:
I’m skeptical especially given the only effective solution is consistently to raise the lights, but can you elaborate?
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not sure what you want me to elaborate on…. lol that is not what light burn looks like.

you can tell us about your feeding and watering habits and maybe we can help guide you towards better practices in the future. The pictured plant(s) are beyond recovery. Just try to keep them alive and hope they finish enough this time.
 
Fordprefect42

Fordprefect42

Well-Known Member
Thundercat said:
not sure what you want me to elaborate on…. lol that is not what light burn looks like.

you can tell us about your feeding and watering habits and maybe we can help guide you towards better practices in the future. The pictured plant(s) are beyond recovery. Just try to keep them alive and hope they finish enough this time.
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Typically it’s been every couple of days assuming it seems dry although I typically see this on at least one plant in hydro too. Raising the lights a bit has always stopped it in its tracks.

Nothing else worked. I checked ph daily anyway , but recalibrated my meter, recalibrated again, changed reservoirs, added calmag, nothing else worked.
 
calvin.m16

calvin.m16

Well-Known Member
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Some of these colas are 3 inches from the 720 watt LEDs with no serious signs of stress other than leaves slightly pointing down (buds still getting CHONKY) There is probably 6-8 inches from my tops.

What you're showing does look kinda like light burn but also other issues.

What is your Air Temperature and Humidity?
What are your feeds like? How strong is your feed EC/PPMs?
Are you in soil, coco, hydro?
What is your pH of your runoff and input?
 
Fordprefect42

Fordprefect42

Well-Known Member
calvin.m16 said:
View attachment 5308037

What is your Air Temperature and Humidity?
What are your feeds like? How strong is your feed EC/PPMs?
Are you in soil, coco, hydro?
What is your pH of your runoff and input?
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Per above this is a soil grow although it’s no different in hydro. This plant is just an extreme case. Normally I just raise the lights a bit and that’s that. It usually starts with a few orange spots so initially I thought calmag, but since calmag doesn’t help I figured that wasn’t it. Humidity has been around 55 and air temp 78 or so. In hydro I have used the gh trio and nothing else other than calmag with EC typically getting up to 1.2-1.4 eventually, but not much beyond that as I’ll start seeing the EC higher at each res check. I try to keep it at a level where it’s stable and not increasing or decreasing. I’m militant about daily ph checks so I’m pretty much 100% sure it isn’t that in hydro. I’ve got a gallon of ph calibrator and I’ll check calibration every couple weeks.

I’ve been using Dr earth in soil. This is my first soil grow so I’ve more or less been following the feeding schedules from the manufacturer. I haven’t tested run off, but since this is a general problem in my environment I wasn’t looking for soil specific problems. It’s just weird. I’ve had some really solid yields in hydro, but it started occurring to me they could be better if I could pound them with light without using co2.

Fwiw this one turned in a matter of a few days away from the room, and I was pretty shocked to find it like that, but it hasn’t gotten worse.
 
calvin.m16

calvin.m16

Well-Known Member
Fordprefect42 said:
Per above this is a soil grow although it’s no different in hydro. This plant is just an extreme case. Normally I just raise the lights a bit and that’s that. It usually starts with a few orange spots so initially I thought calmag, but since calmag doesn’t help I figured that wasn’t it. Humidity has been around 55 and air temp 78 or so. In hydro I have used the gh trio and nothing else other than calmag with EC typically getting up to 1.2-1.4 eventually, but not much beyond that as I’ll start seeing the EC higher at each res check. I try to keep it at a level where it’s stable and not increasing or decreasing. I’m militant about daily ph checks so I’m pretty much 100% sure it isn’t that in hydro. I’ve got a gallon of ph calibrator and I’ll check calibration every couple weeks.

I’ve been using Dr earth in soil. This is my first soil grow so I’ve more or less been following the feeding schedules from the manufacturer. I haven’t tested run off, but since this is a general problem in my environment I wasn’t looking for soil specific problems. It’s just weird. I’ve had some really solid yields in hydro, but it started occurring to me they could be better if I could pound them with light without using co2.

Fwiw this one turned in a matter of a few days away from the room, and I was pretty shocked to find it like that, but it hasn’t gotten worse.
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Hydro you need to be even more so cautious of pH swings actually as the water is your only buffer. Light burn will show as a calmag looking carnage at the top leaves only, usually mid canopy when I see it, I just pluck those leaves away. Another tip from a pro grower I forget his name, woops, he snips the tips of the bleached buds off and they just grow fat and wide like a turtle shell, I've tried it, it works. More light = more grams. Something in the feed is probably off, possibly even toxic.
 
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