Fan leaves yellowing 6 weeks into flowering.

[live4flight]

Hi everyone, I am new to to RUI community and a new grower. The fan leaves on the top of the plant are turning yellow and getting worse. Plants are under 600w hps. Growing in FFOF. Using Humblodt Nutes. Temps are around 78-80 during the day and about 60 at night. RH is right around 20%. ive attaches a couple pics.

Thanks!

 

[Popcorn900]

It's normal for a plant to yellow when it is almost done. But...................

 

[CouchlockOR]

It's normal for a plant to yellow when it is almost done. But...................

You are only partially correct.

During flushing or just watering in the last week or two the plants will naturally turn yellow as the plants use up the stored energy in the leaves. If the correct amount of nutrients are being applied, the plant should be green until harvest. Yellowing naturally happens over the entire plant evenly. In my experience they can be either way depending on how water or nutrients are applied in the final weeks.

There is a definite nutrient disorder showing in the pic. Yellow leaves with green veins can be one of several disorders. Macro and micro. To me it looks like maybe iron. To fix this issue or any other nutrient disorder take these steps.
1. Flush the plant with water. If you have water out of the pH range of 6-7 adjust it with a good pH up or down solution. GH pH UP/DOWN is a great choice. It is much more stable than using baking soda or lemon juice. For every gallon of soil flush with 3-4 gallon of pH adjusted water.
2. Make sure you are using a balanced nutrient regimen. (just because you may use an entire nutrient line up doesn't mean you are simply good to go.) Fertilized with a correct pH balanced solution.
3. Test run off water or nutrient solution for pH. Runoff pH should be in the correct range of 5.5-6.5. If it is out of range compensate with higher or lower pH water or nutrient solution. ie if runoff is 7.5 water with 5.5 and the average is 6.5. This is a good way to start.

On another subject your temps are way too high. And the temperature difference is too great. Keep temperatures below 75 with 70 being optimal unless using CO2. Also temperature differences should be kept to 10 degrees or less. ie High 70 low 60. This will reduce stress, allow for proper nutrient up take and metallization as well as reducing a dew point that increases the potential for powdery mildew.

One last thing bleaching can occur to the tops if the light is too close to the tops. Keep the 600 about 12 inches away. More if it's not vented.

 

[topfuel29]

You have a Severe Magnesium Deficiency.
IMO-Don't worry about it. Your on week 6, couple weeks to finish. No problem.
Chalk it up as experience.
Next time use Cal/Mag once a month from start to finish.
Watch your Leaves, if there not Green take a pic, then come here to RIU

Good Luck on Your Grow.

 

[live4flight]

You are only partially correct.

During flushing or just watering in the last week or two the plants will naturally turn yellow as the plants use up the stored energy in the leaves. If the correct amount of nutrients are being applied, the plant should be green until harvest. Yellowing naturally happens over the entire plant evenly. In my experience they can be either way depending on how water or nutrients are applied in the final weeks.

There is a definite nutrient disorder showing in the pic. Yellow leaves with green veins can be one of several disorders. Macro and micro. To me it looks like maybe iron. To fix this issue or any other nutrient disorder take these steps.
1. Flush the plant with water. If you have water out of the pH range of 6-7 adjust it with a good pH up or down solution. GH pH UP/DOWN is a great choice. It is much more stable than using baking soda or lemon juice. For every gallon of soil flush with 3-4 gallon of pH adjusted water.
2. Make sure you are using a balanced nutrient regimen. (just because you may use an entire nutrient line up doesn't mean you are simply good to go.) Fertilized with a correct pH balanced solution.
3. Test run off water or nutrient solution for pH. Runoff pH should be in the correct range of 5.5-6.5. If it is out of range compensate with higher or lower pH water or nutrient solution. ie if runoff is 7.5 water with 5.5 and the average is 6.5. This is a good way to start.

On another subject your temps are way too high. And the temperature difference is too great. Keep temperatures below 75 with 70 being optimal unless using CO2. Also temperature differences should be kept to 10 degrees or less. ie High 70 low 60. This will reduce stress, allow for proper nutrient up take and metallization as well as reducing a dew point that increases the potential for powdery mildew.

One last thing bleaching can occur to the tops if the light is too close to the tops. Keep the 600 about 12 inches away. More if it's not vented.

Thanks for the response! I was nervous about the day/night temp difference. I am going to start running a small heater at night. I flushed about 2 weeks ago and the problem has gotten worse since then.

 

[live4flight]

You have a Severe Magnesium Deficiency.
IMO-Don't worry about it. Your on week 6, couple weeks to finish. No problem.
Chalk it up as experience.
Next time use Cal/Mag once a month from start to finish.
Watch your Leaves, if there not Green take a pic, then come here to RIU

Good Luck on Your Grow.

Thanks! Do you think that I should try foliar feeding with cal/mag to help the situation?

 

[Herb Man]

Also your humidity is too low.

Some say it doesn't matter, but I have found it does.

So bought a humidifier and keep it at around 40 in flowering.

The plants appreciate it.

 

[Herb Man]

It's normal for a plant to yellow when it is almost done. But...................

I try to give them what they need to keep them green for as long as poss, a little sulfur, Fish, Blood & Bone Meal, Bat Guano and Molasses, all through flowering.

I aim to keep them green up until the last week or two of flowering, when they naturally yellow as they do in nature, signaling there readiness.

Preventions better than cure.

 

[qroox]

It's normal for a plant to yellow when it is almost done. But...................

It's normal to die if you do not eat a thing,if that's what you're saying..Should you die ? Of course not.Same goes for MJ.High N food guyz.Keeping them green,will get you more buds.It's normal in nature,not in our gardens.
Lack of Mg ..It occurs commonly in foliage plants because it is leached and not replaced.Epsom salts at a rate of 1 teaspoon per gallon maybe used once or twice during flowering.

 

[neonknight420]

You have a iron def.

 

[Cpappa27]

Some strains require a lot of cal mag during flowering.

 

[solitarygrower]

You have a iron def.

Iron-def might end up like that, but only if the leaves yellowed from the petiole and towards the tips.
The interesting thing is that a lot of deficiency guides show Iron def as starting with yellowing margins around the whole leaf... (which IMHO is not correct for cannabis).