Leaves are turning yellow and dying. Only affects some plants.

[Bumblebeer]

I'm a member of my state's industrial hemp pilot program. I'm growing 1.5 acres this year split across two strains, sweetened and stout. The are in the same field and have received the same treatments and fertilizers. The sweetened variety seems to be doing just fine, however the stout strain is having some serious problems.

I noticed the problem starting about 5 days or so ago and it has steadily gotten worse. What's happening is that the lower leaves are turning yellow, then starting to brown and curl up, then they die and fall off. It seems to be happening to some plants more than others, and like I said it's only happening with the one strain. Some are so bad now that I'm sure I'll lose the plant.

I first thought it may have been water stress, so I irrigated more. No luck. I then thought it may be nutrient deficiencies (nitrogen?) But after consulting with an experienced local, he doesn't seem to think that's the problem. In any case I sent a soil sample off to my university soil testing lab. When I get those results back I should know about nutrients for sure. Also I bought a PH probe I will be testing the soil with later today. However, I put lime on the field at the beginning of the year to correct the PH so I don't think this is the problem, but at least I can rule it out.

Yesterday I pulled one of the plants to check the roots. They looked healthy, so that rules out root rot, or over watering.

At this point I'm fairly certain it is some sort of fungal disease since I can't find any leaf or stem damage that would indicate bugs or pests. I've consulted the big green book, but I can't nail down exactly what this is. I'm not seeing any spores or mycelium.

Any help would be greatly appreciated.

 

[buzzmobile]

Looks more like magnesium deficiency.
https://www.royalqueenseeds.com/blog-magnesium-deficiency-in-cannabis-plants-n590

Magnesium deficiency is the definition of a bottom to top nutrient imbalance in cannabis. Growers will first notice unhealthy looking lower growth. It’s the oldest and lowest leaves that will signal the advance of a magnesium deficiency. In the beginning, bottom leaves will yellow and the tips will dry out into a crunchy brown.

Unfortunately, magnesium deficiency is mobile, so it will spread up the plant if left unchecked. As the deficiency spreads to the shoots, they will turn purple and leaf chlorosis will accelerate. Grower reaction time, as always, will be the defining factor. Don’t mistake magnesium deficiency for nitrogen starvation.

Probably the biggest mistake novice growers make is rushing to apply a quick fix by increasing nutrient doses. In fact, this will likely lead to nutrient lockout. No matter the growth stage or medium, yellow leaves and brown spots starting from the bottom are a red flag for magnesium deficiency. Micronutrient deficiencies always start in the root zone; magnesium deficiency is no exception.

 

[slownickel]

Phosphorus deficiency. From the look of all that grass there is no Calcium either. Post the results of the lab.

 

[Teddybrae]

Mate ... that looks SO BAD I 'm wondering about spray drift. Any Glyphosate being sprayed nearby?

 

[budsnblunts]

When leaves die and canabilize from the bottom up wards I usually lean towards a nitrogen deficiency. Can you do a large top feed of a rich chick shit mix perhaps?

 

[Lost in a SOG]

I mean if you limed it earlier in the year potentially some bits were more in need than others and these plants happen to be in too high pH..

 

[ambertrichome]

I agree with budsnblunts. Usually when they turn yellow, and die from the bottom up, its a Nitrogen deficiency.
Check PH too, as if tis off they cant eat, starving them of everything. Nitrogen being one.

Have they been getting Nitrogen?? Its a myth weed doesn't need Nitrogen during flowering.

In reality, it needs more and more up to a certain point, and in reality, needs more of everything until the last couple/few weeks before harvest.
But if organic, they just need a good fertile soil source, with lots of microbial activity. Feed the microbes, and water.

Nitrogen for plants is the same thing as Protein for humans/animals.

Plants skip the digestive process of turning protein into Nitrogen.

Positive Nitrogen Balance in Humans/animals is called Anabolic, or building up.

If you go Catabolic, you eat yourself/muscles.

 

[jackspratt61]

Follow slownickel friend. Check his post history. Good learning!

 

[ambertrichome]

Calcium/Magnesium Deficiency usually starts on the new growth