is this typical of powdery mildew?

11 years ago

is this a result of powdery mildew or something else altogether? i did have powdery mildew on these cucumbers. sprayed Fertilome, but did not seem to help. i have pruned some leaves to get rid of it, but whatever this is keeps affecting the plant. i pulled up one vine earlier due to this and sprinkled some powdered sulfur on the soil but was hoping to not lose this one too. this is raised bed, about 1:1 compost to soil. every three months very light Miracle Grow generic. the new growth at the tips of the vine is nice and healthy green (you can see this in the background), but the older leaves look like this and are very brittle. fruit is not affected. thanks for any clues!

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Comments (10)

rhizo_1 (North AL) zone 7
11 years ago
It is one hundred percent NOT powdery mildew, nor can I think of any other fungal disorder that this resembles.
Kimmsr
11 years ago
Powdery Mildew appears as a whiteish dust on the leafs surface and it can be wiped off. Those leaves are demonstrating Chlorosis, yellowing, for some reason and that is mostly the result of a nutrient imbalance. Some may tell you this is the result of a Nitrogen or Iron deficiency which might possibly be or it might be because of a wrong soil pH that is preventing proper utilization of some nutrtient or it may be that there is too much of something that keeps the plant from properly utilizing some other nutrient.
Excess Phosphorus in the soil can keep a plant from utilizing Zinc, Iron, and Copper while excess Potash can inhibit utilization of Nitrogen. Excess Magnesium can inhibit utilization og Calcium and vice versa, and both are needed for a plant to produce Chlorofil which is what makes leaves green.
What is your soils pH?
What is the balance of Ca to MG?
How much organic matter is in that soil?
How well does that soil retain moisture?
How well does that soil drain?
What kind of life is in that soil?
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Dumping limestone on the soil will have no effect on the development of PM and will likely screw up your soil pH. PM doesn't survive in the soil - it needs living plant tissue - so soil treatments are a waste of time. The development of PM is an environmental condition determined primarily by weather - warm, humid nights and dry soils (as are common in late summer) are ideal conditions for pathogen incubation It would be far more practical to treat susceptible plants before you see any signs of the disease. And to follow the cultural pactices that are recommended to avoid PM in the first place. ETA: milk has a pH of 6.5 to 6.7, so slightly acidic.....not alkaline. And lactic acid, which is what is the effective PM control in milk, is very acidic at a pH of 2.4. It is this extreme acidity that makes the PM disinclined to develop or spread.
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melvee
Original Author
11 years ago
i guess i need to get out the soil test kit i have never used. soil drains well, raised bed also housing Derby beans, California Wonder sweet peppers, and some marigolds. everything else is thriving with nice, green growth and large fruit. thanks for your info, tho. i will get on it today. what would be a good fertilizer for this? is the Miracle-Gro insufficient to correct this?
steven1032
11 years ago
as long as it has all the macro and micro nutrients in it. new growth is iron problem and old growth is nitrogen problem.
melvee
Original Author
11 years ago
nitrogen and phosphorus are low, pH is a tad high. i have sulfur i can use for the pH but probably won't do that until the fall. anything i can use to raise the nitrogen and phosphorus immediately?
Kimmsr
11 years ago
Chlorosis appears when there are any one of several nutrient problems.
Nitrogen - Lower leaves yellow, overall plant light green, growth stunted.
Potassium - Tips and edges of leaves yellow, then brown, stems weak.
Magnesium - Interveinal chlorosis, growth stunted.
Zinc - Interveinal chlorosis, leaves thickened, growth stunted.
Iron - Interveinal chlorosisl, growth stunted.
Sulfur - Young leaves light green overall, growth stunted.
Boron - Young leaves pale green at base and twisted. buds die.
Copper - Young leaves pale and wilted with brown tips.
Manganese - Intervinal chlorosis on young leaves with brown spots scattered through the leaf.
Molybdenum - Interveinal chlorosis, growth stunted.
From the Rodale Encylopedia of organic gardening.
calliope
11 years ago
As long as your plant is producing a good crop and the fruits are normal and the new growth is green and the white leaves are on the lowest part of the plant, they may just be senile, old leaves.
ken_adrian Adrian MI cold Z5
11 years ago
the use of senile cracks me up ..

i would call them overly mature.. and the plant is shedding them .. it happens all the time on a lot of annuals.. the oldest leaves are just 'spent' ...

ken
calliope
11 years ago
Senile has become a perjorative word. IOW it originally mean 'overly mature', but got stolen by masses to refer to dementia. In zoology and biology and especially medicine referring to something as senile has nothing to do with its mental status, but that it has progressed past its prime.
Tiffany, purpleinopp Z8b Opp, AL
11 years ago
Helpful list, Kim, and interesting factoid, Calliope.

is this typical of powdery mildew?

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rhizo_1 (North AL) zone 7

Kimmsr

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is this typical of powdery mildew?

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