White pumpkin leaves

Pumpkin    UK England Kent

Why are the leaves of my pumpkin plant going white and how to get rid of it organically ?

Posted by: Andrew (1 point) Andrew
Posted: July 26, 2014

David Hughes commented,
please provide pictures. From a distance and close up. That helps. Also, are they in a patch with others? What do the others look like
almost 6 years ago.


This looks like powdery mildew which is a fungal infection affecting many plants and known to infect Cucurbits around the world. (see also this question we received https://www.plantvillage.com/posts/10...)

Sphaerotheca fuliginea and Erysiphe
are the two most commonly recorded
cucurbit powdery mildew pathogens accoring to the APS compendia https://www.apsnet.org/apsstore/shopa... . The former is considered to be more common worldwide

Powdery mildew occurs mostly on leaves. It grows quickly (within 3-7 days from infection to symptoms). Tends to occur on older leaves first and those in shade. Low light and high humdity promote growth.

Getting rid of it organically

Copper sprays: Spraying plants with copper and sulfur has occurred for over 100 years. It was and still is called Bordeux Mix as it was discovered in Bordeux vineyards (see my blog post from way back https://www.plantvillage.com/blog?loc...)
An example of the product is here http://www.vitax.co.uk/home-garden/vi...
Copper is sometimes considered organic, sometimes not. the RHS have some details here http://www.rhs.org.uk/advice/pdfs/fun...

The reason copper can be problematic is that it is toxic to other organisms and can build up on commercial farms. Recently the EU ruled on it to reduce is use in potato farms http://croplifefoundation.files.wordp...

It would combat the disease and is not a synthetic fungicide

Milk is often suggested as a control. Somepeople assume that milk must be an old wife's tale but there are studies that show that at high concentrations the applciation of milk to the leaves is better than fungicides in controlling

"Milk applied twice a week at concentrations of 10% and higher controlled powdery mildew on zucchini squash at least as effectively as conventional fungicides"
Wagner Bettiol, 1999 http://www.sciencedirect.com/science/...

this is from the same paper
"Cow milk may have more than one mode of action in controlling zucchini squash powdery mildew. Fresh milk may have a direct effect against S. fuliginea due to its germicidal properties. Milk contains several salts and amino-acids and these substances have been shown to be effective in controlling powdery mildew and other diseases . Several authors have shown that sodium bicarbonate, oxalate, dibasic or tribasic potassium phosphate, and other salts and amino-acids have been efficient in the induction of systemic resistance . Therefore milk may also indirectly affect S. fuliginea by inducing systemic resistance.
Milk is not a potential environmental or food contaminant, consequently it can be used in organic agriculture. Several organic growers have been spraying 5% cow milk once a week to control powdery mildew on zucchini squash and cucumber."

The mode of action is the production of free radicals following the exposure of milk to light. This in turn causes a collapse of the fungal hyphae (the tubes of fungi, which they extend to grow and feed). Here is a paper (behind a paywall, but you can see the abstract) http://link.springer.com/article/10.1...

The application of milk works best on sunny days

Here is some more


Besides milk and copper one can achieve success with different salts and clay. All similar in that they effect the growth of the fungus.
For example, baking soda. See this video http://www.youtube.com/watch?v=wg-TH2...
see a nice history here; the idea has been around since 1933 at least https://attra.ncat.org/attra-pub/down...

Posted by: David Hughes (54 points) David Hughes
Posted: July 27, 2014

This is definitely Powdery Mildew. In my experience, powdery mildew tends to be more of a cosmetic problem than anything. It is certainly far less aggressive than other diseases/fungal problems. Plants typically survive a long time with the disease and continue to grow and send out new leaves. Fruits are typically unaffected and grow mostly normally. My zucchini suffer from this disease in mid to late summer every year, later spreading it to my cucumbers, but I rarely bother even attempting to treat it as they all survive to a killing frost and produce scads of fruit even with the disease.

In my opinion, 'organic' controls do not work that well for many diseases. Prevention is more key, and can be done by using resistant varieties of plants, keeping them well spaced and with good air circulation, avoiding over-fertilizing, and using pre-emptive applications of fungicide, organic or otherwise. Hand picking of infected leaves may help with minor infestations. Baking soda + some dish soap in water is also supposed to help with prevention if applied periodically throughout the season.

It's obviously too late for you to prevent it now. You are unlikely to be able to get it to go away once it has appeared, although you may be able to control it or help to limit its spread. If you do wish to try to fight it, you may try copper fungicides, neem oil spray, or a milk solution.

Posted by: Allison (2 points) Allison
Posted: July 29, 2014

Powdery Mildew (PM). As was said before infects most members of the cucurbits.

The milk applications work, but there is more to the "why" then that they break down hyphae.

Lactic Acid Bacteria (LAB) what most know as "Active Cultures" in Greek yogurt, Kefir, and raw milk. LAB are the work horses of the microbe world, they can be either anaerobic or aerobic. They break down fungi and odors, certain bacterias, and even ward off bad predatory insects. With milk being sprayed on leaves the LAB can colonize on the plant better, in turn they break down the PM. But if you already have a concentrated LAB (easily made yourself) you can cut the working time down and see big results in 24 hours.

Unlike Copper sprays which work mainly on the outside of the plant and do little for the internal infection, LAB lives right inside the plant when you spray it on and actually beats the fungal infection from the inside out. After applying you can see green coming back, and leaves standing up better in just 24 hours. Not to mention lots of PM having vanished over night.

The catch is you have to apply in the evening, and UV kills them. So by applying in the evening you allow the LAB plenty of time to colonize the garden.

Type Lactic Acid Bacteria into Youtube.com and you will find lots of good info on how you can start making it yourself.

Posted by: Travis (1 point) Travis
Posted: August 18, 2014

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