Take Control Of Powdery Mildew

What is It?

One thing that you can count on in the early summer in Texas is humidity and powdery mildew.  They seem to come as a team.  We are going to find out how to take some really important steps to avoid powdery mildew.

Powdery Mildew is a fungus that overwinters on leaves.  It is spread by the wind, splashing of rain on plants and insects and is very active during times of high humidity  There are many different kinds of spores that affect various plants. Powdery mildew is host specific.   The powdery mildew that affects your squash is not the same that affects your phlox.

Powdery mildew looks like white or grey concentric circles on the leaves of plants. The circles may turn black and the leaves may turn yellow and die.  The fruit may fail to form or fall off of the plant.

Powdery mildew usually takes about 7-10 days to complete the life cycle.  If you must spray a fungicide it is recommended that you spray it every 7 days to deep ahead of the spores from reproduction.


There are a lot of ways that you can keep from getting powdery mildew.  If you take all of the precautions you should be safe.  But if the wind blows some spores your way, we will go over organic solutions in the next section.

Plant Resistant Varieties – Who would have thought that mother nature could have made it so easy.  When you are looking at the gardening sites there are codes to tell you what varieties are resistant to what diseases.  PM is usually the       code for powdery mildew.

Plant In Full Sun– Stay out of the shade.  The shady environments are more humid and conducive to powdery mildew.

Air Circulation – Good air circulation is key to keeping powdery mildew at bay.  So make sure to give your plants plenty of room and don’t crowd them.

Wash Off Plants – Simply washing off your plants will help to wash off the spores.   Once your plants have powdery mildew, it is important to wash the spores off before you spray on a fungicide.

Water In The Morning – watering in the afternoon and evening creating a damp humid environment.  Powdery mildew thrives in moist conditions.

Use Organic Fertilizers Conventional fertilizers have a high nitrogen rate compared to the slow release of organic fertilizers. High nitrogen causes fast young growth where PM thrives.

Rotate Crops – Make sure you don’t plant your crops in the same area of the garden or there may still be spores in the soil.  Crop rotation is good on so many levels.

Clean Plant Debris – At the end of the season clean up plant debris and leaves and compost them or spores will form and you may be breeding a monster.  It is important that you throw away infected plants with powdery mildew and do not compost them.

Disinfect Tools – Make sure that you don’t spread disease.  You should be careful to disinfect your tools with one part bleach to four parts water.  Make sure when you are using a tool to trim off infected leaves that you disinfect between each plant.

Cultural Methods

If you have powdery mildew there are some methods that you need to take to help get rid of it quickly.  The key to success is early detection and fast treatment.  If powdery mildew gets into advanced stages you might as well just pull out the plant and save yourself some money.  So if you have it act fast NOW!

Start by pruning off severely infected leaves and disposing of them in the trash. Next wash off the leaves with plain old water. You are just washing the spores off of the plant  A good dose of compost tea will help strengthen the plant and it have a natural fungicide action. If you want to add some garlic in there the last day of brewing, that will help as garlic has a natural fungicide as well.  You want to make sure that you are applying a fungicide every 7 days until the problem is gone.  If it rains, reapply. be careful with copper not to exceed the listed dose as it will build up in the soil.


Skim Milk – is used as a barrier and a fungicide.  Use 1 part milk to 9 parts water and spray all surfaces until dripping.

Sodium Bicarbonate – 4 tsp baking soda,  1/2 tsp liquid soap, 1 gallon water, 1 tbl dormant or horticultural oil can also be added.  Don’t add oil in temperatures over 90 degrees.

Cornmeal Drench 1 cup cornmeal to 1 gallon water let soak overnight.  Drain and discard the solids.  Spray the drench on the effected plants.

Cornmeal – 2 pounds cornmeal worked into 100 square feet of soil.

Potassium bicarbonate – a naturally occurring substance.

Azadirachtin – Made from the oil in neem tree seeds.  Be sure not to apply in temperatures over 90 degrees

Sulfur – Plants can be photosensitive in summer temperatures.

Streptomyces lydicus – is a naturally occurring bacterium found in the soil.  It can be applied to soil mixes or to the foliage.

L-Glutamic acid – is one of the major amino acids found in both animal and plant proteins.  it is used to control powdery mildew in grapes.

Bacillus pumilis strain QST 2808 – is a naturally occurring bacterium found in both soil and water.  It acts as a barrier by preventing spores from forming on plants and  then colonizes the spores.  It also stimulates the plants own resistance system  thus  inducing systemic acquired resistance (SAR).

Jojoba Oil – a naturally occurring oil.  Do not use in temperatures over 90 degrees.

Copper Oxide – a naturally occurring mineral used as a dust or a spray.  Brassica is phytotoxic to copper.

Trichoderma harzianum- is a naturally fungi that is used to treat several pathogens.

Bacillus subtilis QST 713 – a widespread bacterium found in air, water and soil.  it works by competing for nutrients on growth sites on plants. it also works by colonizing and attaching to fungal pathogens.

Rosemary Oil – A naturally occurring oil, be careful not to use in temperatures over 90 degressor you may burn the plants.

Kaolin Kaolin clay is a particle film barrier  and can offer some protection for the organic grower by blocking out the spores. Make sure to spray kaolin on both the underside and the top of the plant leaves.

Pseudozyma flocculosa is a naturally occurring fungus that is used for the control of powdery mildew in greenhouses on cucumbers and roses.


3 Responses

  1. Excellent Post! I experienced white powdery mildew one time on my squash. I did try a few home remedies i found online but they didn’t seem to be working. I eventually bought a product called Green Cleaner… http://www.greenerhydroponics.com/Old-Stage-_bymfg_780-0-1.html
    That did the job and saved my poor plants. Keep a close eye out for mildew and treat on sight.

  2. Hey guys i see that you have copper oxide listed as a way to get rid of powdery mildew on plants and that is a vary true statement infact theres a product ive been recently testing i just found it at a local store its called CuH2o and its to do with copper sulfate pentahidrate but in a liquid form and its proven to work great after a 3 week test on my indoor squash beacuse i live in MI and its winter its work fantastically infact within 24 hrs i noticed a difference and after a light wash ever 3 days for 3 weeks its shown a huge growth spurt and a healthier lush to the squash indeed im vary happy with the copper oxide / cuh2o (copper sulfate) method cuh2o.info is the site ive researched the product on great article ive found it useful.

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