Lemon Cucumber and Zucchini foliage white coating

Asked July 28, 2019, 11:05 AM EDT

Both of these plants get a white coating on the leaves. It looks powdery but doesn't wash off. Is this normal? Also, the lemon cucumber plant foliage has a lot of dead leaves. I am growing both plants in large plastic tubs. I'm pretty much watering daily. The cucumber especially seems to need the daily watering or it starts wilting. We are also growing raspberries, strawberries, blueberries pear tomatoes, beefsteak tomato, and green peppers very successfuly. All plants are loaded. The zucchini production is kind of mediocre. I use Miracle Gro when I water with a hose attachment. Thank you for any advice to make my cucumbers and zucchini happier! Having a grand time with our gardening project.

Linn County Oregon powdery mildew zucchini

1 Response

Hi and thanks for contacting Ask an Expert. Nice backyard garden, love the tubs.
It does look like you do have a bit of powdery mildew on your cucumbers. This is a fungus that can be eliminated with fungicide. There are several fungicides on the market that you can use. I recommend getting two different types and alternating them. Safer brand fungicide spray contains sulfur and can help maintain a healthy plant. Since your cucumber plant only has a little, spray that on the leaves both sides. Follow the directions exactly. Another is an oil 100% Neem oil usually comes in a concentrate and you dilute it about 1.5 teaspoons per quart of water, but again follow the direction, do not buy anything with added ingredients, just 100% Neem oil. Another aid is a bacteria that comes in a spray bottle called Serenade. This is a bacteria that attacks fungal spores. All of these are recommended for organic gardens.
Next season look for disease resistant cucumber varieties to mildew, there are some on the market. Also to increase the overall health of your plant, add compost tea. If you do not have any compost, you can purchase it. Take a bucket, add compost about 1/3 of the bucket and then fill with water. Let it stand overnight and then pour it on the soil around the plant. The wet compost can be placed around the plant as well to hold in moisture. The roots will be able to take up the water with the extra nutrients quickly. You can do this for all your plants but not tomatoes or your zucchini - too much nitrogen.
The dried leaves on your cucumber could be from uneven watering, very hot weather, wind or an early mold. I say early because I do not see any dried leaves now. You have plenty of flowers so you should have lots of cucumbers in the coming weeks. Be careful not to spray anything that will kill your pollinators. They will transfer pollen from one blossom to the next and give you more vegetables.
Always read the directions very carefully on anything you spray. Both sulfur and Neem oil will kill pollinators so spray at night or early in the morning before they are out. You must wait 10 days after spraying sulfur to spray another fungicide.
Your zucchini is doing beautifully, your leaves look tremendous. I think you have enough nitrogen in the soil but not enough phosphorus. You want the plant to make flowers. You can buy liquid "Bloom" fertilizers.. Look for the middle number on the bottle to be higher than the other two. Fertilizers have three numbers 1-2-3 or 3-3-3 or really many combinations. You need one that says 0-6-2 or something similar. The first number refers to nitrogen which your plant has plenty of and the second is phosphorus which promotes blooms and the third is potassium that aid in the overall health of the plant. Again follow the directions and the plant should start to produce blossoms. I suggest stopping the Miracle Grow for the zucchini.
Look for cucumber beetles on both plants usually in the blossoms. They will eat your plants. They look like a lady bug in shape but are lime green with black spots. There is a cousin that is lime green and black striped but similar in body shape, Bad guys. They will also eat all types of flowers.
I have added a link from Texas A&M because of its description of so many plants and how to grow them. They also have a section on diseases and insects but they list some toxic sprays. The ones I have listed in this answer are approved for organic gardening, many others are not. Look for "OMRI" on the labels. These are approved for organic garden.
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