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Blossom End Rot, Powdery Mildew, and Nutrient Deficiency on Cucumber and Squash

Updated: Aug 15, 2019

Greetings Gardening Friends!

Here in Portland we are about two months into the summer growing season. The season got off to a slow start with cold night temperatures throughout May. And this summer the temperatures have been cool and mild with more days of rain than usual.

Today I'd like to share with you about three problems I am seeing in my vegetable garden on my cucumber and squash plants: yellowing leaves, powdery mildew, and blossom end rot.

First, lets talk blossom end rot. Like I said blossom end rot most frequently occurs on tomatoes. It can also affect cucumbers, pumpkins, and squash. Even melons and peppers! Here are some pictures of my own garden this week to show you what blossom end rot looks like:

Blossom end rot is not a disease. Blossom end rot results from a calcium deficiency. I always recommend when planting tomatoes to add a calcium source into the planting hole at planting time. This is a tablespoon each of garden lime and either bonemeal or rock phosphate. Because I do this annually at planting time my tomato plants are no longer bothered by blossom end rot.

This year I am growing 2 cucumbers, 2 summer squash, and 2 winter squash all in large black plastic pots. I filled the pots with half and half mix of potting soil and vegetable planting compost and fertilized with organic granular vegetable fertilizer. I placed the pots in a full sun location receiving 8 hours of sun all after 11am. I planted the plants late in May when night temperatures seemed as close to optimal as we were going to get. The plants thrived and grew very large and began producing flowers and fruit at the beginning of July. Quickly one of the summer squash plants got blossom end rot. I've harvest about a half dozen squash and lost about a half dozen to blossom end rot.

At this point adding lime and bonemeal or rock phosphate to the soil is a little late. These types of organic granular sources of calcium slow release and are not immediately available to the plant. So I am trying this:

I purchased this product from Garden Fever Nursery in NE Portland. It is a ready to use spray applied to the fruit and leaves. This type of calcium is highly soluble, meaning readily available to the plant. I applied this spray this morning and I will keep you posted about the result.

In my further research of blossom end rot on cucumbers and squash I learned that heavy rains can cause calcium leaching from the soil. Do you remember that a few weeks ago we had some epic thunderstorms with so much rainfall per minute we experienced flash flooding? From this lens the blossom end rot on my plants makes a little more sense.

UPDATE ON 7-29-19: I did two applications of the rot-stop spray two weeks apart. I've had no further blossom end rot on any of my squash plants! --Jolie

Another thing I learned is that high nitrogen in the soil can affect calcium absorption. I already knew that high nitrogen fertilizing can attract an abundance of aphids to plants. So it is important to remember more is not better when it comes to manure and fertilizer in the edible garden.

Second, I'd like to talk about yellowing leaves on cucumbers and squash. Here are some photos from my garden about two weeks ago:

When I first observed these leaves I thought perhaps a fungal disease was the culprit. However, I saw no indication of powdery mildew, downy mildew, or cucumber mosaic virus on any of my plants. The leaves all looked healthy with the exception of yellow leaves turning to crinkly brown. These yellow leaves have all signs pointing to a nitrogen deficiency. However, let's keep in mind the manure and fertilizer applied to the pots these plants are grown in. They have been provided with plenty of nitrogen. So, what's the problem here?

Let's go back to what I said earlier about heavy rains leaching calcium from the soil. Heavy rains that come on suddenly can result in all kinds of nutrient deficiency, not only calcium. Nutrient deficiency stresses the plants causing yellowing leaves and blossom end rot. To assist in nutrient absorption I applied a dose of organic granular fertilizer and liquid compost tea to the soil of each pot. Fingers crossed we are done with summer thunderstorms and heavy rain fall so these plants can stabilize.

This morning as I was watering the garden I realized powdery mildew has just established itself on my sunburst patty pan squash plant. This is what it looks like:

Powdery mildew is a fungal disease that attacks cucumbers, melons, pumpkins, and squash. It sometimes targets lettuce, herbs like sage, and annual flowers like calendula in my own garden. Powdery mildew is very common in Portland. Powdery mildew is spread by water splashing from soil to leaf to leaf. I always recommend watering by hand with a watering wand or installing a drip irrigation or soaker hose system. This will ensure water reaches the soil not the foliage.

In previous years I have sworn by applications of compost tea begun at planting time and every 3 weeks throughout the growing season. Compost tea can be purchased by the gallon for $3.99 at Garden Fever Nursery in NE Portland. It is affordable, safe to use, totally natural, and has no negative effect on any beneficial bugs. Perfect for the organic edible garden!

Since I am growing all the squash family plants in containers with brand new planting mix and powdery mildew is soil-born I figured I was pretty safe this year and did not start my preventative applications of compost tea. Well, it is the 3rd week of July and powdery mildew has found my new garden. Luckily, last week I was at Garden Fever for blossom end rot spray and I picked up a gallon of compost tea.

This morning I applied the end-rot spray on my plants so I will wait a few days before applying the compost tea. Compost tea is ready to use, no need to dilute it. It will not burn plants. I use a clean spray bottle, fill it with compost tea, and spray liberally on both sides of leaves of all cucumber, melon, pumpkin, and squash plants. Then I pour about 1 cup of compost tea into the soil around each plant. Considering powdery mildew is taking hold on one plant, I did not do earlier preventative applications, and I don't want it spreading to all my plants I will begin compost tea applications every 2 weeks the rest of the summer.

Lastly, if your cucumber, melon, pumpkin, and squash plants are big leafy green, have flowers, and are not producing fruit it is most likely a pollination issue. Plants in this family female and male flowers on the same plant and require a pollinator to pollinate them. Common garden pollinators are bees. Your garden becomes more welcoming to bees by not spraying, even organics, pesticide fungicide & herbicide. Bees love gardens full of flowers. Plant some companion flowers near your squash family plants. And if bees still do not visit, you can hand pollinate your plants by using a clean q-tip or paint brush. Take pollen from male flower and spread inside the female flower.

If your plants are lush and large and have produced no flowers you can encourage flowering by applying an organic liquid "bloom" fertilizer like this Fox Farm brand Big Bloom available at Portland Nursery. Garden Fever also had a good one and I can't remember the brand just now. A bloom fertilizer is higher in potassium, so when you look at the three numbers on fertilizer it is the middle number like this 0-10-0. An organic liquid fertilizer is water soluble and immediately available to your plants.

Hoping that was helpful information and not depressing! On the happy happy side I have harvested lots of delicious 'Success' yellow summer squash, 'Sunburst Patty Pan' summer squash, 'Miniature White' cucumbers, and 'Marketmore' cucumbers. Those cucumbers have been sweet, not bitter, and so yummy in salad. I've steamed those summer squash to eat with sesame oil chicken & rice. I've also shredded them to bake in savory squash and herb no-grain dairy-free bread.

Happy Gardening,


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