Roots, Shoots, Fruits & Flowers: Tomato Disease & Blossom End Rot in Squash

430_tomato_leaf_and_septoriajpgA tomato plant with suspected Septoria fungal infection.
Photo: Liz Black.

Tomato Disease

Liz sent some clear pictures of her tomato leaves and asked, “I have some vibrant tomato plants in a raised garden bed but some of them are beginning to get black edges on them which is concerning me. I am not sure if I fertilized them too much or if it is something else.

I have attached some photos, so hopefully you can tell me what I need to do to continue having healthy tomato plants so I can have some delicious homegrown tomatoes in the near future!”

Dan Gill, retired AgCenter horticulture specialist, addressed this very same issue in 2015, “This is Septoria leaf spot, a common fungal disease of tomatoes.

Remove diseased leaves. If caught early, the lower infected leaves can be removed, bagged and disposed of. However, removing leaves above where fruit has formed will weaken the plant and expose fruit to sunscald. Do not compost diseased plants.

Improve air circulation around the plants. Make sure plants are spaced properly.

Mulch around the base of the plants. Mulching will reduce splashing soil, which may contain fungal spores associated with debris. Apply mulch after the soil has warmed.

Do not use overhead watering. Overhead watering facilitates infection and spreads the disease. Use a soaker hose at the base of the plant to keep the foliage dry. Water early in the day.

Use crop rotation. Next year do not plant tomatoes back in the same location where diseased tomatoes grew. Wait 1–2 years before replanting tomatoes in these areas.

Use fungicidal sprays. Fungicides will not cure infected leaves, but they will protect new leaves from becoming infected. Apply at 7 to 10-day intervals throughout the season. Apply chlorothalonil, maneb, macozeb, or a copper-based fungicide, such as copper hydroxide, copper sulfate, or copper oxychloride sulfate. Follow harvest restrictions listed on the pesticide label.”

428_fig_2_squash_and_BERjpgSmall squashes with blossom end rot, a calcium deficiency.
Photo: Bob Shirley.

Blossom End Rot in Squash

Bob sent a couple of pictures and asked, “Could you tell me what is wrong with my squash?”

A couple of horticulturists with the AgCenter wrote a passage about “blossom end rot” (BER) in 2005, “Blossom-end rot can occur when sunny days follow a cloudy, wet period. It is a calcium-deficiency disorder in the plant and not a pathenogenic disease. Some cultivars are more prone to this condition.

Calcium moves slowly in plants and even slower in the fruit, so deficiencies can occur even when soil tests indicate that calcium is adequate. Blossom-end rot often occurs on the tomato first. It may also be a problem on peppers, squash and watermelons. It is more common on fruit that is one-third to one-half grown, and it occurs on the blossom end of the fruit.

It begins as a small, water-soaked spot and develops into a dark brown, leathery spot that may involve half the fruit. The surface of the spot shrinks and becomes flat or sunken. Blossom-end rot is caused by a lack of calcium in the developing fruit. The uptake of calcium from the soil by the tomato plant can be reduced by fluctuations in soil moisture – either excessively wet soil or excessively dry soil.

The disease commonly occurs when plants are growing rapidly and luxuriantly early in the season and are then subjected to prolonged dry weather. The disease may be more serious on the windward side of a garden and on staked tomatoes rather than on unstaked or bushy plants.

Prevent blossom-end rot by maintaining a soil pH around 6.5 and uniform soil moisture by irrigating and mulching and avoid heavy applications of nitrogen.

Control blossom-end rot by spraying foliage with 2 level tablespoons of 96 percent calcium chloride in 1 gallon of water at seven- to 10-day intervals. Do this for three to four applications. Begin spraying with first appearance of symptoms. Overdosing plants with calcium chloride may result in leaf burn. Spray on cloudy days or wait until the sun is low.

Calcium nitrate also may be used. Use 1 rounded teaspoon per plant. Apply calcium nitrate into the soil about 8 inches from tomato plant stems. A second application may be needed several weeks later as well. If foliar applied, use 2 level tablespoons per gallon of spray applied late in the day.

If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337-463-7006 or Also, you can be on the “green thumbs” email list by emailing your request to the address above.

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”

4/30/2020 2:23:41 PM
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