Watermelon rotting on vine

What do I do about blossom end rot?

Blossom end rot is a dark, rotten spot that occurs at the end of a fruit. Usually this occurs as a result of inconsistent available water supply. When the soil becomes too dry for a period of time, calcium becomes bound in the soil and is unavailable to the plants for fruit development. But if your soil ph is off, calcium may be unavailable even if the water content is good. Or maybe there simply isn’t enough calcium in the soil to begin with.

First, be sure you only have 2 plants per hill per 80sf. If you have more than that, thin them down to 2 or 3 at the most of the strongest vines. This will take pressure off the vines competing for available nutrients. You will have better fruit development.

Assuming you have thinned to 2 or 3 vines:
1) If you have been in very dry conditions, provide consistent irrigation at a rate of 1 inch per week. That will free the calcium up and your vines can reset new healthy fruit.

2) If your ph is off, add dolomitic lime at 5 pounds per 100 sf to raise the ph one point in loam soil. Double it for clay. Halve it for sand. Dolomitic lime adds calcium. You can’t have too much calcium in the soil, so don’t worry. The plant will only use what it needs even if there is “too much.” If you can gently scratch it in without disturbing the plant too much, that’s a good thing. Then water it in liberally to make it available to the roots.

3) If there isn’t enough calcium, add dolomitic lime. Follow steps above, although calcium shouldn’t be low if you used the stable horse or cow manure as recommended. Pluck all the diseased fruit and dispose of them away from your field. Your plants should refruit.

And don’t feel bad! I’ve used the same remedies in my field because of drought that resulted in blossom end rot.

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Q: Last year I had the ends rot out of watermelon and cantaloupe. What can I put on the plants to prevent the end rot?

Q: Last year I had the ends rot out of watermelon and cantaloupe. They bloom but no fruit developed. This year, I planted zucchini instead and I am getting the same problem. The fruit is rotting out from the bloom end. I now have cantaloupe in bloom, but no fruit started.
A: Blossom end rot is a common problem on plants in the melon family. The root cause generally is the lack of calcium in the soil or the ability of the plant to update calcium. We would suggest you have your soil tested every few years. The cost is minimal ($7) and the University of Florida will run a complete nutrient analysis for you – money well spent. Vegetables grow best when the pH of the soil is close to 6.5. In addition to being sure the soil has enough calcium it is equally important that water be available on a regular basis so the uptake of nutrients to the plant is efficient. If the plants experience drought at the time when the blossom or fruit is forming then maturity of the fruit or rot can occur. You can come to the Yulee satellite office or the main office in Callahan to obtain a soil test kit. Call us for directions 904 – 530-6350 – Yulee or 904 530-6353 – Callahan.

by kathywarner

Posted: June 13, 2017

Category: Fruits & Vegetables, Home Landscapes, Pests & Disease

Tags: blossom end rot, melon, squash

Watermelon Bottom Turns Black: What To Do For Blossom Rot In Watermelons

You know it’s summer when the watermelons have grown so big they’re almost bursting out of their skins. Each one holds the promise of a picnic or party; watermelons were never meant to be eaten alone. But what do you tell your friends and family when the watermelon bottom turns black? Sadly, your fruits have succumbed to watermelon blossom end rot, and although affected fruits aren’t treatable and probably aren’t palatable, you can save the rest of the crop with some fast modifications to the bed.

Why is Watermelon Rotting on Bottom?

Watermelon blossom end rot isn’t caused by a pathogen; it’s the result of fruit that lacks the correct amount of calcium to develop properly. When fruits are growing rapidly, they need lots of calcium, but it doesn’t move through the plant very well, so if it’s not available in the soil, they will be deficient. A lack of calcium ultimately causes rapidly developing cells in fruits to collapse on themselves, turning the blossom end of the watermelon into a black, leathery lesion.

Blossom rot in watermelons is caused by a lack of calcium, but simply adding more calcium isn’t going to help the situation. More often than not, watermelon blossom end rot occurs when water levels are fluctuating during fruit initiation. A steady supply of water is required to move calcium to these young fruits, but too much isn’t good, either – good drainage is necessary for healthy roots.

In other plants, excessive applications of nitrogen fertilizer can initiate wild vine growth at the expense of fruits. Even the wrong type of fertilizer can lead to blossom end rot if it binds the calcium in the soil. Ammonium-based fertilizers can tie up those calcium ions, making them unavailable to the fruits that need them most.

Recovering from Watermelon Blossom End Rot

If your watermelon has black bottom, it’s not the end of the world. Remove the damaged fruits from the vine as early as possible to encourage your plant to initiate new flowers, and check out the soil around your vines. Check the pH — ideally, it should be between 6.5 and 6.7, but if it’s under 5.5, you’ve definitely got a problem and will need to quickly and gently amend the bed.

Look at the soil while you’re testing; is it sopping wet or powdery and dry? Either condition is blossom end rot waiting to happen. Water your melons just enough that the soil stays moist, not wet, and never let water puddle around the vines. Adding mulch helps keep soil moisture more even, but if your soil is clay-based, you may have to mix in a considerable amount of compost at the end of the season to get good watermelons next year.

Most people don’t want to grow watermelons because of rot. Another common reason is the small watermelon fruits that usually fall off the plants instead of growing into the giant fruits. There are four main reasons the small fruits fall off.

1. There could be are too many fruits on a plant

Most watermelon varieties can’t carry more than three fruits on each plant. Therefore, if the plant produces more than three fruits, it aborts the youngest fruits to preserve the older and larger ones. So, count how many healthy watermelons are on each the plant before you get discouraged.

2. The plant isn’t healthy enough

An unhealthy plant can’t support as many melons as a healthy one. Therefore, if the plant looks yellow, stunted or in any way less than healthy, that could be the reason your baby melons are falling off.

3. The female blossoms weren’t pollinated enough

Fruits that don’t get enough pollen during fertilization eventually get rejected by the plant. Honeybees must visit a single female flower at least six to eight times and fertilized with between 500 and 1000 grains of pollen, distributed over all the lobes of the stigma, before it is considered adequately pollinated.

You might also like: How to grow watermelons

4. The fruits have a fungal disease

There are several types of fungi in the soil that affect melons and cause rot:

Blossom End Rot

This rot causes the blossom end of the melon to turn brown and look like it’s collapsing inward. Blossom end rot usually happens when there isn’t enough rainfall. To avoid this rot, mulch the base of the plants to help keep the roots cool and moist. Rather than a usual mulch, try to use black plastic around the base of the plant to also block weeds. Furthermore, water regularly and remove any damaged fruit.

Belly Rot

This rot is caused by a fungus, Rhizoctonia solani Kuhn. It is most common during warm, humid or exceptionally rainy weather. A black or brown spot appears on the fruit where it touches the ground and then spreads to the rest of the fruit. The spot will looks sunken and spreads very quickly. Try to remove the affected melons and improve drainage. Also, try to keep the developing fruit off the ground.

Gummy Stem Blight

This rot also known as black rot, is caused by the fungus Didymella bryoniae. The leaves appear yellow in the early stages and the watermelons appear sunken, with dark spots as the infection progresses. These are a greasy-green color at the beginning, but turn dark, brownish-black as the spots enlarge. So, check your plants regularly for signs of black rot. Use fungicides to help prevent gummy stem blight.

Bacterial Fruit Blotch

This fungus causes dark, water-soaked blotches of rot on the fruits. The rind has greasy-looking areas with white mold either on the spot or on the fruit’s stem. The fungus can live in the soil for years so avoid panting where you’ve has this problem before. Ensure there’s adequate drainage, especially after heavy rain. There are also fungicides for bacterial fruit blotch. However, you have to follow manufacturer’s instructions carefully.

Rind Necrosis

Some watermelons have dry, light brown spots. This disease doesn’t affect the flesh of the fruit itself and you can’t rind necrosis. It just makes the fruit look ugly. To avoid it, plant watermelon varieties that are labeled rind necrosis resistant.

How to prevent rot

Next time you plant watermelons, ensure it’s a completely different area from the one you planted in before. Most importantly, only buy only treated seeds to ensure they don’t have diseases. Furthermore, re-evaluate farming practices such as using too much fertilizer or over/under watering the plant. Check the watermelon vines throughout the growing cycle for signs of diseases. If you catch the disease early, you can minimize the damage. And, if some of the vines have diseases, pull them up and destroy them or bury them to prevent the spread of infections.

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