Alternaria Leaf Spot Of Turnip – Treating Turnips With Alternaria Leaf Spot

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By: Mary H. Dyer, Credentialed Garden Writer

Alternaria leaf spot is a fungal disease that causes big problems for a variety of plants, including turnips and other members of the Brassica family. If left untreated, alternaria leaf spot of turnips can cause significant decrease in yield and loss of quality. Getting rid of alternaria leaf spot of turnip isn’t always possible, but you can take steps to keep the disease in check. Read on to learn more.

Symptoms of Alternaria Leaf Spots on Turnips

Alternaria leaf spot of turnip shows up on leaves first, displaying small, dark brown or black spots with a yellow halo and concentric, target-like rings. The lesions eventually develop a thick buildup of spores and the centers of the holes may fall out, leaving a shot-hole appearance. The spots also show up on stems and blooms.

The infection is frequently introduced on infected seed, but once established, it can live in the soil for years. The spores are spread by splashing water, tools, wind, people and animals, mostly in warm, humid weather conditions.

Turnip Alternaria Leaf Spot Control

The following tips can help with preventing and treating turnips with alternaria leaf spot:

  • Purchase certified disease-free seed.
  • Plant turnips in well-drained soil and full sunlight.
  • Apply fungicides at the first sign of disease, and then repeat every seven to 10 days throughout the growing season.
  • Practice crop rotation. Avoid planting cruciferous crops such as cabbage, kale, broccoli or mustard in the infected area for at least two or three years.
  • Keep weeds in check. Many, especially cruciferous weeds like mustard and queen anne’s lace, may harbor the disease.
  • Destroy diseased plant parts by burning, or dispose of them in sealed plastic bags. Never compost infected plant debris.
  • Plow the soil thoroughly immediately after harvest and again before planting in spring.
  • Spray aphids with insecticidal soap spray; the pests may transmit disease.
  • Avoid high-nitrogen fertilizer, as lush foliage is more susceptible to foliar diseases.
  • Water at ground level using a soaker hose or drip system. Avoid overhead sprinklers.

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Alternaria leaf blight

The fungus Alternaria cucumerina causes Alternaria leaf blight. This disease is most common melon, but can also affect cucumber, pumpkin and squash. Alternaria leaf blight does not commonly infect fruit. It can reduce yield and quality through reduced plant vigor and sunscald of exposed fruit.

Alternaria species are simple parasites that survive saprophytically outside the host. Diseased crop debris is the primary site of survival from year to year. Resting spores (chlamydospores, microsclerotia) have been reported. The diseases are favored by warm temperatures (60-78° F) and at least 12 hours of relative humidity of 90 % or more. The fungi sporulate profusely and are spread throughout fields by wind, splashing water, equipment, and workers. The main means of introduction into new areas is on infested seed.

Alternaria infection can be mainly cosmetic, but results in crop rejection by distributors and customers. Infection of broccoli and cauliflower heads can lead to complete deterioration of the heads and result in total loss of marketability. Affected cabbage do not store well as lesions provide entry for secondary soft-rotting organisms. Control of Alternaria leaf spot on cabbage heads in the field is necessary for long-term storage. Heavy infections of foliage reduce plant vigor and yield. Pod infections cause distortion, premature shattering, and shriveled, diseased seed that germinates poorly.

A Short Tutorial on Turnips

Before we jump in, keep this in mind:

If you keep your plants evenly watered, make sure they have adequate air circulation, and observe good gardening practices like testing your soil and rotating your crops, this will go a long way toward avoiding all of the issues we’ll be discussing.

How’s that for motivation for being a responsible gardener?

If you haven’t read our guide to growing turnips yet, now is an excellent time to check it out.

Here’s a quick rundown of the basics:

Turnips, Brassica rapa subsp. rapa, are suitable for growing in gardens in USDA Hardiness Zones 2-9. They prefer cool weather, which is why they’re usually grown in the spring or fall, or as a winter crop in warmer areas.

These root crops need well-draining, loose, nutrient-rich soil to thrive. They also require consistent, even moisture.

If you leave your turnips in the ground too long, you leave them open to various risks that could result in cracking, so pull them as soon as they’re ready.

Harvest time will vary, depending on the variety you’re growing, but most cultivars mature in 30 to 60 days.


If you leave growing turnips long enough, they’ll bolt to seed, which can be a good thing if you want to save a few for next year. Choose a couple of plants to leave in the ground. Let them flower in the spring and allow the seed pods to turn brown.

Snip the pods off and dry them indoors in brown paper bags. When they are dry, break them open. Store seeds in a paper envelope.


Pick small tender leaves for salads. Slightly larger leaves can be cooked in dishes or wilted in a pan. If the leaves are too big, they are usually bitter and not worth eating.


The roots are ready for harvest after 5-6 weeks for early varieties and 6-10 for standard types.

Harvest turnips when they are the size of a golf ball to a tennis ball. Some turnips are tasty when allowed to grow large, but check that’s the case with your variety. To harvest, dig around the root to loosen it and then pull it gently out of the soil.


Consume the leaves when you pick them because they will wilt rapidly. If you do want to store them, wash thoroughly and place in a plastic bag or cloth wrap in the fridge. I have kept them this way for up to four days.

You can store the root in the fridge for up to two weeks. Turnips store well in a root cellar or cool basement, where you can keep them for months. Place unwashed turnips in a single layer covered in straw. Check them regularly to make sure they aren’t going bad.

You can eat turnips in so many ways. Soups, stews, fried, boiled, sautéed, roasted and eaten raw in salads. Don’t be afraid to experiment. Who knows, you may even convert the kiddos. Do you have any great recipes to share with us on how to use your turnip harvest?

Watch the video: Webinar - Comparing Fungal and Bacterial Leaf Spots

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