How To Prevent and Deal With This Disease

As growing environments change with the climate, so does the prevention and control of diseases. One crop increasingly under pressure is the good old reliable family food hero, the potato.

Blackleg is a common disease that appears anywhere potatoes are grown. Even more problematic is that treatment is limited. That’s why prevention is key.

Read on and arm yourself with how to ward off the crop-destroying disease potato blackleg.

What Is Potato Blackleg?

Potato blackleg is a serious, highly infectious disease that threatens any potato growers’ efforts.

It is primarily caused by the bacteria Pectobacterium atrosepticumas well as other species in the Pectobacterium and Dickeya (formerly Erwinia) genera, such as P. carotovorum, P. parmentieri, D. dianthicolaand D.solani.

These pathogens are a worldwide threat, with the ability to cause widespread agricultural and horticultural loss.

Some people confuse bacterial soft rot caused by P. carotovorum and Dickeya dadantii with potato blackleg, since the bacteria can cause both diseases.

Although it used to be a big problem in the late 1800s, we’ve gradually figured out how to prevent it. Of course, you need to know about the disease and what prevention requires, or else you’ll be at risk of a disease that can’t be cured.

The bacterium attacks all parts of the potato plant.

Vectors For Potato Blackleg

The bacteria that cause this disease can spread rapidly throughout a potato field. As plant pathogens go, it’s relatively short-lived, with a lifespan of just a few months. But during those months, it moves quickly.

The bacterial pathogens require damp and moist conditions to reproduce and spread. The ideal conditions are wet for longer than normal periods, and temperatures are around 60-80°F.

Irrigation systems may aid the bacterium’s movements, particularly if the water used is from an untreated source like a well or canal.

Although short-lived, the movement of infected soil, topsoil, manure, and compost can cause transmission from one garden area to another. For example, infected compost used to heap around potato plants can spread the bacteria.

Weeds can host diseases but also condition the soil to make it more hospitable for bacteria to build up by blocking out vital sunlight, which assists moisture in building up. Consistently wet soil is unable to breathe, which encourages pathogens to develop.

The disease is also carried in potato tubers, roots, stems, and leaves. If you purchase contaminated tubers, it could infect your entire garden.

Parasitic nematodes in the soil can also carry and spread the bacteria. Parasitic plant nematodes feed off of tubers, roots, and plant parts in the ground. It feeds via a stylet, a piercing type spear that inserts into the plant’s layers, sucking nutrients from cells.

Signs And Symptoms of Potato Blackleg

When we know the signs and symptoms of potato blackleg, we can take prompt action.

Potato blackleg generally begins at the tuber. From there, it travels through the plant’s central vascular network before the signs and symptoms appear. Watch for the following:

1. Wilting of Leaves

One indicator of potato blackleg is the wilting of the leaves. This symptom may be spotted first, but at this point, the disease is well advanced. As leaves lose their ability to photosynthesize because of the infection, they can’t move moisture and nutrients.

Some leaves may start to open but suddenly fail to develop and die.

2. Discoloration

Due to the lack of nutrient uptake, the potato plant will gradually lose its green color and turns yellow. Discoloration spreads upwards from the initial point of infection, the tuber, to other more visible plant structures, like the leaves.

3. Lesions

As the leaves change and become distorted, circular, brown lesions with grayish-black centers form.

As the bacterium continues through the central ventricular system, the plant will start to turn black. Stems turn brown and then black as the disease becomes more severe.

4. Rotting Tubers

The bacterium that causes potato blackleg can cause the tubers to rot. This starts as dark, sunken spots on the surface of the tuber. These spots may eventually merge and turn the tuber into a slimy, black mass.

In addition to rotting, the tubers may also become soft and mushy.

This is because the bacterium associated with potato blackleg attacks the cellular structure and wall of the potato. This cellular onslaught causes instability and collapse of the tuber, the potato.

5. Foul Odor

As the tubers rot, they may release a foul odor as the bacteria break down the organic matter and produce gases.

This smell can come from the tubers or the base of the stem. Take a whiff and be prepared for a strong and rather unpleasant smell.

6. Damp Soil

Due to the potato’s fibers breaking down, the soil in which it sits may appear unusually damp, clumped, and muddy, even in dry conditions and without being watered.

Potato blackleg wants to spread as quickly as possible. It will utilize the collapse of the host potato plant to infiltrate the soil, where it can briefly survive, and then move on to another neighboring host.

7. Stunted Growth

Such disruption of nutrient uptake and the destruction of stem tissue will stunt the growth of the host potato plants. This means smaller plants and fewer or smaller tubers underground.

They are unlikely to produce as many potatoes as a consequence. Heavily infected plants may not produce any usable tubers, resulting in a lower yield.

8. Plant Death

If this disease is left untreated, it can cause the complete collapse and death of the host plant, including its root system, and tubers.

9. Symptoms in Other Plants

Just watching for signs and symptoms in the potato plot may not provide an early enough indication of the disease’s arrival. After all, if you wait for the potato to start breaking down, it’s too late to fix it.

The first signs of this problem could show in plants near the potatoes.

Wilting, yellowing, and blackening could occur to other plants, particularly ones susceptible to the pathogens associated with blackleg disease. Remember, the same bacteria that causes potato blackleg also causes bacterial soft rot in other species.

Watch for symptoms in carrots, parsnips, broccoli, cornand sunflowers.

Preventing and Controlling Outbreaks

If you’re growing potatoes, you must take steps to prevent blackleg. It should always be a part of the growing process.

Unfortunately, there are no specific cultivars that are resistant to the bacterium that causes the disease. There are just so many strains, and they are constantly adapting that once a resistant potato is bred, the bacteria adapt.

So, let’s talk prevention. It all starts with the seed tuber you purchase.

Know Your Seed Source

Only purchase or use good quality seed tubers from reputable sources. Many sellers will certify their tubers to be disease-free, so look for the label.

If storing potatoes to use for next season’s crop, make sure they aren’t from infected plants.

Use Clean Water

Avoid using contaminated water for irrigation. If you are using canal or well water, you might want to treat or filter it first if your neighbors are growing susceptible plants.

If you have an outbreak, make sure to clean your irrigation equipment. That means cleaning out any drip lines, hoses, or watering cans.

Too much water, splashing water, and high humidity heighten the risk of promoting bacterial issues. Don’t water on the plant leaves, but at the soil level. Prune plants and space them well apart to reduce humidity.

Crop Rotation

Crop rotation will help to reduce the build-up of blackleg-causing bacterium. It’s always a smart technique, no matter what you’re growing. Every other year, plant something not in the nightshade family in the area.

If an infection occurs, avoid replanting potatoes in that spot for three years. Plant only non-host species, such as legumes or small grains.

Keep Things Clean and Tidy

Proper sanitation practices, including disinfecting farm equipment and tools, are essential. Anytime you work in the garden, clean your shovels, pruners, wheelbarrow wheels, etc., with 10 percent bleach solution or hot, soapy water.

Control weeds in and around potato-growing areas. Use small tools, such as hand cultivators, to avoid damaging potatoes growing in the ground.

Plant in the Right Area

Avoid planting in heavy, water-logging soils. If your soil is clay-based, consider using soil conditioners, raised beds, or containers. If you plant in the ground, amend it at least two feet deep.

Always add good quality organic mulch and compost to potato patches in order to assist with free drainage.

Test Soil and Feed Accordingly

Test your soil before planting. That way, you will know what your soil lacks and what it has an excess of. If your soil is standard, apply a vegetable-specific fertilizer according to the instructions.

Excessive nitrogen levels can make these plants more susceptible to infection, so be cautious not to overfeed your plants.

Keep An Eye Out

Monitor the growth of your potato plants. Early detection, especially at the beginning of the growth phases of the plant, is vital. If you catch it right away, you might be able to start a new crop in a different area.

Monitor what diseases are happening near your location. You can sign up for updates via the USDA website.

Check Weather Forecasts

When heavy rain is due for extended periods and drainage may be an issue, consider covering the potato bed, containers, or rows. You can use plastic sheeting that still lets light in but protects the plants from too much water.

Electronic weather stations can give you prior warnings so you can act promptly.

A rain gauge can be a handy tool. It will help you work out when to water and when there’s sufficient rainfall so you can turn off irrigation.

Remove Infected Plants

If your plants are infected despite your preparation, the plants should be removed immediately and destroyed. Don’t put the plant in your compost; it should be bagged and put in the garbage or burned.

Make sure all tubers connected to that infected plant and the surrounding soil are taken out, as well.

Once it rears its head, there is little that can be done. Remember, with this disease, the signs above the ground are secondary to what is happening underground.

Any saved tubers from a symptomatic plant will likely be infected, and if used for future planting, resulting in continued disease and crop failures.