If you’re someone interested in agriculture, you might know that plants get affected by many diseases. Diseases such as a shot hole, black knot, rust, or powdery mildew are headaches to farmers and agriculture enthusiasts as they damage their vegetables and fruits. Similarly, there is a tuber disease called potato scab, common in all the regions across the globe where potatoes are grown.
In today’s article, we will take a closer look at potato scab disease, its causes, and how you can prevent it from ruining your crops.
Potato Scab – A Brief Introduction
It is a disease of potato tubers that can affect potatoes no matter where they are grown. Although it is common in thin-skinned potatoes, you might also see root crops such as beetroot, carrot, reddish, and turnip get affected by it. This disease usually doesn’t affect all the produce at once, but some scab potato pieces may still affect the appearance of the total yield.
You might observe scab problems in a home garden or a farm where tuber plants are grown. The occurrence of these scabs may vary according to the field or season. Soil moisture, soil texture, and other factors affect this variation. Farmers hate potato scab as they lose a lot of money when their potatoes get damaged.
The disease affects farmers and agriculturists when they try selling their crops in the market. This common scab makes the potatoes ugly, which isn’t very attractive to the buyers.
How Does The Disease Look?
The potato scab disease causes dark brown, corky, and rough patches on the potato’s skin surface. These patches may be slightly raised or cause the surface to seem hollow. The scab lesions may affect a small area of the tuber surface. Or, it can also cover the entire surface area of the potatoes.
You might scab lesions on the root surfaces. If the disease severity is too much, large, deep holes or pits may form on the crop surfaces. The ridged portions may also form circular rings. No wonder common scab damages the looks of any root vegetables!
How Are These Scabs Caused?
This potato ailment is mainly caused due to an organism called Streptomyces scabies, which is a bacteria. The bacteria can live and survive in alkaline soils or where there isn’t high soil acidity. You will also find them in soils with a very high amount of organic matter content and gravelly soils, which are dry.
The Streptomyces scabies bacteria are transmitted to crops and potatoes by water, wind, and infected seed tubers. It enters through pores in the stems of potato tubers and also developing tubers via their wounds. When they first get affected, the common scab infection causes a reddish-brown appearance on the seed potatoes.
As these tubers grow, the spots or lesions get bigger and corkier. The acid scab pathogen doesn’t stop there yet; it enters through the pores of the potatoes. S acidiscabies also make the spores fall into the soil, where the pathogen can infest the soil again. This acid scab may also survive among the potato tubers in storage.
So, you need to make soil amendments and check the soil conditions before you decide to grow plants, where the pathogen strain has made its mark. Some farmers use this pathogen in fresh manure, as it easily passes through an animal’s digestive tract.
How To Treat And Control Common Scab?
There are specific steps you need to take to treat and control the effect of scabies on a potato. Let’s have a look at them in detail.
The disease cycle of common scab reduces when they are exposed to soil ph levels below 5.2. That’s why potatoes are generally grown where soil ph level is within 5.0 to 5.2. As the acid scab doesn’t do well in low ph soils, this is an effective way to control the condition. Scabs don’t also stay well with other microbes in the soil, so a little seed treatment will also help.
Proper crop rotation not only reduces these bacterial organisms to spread over your potatoes and vegetables but also helps in keeping pests away. The process reduces the inoculum levels in the fields where veggies are grown, which hampers the growth of the bacterium.
If you conduct crop rotation with small grains such as corn can also help you in restraining scabies in your potatoes. As S acidiscabies infection might get aggravated by growing plants like red clover in your garden, it’s best not to use it during crop rotation.
Soil types having high organic matter content and light-colored soils are breeding grounds for scabies. Along with these, coarse soils also let scabs grow due to their ability to hold soil moisture. Eroded parts of your garden or field also welcome scabs readily.
Therefore, dont try to grow potatoes or other vegetables in these types of soils. People also supply manure to these soils, which should also be avoided.
Using Resistant Varieties
Field screening programs have been used to identify that resistant variety can be used for treating scabies. These resistant varieties are completely immune and might get infected by the disease, but the screening programs have still been able to connect it with scab management. Thus, planting resistant cultivars are one of the easiest ways to fight common scab.
If you want to implement this strategy, it is best to consult an agricultural engineer or soil expert.
Checking Soil Moisture
Before you carry out any seed treatments or experiments, you need to check the soil’s moisture where you plan your tubers. If the moisture is maintained at levels -0.4 bars and above, you can prevent potato scab significantly. It will control bacterium from infecting your veggies during the first 2 to 6 weeks of tuber development.
As the scab lesions are observed in low soil ph and high moisture levels, increasing the moisture to almost 85% will reduce their effect. This might be effective during any season.
Potato Scab Prevention
Many people, including gardeners, suggest some gardening tips to prevent scabs, which are –
- Only plant scab-resistant, certified, and disease-free potatoes from a reputed source
- Use potato varieties such as Superior and Norland, which have resistance to common scab
- Avoid applying fertilizers containing potassium nitrate or calcium
- Don’t plant potatoes in the same spot frequently
- The ph levels of soil must be between 5.0 and 5.2 or around 6.5 for home gardens to prevent scab lesions
- Avoid adding fresh manure and compost to potato beds
- Perform a three years crop rotation between potatoes and other varieties of plants like corn and peas
- During the initial weeks of tuber formation, try keeping the soil cool and moist to scab infection
- As a rule of thumb, always water potatoes sufficiently when they’re growing tubers
By now, you would’ve got your answer to the question, what is potato scab? Even though scabies looks bad on potatoes, they are still usable and edible. You have to peel the infected area or cut the portion out, and you are golden. The potatoes are ready to be cooked!
If your potatoes are already scab-infested, try to keep them in the dark and cool area to prevent further infestation.
James Fields is the founder of Gardener to Farmer. His passion for gardening goes back to his childhood days when he would visit his grandfather during the holidays and help him with the plants in the backyard. This has now translated to creating a dependable resource for gardening.