What is Potato Scab?
This is a disease from Streptomyces scabies, a bacterium-like organism. Aside from root crops, the pathogen can also be present in a wide array of plants, which can significantly reduce seedling growth. Its first detection was in 1892. At such time, it still belongs to the classification of fungus. It is one of the three Streptomyces that is of economic importance. The bacterium affects potatoes that are still in their initial stages of development. Wounds of tubers are also common entry points.
The bacterium that causes potato scab can overwinter either in the soil or leaves. The transmission of the disease happens through the wind, water, and infection in seeds. Also, since the bacterium can survive in an animal’s digestive tract, it can also spread through manure.
There are different factors that can increase the likelihood of potato scabs and one of the most common is the acidity of the soil. A pH level that is more than 5.2 will make the host susceptible to scabs. To add, they also favor temperature that ranges from 50 to 88 degrees Fahrenheit. Also, it will be more common if the soil is light-textured or if it is abundant with organic matter.
Identifying Potato Scab’s Damage
From the name of the disease, it is pretty much obvious that its most common host is a potato. Aside from potatoes, however, the bacterium can also affect radish, rutabaga, turnip, salsify, parsnip, and carrot, among others.
The following are some of the most common indications that your crops are suffering from potato scab:
- The appearance of lesions will be the most visible symptom of this disease. The size and shape will vary depending on the extent of the damage or the health of the host. There will be shallow or deep holes, raised areas, and corky tissues.
- In most cases, the lesions will be circular and separate from each other. As the infection worsens, however, they will coalesce and will form a larger scab. The pits will also be deeper. The scabs can have a depth of one to ten millimeters.
- Above the ground, such as in the stems or leaves, there will be no signs that your plants are already suffering from potato scab.
Results of Infestation
The infection will inevitably lead to an unattractive appearance of the crop. The lesions will make the tubers or the host unmarketable. While you can still eat them by simply removing the scab, it will be hard to market such fruits. Therefore, amongst commercial growers, the infestation of potato scab will lead to loss of profit.
How to Get Rid of Potato Scabs
Natural and Organic Solutions
Here are some of the best preventive and control measures for potato scab:
- Choose the varieties of potatoes or root crops to plant. Pick those that are resistant to the disease. To be specific, some of the cultivars that are resistant to potato scab include King Edward, Golden Wonder, Pentland Crown, Arran Pilot, and Juliette, among others. When buying seeds, purchase only from reputable sellers and make sure that they are free of the disease. See to it that the seeds are certified.
- Crop rotation is another solution that holds a lot of promise. As much as possible, rotate crops after every four years. After growing potatoes, avoid growing beet, radish, and turnip, among other common hosts. Rather, consider growing alfalfa, soybeans, and rye as they are less susceptible to potato scab.
- Watering will also help, but avoid overdoing it. The key here is to retain the moisture in the soil. Sufficient irrigation is especially important during the early stages of the root crop, which is also the point at which it is most susceptible to the disease. It will be best to retain the dampness of the soil by as much as six weeks. Nonetheless, keep in mind that too much moisture can be also bad as it can encourage other fungi and bacteria.
- You will also benefit from controlling the pH level of the soil bed. The maximum pH level should be 5.8. You can purchase a soil test kit to know if the pH of the soil is at the right level. You can add elemental sulfur to the soil to reduce the alkaline. Ammonium sulfate, a fertilizer that produces acid, will also be good as it can raise the acidity of the soil.
- When it comes to soil amendment, the use of agricultural gypsum is also effective against potato scabs. This is common for commercial growers. To be effective, the application rate should be 25 pounds of gypsum per 2,000 square feet. This will help in the improvement of calcium in the soil while also increasing the protection of the plant from the pathogen.
- Limit the use of fertilizers in your crops. Even organic fertilizers, such as manure, will be harmful. Large quantities of manure will encourage the growth of bacteria.
Although chemicals have a negative reputation in the treatment of plant diseases, there are still many who resort to their use. This is especially the case amongst commercial growers who will do what it takes to spare their crops from damage and to prevent financial losses.
In one study about the treatment of potato scab and chemical controls, Capitan, a fungicide, ranked as the most effective in the management of the disease. Rizolex is another fungicide that showed favorable outcomes. Nonetheless, it is important to note that chemicals have a low-level of effectiveness. It is best to have an integrated approach using a combination of natural methods to get rid of potato scab.