Potato Diseases: Rhizoctonia solani

Summary

Rhizoctonia is a serious potato disease that affects both stems and tubers, leading to stunted plants, deformed tubers, and reduced quality. The disease can be introduced through infected seed pieces or soil, especially in fields with short rotations. To control Rhizoctonia, growers can apply fungicides in the furrow at planting or treat the seed, sometimes combining both methods for optimal results. While it rarely impacts overall yield, it can significantly degrade potato appearance, leading to consumer rejection due to unsightly 'dirt' that doesn't wash off. Effective management ensures healthier crops and improved marketability.

Takeaways

• 😀 Rhizoctonia is a serious disease that affects both potato stems and tubers, requiring effective control methods.
• 😀 Proper fungicide application in the furrow at planting can help manage Rhizoctonia when planting into infected soil or fields with short rotations.
• 😀 Potatoes planted without a fungicide treatment tend to show stunted growth and smaller plants compared to those treated with a fungicide.
• 😀 Two primary chemical control methods for Rhizoctonia include spraying a fungicide in the furrow and treating the seed itself.
• 😀 Combining a seed treatment with a fungicide in-furrow spray can provide the best control and result in healthier plants.
• 😀 Rhizoctonia can originate from two sources: the soil, where it can eventually die out if potatoes are followed by non-host crops, or from infected seed pieces.
• 😀 The Rhizoctonia fungus can grow on the seed and spread to the stem, causing damage such as cankers that appear brown or striped.
• 😀 Symptoms of Rhizoctonia damage include the clipping of stolons, which can stunt tuber development or cause small, deformed tubers.
• 😀 While severe Rhizoctonia infection may reduce potato yields, it more commonly affects the quality of the tubers.
• 😀 Potatoes affected by Rhizoctonia often have a dark, dirt-like appearance on the tuber that does not wash off, reducing market appeal.
• 😀 Controlling Rhizoctonia is essential for improving the visual quality of harvested tubers, which directly impacts consumer demand.

Q & A

What is rhizoctonia and how does it affect potatoes?

Rhizoctonia is a fungal disease that affects both the stems and tubers of potatoes. It causes stunted growth, fewer tubers, and deformed or undersized potatoes, often leading to poor quality and reduced marketability.

What are the two main methods for managing rhizoctonia in potatoes?

The two main methods for managing rhizoctonia are spraying a fungicide in the furrow at planting and treating the seed before planting. In some cases, both methods are combined for optimal control.

Why is spraying fungicide in the furrow important when planting potatoes?

Spraying fungicide in the furrow at planting helps prevent the spread of rhizoctonia in fields where the disease is expected, especially in fields with short crop rotations or where rhizoctonia is present in the soil.

How does rhizoctonia spread in potato fields?

Rhizoctonia can spread from the soil or from infected seed pieces. It can grow in the soil and infect potatoes through the seed piece, or it can be introduced into the field when planting potatoes infected with the fungus.

What are the visible symptoms of rhizoctonia on potato plants?

Rhizoctonia causes large cankers on the stems of potato plants, turning them brown and often striped. In severe cases, it can clip off the stolon, preventing the formation of tubers or leading to very small, deformed tubers.

How does rhizoctonia affect potato yield?

Rhizoctonia can reduce yield by causing fewer tubers to form, and the tubers that do develop may be smaller and deformed. In severe cases, the disease can lead to significant yield loss.

What is the impact of rhizoctonia on potato quality?

Rhizoctonia primarily affects the quality of potatoes. Infected tubers often develop black marks that resemble dirt but cannot be washed off, which reduces their appeal in the market as consumers may not buy potatoes with these unsightly marks.

Can rhizoctonia survive in the soil after potatoes are harvested?

Rhizoctonia can survive in the soil, but its presence diminishes over time when a non-host crop is planted after potatoes. Crops that don't host rhizoctonia can help reduce its spread.

What are the advantages of using both seed treatment and fungicide spraying?

Using both seed treatment and fungicide spraying provides enhanced control over rhizoctonia. This combination helps protect the plant both at the time of planting and as it grows, ensuring healthier plants and better-quality tubers.

What happens to potatoes when rhizoctonia infects developing tubers?

When rhizoctonia infects developing tubers, it may cause them to be deformed or smaller in size. In some cases, the tuber may not form at all if the fungus cuts off the stolon, which is the stem that connects the tuber to the plant.