Why Do My Apples Have Brown Spots and How to Prevent It?

Growing apples can be a rewarding experience, but encountering blemishes like brown spots can be frustrating for farmers and gardeners alike. The likely culprit of these ugly brown spots is something called bitter pit. Let’s dive into what bitter pit is, its causes, and how to prevent it so you can enjoy a fresher, healthier apple harvest this season! 

What is Bitter Pit?

Bitter pit is a disorder that manifests as small, dark brown, sunken spots on the surface of apples. These spots are typically more visible near the calyx (bottom) end of the fruit. Beneath these surface blemishes, you’ll find dry, corky tissue that can affect the apple’s flavor, giving it a bitter taste.

While bitter pit may resemble a fungal or bacterial infection, it is not caused by pathogens. Instead, it’s a physiological issue linked to nutrient imbalances within the apple.

Causes of Bitter Pit

The primary cause of bitter pit is calcium deficiency in the fruit. Calcium is essential for cell wall structure and strength, and when apples lack sufficient calcium, their cells become prone to breakdown, leading to the telltale spots.

Several factors can contribute to calcium deficiency, including:

• Soil Imbalance: Low calcium levels or excessive potassium and magnesium in the soil can hinder calcium uptake by the tree.
• Irregular Irrigation: Fluctuating water levels can disrupt nutrient absorption.
• Fruit Load: Trees carrying a heavy fruit load often distribute nutrients unevenly, leaving some apples calcium-deficient.
• Varietal Susceptibility: Certain apple varieties, such as Honeycrisp, are more prone to bitter pit.

Why are Honeycrisp Apples More Susceptible to Bitter Pit?

The reason Honeycrisp apples are more likely to contract bitter pit is because they pick up potassium very easily– so abundantly, in fact, that it decreases uptake of calcium. So while many people think that this disorder is caused by a calcium deficiency, which it is, the true problem is not always quite as easy. Sometimes it is also a potassium excess that is causing the potassium deficiency.

How to Prevent Bitter Pit in Your Apples

Preventing bitter pit starts with proactive orchard management. Here are some key strategies:

Soil and SAP Testing

Conduct regular soil and SAP tests to monitor nutrient levels and identify deficiencies before they affect your apples. Testing ensures a targeted approach to fertilization and nutrient management, giving your apples the best chance at thriving. It is impossible to know exactly what nutrients you need without having the proper data from these tests. 

Improve Calcium Deficiency in Apples

We learned that a deficiency in calcium is a major contributor to bitter pit, so let’s help balance our nutrients and give our apples the calcium they need with the right fertilizers for apples to fight off bitter pit.  

• Incorporate Lime into the Soil: Incorporating a lime fertilizer, which is a great option for increasing PH and correcting calcium deficiency.
• Amend Soil with Gypsum: A gypsum fertilizer will help with high-magnesium soil, and will add a boost of calcium. 
• Apply Calcium Sprays: Foliar sprays containing calcium can deliver nutrients directly to the fruit and help stave off bitter pit. This is a more immediate and last-minute course of action if it is too late to amend the soil.

We have also found that ensuring generous levels of boron and manganese has helped with the uptake of calcium and potassium. Along with this, certain amino acids can increase the uptake of calcium by up to 3x. These amino acids are combined in a formula specifically designed to help plants absorb calcium faster. 

Using the right fertilizers can make a significant difference in preventing bitter pit. Look for options that include calcium but avoid over-applying potassium or nitrogen, as these can exacerbate the issue. 

Proper Calcium Release

Peak supply of calcium is actually needed at cell division, and not at the fruit-fill stage. The best time to apply these amendments for calcium is in May/June if you are in the Northeast. If you are applying soil amendments, then apply them in time to have the most release in late Spring. 

Irrigation Management

Consistent watering is essential for healthy nutrient uptake and minimizing fruit stress. Overwatering or irregular irrigation can lead to nutrient imbalances, exacerbating bitter pit. Drip irrigation systems or moisture sensors can help you maintain optimal soil moisture levels.

Pruning & Thinning 

Thinning: Reduce the number of fruits per tree to allow for better calcium distribution among apples. Fewer fruits mean each one receives more of the nutrients it needs.

Pruning: Maintain proper canopy airflow and light penetration through strategic pruning. This not only supports healthy fruit development but also prevents the conditions that may promote disease.

How an Agriculture Consultant Can Help You Grow Better Apples

Managing bitter pit can be complex, especially when balancing soil chemistry, irrigation, and tree health. This is where an agriculture consultant can provide invaluable assistance. Consultants bring expertise in:

• Conducting soil and tissue tests to diagnose issues.
• Recommending tailored nutrient management plans.
• Advising on irrigation and pruning techniques.
• Helping you select apple varieties less prone to bitter pit.

By working with a professional, you can ensure your apple orchard thrives, yielding healthy, delicious fruit that’s free of bitter pit. Contact a regenerative agriculture consultant today from Keystone Bio-Ag to help develop an orchard management plan for your apples.