Buckeye Rot

Are damaged areas on tomatoes due to dehydration, deficiency, or disease? Is it blossom end rot, sunscald, or buckeye rot? And what can you do about it?

Buckeye rot of tomato (Don Ferrin, Louisiana State University Agricultural Center, Bugwood.org) CC BY 3.0

Let’s look at all three in more detail so you will know what to do if you see damaged areas on your tomatoes or peppers.

Blossom end rot

Blossom end rot occurs when young fruits do not have enough soluble calcium early in their development. This does not necessarily mean your soil is deficient in calcium. You can’t know that without a lab-based soil test. [I’ve said it before, I’ll say it many times again – get your soil tested by a lab every few years. Email me if you need help.]


Inadequate irrigation is the usual culprit behind blossom end rot. Calcium doesn’t move around easily, once it enters a plant.

Tomato with blossom end rot (Kate Russell)

If there isn’t enough water available to move the calcium to where it is needed, cell walls surrounding the blossom end of the fruit will collapse, creating a uniformly dark brown or black area ONLY on the lower sidewall or blossom end of the fruit. If you see blossom end rot, irrigate more heavily and more often.

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​If the damaged area is lighter in color and higher up the side of your fruit, it may be sunscald.

Sunscald

Like us, fruits are susceptible to sunburn. This happens most often when there isn’t enough leaf cover. That can happen when we prune too heavily or when there is insufficient nitrogen available. Nitrogen is responsible for lush, vegetative growth. Sunscald dries to a tan color. The problem is, you don’t want to add nitrogen while plants are producing fruit because they will shift from fruit to leaf production. The solution, in this case, is to provide sun protection in the form of shade cloth or other physical barriers.


​If the damage is a dark brown bull's eye, you may be looking at buckeye rot.

Sunscald of bell pepper (Kate Russell)

Buckeye rot symptoms

Buckeye rot is a disease caused by three different types of Phytophthora: P. capsici, P. drechsleri, and P. nicotiana var. parasitica. Phytophthoras are water molds (oomycetes) responsible for several plant diseases. This disease is common in the southeast and south-central regions of the United States but has been found elsewhere. It occurs most often after extended periods of warm, wet weather with temperatures ranging from 75°F to 86°F. Buckeye rot can infect tomatoes, peppers, and eggplant, as well as pineapples, potatoes, and tobacco.


​At first, all you may see are smooth, grayish-green water-soaked spots. Damping-off and stem cankers may also appear. As the disease progresses, those lesions turn into the classic bull’s eye pattern of large, concentric rings, alternating between light and dark brown. The edges of these lesions will be smooth but not clearly marked. Eventually, white fungal growth can be seen on the lesions.


Other diseases that may exhibit similar symptoms include anthracnose, cucumber mosaic virus (CMV), and late blight. In each case, some differences can help you diagnose the problem:

• anthracnose – irregular lesions on leaves, as well as fruit
• cucumber mosaic – downward leaf cupping and deformed midribs
• late blight – lesions are rough and raised and leaves are also affected

Buckeye rot management

Starting with healthy, disease-free seeds and plants is the first step toward preventing nearly all plant diseases. Since buckeye rot spores can travel on seeds, transplants, clothing, and garden tools, it’s a good idea to keep things clean. Spores can also be splashed onto healthy plants by rain and overhead watering, so use soaker hoses or water at ground level and allow the soil surface to dry out between waterings. Mulching around plants can reduce the splash effect, as well as reduce weeds and evaporation.


You can reduce the chance of many fungal diseases by providing good drainage and reducing soil compaction. Since buckeye rot spores are found in soil, the disease is most likely to affect fruits closer to the ground. If you keep fruit up high with stock panels, tomato cages, or trellising, you can reduce the likelihood of buckeye rot occurring. Three-year crop rotations are also believed to help prevent buckeye rot.


​Now you know.