Apricot Scab Treatment – How To Manage Apricots With Peach Scab

By: Teo Spengler

Peach scab on apricots results from the fungus Cladosporium carpophilum. It also affects nectarines, plums and peaches. Most apricots with peach scab are those grown in home orchards since commercial growers take precautions to prevent it. Read on for tips on how to stop apricot scab from ruining your backyard fruit production.

Apricots with Peach Scab

Anyone hoping for luscious, juicy apricots from the home orchard needs to know about peach scab on apricots. This fungal disease is also called “freckles,” since small dots show up on the fruit.

You find peach scab on apricots more often after a warm, wet spring. The fungus creates lesions on young twigs where the spores overwinter. These spores cause spring infections as the weather warms. They grow fastest at temperatures of about 65 to 75 degrees F. (18-24 C.).

But you won’t necessarily see symptoms immediately after infection, however. They may show up as long as 70 days later. Still, you can and should start apricot scab treatment earlier.

How to Stop Apricot Scab

Treating apricot scab starts with making good choices about where to plant your apricots and how to care for them. Perhaps the most important thing to remember is to keep apricot and other susceptible trees out of low-lying sites with poor air and soil drainage.

Another good prevention tip to stop apricot scab is to prune trees carefully to open up the center. If you use the open-center pruning system, it provides good air circulation within the canopy that slows or stops fungus activity.

Don’t spend too much time looking for a scab-resistant apricot cultivar. Most experts agree that cultivars are all susceptible to this fungal disease. If you require further apricot scab treatment, look to fungicides.

Fungicides are the big weapon in treating apricot scab. You’ll need to find a fungicide recommended for this disease, then spray according to label directions. Often, you’ll need to spray every two weeks from the time the petals fall until 40 days before harvest. The most critical time to spray when you are treating apricot scab is from the time of shuck split to five weeks after bloom.

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A rampant fungal infection can keep you from enjoying fruit off your tree when harvest time arrives, and it can sometimes kill the tree. The fungus can spread to other plants and trees in your yard, but using a fungicide can help eradicate the disease before it goes yard-wide. There are aggressive chemical options as well as organic ones to consider.

The bacteria that cause bacterial spot overwinter in buds, protected areas on the woody surface of the tree (e.g., cracks in the bark), and in leaf scars that became infected during leaf drop the previous season.

Leaf scar infections usually develop into spring cankers. The bacteria are spread from cankers in dripping dew and in splashing and/or wind-blown rain to the newly emerging leaves. They can also infect through natural openings or wounds in leaves and fruit.

Optimal temperature for bacterial multiplication in leaves and for infection of leaves and fruit ranges from 20 to 30ºC. Leaf wetness is necessary for pathogen infection: from 3 to 6 h of wetness is enough to cause high disease severity at optimal temperatures.

Bacterial spot multiplication in leaves is favored by wet conditions that cause water congestion in plant tissue. Rains, dew and high relative humidity assist bacterial entry into plants and multiplication. Wetness in the morning is not a optimal for infection as wetness that lasts a day or more. This sensitivity to wetness is evident in the symptoms. Tips of leaves, where moisture evaporates more slowly, show the spot lesions and chlorosis more quickly than the base of leaves.

Spread and entry of the bacterial spot pathogen into plants is favored by abrasions and nicks caused by blowing sand, especially on outside peach rows adjacent to field roads. High wind speeds from sprayers may also help to spread bacterial spot.

Fruit are very susceptible to infection as soon as they are exposed at shuck split through pit hardening but new infections can develop until harvest. Severe fruit infections are more common when frequent periods of rainfall or even extended heavy dews and very high humidity occur from late bloom to near pit-hardening.

Cueva (copper octonoate) is the only product labeled for bacterial spot in stone fruit. Use at 1% v/v in 470-940 L/ha. Do not apply at less than 7-day intervals and avoid applying copper under slow drying conditions. This is to avoid the accumulation of toxic copper ions. There will always be some injury resulting from copper applications to peach and nectarine the goal is to make sure the cure is not worse than the disease. Differentiating between bacterial spot and copper phytotoxicity can be challenging. The image and table below provide some differences.

Although foliar lesions have been reported in the literature, they are very infrequently observed so one of the main ways to differentiate between peach scab and bacterial spot is the absence of foliar symptoms in scab.

Epidemics occur most readily when conditions are humid, rainfalls are frequent, and temperatures range between 18 and 24°C. However, infection can still occur as low as 4-7°C and as high as 32-35°C. Since fungal spores are spread primarily by rain splash, it is common for clusters of small lesions to develop at the top of the fruit near the stem where rain most frequently contacts the fruit.

Peaches are most susceptible during the shuck-split stage of growth. Because they lack fuzz, nectarine fruit can be infected earlier than peaches: 1–2 weeks after petal fall. Although fruit may become infected shortly after shuck split and continue to be susceptible to infection throughout the growing season, symptoms are typically not visible on fruit for six to ten weeks so only those infections which are initiated between shuck split and six weeks before maturity will exhibit symptoms before harvest.

It is critical to get some fungicide protection in place in blocks with a history of scab before the next rain event. A scan of the literature shows that the most effective products to manage peach scab include captan, Senator, Flint, Pristine, Inspire Super, Luna Sensation, Syllit and Sercadis. Fontelis, Group 3 fungicides and sulphurs will also give some protection. Be aware of the extended restricted entry intervals relative to fruit thinning if you use the WSP formulations of captan. WDG formulations can be used according to the existing label for this season only.

Synthetic Products

Chlorothalonil is one non-copper, synthetically derived fungicidal spray product effective at preventing peach leaf curl that is also approved for use by home peach growers. Other synthetic fungicides considered to have reduced environmental risks and to be suitable for use in a preventative spray program for peaches include products containing azoxystrobin, trifloxystrobin and fludioxonil. All three have proven effective at protecting peach trees from brown rot, a common fungal infection that causes peach blossom blight early in the growing season and raised brown cankers on the fruit.

Watch the video: Horticultural Oil: Why Spray our Fruit Trees

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