It’s Easy To Misdiagnose Bacterial Spot On Peaches

Bacterial spot is a major disease for peach and nectarine growing areas experiencing warm, wet springs and summers. Effective management requires a diverse toolbox to combat the disease from shuck split through cover sprays. One such tool is the use of copper. But problems can result.

Copper works very well keeping fruit clean of bacterial spot and does not cause fruit damage, like fruit russeting observed on apples when copper is used post dormancy.

Although the fruit are durable to copper, the leaves of stone fruit are very sensitive to copper injury. Unfortunately, there can be confusion telling the difference between bacterial spot disease and copper injury on leaves.

How Copper Works
Copper injury peach leaf_KPeterWhen using copper, it is important to understand how it works to control pathogens to appreciate how it can cause damage to plant tissue. Copper is a general biocide, which means copper ions will kill fungi, bacteria, and plant tissue.

Two types of copper are available to growers: fixed coppers and bluestone coppers. Fixed copper is safer for plant tissue than “bluestone” copper because it is insoluble in water. Since fixed coppers have low solubility in water, there is a lower risk for injury and may be used throughout the growing season.

When fixed copper is sprayed onto leaves, the copper particles will persist on the plant surface after the spray dries. Each time the plant surface becomes wet, copper ions will be released gradually from copper deposits.

Residual protection against plant pathogens occurs as a result of the gradual release of copper ions from the copper deposits. Copper sprays act as a protectant by killing pathogens that are on the surface of plant tissues, but cannot affect the pathogen once it enters the tissue.

Copper accumulation can increase on plant tissue when sprayed repeatedly. As a result, foliar injury on the oldest leaves is normal and expected when using repeated copper applications as it indicates the copper is working to control the bacterial spot pathogen. However, excessive injury can occur when the copper becomes more soluble, such as during slow drying (rainy) conditions and when applied in an acidic solution.

Higher solubility means there is no gradual release of the copper ions. When this occurs, all of the copper ions are available at the same time when applied, thereby blasting the leaf tissue with the maximum amount of biocide power copper can give. Common forms of fixed coppers include Cuprofix, Kocide, Champ, C-O-C-S WDG, Badge, Nordox 75 WG, and Cueva.

In contrast to fixed coppers, bluestone (copper sulfate pentahydrate) is highly soluble and copper ions can damage exposed plant tissue. Bluestone is often combined with lime to help “tie up” copper ions and slow their release (e.g. Bordeaux mixture). There is no residual activity of bluestone such that copper ions are released rapidly upon application. Bluestone is often used as a dormant spray when minimal amount of green tissue is exposed. Common brands of bluestone include MasterCop and Phyton.

Bacterial Spot Leaf Symptoms
Bacterial spot peach leaf_KPeterBacterial spot symptoms are always angular lesions and this is due to the lesion being bordered by the leaf’s veins. The angular lesions are typically small; however, they can coalesce to form larger lesions. Often times, you will see lesions along the midrib of the leaf, the tip of the leaf, and along the edges. It does not take many lesions on the leaf for the leaf to turn yellow or to fall off. Lesions can occur on older and younger leaves.

Unlike bacterial spot, copper injury is indicative of a lot of round, circular lesions of variable sizes on the leaf. The reason there are a lot of lesions is due to the spray pattern that occurs on the leaf: every droplet of water most likely contains copper particles. The pattern of the lesions is random, as opposed to following the veins like bacterial spot. The appearance of the leaves is reminiscent of “Swiss cheese.”

As a result of repeated copper sprays, the damage will often result in premature defoliation of older leaves due to higher amounts of residual copper. In contrast, younger leaves will typically look “much healthier” than older leaves since they have less residual copper. Severe premature defoliation will cause tree stress and small fruit size.

Topics: , ,

Leave a Reply

Stone Fruit Stories
Stone Fruit
August 29, 2017
What Will Be the Next Generation of Cherry Canopies?
Take a look at what the future has in store for NC-140 Sweet Cherry Canopy Architecture and Rootstock Trials. Read More
Insect Control
August 22, 2017
Stink Bug Threatens High-Dollar Crops in California
While populations are low, it appears invasive pest has recently stumbled upon the state’s peaches and almonds. Read More
Stone Fruit
August 1, 2017
Researcher: Cherry Growers Must Use Disease Management Strategies When it Comes to SWD
Dave Jones, Extension Educator with Michigan State University, says growers are well accustomed to monitoring and thinking ahead. Read More
Stone Fruit
July 31, 2017
Clemson Peach Breeding Hones in on Disease Resistance, Flavor
In spite of the March freeze that devastated growers in the region, one producer says breeding for taste and quality needs to prevail. Read More
Disease Control
July 25, 2017
Brown Rot Sinks its Teeth into Michigan Cherries
Unseasonably wet weather causes outbreak, and growers are warned it can spread to peaches. Read More
Stone Fruit
July 6, 2017
Oriental Fruit Moth One Shifty Pest
This moth has many characteristics that have allowed it to adapt and thrive in many peach and nectarine growing regions. Read More
Stone Fruit
July 5, 2017
Floyd Zaiger is the Sweetness Scientist Behind Zaiger Genetics
Floyd Zaiger’s innovative lab extends to the orchard, where he and his kids’ crosses produce some of the world’s most fabulous fruit. Read More
Apples & Pears
June 19, 2017
Bee-ware: New Resources Released for National Pollinator Week
New videos, webinars available during week-long observance. Read More
Stone Fruit
June 17, 2017
Keep an Eye out for Peach Leaf Curl
Follow these tips to prevent the disease next year. Read More
Stone Fruit
June 12, 2017
Monster Sweet Cherry Crop Expected
But the tart cherry crop is forecasted to drop nearly one-quarter from 2016. Read More
Stone Fruit
June 6, 2017
California Dried Plum Crop Expected To Double
After the disastrous 2016 bloom, a more normal crop this year has the prune industry back on track. Read More
Stone Fruit
June 5, 2017
Michigan State University Awarded Grant to Tackle Spotted Wing Drosophila
Research team seeks solutions to protect state’s cherry crop. Read More
Stone Fruit
June 4, 2017
Multiple Leader Training Optimizes Sweet Cherry Labor Efficiency
The final intensive training system to be examined in the North American NC-140 Sweet Cherry Canopy Architecture and Rootstock Trial Read More
Stone Fruit
May 23, 2017
Northeast Peach Crop Rebounds
After a mild winter and relatively uneventful bloom time, the crop is setting up nicely for the region. Read More
peach buds and blossom
Stone Fruit
May 8, 2017
USDA Researchers Say Georgia Peach Crop Worst in 100 Years
Spring freeze, not enough chill hours make for a tough growing season. Read More
The Latest
Stone Fruit
September 25, 2017
Many Pollinators Boost Cherry Yields — N…
Researchers are finding a multi-pronged approach to pollinators give both sweet and tart cherry growers the best results. Read More
Stone Fruit
September 9, 2017
Southeast Peach Prices Soar with Small C…
While the Georgia and South Carolina peach crop is tiny, locally grown peaches are selling for big bucks. Read More
Farm Marketing
August 31, 2017
Winning at Farmers’ Markets – Secr…
Small farmer Rodney Stackhouse cashes in at 25 farmers’ markets a week by growing 200-plus varieties of stone fruit and empowering a crackerjack staff. Read More
Stone Fruit
August 29, 2017
What Will Be the Next Generation of Cher…
Take a look at what the future has in store for NC-140 Sweet Cherry Canopy Architecture and Rootstock Trials. Read More
Insect Control
August 22, 2017
Stink Bug Threatens High-Dollar Crops in…
While populations are low, it appears invasive pest has recently stumbled upon the state’s peaches and almonds. Read More
Stone Fruit
August 1, 2017
Researcher: Cherry Growers Must Use Dise…
Dave Jones, Extension Educator with Michigan State University, says growers are well accustomed to monitoring and thinking ahead. Read More
Stone Fruit
July 31, 2017
Clemson Peach Breeding Hones in on Disea…
In spite of the March freeze that devastated growers in the region, one producer says breeding for taste and quality needs to prevail. Read More
Disease Control
July 25, 2017
Brown Rot Sinks its Teeth into Michigan …
Unseasonably wet weather causes outbreak, and growers are warned it can spread to peaches. Read More
Stone Fruit
July 6, 2017
Oriental Fruit Moth One Shifty Pest
This moth has many characteristics that have allowed it to adapt and thrive in many peach and nectarine growing regions. Read More
Stone Fruit
July 5, 2017
Floyd Zaiger is the Sweetness Scientist …
Floyd Zaiger’s innovative lab extends to the orchard, where he and his kids’ crosses produce some of the world’s most fabulous fruit. Read More
Apples & Pears
June 19, 2017
Bee-ware: New Resources Released for Nat…
New videos, webinars available during week-long observance. Read More
Stone Fruit
June 17, 2017
Keep an Eye out for Peach Leaf Curl
Follow these tips to prevent the disease next year. Read More
Stone Fruit
June 12, 2017
Monster Sweet Cherry Crop Expected
But the tart cherry crop is forecasted to drop nearly one-quarter from 2016. Read More
Stone Fruit
June 6, 2017
California Dried Plum Crop Expected To D…
After the disastrous 2016 bloom, a more normal crop this year has the prune industry back on track. Read More
Stone Fruit
June 5, 2017
Michigan State University Awarded Grant …
Research team seeks solutions to protect state’s cherry crop. Read More
Stone Fruit
June 4, 2017
Multiple Leader Training Optimizes Sweet…
The final intensive training system to be examined in the North American NC-140 Sweet Cherry Canopy Architecture and Rootstock Trial Read More
Stone Fruit
May 23, 2017
Northeast Peach Crop Rebounds
After a mild winter and relatively uneventful bloom time, the crop is setting up nicely for the region. Read More
Stone Fruit
May 8, 2017
USDA Researchers Say Georgia Peach Crop …
Spring freeze, not enough chill hours make for a tough growing season. Read More