Category: Fruit

Russet on Apples: Current Understanding and Management

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Russet on Apples: Current Understanding and Management

By John Skae, Candidate for B.S. in Physiology and Neurobiology, and  Macarena Farcuh, Ph.D. Assistant Professor and Extension Specialist,  UMD

What is russet on apples?

Russet on apples is a disorder of the skin that results in discoloration and changes to the expected smooth texture of the skin of apples. Russet appears as a spectrum from mild brown weblike patterns to severe rough changes on the surface of apples and many variations in between (Fig. 1). Russeting is only skin deep and thus will not affect the flesh of the fruit. It can occur due to naturally-occurring weather conditions, particularly humid and wet weather.

Fuji apple expressing russeting.
Fig 1.) Fuji apple expressing russeting. Source: John Skae, University of Marylan

Russeting can ultimately reduce the market value of apples, decreasing grower profitability. According to the US Department of Agriculture, the presence of russet disqualifies apples from the US Extra Fancy, US Fancy grades if smooth, solid russeting is more than 10%, while excessive russeting or smooth net-like russeting exceeding 25% excludes fruit from the US No. 1 grade categories.

Apples can begin to russet within the first 30-40 days of development, starting at petal fall. The earlier the tissues are damaged, the more dramatic the damage will be. But it is important to mention that russet can also be developed later during the growing season. Russeting occurs because cracks begin to develop underneath the cuticle of the apple. The damage in the epidermal cells underneath the cuticle turns brown. The cells are then pushed upwards towards the skin because new cork cells are growing underneath the affected epidermal cells. Once the damaged cells reach the surface of the apple, they form phellogen, a wound-sealing tissue created as a result of the russeting reaching the surface. Although russeting affects the cosmetic appearance of apples, it does not harm fruit flesh taste.

What factors cause or contribute to apple russeting?

Some cultivars produced by selective breeding are more prone to russeting than others as these can alter the genetic makeup of the apple to express russet. For example, Golden Delicious apples are highly susceptible to russet, while Red Delicious apples rarely express the russeting disorder.

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Spots on Honeycrisp Apples: What are They and How to Differentiate Them?

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Spots on Honeycrisp Apples: What are They and How to Differentiate Them?

 Zarah Ahmed, Candidate for B.S. in Physiology and Neurobiology & Macarena Farcuh, Ph.D., Assistant Professor and Extension Specialist University of Maryland, College Park

What are physiological disorders?

Physiological disorders can be defined as abnormal growth patterns that can impact the external and internal conditions of fruit. They are not caused by insects, pests, or mechanical damage, but rather by environmental factors or production practices (pre- and postharvest). The development of physiological disorders will directly impact fruit quality, thus increasing fruit losses and reducing fruit marketability and profitability.

Particularly for Honeycrisp apples, there are different types of physiological disorders that can develop both on the tree as well as during storage, but only some of them are characterized by the development of spots in the skin and sometimes flesh. Some of these include bitter pit, lenticel blotch pit and lenticel breakdown. Being able to differentiate among these will be beneficial in identifying them properly and working to prevent their future incidence.

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Who has Been in My Strawberries? Slugs and Sap Beetles, Two Common Insect Pests on Strawberries.

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By Sankara Ganesh, Maria Cramer, and Kelly Hamby.
Department of Entomology, University of Maryland, College Park

The cool, wet spring weather we have been experiencing favors slugs, so be on the lookout for slug damage. Slug damage may easily be confused for sap beetle feeding, but management of these pests is very different, so it is important to correctly identify the problem. Both pests can be common in matted row production.

Damage: Slug feeding renders fruit unmarketable and susceptible to infestation by other pests including sap beetles. Sap beetle adults are attracted to ripening, ripe, and overripe fruit and directly cause damage through feeding, but may also introduce pathogens and contaminate fruit with larvae. Sap beetles tend to leave behind circular holes while slug damage is often irregularly shaped, and both can cause moderate to deep holes. However, slugs will also feed on leaves and leave behind slime trails.  Monitoring is important to conclusively determine which pest is causing damage.

Figure 1. 1A) Slug feeding on unripe strawberry (K. Hamby). 1B) Slug feeding damage (M. Cramer).
Figure 2. 2A) Sap beetle feeding on strawberry (K. Hamby) 2B. Sap beetle feeding damage (N. Hummel, LSU)

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Bruising on Strawberry Leaves

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By Jerry Brust, UME

Over the years I have seen dark spots on the foliage of strawberry plants (Fig.1). These spots can look pretty bad at times and are thought to possibly be the start of some disease such as angular leaf spot or anthracnose. The dark spots are usually on the upper or lower surface of the leaf, but at times can be found on both surfaces of a leaf, which can indicate a biotic source for the problem. These damaged areas of strawberry foliage can be very disconcerting when they appear as dark spots on the stems (Fig 2).

Fig.1) Dark spots on strawberry leaves often mistaken for the start of a foliar disease.

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Apple Scab Alert!

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Despite cooler temperatures during the past few days, apple scab (Venturia inaequalis)  spores continue to mature. A significant apple scab infection event is forecasted April 5 to 7, 2022, in Pennsylvania and surrounding area. For those with green tissue present on their apple trees, protection is necessary for this event.
The apple scab fungus overwinters in infected leaves.  As it warms up in the spring they mature and produce spores that are discharged into air currents and carried to developing apple buds. The disease negatively affects fruit size and quality (due to blemishes and poor ripening). Over time, repeated defoliation from the disease reduces tree vigor, growth, and yield. 
Apple scrub leaf lesions.
Photo by Penn State Department of Plant Pathology & Environmental Microbiology Archives , Penn State University, Bugwood.org
Apple scab produces gray-to-olive green lesions on the leaves ( as seen above), but may also be seen on blossoms, sepals, petioles, pedicels, and fruit. On leaves, lesions first appear on the undersides of young leaves in the spring as they unfold and are exposed to infection. Leaves are susceptible to infection for about 5 days after they unfold. Fruit may become infected at any time in its development. Typical fruit lesions are distinct, almost circular, rough-surfaced, olive-green spots up to ¾ inch in diameter. 
Control information can be found on Penn State Extension website:  https://extension.psu.edu/2022-disease-update-apple-scab-infection-event-april-5-7-2022 

Blueberry IPM Post Bloom – Diseases Pathogens

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By Haley Sater
Agriculture Agent, Wicomico County
University of Maryland Extension
HSater@umd.edu

( Article from May 2021 issues of UME Fruit and Vegetable Newsletter)

Most blueberry cultivars here in Maryland bloomed and green fruit are developing. Now is the time when a variety of pathogens and pest will begin to take up residence in your field which can harm your developing crop. It is important to perform routine scouting throughout your farm and make sure that you’re not seeing symptoms of some of
the common pests and pathogens. Below is a description of several of the most common diseases and pests you may find at this time in your blueberries.

Pathogens to be on the lookout for:
During the cool, wet days where temperatures do not reach above 70 degrees you may begin to see symptoms of several fungal pathogens including botryosphaeria canker or stem blight, botrytis, anthracnose and powdery mildew. These conditions make for an ideal environment for some of these fungal pathogens to grow or spread.

Blueberry Pathognes
A.)  Botryosphaeria stem blight, Bill Cline NCSU.  B.) Botrytis, Caleb Slemmons, National Ecological Observatory Network. C.) Anthracnose, Bruce Watt, University of Maine D.)  Powdery Mildew, Florida Dept. of Agriculture. Bugwood.org

Botryosphaeria stem blight (A) will exhibit dieback symptoms. It is initially detectable as yellowing and reddening of leaves which will move down then stem as vascular tissue becomes blocked by the pathogen. Whereas, botryosphaeria canker will develop as stem lesions which will sometime become swollen resulting in the formation of a canker. If botryosphaeria stem blight or canker is observed the best method to prevent the spread is pruning the infected tissue and fruit clusters six inches below any infected stems. Then, remove pruned branches from the field.

Botrytis (B) also known as gray mold, affects both fruit and the plant. It infects the fruit from bloom. As with botryosphaeria, the best tactic to reduce the spread of this disease is by pruning out infected fruit clusters and wood, then removing clippings from the field.

Anthracnose (C) will appear as stem, bud and leaf lesions and may have orange spore masses. Infections will cause leaf browning and will move from top of the leaf to the bottom. If untreated, anthracnose will also cause fruit rot. Fungicides may be used to prevent further development of anthracnose during the green fruit
development stage.

Powdery mildew (D) will start as chlorotic discoloration spots and develop into powdery masses on leaves. The infection usually begins in the spring with young leaves and may become more severe throughout the season eventually causing defoliation. However, while unsightly, powdery mildew will not significantly damage the developing fruit crop and therefore no action is required.