All posts by hudelson

Disease - Vegetable

Blossom End Rot

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Ann Joy and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0022

What is blossom end rot?

Blossom end rot is a physiological disorder of tomato in which the tissue of the blossom end of the fruit (the portion of the fruit opposite the stem) breaks down and rots, thus reducing yield. Pepper, eggplant and vine crop (e.g., cucumber, pumpkin, squash, watermelon) fruits can also be affected.

What does blossom end rot look like?

Blossom end rot often occurs on the first fruits formed on plants. Initially, water-soaked spots (resembling small bruises) appear, most often on the bottoms of fruits. On peppers these spots can resemble sunscald and can form on the sides of the fruits near the blossom end. Spots enlarge, becoming dark brown to black, sunken and leathery. Half the fruit may eventually be affected. Sometimes, when a fruit is cut, the exterior will be sound, but the interior will be discolored and shrunken. Often, bacteria and fungi invade the discolored areas, leading to further tissue decay.

What causes blossom end rot?

Blossom end rot is caused by a lack of calcium in the fruit. This lack of calcium may be due to low calcium levels in the soil. More often however, there is plenty of calcium in the soil, but its availability for uptake and transport to fruits is impaired. Drought stress, alternating soil moisture extremes, and damage to a plant’s roots all can inhibit calcium uptake, as can waterlogged or cold soils, and high concentrations of ammonium (NH₄⁺), potassium (K+), and magnesium (Mg⁺⁺) in soil. Movement of calcium within plants depends on active transpiration (i.e., loss of water through above-ground plant parts). Because leaves transpire more than fruits, calcium moves more easily into leaves where it remains. Calcium is not later redistributed from leaves to fruits. This preferential distribution of calcium to leaves can be made worse by over-fertilizing with nitrogen which promotes excessive production of leaves. In addition, high relative humidity OR low relative humidity in combination with hot, windy weather can limit transpiration, thus preventing calcium from reaching fruits.

How can I control blossom end rot?

Avoid conditions where there is too much or too little water. Water evenly and mulch the soil to retain moisture during dry periods. Avoid practices that would damage roots (e.g., cultivating too near plants thereby cutting roots). Use nitrate (NO₃^–) rather than ammonium (NH₄⁺) forms of nitrogen fertilizer. DO NOT over-fertilize. Have your soil tested periodically to determine if there is sufficient calcium in the soil. If not, add calcium (e.g., bonemeal or lime). Check the soil pH on a regular basis, particularly if you use lime as a calcium source. Use of lime tends to increase soil pH. A pH of about 6.5 is ideal for growing most vegetables. Finally, grow vegetable varieties/cultivars that are tolerant of calcium deficiencies and less likely to show blossom end rot symptoms.

For more information on blossom end rot:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).

References to pesticide products in this publication are for your convenience and are not an endorsement or criticism of one product over similar products. You are responsible for using pesticides according to the manufacturer’s current label directions. Follow directions exactly to protect the environment and people from pesticide exposure. Failure to do so violates the law.

Thanks to Karen Delahaut, Kristin Gies, and Barb Larson for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental, Disease - Field and Forage, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Needled Woody Ornamental, Disease - Vegetable, Misc

Black Walnut Toxicity

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Ann Joy and Brian Hudelson, UW-Madison Plant Pathology; Laura Jull, UW-Madison Horticulture

Last Revised: 02/28/2024

D-number: D0021

What is black walnut toxicity?

Black walnut trees (Juglans nigra) produce a toxic substance (called juglone) that prevents many plants from growing under or near them. Related trees like butternut (J. cinerea) and shagbark hickory (Carya ovata) also produce juglone, but in lower concentrations than black walnut. Juglone occurs in all parts of black walnut trees, but especially in buds, nut hulls and roots. The toxic effects of a mature black walnut tree can extend 50 to 80 feet from the trunk of the tree, with the greatest toxicity occurring within the tree’s dripline. In this area, plants susceptible to juglone may wilt or die; plants tolerant to juglone will grow normally. Vegetables such as tomato, potato, eggplant and pepper, and ornamentals such as lilac, peony, rhododendron and azalea are particularly sensitive to juglone.

Wilting of eggplant due to black walnut toxicity.

What do the effects of black walnut toxicity look like?

Plants sensitive to juglone may be stunted, have yellow or brown, twisted leaves, exhibit wilting of some or all plant parts, and die over time. Often, the vascular (i.e., water-conducting) tissue of affected plants will be discolored. Symptoms may occur rapidly, even within a few days after sensitive species are transplanted into a walnut tree’s root zone. Alternatively, some plants may survive for years near a young walnut tree but then wilt and die as the tree increases in size. Black walnut toxicity can be confused with wilts caused by bacterial and fungal pathogens (e.g., see UW Plant Disease Facts D0121, Verticillium Wilt of Trees and Shrubs, and D0122, Verticillium Wilt of Vegetables), herbicide injury (see UW Plant Disease Facts D0060, Herbicide Damage), or drought.

How do I avoid problems with black walnut toxicity?

There is no cure for a plant affected by walnut toxicity. Removing a walnut tree may not be practical, as the tree could be the focal point in a landscape. In addition, even if a walnut tree is removed, juglones will not immediately be eliminated, because it is next to impossible to remove all root pieces from the soil and remaining pieces may continue to exude toxins for several years as they decay.

When establishing a garden around a walnut tree, try to plant species that are tolerant to juglone (see table on the reverse side). If you are growing sensitive species near a walnut tree, transplant them elsewhere in your garden. If you must grow sensitive plants near a black walnut, keep beds free of walnut leaves and hulls, and remove walnut seedlings as they appear. Grow shallow rooted woody and herbaceous plants, and improve drainage to help diminish the effects of juglone. Alternatively, consider building raised beds with wood, stone, or concrete barriers that limit root growth through and under the beds.

When disposing of bark and wood from a walnut tree, do not use these materials for mulch.

The information in the following table is intended to provide guidance in selecting plants to grow near walnut trees. Inclusion of plants in this table is based on observation, not on formal testing. In addition, the plant lists in this table are by no means exhaustive. Oftentimes the juglone sensitivity or tolerance of specific plants has never been observed or documented. Finally, sources often disagree on whether particular plants (e.g., columbine, lily, narcissus, tulip) are juglone sensitive or tolerant. Some varieties may be susceptible while others may be tolerant. Most plant species with conflicting information regarding their sensitivity or tolerance to juglone have not been included in the table.

	Sensitive to Juglone	Tolerant of Juglone
Vegetables	asparagus, cabbage, eggplant, pepper, potato, rhubarb, tomato	beans, beet, carrot, corn, melon, onion, parsnip, squash
Flowers	autumn crocus, chrysanthemum, forget-me-not, petunia, peonies	aster, astilbe, bee balm, begonia, black-eyed Susan, bluebell, calendula, crocus, daylily, ferns, grape hyacinth, some hosta varieties, hollyhock, impatiens, Jack-in-the-pulpit, Jacob’s ladder, marigold, morning glory, pansy, phlox, Siberian iris, squill, sweet woodruff, trillium, zinnia
Trees	alder, apple and crabapple, basswood, pine, spruce, silver maple, white birch	black locust, catalpa, Eastern redbud, hackberry, Canadian hemlock, hickory, most maples, oaks, pagoda dogwood, poplar, red cedar
Shrubs and Vines	azalea, blackberry (and most berries other than black raspberry), cotoneaster, hydrangea, lilac, mountain laurel, potentilla, privet, rhododendron, yew	arborvitae, bittersweet, black raspberry, clematis, currant, forsythia, euonymus, greenbrier, most honeysuckle, pachysandra, rose-of-Sharon, sumac, most viburnum, Virginia creeper, wild grape, wild rose, willow, witch hazel
Field Crops and Grasses	alfalfa, tobacco	fescue, Kentucky bluegrass, orchard grass, soybean, timothy, wheat, white clover

For more information on black walnut toxicity:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Lisa Johnson, Mike Maddox and Patti Nagai for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental

Black Spot

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Adrian Crabb* and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0020

What is black spot?

Black spot is a common and potentially serious leaf disease affecting many types of roses. Black spot is found wherever roses are grown.

Typical spotting and yellowing of rose leaves due to black spot.

What does black spot look like?

Black spot lesions (i.e., infected areas) are roughly circular and may be up to ½ inch in diameter. Lesions often have feathery margins and are dark brown to black in color. Black spot initially appears during periods of wet weather, particularly when rose leaves are first emerging. The disease starts on lower leaves but will spread to the entire plant. Severe black spot leads to yellowing of leaves and defoliation. Black spot can also develop on one-year old canes, leading to raised, purplish-red blotches that blacken and blister.

Where does black spot come from?

Black spot is caused by the fungus Diplocarpon rosae, which survives in rose leaf litter and in infected rose canes. Spores of the fungus are easily spread to emerging leaves by wind or splashing rain.

How do I save a rose with black spot?

If your rose has little or no defoliation, and the weather is dry, then no treatments are necessary. If your rose has a history of severe black spot, and the weather for the growing season is predicted to be wet, consider applying preventative fungicide treatments. Fungicides containing chlorothalonil, copper sulfate, and myclobutanil can be highly effective in controlling black spot. Neem oil is another organic product (in addition to copper sulfate) that has been shown to provide some black spot control. Treat every seven to 14 days from bud break until wet weather subsides. DO NOT use the same active ingredient for all treatments. Instead, alternate the use of at least two active ingredients (particularly if you decide to use myclobutanil) to help minimize problems with fungicide-resistant strains of the black spot pathogen. Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the fungicide(s) in the safest and most effective manner possible.

How do I prevent problems with black spot in the future?

Select rose varieties that are hardy in your area and that have a high level of black spot resistance. The hybrid shrub rose Rosa ‘Meipotal’ (Carefree Delight^®), rugosa rose varieties such as ‘Blanc Double De Coubert’ and ‘Fru Dagmar Hastrup’, climbing roses such as Rosa × Kordesii ‘William Baffin’ and Rosa × Kordesii ‘Henry Kelsey’, and roses in the Knockout^® series all have excellent resistance to black spot. Plant roses in a high light environment, and space shrubs far apart. This will promote good airflow and quick drying of foliage. Promptly remove diseased leaf litter. Prune diseased branches six to eight inches below any obvious infections. Prune only in dry weather. Disinfest pruning tools between cuts by treating them for at least 30 seconds with 70% alcohol (preferable for metal tools) or a 10% bleach solution. Rubbing alcohol and spray disinfectants often contain at approximately 70% alcohol. If you use bleach, be sure to thoroughly rinse tools and oil them after pruning to prevent rusting. Water roses at the base using a soaker or drip hose to minimize wetting of leaves and reduce movement of spores of the black spot pathogen. DO NOT overhead water (e.g., with a sprinkler).

For more information on black spot:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

*Completed as partial fulfillment of the requirements for Plant Pathology 300 – Introduction to Plant Pathology at the University of Wisconsin Madison.

Thanks to Mike Maddox, Judy Reith-Rozelle and Ann Wied for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Vegetable

Black Rot of Crucifers

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Andrew Pape*, UW-Madison Plant Pathology

Last Revised: 02/28/2028

D-number: D0019

What is black rot?

Black rot is a potentially lethal bacterial disease that affects cruciferous vegetables such as broccoli, Brussels sprouts, cabbage, cauliflower, kale, rutabaga and turnip, as well as cruciferous weeds such as shepherd’s purse and wild mustard. Black rot occurs worldwide wherever cruciferous plants are grown and makes cruciferous vegetables unfit for the marketplace or the table.

Black rot causes V-shaped yellow and brown/ dead areas in affected leaves. (Photo courtesy of Amanda Gevens)

What does black rot look like?

Black rot symptoms may not develop for more than a month after cruciferous vegetables start to grow. Initial symptoms are irregular, dull, yellow blotches that appear on the edges of leaves. As the disease progresses, these blotches expand into V-shaped areas with the wide part of the “V” at the edge of the leaf and the point of the “V” toward the attachment point of the leaf to the plant. The V-shaped areas are initially yellow, but eventually become brown and necrotic (i.e., dead) in the center with a yellow border or halo. Veins in affected areas are brown or black, forming to a net-like pattern (often most visible when leaves are held up to the light). Later, interior stem tissue (specifically the water conducting tissue) will also turn brown or black. At this point, affected plants tend to show symptoms of wilting. Black rot can also predispose vegetables to other rot diseases such as bacterial soft rot (see UW Plant Disease Facts D0010, Bacterial Soft Rot).

Where does black rot come from?

Black rot of crucifers is caused by Xanthomonas campestris pv. campestris (Xcc). This bacterium is most often introduced into a garden on or in seeds and transplants of susceptible vegetables. By some estimates, a single infected seed in 10,000 can lead to a severe outbreak of the disease if environmental conditions are favorable. Favorable conditions include warm temperatures (approximately 80°F) and high humidity. Once introduced into a garden, Xcc can survive in residues from susceptible vegetables or on weed hosts. Xcc can subsequently enter susceptible plants through roots, through natural openings in leaves or through wounds made by tools, rough handling, or insect feeding. Cruciferous plants grown near infected plants and healthy plants handled with the same tools as diseased plants are at highest risk of becoming infected.

How do I save a plant with black rot?

There are no curative treatments available to combat black rot once the disease has occurred. However, when disease severity is low, copper-containing fungicides/bactericides that are labeled for use on cruciferous vegetables may help limit additional disease. See UW Plant Disease Facts D0062, Home Vegetable Garden Fungicides for specific products. Be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the product in the safest and most effective manner possible. At harvest, vegetables with low levels of black rot may be salvageable. Remove symptomatic leaves (or other plant parts) and store the remaining parts of the vegetables in a cool but not overly wet environment.

How do I avoid problems with black rot in the future?

Prevent introduction of Xcc into your garden by using certified disease-free crucifer seeds and transplants. If certified disease-free seed is not available, use hot water seed treatments to eliminate Xcc. See UW Plant Disease Facts D0064, Hot-Water Seed Treatment for Disease Management, for details on this process and the proper temperature and treatment time for specific types of crucifer seeds. DO NOT plant cruciferous vegetables in the same area of your garden every year; rotate (i.e., move) these vegetables to different locations within your garden. For more information on rotation see University of Wisconsin Garden Facts XHT1210, Using Crop Rotation in the Home Vegetable Garden.

Once your cruciferous vegetables are growing, be sure to fertilize them appropriately. In particular, inadequate nitrogen can predispose plants to black rot. Also, be gentle with cruciferous vegetables to prevent any wounds that might serve as entry points for Xcc. DO NOT use a sprinkler to water your vegetables as this can splash Xcc from plant to plant. Instead, use a soaker or drip hose that applies water directly to the soil. Avoid working with plants when they are wet to help limit spread of Xcc. If severe black rot develops, promptly remove symptomatic plants as well as all cruciferous plants within a three to five foot radius. Dispose of these plants by burning (where allowed by local ordinance), burying or composting them. If you decide to compost, make sure your compost pile heats to a high enough temperature and that any infested material decomposes for at least one year before it is reincorporated into your garden. For more information on how to properly compost, contact your local county Extension office. Finally, decontaminate any pots, tools, or other gardening items that have come into contact with Xcc-infected plants or Xcc-infested debris by treating them for at least 30 seconds with 70% alcohol (preferable for metal tools because of its less corrosive properties) or 10% bleach. Rubbing alcohol and many spray disinfectants typically contain approximately 70% alcohol. If you use bleach on metal tools, be sure to thoroughly rinse and oil them after use to prevent rusting.

For more information on black rot:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

*Completed as partial fulfillment of the requirements for Plant Pathology 558 at the University of Wisconsin Madison.

Thanks to Amanda Gevens, Donna Henderson, Chelsea King, Tami Pape, Craig Saxe and Brenden Sheehy for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental, Disease - Fruit Crop

Black Knot

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0018

A typical older black knot gall with colonization by whitish secondary fungi. (Photo courtesy of Patricia McManus)

What is black knot?

Black knot is a disfiguring and potentially lethal disease of trees and shrubs in the genus Prunus. This genus includes stone fruits such as wild, fruit-bearing and ornamental plums and cherries.

What does black knot look like?

During the first year of infection, black knot-infected trees develop greenish-brown to brown swellings on affected branches and trunks. During the second year, these swellings enlarge into the ugly, black, erupting tumors (galls) characteristic of the disease. These galls resemble animal feces attached to branches (affectionately referred to as “poop-on-a-stick”). Older (greater than two years old) gall tissue often dies and then is colonized by fungi that give the gall a whitish or pinkish color. Severe black knot infections may cause general tree decline or death if galls girdle large limbs, or tree trunks.

Where does black knot come from?

Black knot is caused by the fungus Apiosporina morbosa, which survives in black knot galls on infected Prunus trees. Spores of the fungus are released from these galls and infect new branches in late spring or early summer during periods of wet weather and mild temperatures (55°F to 75°F).

How do I save a tree with black knot?

To manage existing black knot galls, simply remove the galls each winter from infected trees, then burn (where allowed by local ordinance) or bury them. Prune branches six to eight inches below each gall. On trunks, you can use a chisel to remove tissue from at least one inch beyond the infected area. Keep in mind however, that doing this creates a wound that can provide an entry point for other serious Prunus pathogens such as the bacteria that cause bacterial canker (see UW Plant Disease Facts D0009, Bacterial Canker). After removing galls, be sure to clean pruning tools between cuts by treating them for at least 30 seconds with 70% alcohol (e.g, rubbing alcohol or spray disinfectants) or a 10% bleach solution. This will prevent accidental movement of the black knot fungus from branch to branch, or from tree to tree as galls are removed. If you use bleach, be sure to thoroughly rinse your tools after you are done pruning and oil them to prevent rusting.

How do I avoid problems with black knot in the future?

In established plantings, remove any volunteer or wild cherry or plum trees from within 500 feet of susceptible fruit-bearing or ornamental cherries or plums. When purchasing new cherries and plums, carefully inspect trees prior to purchase to be sure they are free of black knot. When available, buy black knot-resistant ornamental cherry or plum species or varieties such as Prunus ‘Accolade’, Prunus sargentii, and Prunus maackii. DO NOT attempt to control this disease using fungicide treatments, as these treatments are expensive and not likely to be effective.

For more information on black knot:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Patty McManus and Teryl Roper for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Fruit Crop

Bitter Pit and Cork Spot

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Teryl Roper, UW-Madison, Department of Horticulture

Last Revised: 02/28/2024

D-number: D0017

Bitter pit and cork spot are common disorders of Wisconsin apples. These two disorders do not occur every year, but when weather conditions are just right (or just wrong, depending on your perspective), they can be major problems. This fact sheet describes the causes of the disorders and what can be done to reduce the severity of the problems.

The name bitter pit will be used for both cork spot and bitter pit since they are related disorders. Bitter pit shows as brownish spots in the fruit flesh. The spots actually occur in the outer layers of the fruit but are visible through the skin. Bitter pit may develop before or after harvest. Cork spot develops before harvest. The flesh layers underlying the skin collapse, become brown and take on a “corky” appearance. The exact underlying cause of these disorders is not known, however, they are both known to be calcium related.

Several factors are associated with development of bitter pit.

High tree vigor.

Trees that are invigorated by heavy pruning, light crops, or nitrogen applications beyond sufficient ranges have a higher incidence of bitter pit. Pruning is vegetatively invigorating and trees that are heavily pruned will also have light crops and substantial vegetative growth. High nitrogen fertilizer doses also lead to substantial vegetative growth. Vegetative growth competes with fruit for available calcium. If calcium is shunted to vegetative growth, it is not available for fruit growth. Further, since calcium moves with water in the transpiration stream, greater leaf area will shunt more water (and calcium) to the leaves rather than fruit.

Moisture stress.

Trees that have received either too much or too little water are more prone to bitter pit. The typical situation is too little water. Related to moisture stress is high temperature. Hot days lead to greater evapotranspiration from leaves. Calcium moves in the xylem along with the water that “feeds” the transpiration needs and ends up in leaves rather than fruit. Once in the leaves, calcium is immobile and will not move back to fruit.

Large fruit.

Large fruit are more generally more susceptible to bitter pit than smaller fruit. A light crop will not only lead to vegetative vigor, but also to larger fruit and these fruit are more likely to show bitter pit.

To reduce the incidence of bitter pit in apples:

Provide irrigation.

Most years, irrigation is not critical in Wisconsin and the cost of irrigation can be high. During dry spells or drought years, however, irrigation is very valuable for maintaining soil moisture levels and reducing tree stress.

Apply calcium sprays.

Since calcium is immobile in plants once it has reached its destination, it is good practice to apply calcium to a tree so that some will end up on the fruit and be absorbed through the cuticle. You can use either calcium nitrate or calcium chloride, but calcium chloride is far cheaper. An additional downside to calcium nitrate is that it aggravates the “too much vigor” problem. Use four pounds of calcium chloride per acre, beginning with the first cover spray through late July. Then increase the calcium chloride rate to 6 lbs. per acre. For small orchards, this is equivalent to approximately 6 oz. of calcium chloride per gallon. During prolonged dry weather, eliminate calcium chloride applications to prevent buildup on the foliage and fruit that may cause burning. Do not make another application unless it has rained since the previous application. There are different calcium chloride products. Research in several states has shown that all products are equally effective if applied at the same rate of calcium, so use the cheapest option.

Include calcium in postharvest dip tanks or wash water.

Michigan research has shown that a 4% dip or drench of calcium chloride will reduce the incidence or delay development of bitter pit in storage. Mix the solution as 33 pounds of calcium chloride per 100 gallons of water. After storage, fruits must be washed again to remove the calcium deposits.

Remember that calcium chloride is corrosive to metal so be sure to clean all equipment thoroughly after using calcium chloride. Painting and upkeep becomes even more important if calcium chloride is used.

I wish there were some “magic bullet” that would reduce the incidence and severity of bitter pit. Unfortunately, the problem is weather related and has several variables that determine its severity and incidence. In general, techniques that keep vigor under control and maintain a reasonable crop load (to keep competing calcium sinks from accumulating calcium that should go to fruit), coupled with applying calcium in cover sprays and at post harvest will help reduce the problem. There are no easy solutions.

For more information on bitter pit and cork spot:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Misc

Bird’s Nest Fungi

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Amy Gibbs and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0016

What are bird’s nest fungi?

Bird’s nest fungi are a group of organisms named for their resemblance to miniature bird’s nests. These fungi are found all over the world, growing and reproducing on decomposing organic matter. In temperate regions, bird’s nest fungi can be found virtually anytime there are damp, shady conditions, but they are most commonly seen in the autumn.

Fruiting bodies of Crucibulum laeve found on decaying wood. (Photo courtesy of Mark Steinmetz)

What do bird’s nest fungi look like?

Bird’s nest fungi can be identified by the appearance of a brown, gray, or white outer “nest”, with brown or white “eggs” inside. The “eggs” are actually spore-containing structures called peridioles that rest inside the cup-shaped fruiting body (reproductive structure). Individual fruiting bodies are usually only ¼ to ½ inch in diameter and vary in shape, size, and color depending upon species.

Where do bird’s nest fungi come from?

Bird’s nest fungi are classified in the fungal group gasteromycetes. Cyathus spp., Nidula spp., Crucibulum spp., Nidularia spp., and Mycocalia spp. are the most common genera of bird’s nest fungi. These fungi are often found in moist, shaded areas, and typically survive on soil, plant remains, decaying wood, or horse and cow excrement. The characteristic “cup and egg” structure of the bird’s nest fungi provides a unique method of dispersing spores. In a storm, the “eggs” are splashed out of the “cups” by raindrops. “Eggs” can travel a three feet or more before sticking to another object. When the “egg” dries, it splits open releasing fungal spores.

What do I do with bird’s nest fungi in my yard?

Bird’s nest fungi are not harmful to living plants, and control of these fungi is typically not necessary. In fact, bird’s nest fungi can be fascinating organisms to observe when you find them in your yard. On occasion, bird’s nest fungi can be a nuisance, particularly when the “eggs” stick to objects such as houses or cars where they are difficult to remove. If bird’s nest fungi become a nuisance, the number of fruiting bodies can be reduced by decreasing irrigation and raking the affected area. The use of non-mulch groundcovers, such as ivy, can also reduce the occurrence of these fungi. Fungicides are not recommended for treatment of bird’s nest fungi.

For more information on bird’s nest fungi:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

Thanks to Kristin Kleeberger, Mike Maddox, and Ann Wied for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Vegetable

Bacterial Wilt of Cucurbits

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: José Pablo Soto-Arias*, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0014

What is bacterial wilt?

Bacterial wilt is a common and destructive disease that affects cucurbits (i.e., plants in the cucumber family), including economically important crops such as melon (Cucumis melo), cucumber (Cucumis sativus) and, to a lesser extent, squash and pumpkin (Cucurbita spp.). This disease is distributed throughout the United States; and can be found anywhere that cucurbits are grown.

Sudden wilting and eventual death of melon, cucumber and squash plants can be due to bacterial wilt. (Photo courtesy of ISU-PIDC.)

What does bacterial wilt look like?

The most distinctive symptom exhibited by a plant with bacterial wilt is wilting and ultimately death. These symptoms are a consequence of the blockage of water movement inside of the plant. Symptoms appear first on leaves of a single runner (vine). Leaves may develop chlorotic (i.e., yellow) and necrotic (i.e., dead) areas as the disease progresses. Symptoms typically develop rapidly along individual runners, and eventually, the plant’s crown is affected, resulting in the entire plant dying. To determine if a symptomatic plant has bacterial wilt, cut a wilted vine near the base of the plant. Next cut a section from this vine and look for sticky threads to form between the two vine sections as you slowly pull them apart. The presence of these sticky threads is diagnostic. This technique works best for cucumbers and melon, but less well for squash and pumpkins.

Where does bacterial wilt come from?

Bacterial wilt of cucurbits is caused by the bacterium Erwinia tracheiphila. This bacterium is moved from plant to plant by two insects: the striped cucumber beetle (Acalymma vittatum) and the spotted cucumber beetle (Diabrotica undecimpunctata). See University of Wisconsin Garden Facts XHT1092, Cucumber Beetles, for details on these insects The bacterium primarily overwinters in the guts of adult beetles, and is released when beetles feed on healthy cucurbit plants and excrete contaminated frass (i.e., feces) onto fresh feeding wounds. E. tracheiphila has been found in association with wild cucurbits and other plants such as goldenrods (Solidago nemoralis and S. altissima), Johnson grass (Sorghum halepense) and even corn (Zea mays). However, most of these plants never show wilt symptoms, and none are considered an important reservoir for the bacterium.

How do I save a plant with bacterial wilt?

Bacterial wilt cannot be controlled once a plant is infected. In particular, chemical sprays are not effective for control once plants show symptoms. If you find bacterial wilt in your garden, immediately remove infected plants, and dispose of them by burning (where allowed by law) or burying them. DO NOT compost infected plants. Prompt removal and disposal of infected plants is important not only because they serve as a source of E. tracheiphila, but because they attract more cucumber beetles, thus increasing the risk of spread of the bacterium to other, healthy plants.

How do I avoid problems with bacterial wilt in the future?

Management of bacterial wilt relies on control of cucumber beetles to prevent infection. Target non-chemical and chemical control methods to protect plants at the beginning of the growing season when plants are more attractive to cucumber beetles. Use mechanical barriers, such as row covers, to protect plants from cucumber beetle feeding. Also, inspect cucurbits on a regular basis for cucumber beetles and their damage (two to three times per week early in the season, and weekly thereafter). When cucumber beetle numbers are high (more than 20 per plant), spray plants with an appropriate insecticide (see UW Garden Facts XHT1092 for recommended insecticides). Be sure to read and follow all label instructions of the insecticide(s) that you select to ensure that you use the insecticide(s) in the safest and most effective manner possible. Cucurbit varieties resistant to bacterial wilt are not currently available. However, some cucurbits such as watermelons and pickling cucumbers tend to be less attractive to cucumber beetles and thus tend to have fewer problems with bacterial wilt. These crops can be used as alternatives to more susceptible cucurbit species.

For more information on bacterial wilt of cucurbits:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

*Completed as partial fulfillment of the requirements for Plant Pathology 558 at the University of Wisconsin Madison.

Thanks to Kimberly Cowles, Amanda Gevens, Kristin Krokowski, Jenna Lind, Dan O’Neil, Isael Rubio-Salaz ar and Tom Wilson for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Broad Leafed Woody Ornamental

Bacterial Wetwood

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Mary Francis Heimann*, O.S.F. and Brian Hudelson, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0013

What is bacterial wetwood?

Bacterial wetwood, also known as “slime flux”, is a visually frightening-looking, but typically non-lethal, disorder of many types of deciduous trees. This disorder can reduce the aesthetic appeal of landscape trees, and more seriously, can substantially reduce the value of forest trees used for lumber. Bacterial wetwood most commonly affects elm and poplar, but can also be a serious problem on aspen, maple, and mulberry.

Bacterial wetwood leads to discolored, rancid-smelling areas on tree trunks.

What does bacterial wetwood look like?

Trees suffering from bacterial wetwood have areas where liquid oozes from their trunks. This ooze may flow freely at certain times of the growing season, but then may stop flowing at others. The ooze leads to streaked, discolored, water-soaked areas on tree trunks. The ooze is often colonized by bacteria, as well as yeasts and other fungi. These organisms can give the ooze a slimy, sometimes brightly-colored (i.e., pink or orange) appearance as well as a highly disagreeable, rancid smell. Internally, bacterial wetwood can be associated with localized areas of wood decay.

Where does bacterial wetwood come from?

Bacterial wetwood arises when localized wet areas develop in the heartwood or sapwood of tree trunks. These areas are colonized by a diverse assortment of bacteria (e.g., Enterobacterium, Klebsiella, Pseudomonas and many others) that can enter trees through root, branch or trunk wounds. As these bacteria feed and grow, often under anaerobic conditions (i.e., conditions without oxygen), they can produce gases such as methane, carbon dioxide, or nitrogen gas. These gases build up pressure, causing movement of interior liquids to the exterior of the trunk where they escape through wounds and cracks.

How do I save a tree with bacterial wetwood?

Bacterial wetwood is a chronic disorder and affected trees cannot be cured. To limit the unsightly staining of bark caused by bacterial wetwood, try to identify where the ooze is exiting from the trunk and insert a long, plastic tube at this location to direct the ooze away from the trunk and to the ground at the base of the tree. There has been speculation that the build-up of gases due to bacterial wetwood might cause a tree to explode. However, there have been no reliable reports of this ever happening.

How do I avoid problems with bacterial wetwood in the future?

There is little you can do to prevent problems with bacterial wetwood. Many affected trees were likely invaded by wetwood-associated bacteria in the seedling stage. Developing a healthy tolerance for bacterial wetwood, when it occurs, is perhaps the best method for coping with this disorder.

For more information on bacterial wetwood:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

*Mary Francis Heimann is a Distinguished Outreach Specialist Emerita at the University of Wisconsin-Madison.

Thanks to Mike Maddox, Patti Nagai and Christine Regester for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.

Disease - Herbaceous Ornamental, Disease - Vegetable

Bacterial Soft Rot

July 6, 2015 hudelson

UW Plant Disease Facts

Authors: Tobias Lunt*, UW-Madison Plant Pathology

Last Revised: 02/28/2024

D-number: D0010

What is bacterial soft rot?

Bacterial soft rot describes a group of diseases that cause more crop loss worldwide than any other bacterial disease. Bacterial soft rots damage succulent plant parts such as fruits, tubers, stems and bulbs of plants in nearly every plant family. Soft rots commonly affect vegetables such as potato, carrot, tomato, cucurbits (e.g., cucumbers, melons, squash, pumpkins), and cruciferous crops (e.g., cabbage, cauliflower, bok choy). These diseases can occur on crops in the field as well as on harvested crops in storage. Rot can occur over a wide temperature range (with the worst decay between 70 and 80°F) and is particularly severe when oxygen is limited.

Bacterial soft rots cause the collapse of plant parts such as potato tubers. (Photo courtesy of the UW-Madison/Extension Plant Disease Diagnostics Clinic)

What does bacterial soft rot look like?

Soft rot bacteria degrade pectate molecules that bind plant cells together, thus causing plant structure to fall apart. Woody tissues are not susceptible. Initially, bacterial soft rots cause water-soaked spots. These spots enlarge over time and become sunken and soft. Interior tissues beneath the spots become mushy and discolored, with the discoloration ranging anywhere from cream to black. Seepage from affected areas is common. Soft rots are known for a strong, disagreeable odor that accompanies the breakdown of plant tissue.

Where does bacterial soft rot come from?

Soft rots are caused by several bacteria, most commonly species of Pectobacterium [particularly Pectobacterium carotovorum (previously called Erwinia carotovora)], Dickeya species [particularly Dickeya dadantii (previously called Erwinia chrysanthemi)], and certain species of Pseudomonas, Bacillus and Clostridium. These bacteria can enter plants through wounds caused by tools, insects, and severe weather such as hail, as well as through natural openings. The bacteria can be spread from plant to plant by insects, on contaminated tools, or by movement of infested plant debris, soil, or contaminated water. Bacterial soft rots tend to be more of a problem during wet weather and can be more severe when plants lack sufficient calcium.

How do I save a plant with bacterial soft rot?

Once soft rot bacteria have infected plant tissue, there are no treatments. Immediately remove and discard infected plants or plant parts. DO NOT bury or compost this material.

How do I avoid problems with bacterial soft rot in the future?

Avoiding wet conditions is key for managing soft rot. Plant vegetables in well- drained soils, and control watering times and amounts, making sure plants are watered adequately (but not excessively) and uniformly. DO NOT crowd plants; wider spacing will promote more rapid drying of plants and soil. Make sure that soil fertility (particularly soil calcium) is optimal for the vegetables that you are growing based on a soil nutrient test. Add calcium (e.g., bone meal) at planting as needed.

Use soft rot-resistant vegetables in rotation with susceptible vegetables. Corn, snap beans and beets are vegetables that are not considered susceptible to soft rot. When growing broccoli, avoid varieties with flat/concave heads that trap moisture and promote soft rot. Instead, select varieties with domed heads where water readily drains away.

Avoid damaging vegetables when weeding and during harvest. Minimize any handling of soft-rotted plants, but if you must handle such plants (e.g., to remove them from the garden), wash your hands afterwards with soap and water. Decontaminate garden tools before and after use by treating them for at least 30 seconds with 10% bleach or preferably (because of its less corrosive properties), 70% alcohol. Rubbing alcohol and many spray disinfectants typically contain approximately 70% alcohol. Also, keep insects that can wound vegetables such as cabbage maggot under control (see University of Wisconsin Garden Facts XHT1030, Cabbage Maggot, for details).

Harvest only during dry conditions. Closely inspect vegetables from infected gardens that will go into long-term storage, and be sure not to store any diseased vegetables. Cure vegetables where appropriate prior to storage. Store vegetables in a cool, dry, well-aerated place to suppress bacterial growth.

At the end of the growing season, remove any infested plant debris remaining in your garden, and destroy the material by burning (where allowed by local ordinance) or landfilling it. If soft rot is a serious, recurring problem in an area in your garden, DO NOT grow susceptible crops in that area for a minimum of three years.

For more information on bacterial soft rot:

Contact the University of Wisconsin Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 or pddc@wisc.edu.

This Fact Sheet is also available in PDF format:

Full Color PDF

*Completed as partial fulfillment of the requirements for Plant Pathology 558 at the University of Wisconsin Madison.

Thanks to Breann Bender, Amy Charkowski, Mary Pelzer, Scott Reuss, Isael Rubio – Salazar and Mary Thurber for reviewing this document.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.

Submit additional lawn, landscape, and gardening questions at https://hort.extension.wisc.edu/ask-a-gardening-question/.