All posts by hudelson

March 2022: Checking Out the New Gym (or Flexing Your Muscles on a New Wisconsin Disease)

I’ve been around long enough at the PDDC (25 years next summer) that most of the diseases that I see at the clinic are old friends.  Rhizosphaera needle cast, oak wilt, Verticillium wilt and many others are part of the cast of plant disease characters that I see in Wisconsin every year.  It’s relatively rare that I see brand new diseases.  In recent years, boxwood blight, Neopestalotiopsis leaf spot and fruit rot of strawberry and zonate leaf spot (a disease that had been on my bucket list for years) are new diseases that have crossed my doorstep.  In 2022, I’m watching for yet another new disease:  Japanese apple rust.

Japanese apple rust is a type of Gymnosporangium rust caused by the fungus Gymnosporangium yamadae.  This fungus is native to Asia (specifically China, Korea and Japan) and was first detected in the United States in Delaware and Pennsylvania in 2008 (with a first formal published report in 2009).  In 2021, Sam Fieweger of the Wisconsin Department of Agriculture, Trade and Consumer Protection (WI DATCP) Plant Industry Bureau Lab confirmed the first detection of the disease in Wisconsin.  The disease was identified on a crabapple tree in a nursery in southeast Wisconsin.

Like other Gymnosporangium rusts, Japanese apple rust is an altnernating rust.  The causal fungus requires two different host plants to complete its life cycle.  It spends half of its life on a wide range of apples/crabapples (Malus spp.) and the other half on Chinese juniper (Juniperus chinensis, Japanese garden juniper (Juniperus chinensis var. procumbens) and Sargent juniper (Juniperus chinensis var. sargentii).

Japanese apple rust on juniper.  Photo courtesy of Nancy Gregory, University of Delaware.

Typical symptoms of Japanese apple rust are not radically different than those of other Gymnosporangium rusts.  On juniper hosts, the disease leads to the formation of relatively small branch galls that ooze orange gelatinous arms/masses in the spring.  These galls/masses look (at least to the casual observer) not that different from those produced by cedar-apple rust (CAR) and (particularly) cedar-hawthorn rust (CHR), two common Wisconsin Gymnosporangium rusts.  On apple/crabapple hosts, symptoms of Japanese apple rust are again similar to those of CAR and CHR:  large, brightly-colored leaf spots.  In the cases of CAR and CHR, the spots are yellow to orange.  In the case of Japanese apple rust, the spots are fuchsia to red.  On the undersurface of the leaves where the spots are located, short spiny structures eventually form.  These are reproductive structures that produce spores that reinfect the juniper hosts.

Japanese apple rust on crabapple.  Photo courtesy of Nancy Gregory, University of Delaware.

The presence of Japanese apple rust in Wisconsin puts a wrench in the recommendations that I typically make for managing Gymnosporangium rusts.  Chinese junipers are not great hosts for CAR, CHR and cedar-quince rust (the other common Gymnosporangium rust in Wisconsin), so I have historically recommended these junipers for clients who are desperate to grow junipers and apples, crabapples and hawthorns near one another.  If (more likely when) Japanese apple rust becomes more prevalent, Chinese junipers will no longer be a good choice to grow alongside apples and crabapples.  In the future, management of Gymnosporangium rusts will likely have to rely on not growing junipers and apples, crabapples and hawthorns anywhere near each other.

Because Gymnosporangium yamadae is not native to the US, Japanese apple rust is of regulatory importance in Wisconsin (and also elsewhere in the US).  There is interest in determining how widespread the disease may be in the state.  For that reason, I will be providing free diagnostics (as long as I am financially able – the testing is a bit pricey) for suspect Japanese apple rust samples.  The easiest hosts to verify the disease on will likely be apples or crabapples.  So, please watch for those fuchsia to red spots.  If you see anything suspicious, please submit digital photos via my online digital diagnostics form.  Let me know in the “Message” field that you suspect Japanese apple rust, and there will be no fee.  If your photos look suspicious, I’ll request a follow-up physical sample for additional lab testing.

If you have questions about Japanese apple rust or submitting a Japanese rust sample (or need advice about plant diseases in general), feel free to contact the PDDC by phone at (608) 262-2863 or email at  Also check out the PDDC website ( for additional details on plant diseases and sample submission.  Feel free to follow the PDDC on Twitter and Facebook (@UWPDDC) or email me to subscribe to the PDDC listserv, UWPDDCLearn, to receive updates on clinic services and educational materials.

Good luck with your new workout!


March 2022: To Reuse Pots or Not Reuse Pots – That is the Question

I have recently seen comments and discussions on social media about reusing pots from greenhouse or nursery-purchased plants.  In some instances, there has been discussion of returning pots to nurseries and greenhouses for businesses to reuse.

I’m definitely all for reusing pots whenever possible.  It’s an environmentally sound thing to do.  However, keep in mind that you need to be cautious when reusing pots as they potentially can be sources of disease-causing organisms.  These pathogens may be carryovers from plants that you originally purchased in the pots, or they may be pathogens that the pots picked up later as the pots have be stored in your garden or elsewhere on your property.  In particular, damping-off and root rot pathogens can be found in many garden soils, so anytime pots come in contact with garden soil (and it doesn’t have to be a lot), they can potentially become contaminated.  And, it’s not just pathogens that can be an issue.  Insect pests and (gulp!) jumping worms could also potentially be carried via contaminated soil on recycled pots.

So, if you have a collection of old pots and want to reuse them (or even more importantly want to give them to your local nursery or greenhouse), take some precautions prior to reuse or donation.

  • Clean your pots thoroughly with soapy water to remove any bits of soil clinging to the surfaces of the pots that might be harboring pathogens. An added bonus of using an initial cleaning with soapy water is that this should help deactivate plant viruses that might be hanging out on your pots.
  • Soak your pots in a 1.0-1.5% sodium hypochlorite  solution for 20-30 minutes.  Sodium hypochlorite is the active ingredient in disinfecting bleach.  This treatment will help kill pathogens that remain on the surfaces of the pots.  Be cautious when using bleach to avoid contact with skin, eyes and clothing.
  • Thoroughly rinse the pots to remove bleach residues that can be toxic to the new plants that you are trying to grow in the pots.

Note that the treatment outlined above may not be successful in all situations.  Bleach treatments tend to work better on clay or ceramic pots but tend to be less successful for plastic pots.  Be that as it may, seriously consider decontaminating you pots prior to reuse or donation to local businesses.  This will help limit, as much as possible, plant pathogen carryover and spread.

For more information on plant diseases and their management, check out the UW Plant Disease Diagnostics Clinic website ( or contact PDDC staff at or (608) 262-2863.

February 2022: ‘Tis the Season – A Tree Pruning Redux

I often talk about pruning as a method for disease management.  Pruning branches with canker diseases (e.g., Nectria canker, Cytospora canker, golden canker) can be critical in keeping diseases in check and preventing pathogen spread.  Pruning healthy trees and shrubs is also important to promote proper growth, reduce the risk of structural failure during extreme weather (e.g., high winds), and, in some instances, enhance flowering.

When pruning your trees and shrubs, consider the following:

  • Match your pruning technique to the specific tree or shrub you are pruning. Specific trees and shrubs have particular pruning needs, and you need to choose the right pruning technique for the trees and shrubs in your landscape.  Check out the University of Wisconsin Garden Facts Pruning Deciduous Trees, Pruning Deciduous Shrubs, and Pruning Evergreens for details.
  • Prune in the winter, when possible. From a disease standpoint, pruning in the winter is typically optimal.  Disease-causing organisms and insects that carry them are not active, meaning there is less of a chance that infections will occur through pruning wounds.  Are there exceptions?  Absolutely!  Some research indicates that pruning honeylocust in the summer can help reduce the incidence of Nectria canker.  Also, pruning spring-flowering shrubs in the winter reduces flowering, so pruning these plants right after bloom is a better option.
  • Prune when it’s dry. If you prune during the growing season, prune when there’s a stretch of several dry days.  Wet weather is a better environment for disease-causing organisms to infect.
  • Prune to minimize wound size. When removing large tree branches, be sure prune just outside the branch collar (i.e., the slightly swollen area where the branch attaches to the trunk).  This will produce a smaller wound than cutting the branch flush with the trunk.  Similarly, cut smaller branches perpendicular to the long axis of the branch (rather than at an angle).  A smaller wound provides a smaller “target” that plant pathogens have to land on and infect.  A smaller wound also means less time for a tree to produce protective tissue that grows over a pruning cut.
  • Avoid painting pruning cuts. Paint wounds (and do it immediately) only when pruning oaks and elms during the growing season.  This reduces the risk of transmission of the oak wilt and Dutch elm disease fungi.  Painting pruning cuts on other types of trees can slow development of the protective tissue described above.
  • Decontaminate, decontaminate, decontaminate. Optimally, decontaminate tools between every cut.  Check out my January Plant Disease Pointers for details on what to use and how long to treat.  Consider using two sets of pruning tools, one that you decontaminate, while you prune with the other.  If decontaminating between every cut is not feasible, decontaminate as often as possible and definitely between plants.

And with that. . . Happy pruning!

For more information on plant diseases and their management, check out the UW Plant Disease Diagnostics Clinic website (, or contact PDDC staff at or (608) 262-2863.

February 2022: Optimizing Your Diagnosis at the PDDC

Here at the Plant Disease Diagnostics Clinic (PDDC), we strive to provide the best possible diagnoses of plant disease problems.  PDDC staff use a range of techniques to do this including visual and microscopic examination of plant tissue, incubation of tissue in moist chambers to coax fungal pathogens to sporulate, culturing techniques to grow pathogens from tissue, serological tests to detect proteins specific to certain pathogens, and DNA/RNA (i.e., genetic material) detection techniques.  The PDDC’s ability to provide a high quality diagnoses using these techniques however, is dependent on receiving a high quality sample to work with.

Here are some pointers on how to provide an optimal sample so that PDDC staff can provide an accurate, timely diagosis.

Submit a sample when you first see a problem.  Diagnosing plant diseases as early as possible allows for greater flexibility in management of diseases once they are identified.  So, contact PDDC staff as soon as you see a problem.  That said, disease-causing organisms may not produce structures that we need to see to make a diagnosis (e.g., fruiting bodies, spores) early in disease development.  We may need to work with you and have you repeatedly sample and submit materials over time to accurately diagnosis your plant disease problem.

 Consider submitting photos prior to a physical sample.  Sometimes, we can provide a reasonably accurate diagnosis based on photos (tar spot anyone?).  If not, photos can provide useful information on the sort of physical sample that you can send to the PDDC for a more detailed analysis.  You can use the online form at to submit photos.  If for some reason that form doesn’t work for you, feel free to send photos to the clinic email address (  If we are able to provide a diagnosis from your photos, there will be a $20 digital diagnosis fee.  If we make a preliminary diagnosis from the photos but suggest a follow-up physical sample submission for additional testing, the $20 digital fee will be credited towards any lab fees for your follow-up sample.

When submitting a physical sample, make sure you provide the appropriate plant part.  If you have any questions about what to submit, contact the PDDC for advice.  Submitting the wrong plant part can lead to an inaccurate or delayed diagnosis.

For herbaceous plants (e.g., herbaceous ornamentals, vegetables), sending in an entire plant may be the best course of action.  In some situations, symptoms that you see on the leaves of plants are an indication of a problem in the root system.  With trees and shrubs, submitting an entire plant is not practical.  For these plants, submitting subsets of leaves/needles, branches and/or roots will likely be more appropriate.

Whatever you end up sending, send A LOT.  Often, we need to perform multiple tests to diagnose a problem.  We don’t want to run short on tissue.  For leaves, send half a dozen to a dozen (or more) showing a range of symptoms.  For branches, send three or more symptomatic branches (with attached leaves or needles where appropriate).  For roots, send a large handful of the small, fibrous roots.

In particular, appropriate branch selection can be critical for accurately diagnosing vascular wilt diseases such as Dutch elm disease, oak wilt and Verticillium wilt.  For these diseases, select branches that have recently wilted/died back.  DO NOT submit branches that easily snap off.  These branches have been dead too long and cannot be accurately tested for vascular wilt pathogens.  If you suspect Verticillium wilt, select symptomatic branches from as low on the tree as possible as the pathogen that causes this disease infects through the roots.  Choose branches that are roughly one inch in diameter.  Larger diameter branches (particularly from oak trees) tend to have thick bark that is difficult to remove without contaminating underlying tissue where vascular wilt pathogens reside.  This contamination will interfere with growing pathogens from branch tissue and can also interfere with DNA-based tests for pathogen detection.  Sometimes, clients like to send in trunk sections for testing for vascular wilts.  These sorts of samples can work, but only if the trunk slices are no more that about one inch thick.  We need to be able to easily pop off the bark from these slices with minimal contamination of the wood underneath.

Submit your sample as quickly as possible to the PDDC.  If possible, collect samples just before you mail them or drop them off in person.  If there is going to be a delay in submission, keep samples as cool as possible.  High temperatures can kill certain pathogens and can degrade herbaceous plant tissues, leading to what we not-so-affectionately refer to as “slime in a bag”.  Degraded samples make diagnostic testing more difficult, if not impossible.  Mail samples by overnight mail when possible.  If mailing via regular mail, please mail early in the week (Monday or Tuesday) so that samples do not sit around in a mail facility over a weekend.  Click here for details on how to package samples to make sure they arrive at the PDDC in good shape.

Help us, help you.  Providing us with a high quality sample can go a long way in us providing you with a high quality diagnosis.  Let’s work together to make this happen.  If you have questions about submitting a sample (or about plant diseases in general), feel free to contact the PDDC by phone at (608) 262-2863 or email at  Also check out the PDDC website ( for additional details on sample submission.  Feel free to follow the PDDC on Twitter and Facebook (@UWPDDC) or email me to subscribe to the PDDC listserv, UWPDDCLearn, to receive updates on clinic services and educational materials.

Good luck and happy plant disease sleuthing!

January 2022: Decontaminating Your Way to Healthier Plants

When discussing plant diseases and their management, I often emphasize decontaminating pots, gardening tools and work surfaces as one part of a successful disease management strategy.  To kill fungi and bacteria (and to a lesser extent viruses) I often recommend treating items for at least 30 seconds with alcohol, commercial disinfectants, or bleach.

When using alcohol, a 70% solution is optimal for decontamination.  I use ethanol for decontaminating items in my lab, but rubbing (i.e., isopropyl) alcohol is a better option for home gardeners, as it is readily available at a local drugstore or grocery store.  Rubbing alcohol is formulated as a 70% solution and can be used straight out of the bottle.

Commercial disinfectants come in many forms.  I look for products that contain alcohol (you may see ethanol listed as an ingredient) and where the percentage of all active ingredients is as close to 70% as possible.  If you opt to use a spray disinfectant, spray items until they drip and then allow them to air dry.

Bleach is probably the most challenging material to use for decontamination.  Back when I started at the PDDC (almost 25 years ago), most bleach that you could buy at the grocery store was formulated to be 5.25% sodium hypochlorite (the active ingredient), and you just had to make a 10% solution (i.e., 1 part bleach and 9 parts water) to yield an approximate 0.5% solution that is optimal for decontaminating items.  Nowadays, the bleach that you buy can contain very different concentrations of sodium hypochlorite (e.g., 1.8%, 5.25%, 7.5%, 8.25%), and you have to be more careful how you mix up your dilute bleach solution.

Here are some easy instructions on how to dilute the bleach that you buy (assuming it contains 1% or more sodium hypochlorite) to properly to yield a solution that is 0.5% sodium hypochlorite (or slightly higher):

  • Find the percentage of sodium hypochlorite in your bleach in the ingredient list;
  • Multiple that number by two (2);
  • Round the resulting number down to the nearest whole number;
  • Subtract one (1) from that rounded number.
  • This final number is the number of parts of water that you need to mix with one (1) part of your bleach to yield the diluted solution you need for decontaminating items.

When you use bleach on metal tools (alcohol is really a better option for treating metal items), be sure to rinse tools thoroughly with water after treating (to remove bleach residues) and then oil them.  Bleach corrodes metal and will cause metal tools to rust if not used properly.  Also use bleach carefully to prevent contact with your skin and clothing.  Bleach can cause skin irritation/burns and eat holes in your clothes, if not used properly.

Now go forth and decontaminate!

For more information on plant diseases and their management, check out the UW Plant Disease Diagnostics Clinic website ( or contact PDDC staff at or (608) 262-2863.


Root Rots on Houseplants

Wilting of poinsettia associated with Pythium root rot.
Wilting of poinsettia associated with Pythium root rot.

What is root rot? Root rot is a general term that describes any disease where the pathogen (causal organism) causes the deterioration of a plant’s root system. Most plants are susceptible to root rots, including both woody and herbaceous ornamentals. Root rots can be chronic diseases or, more commonly, are acute and can lead to the death of the plant.

How do you know if your plant has a root rot? Homeowners often become aware of root rots when they note that a plant is wilted, even though the soil is wet. Plants with root rots are also often stunted, and may have leaves with a yellow or red color, symptoms that suggest a nutrient deficiency. Careful examination of the root systems of these plants reveals roots that are soft and brown. These roots may have a bad odor.

Where does root rot come from? A large number of soil-borne fungi cause root rots. Pythium spp., Phytophthora spp., Rhizoctonia solani, and Fusarium spp. are the most common root rot fungi. These fungi have wide host ranges, and thus can cause root rots on a wide variety of plants. Most root rot fungi prefer wet soil conditions and some, such as Pythium and Phytophthora produce spores that can survive for long periods in soil or plant debris.

How do I save a plant with root rot? Often the best and most cost effective way of dealing with a plant with root rot is to throw it out. If you decide to keep a plant with root rot, REDUCE SOIL MOISTURE! Provide enough water to fulfill the plant’s growth needs and prevent drought stress, but DO NOT over-water.

Throw out plastic pots if plants grown in them have suffered from a root rot.
Throw out plastic pots if plants grown in them have suffered from a root rot.

We DO NOT recommend use of chemical fungicides for control of root rots on houseplants because of the limited availability of products for use by homeowners, and because those products that are available tend to be expensive.

How do I avoid problems with root rots? First, buy plants from a reputable source and make sure they are root rot-free prior to purchase. Second, replant your houseplants properly. Use a pot with drainage holes, but DO NOT put rocks or gravel at the bottom of the pot. The presence of rocks or gravel can actually inhibit drainage. Use a pasteurized commercial potting mix, NOT soil from your garden. Garden soils often contain root rot fungi. Add organic material (e.g., peat moss) to heavy potting mixes to increase drainage. Third, minimize potential contamination of your plants with root rot fungi. DO NOT reuse potting mix from your houseplants, or water that has drained from your plants, as both potentially can contain root rot fungi. After working with plants with root rot problems, disinfest tools, working surfaces and clay pots with a 10% bleach or detergent solution, or alcohol. DO NOT reuse plastic pots as they are often difficult to disinfest adequately. Finally and most importantly, moderate plant moisture. Provide enough water to fulfill your plants’ needs for growth and prevent drought stress, but DO NOT over-water. In particular, DO NOT allow plants to sit in drainage water. REMEMBER, root rot fungi grow and reproduce best in wet soils.

For more information on root rots: Contact your county Extension agent.


There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.
There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.

What are lichens? Lichens are organisms that arise from mutually beneficial interactions between certain fungi and algae. The fungi provide the physical structures of the lichens, as well as protection for the algae. The algae, in turn, produce food for the fungi via photosynthesis.

What do lichens look like? Lichens come in four basic growth forms. Crustose lichens are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens are leaf-like and composed of flat sheets of tissue that are not tightly bound together. Squamulose lichens are composed of scale-like parts. Fruticose lichens are composed of free-standing branching tubes.

Where do lichens come from? Lichens are everywhere. There are an estimated 13,500 to 17,000 species of lichens, and lichens can be found growing in tropical, temperate and polar regions throughout the world. Lichens will grow on almost any surface that is stable and reasonably well-lit. In temperate regions, lichens can often be found growing on the bark of trees or old fence posts. Others lichens grow in less hospitable places, such as bare rock surfaces or old headstones in graveyards, where they aid in the breakdown of rocks and the formation of soil.

There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.
There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.

How do I save a tree with lichens? DO NOT PANIC! Lichens do not harm trees; they are not pathogens or parasites, and do not cause disease. Lichens are self-reliant, with the algal component of the lichen producing food for the organism via photosynthesis. Lichens absorb water and minerals from rainwater and the atmosphere, and because of this, they are extremely sensitive to air pollution. As a result, the presence or absence of certain lichen species can be used as an indicator of levels of atmospheric pollutants. Information on the abundance and species of lichens growing in an area can give a good indication of the local air quality.

For more information on lichens: Contact your county Extension agent.

Deciduous Tree Leaf Disease Quick Reference

Anthracnose for Quick Guide Anthracnose
Hosts:  Most trees, commonly ash, maple and oak
Pathogens:  Gloeosporium spp. as well as other fungi
Signs/Symptoms:  Blotchy dead areas on leaves
For more information see:  UW Plant Disease Facts D0002
Purple-bordered leaf spot Purple-Bordered Leaf Spot
Host:  Amur, Japanese, red, silver and sugar maple
Pathogen:  Phyllosticta minima
Signs/Symptoms:  Discrete, circular leaf spots with purple borders
For more information see:  UW Plant Disease Facts D0089
 Tubakia leaf spot Tubakia (Actinopelte) Leaf Spot
Hosts:  Oak
Pathogen:  Tubakia spp. (Actinopelte spp.)
Signs/Symptoms:  Discrete circular, or irregular blotchy dead areas on leaves
For more information see:  UW Plant Disease Facts D0118
 Scab Apple Scab
Hosts:  Apple, crabapple, pear, mountain-ash
Pathogen:  Venturia inaequalis, V. pirina
Signs/Symptoms:  Circular, black leaf spots with feathery edges; eventual leaf loss
For more information see:  UW Plant Disease Facts D0004
 Cedar-Apple Rust Gymnosporangium Rusts
Hosts:  Apple, crabapple, hawthorn
Pathogens:  Gymnosporangium spp.
Signs/Symptoms:  Bright yellow-orange, circular leaf spots
For more information see:  UW Plant Disease Facts D0058
 Powdery Mildew Powdery Mildew
Hosts:  Most deciduous trees
Pathogens:  Several genera of powdery mildew fungi
Signs/Symptoms:  Uniform/blotchy powdery white areas on upper and lower leaf surfaces
For more information see:  UW Plant Disease Facts D0087
 Downy Leaf Spot Downy Leaf Spot
Hosts:  Hickory, walnut
Pathogen:  Microstroma juglandis
Signs/Symptoms:  Discrete powdery white areas on lower leaf surfaces
 Clorosis Chlorosis
Hosts:  Oak, red maple
Cause:   Iron or manganese deficiency, often induced by high soil pH
Signs/Symptoms:  Yellow leaves with dark green veins
For more information see:  UW Plant Disease Facts D0030
 Scorch Scorch
Hosts:  Most deciduous trees
Cause:   Water stress induced by drought, high soil salt content, or other water-limiting factors
Signs/Symptoms:  Dead tissue on leaf margins
 Tatters Tatters
Hosts:  Most deciduous trees, but commonly oak
Cause:  Possible early season cold injury
Signs/Symptoms:  Lacy, tattered-looking leaves
For more information see:  UW Plant Disease Facts D0111

For more information on deciduous tree leaf diseases:  See or contact your County Extension agent.

Conifer Disease Quick Reference

Conifer - Root and Crown Rot Root and Crown Rots
Hosts:  All conifers
Pathogens:   Assorted root rot fungi/water molds
Signs/Symptoms:  Poor growth, branch dieback, discolored and deteriorated roots
For more information see:       UW Plant Disease Facts D0094
Conifer Rhizosphaera Needle Rhizosphaera Needle Cast
Hosts:  Colorado blue spruce, other spruces
Pathogen:   Rhizosphaera kalkhoffii
Signs/Symptoms:  Browning/purpling of interior needles of lower branches, followed by needle drop
For more information see:       UW Plant Disease Facts D0093
Conifer - Cytospora Canker Cytospora Canker
Hosts:  Colorado blue spruce, other spruces
Pathogen:   Cytospora kunzei
Signs/Symptoms:  Branch dieback with milky-white patches of dried sap on affected branches
For more information see:       UW Plant Disease Facts D0037
Conifer - Spruce Needle Drop Spruce Needle Drop
Hosts:  Spruces
Pathogen:   Unknown (possibly Setomelannoma holmii)
Signs/Symptoms:  Needle loss and dieback at or near branch tips
Conifer - Cedar Apple Rust Gymnosporangium Rusts
Hosts:  Juniper, apple, crabapple, hawthorn, quince
Pathogen:   Gymnosporangium spp.
Signs/Symptoms:  Brown blobs with orange gelatinous masses (juniper); yellow/orange leaf spots (other hosts)
For more information see:       UW Plant Disease Facts D0058
Phomopsis Tip Blight Phomopsis Tip Blight
Hosts:  Junipers
Pathogen:   Phomopsis juniperovora
Signs/Symptoms:  Browning and dieback of branch tips  in spring and early summer as new growth emerges
For more information see:       UW Plant Disease Facts D0077
Conifer - Diplodia Tip Blight Diplodia Shoot Blight and Canker
Hosts:  Austrian pine, other pines
Pathogen:   Diplodia spp.
Signs/Symptoms:  Dieback of branch tips with dead needles showing uneven lengths
For more information see:       UW Plant Disease Facts D0042
Conifer - Dothistroma Needle_ Dothistroma Needle Blight
Hosts:  Austrian pine, other pines
Pathogen:   Dothistroma pini
Signs/Symptoms:  Needle tip browning and death with a distinct break between live and dead tissue
For more information see:       UW Plant Disease Facts D0043
Conifer - Drought Stress Drought Stress
Hosts:  All conifers
Cause:   Insufficient water
Signs/Symptoms:  Purpling/browning of needles near branch tips or higher up in plants during the summer
Conifer - Winter Injury Winter Injury/Winter Burn
Hosts:  All conifers, particularly yew and juniper
Cause:   Insufficient water
Signs/Symptoms:  Needle browning/bleaching over winter or in spring as plants come out of dormancy
For more information see:       UW Plant Disease Facts D0127
Conifer - Herbicide Damage Herbicide Damage
Hosts:  All conifers
Cause:   Exposure to herbicides
Signs/Symptoms:  Twisted or otherwise distorted growth, needle yellowing or browning, plant death
For more information see:       UW Plant Disease Facts D0060

For more information on conifer diseases:  See or contact your county Extension agent.

Peach Leaf Curl

What is peach leaf curl?  Peach leaf curl is a common disease of peach and nectarine trees throughout the Midwest and eastern U.S.  Where the disease is severe, tree vigor and fruit quality and yield are reduced.  Peach leaf curl often becomes more prevalent after relatively mild winters, which are more favorable for the survival of the organism that causes the disease.  A related disease, plum pockets, affects plums.

Leaf distortions and discoloration typical of peach leaf curl.
Leaf distortions and discoloration typical of peach leaf curl.

What does peach leaf curl look like?  Diseased leaves are distorted with puckered, thickened, twisted areas that can be light green, yellow, or reddish to purple in color.  Leaves later turn brown and fall from the tree.  Diseased shoots are stunted with small, yellowish leaves, or have leaves arranged in tight whorls (rosettes).  Diseased flowers may abort, leading to reduced fruit set, while diseased fruit are bumpy, reddish in color, and fall prematurely.

Where does peach leaf curl come from?  Peach leaf curl is caused by the fungus Taphrina deformans, which overwinters in bark and bud scales of peach and nectarine trees.  Fungal spores infect leaves and shoots in the spring while leaves are still in the bud and as they just begin to emerge.  Mild (50 to 70°F), wet weather during this period favors infection.  Additional spores form on the surface of diseased tissue, and these spores cause new infections if the weather remains mild and wet.

How do I save trees that have peach leaf curl?  Peach leaf curl is unlikely to kill a peach or nectarine tree on its own.  However, if significant premature leaf drop occurs, trees will be susceptible to drought stress and winter injury.  To help maintain tree vigor, apply water (approximately one inch per week) at the drip lines (i.e., the edges of where the branches extend) of peach and nectarine trees during dry periods.  Also, fertilize trees with nitrogen, but avoid fertilizing after August 1; late season fertilization will prevent trees from hardening off properly before winter, making them prone to winter injury.  Finally, thin fruit if the crop load is heavy.

How do I avoid problems with peach leaf curl in the future?  Because Taphrina deformans survives in bark and bud scales, removing diseased leaves in the fall will not reduce disease.  To prevent serious problems with peach leaf curl, plant resistant or tolerant peach varieties (e.g., ‘Frost’, ‘Indian Free’, ‘Q-1-8’, varieties derived from ‘Redhaven’).  Avoid growing susceptible varieties (e.g., those derived from ‘Redskin’).  In addition, consider applying a single fungicide spray in the fall after leaf drop or in the spring before buds begin to swell to control peach leaf curl (and also plum pockets).  Effective fungicide active ingredients include chlorothalonil, copper (e.g., Bordeaux mixture), and ferbam.  Choose a fungicide that is labeled for use on edible fruit crops, and read and follow all label instructions to ensure that you use the product in the safest and most effective manner possible.

For more information on peach leaf curl:  Contact your county Extension agent.