Managing Diseases without Fungicides: A Focus on Sanitation (A Visiting Professor feature)

Submitted by:
Nicole Ward Gauthier,
University of Kentucky Extension Plant Pathologist
PEOPLE: University of Kentucky Department of Plant Pathology Website
Kentucky Diseases of Fruit Crops, Ornamentals, & Forest Trees on Facebook
Amanda Sears, Kentucky Extension Horticulture Agent
Madison County Cooperative Extension Website

Alternatives to Fungicides

When diseases occur in urban landscapes, it is often presumed that fungicides are the most important and effective disease management tools available. However, a good sanitation program can help reduce the need for chemical controls and can improve the effectiveness of other practices for managing disease. This often-overlooked disease management tool reduces pathogen numbers and eliminates infective propagules (inoculum such as fungal spores (figure 1c) , bacterial cells; virus particles; and nematode eggs) that cause disease.

fig 1b marigold botrytis 1525420 (MC Shurtleff, UIll bugwd) (640x412)
Figure 1a. Marigold blossom infected with Botrytis
  Figure 1b. Pathogen levels can build up on marigold flowers if diseased tissue is left in the landscape

Figure 1b. Pathogen levels can build up on marigold flowers if diseased tissue is left in the landscape
close up of infecting spores
Figure 1c. Infecting spores on plant surface

Certain foliar fungal and bacterial leaf spots can become prevalent during rainy or humid growing seasons. When disease management is neglected, pathogen populations build-up and continue to increase as long as there is susceptible plant tissue available for infection and disease development (Figures 1a-c). Infected plant tissue infested soil and pathogen inoculum all serve as sources of pathogens that can later infect healthy plants.

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Figure 2. Fallen leaves can serve as a source of inoculum (fungal spores) for additional infections. Many pathogens overwinter in fallen debris and then produce infective spores the following spring.

Reduction of pathogens by various sanitation practices can reduce both active and dormant pathogens. While actively growing plants can provide host tissue for pathogen multiplication, dead plant material (foliage, stems, roots) can harbor overwintering propagules for months or years (Figure 2).

These propagules can travel via air/wind currents, stick to shoes or tools, or move with contaminated soil or water droplets. Thus, prevention of spread of pathogens to healthy plants and the elimination of any disease-causing organisms from one season to another are the foundations for a disease management program using sanitation practices.

Sanitation Practices

Elimination and/or reduction of pathogens from the landscape results in fewer pathogen propagules. The following sanitary practices can reduce amounts of infectious pathogens:

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Figure 3a. Cankers are common overwintering sites for disease-causing pathogens
  • Remove diseased plant tissues from infected plants. Prune branches with cankers (Figure 3a) well below the point of infection (Figure 3b). Cuts should be made at an intersecting branch. Rake and remove fallen buds, flowers, twigs, leaves, and needles.
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Figure 3b. Remove infected branches, making cuts well below points of infection
  • Disinfest tools used to prune galls and cankers.  Cutting blades should be dipped into a commercial sanitizer, 10% Lysol disinfectant, 10% bleach, or rubbing alcohol between each cut.
  • If using bleach, rinse and oil tools after completing work, to prevent corrosion.
  • Discard perennial and annual plants that are heavily infected and those with untreatable diseases (e.g. root rots, Figure 4; and vascular wilts).  Dig up infected plants to include as much of the root system as possible, along with infested soil.

infected plant                           imag

Figure 4. Heavily infected plants or those with untreatable diseases, such as black root rot (images left and right), should be removed from the landscape.   

  • Trees and shrubs infected with systemic diseases (e.g. Dutch elm disease, Verticillium wilt, bacterial leaf scorch) that show considerable dieback should be cut and the stump removed or destroyed (e.g. by grinding).
  • If infected plants are to be treated with fungicides, prune or remove infected tissue (flowers, leaves) and debris to eliminate sources for spore production or propagule multiplication.  This should be done before fungicide application. Fungicide effectiveness may be reduced when disease pressure is heavy, which can result when pathogen levels cannot be reduced sufficiently by chemical means (fungicides).
  • Discard fallen leaves, needles (Figure 5), prunings, and culled plants. Never leave diseased plant material in the landscape, as pathogens may continue to multiply by producing spores or other propagules.  Infected plant material should be buried, burned, or removed with other yard waste.

pathogen 1       pathogen 2

Figure 5.  Black fruiting structures of the pine needlecast pathogen contain spores (images left and right). Removal of infected plant tissue helps reduce amounts of inoculum in the landscape.

  • Do not compost diseased plant material or infested soil because incomplete composting (temperatures below 160˚ F) may result in survival of propagules.
  • Homeowners should be cautious about storing diseased limbs and trunks as firewood or using the woodchips as mulch.  For example, wood from trees infected with Dutch elm disease should be debarked before placing in a firewood pile.
  • Remove weeds and volunteer plants to prevent establishment of a “green bridge” between plants.  A green bridge allows pathogens to infect alternate hosts until a more suitable one becomes available.  Be sure to remove aboveground parts AND roots.
  • Soil from container-grown plants should not be reused from one season to the next because pathogens can survive in soil.

Additional Resources:

University of Kentucky Extension Plant Pathology Publications

Photo credits:

R.K. Jones, North Carolina State University (Fig. 1A), courtesy Bugwood.org
M.C. Shurtleff, University of Illinois (Fig. 1B), courtesy Bugwood.org
David Cappaert, Michigan State University (Fig. 1C), courtesy Bugwood.org
Theodor D. Leininger, USDA Forest Service (Fig. 2), courtesy Bugwood.org
Joseph O’Brien, USDA Forest Service (Fig. 3, right), courtesy Bugwood.org
Elizabeth Bush, Virginia Tech (Fig. 4, left), courtesy Bugwood.org
Bruce Watt, University of Maine (Fig. 4, right), courtesy Bugwood.org
Andrej Kunca, National Forest Centre, Slovakia (Fig. 5, left), courtesy Bugwood.org
Robert L. Anderson, USDA Forest Service (Fig. 5, right), courtesy Bugwood.org
John R. Hartman, University of Kentucky (Fig. 3, left)

 pdf  Managing Diseases Without Fungicides

Prepping Your Garden for The Next Growing Season

William H. McCaleb, Blog Contributor
Program Assistant for Agriculture and Natural Resources, Halifax County, VA. and Master Gardener

For gardeners in the eastern U.S., last year was a better than normal gardening season. Better than normal yield, better than normal precipitation, and in our case in Virginia cooler than normal which yielded excellent spring cool season crops as well as early summer crops.

But all good things must come to an end; that being the result of several heavy frosts.   With that said, I am looking forward to next year’s challenges and what I want to grow for our family. Oh, for the taste of one more summer ripened tomato, but for now, that is a dream and it is time to reflect on what grew well in the garden as well as what didn’t do so well.  Hopefully you have kept a garden journal to help you in this task. I find that writing down details of what is planted, the orientation, spacing, fertilization/liming rates and frequency, weekly rainfall amounts, production amounts, etc. is helpful as you start planning for the next season.

Like me, you should start thinking about what you want to grow in 2015. Take time to reflect on your 2014 garden production, care, and location. Also, evaluate what went right and what went wrong with the plants and varieties you planted and harvested. This will start you off in the right frame of mind in preparing for the next growing season. Good planning and preparation for next year gives you the tools to have an even better gardening season. A successful vegetable gardener is a happy well fed gardener!

I know, you too are already missing those fresh tomatoes, potatoes, peppers, squash, okra, and other great home grown vegetables we treated ourselves to this year, but the next season is ‘just around the corner’ so to speak. After all the days are getting a little longer. Spring can’t be far away!

If you just happen to live in an area that hasn’t had frost yet, take your prompt from your plants: when annuals and seasonal vegetables turn brown and begin to die back, it is time to clean up your garden.

Clean up the Garden
Your best action is to remove any spent or failing plant materials. Experienced gardeners know that many of the bacteria, fungi, and other disease-causing organisms that caused those diseases. Pathogens that are sources of those diseased plants this past season can survive over the winter in dead leaves, stems, roots, and dropped fruits that get left in the garden. Much like a piece of bread that is kept too long and looks like it has penicillin growing on it, garden debris also will carry the pathogens that can come alive with those same problems when the temperatures begin to rise in the spring. Prevention of diseases and insect infestation now, will keep you from a repeat of problems in next year’s garden.

A good leaf rake, given enough ‘elbow grease’, works well in getting the bulk of dead plant material out of your garden. If you experienced early or late blight or other tomato related diseases this past growing season, you want to make sure you reduce, to the best of your ability, the risk of repeating that problem again next year. Yes, there are many new varieties of vegetables available today that are ‘resistant’ to some of these diseases, but ‘resistant’ does not mean they are immune to them. You don’t want to take the chance of returning pathogens, so do a good job, cleaning and ‘sanitizing’ your garden now. Make sure, when removing the plant debris, that you totally destroy that debris so that no pathogens are left behind.

To Compost or Not!
Can you compost this dead plant material and use it next spring? Information that you find from Extension offices across the U.S. will recommend that you do not. The reason being is that most people do passive composting i.e. put it in a pile, and then using what compost develops, put the compost back in the garden for the next season. It is best to burn the plant material; this will destroy the pathogens and weed seeds as well and return some carbon back into the ground when you spread it out. Please check local/state laws prior to burning. Many states and/or localities have burn bans especially this time of the year. Another method, if your local law allows it you can bag the material and send it to the landfill. Each year there are more localities that ban yard waste from their landfills. If you are not sure, check with your locality to learn more about your local waste and recycling laws.

If you do decide to go with active composting; composting at a temperature 140°F, or higher, will destroy many of the disease organisms as well as many weed seeds. You will need a temperature probe to monitor compost temperatures.   It’s really not hard to source a compost thermometer either through the internet or local retail outlets such as garden centers or nursery supply stores. If in doubt about your compost pile reaching these high temperatures, it is best to side with caution and discard the material by properly bagging it or by burning based on your local ordinances.

Preventing Overwintering Pathogens
Some of our most notorious insects of the garden such as Mexican bean beetle, squash vine borers, European corn borer, cabbage loopers, can also overwinter in garden debris. Larvae will use debris as a safe harbor. Flea beetles and spider mites, as well, can find food and winter shelter in spent plant material and weeds.

After you have finished cleaning up the debris from your garden, it is time to turn over the soil to both aerate and break up any remaining debris into smaller pieces that will be turned under. A good rototiller will help make this job easier. Once buried, any plant material left will decompose more rapidly.

For some pests and pathogens, turning over the soil after removing spent plant materials is recommended as the main line of defense against overpopulation next year. Consider this information from “Home and Horticultural Pests: Squash Bugs and Squash Vine Borers,” from Kansas State University,

“A vigorous autumn… rototilling can physically destroy cocoons and larvae (of the squash vine borer). Brought to the surface, cocoons and larvae are more susceptible to predation by birds and exposed to cold winter elements, leading to their demise. Deep plowing physically destroys cocoons and larvae burying them deep beneath the soil surface so pupated moths become entombed underground.”

Steps to a Healthier Garden
If you haven’t done a soil test in three years or more, it is time to retest and determine the needs of your garden soils based on what you will be growing in the next season. Soil test kits and instructions are available from your local Extension Office. Also, in planning next year’s garden, rotation of your crops is a must do item. This simple action will help keep disease issues down.  If your soil test(s) recommend liming, you can go ahead and put down lime this time of year, allowing it to start adjusting the pH. If the ground is frozen already, wait until spring. As you add lime, you can also help build soil structure by incorporating compost or shredded leaves. These soil additives will also add beneficial micro-nutrients and beneficial organisms. If you want to further build the soil, you may want to consider putting in a cover crop that will not only hold soil, but when tilled in early spring, will further build a healthier garden soil. A legume such as white or red clover would be something to consider. Check with your local Extension Office for best cover crop recommendations for your area.

Prepping Your Garden for the Next Growing Season (pdf)

 References:

http://pubs.ext.vt.edu/426/426-334/426-334.html
http://www.ksre.ksu.edu/bookstore/pubs/mf2508.pdf

image sisters
“Three Sister’s Garden-Fall Clean-up “Southern Virginia Botanical Gardens” Photo by W. McCaleb 10/28/14 Corn, Beans, and Squash was grown here as the native Cherokee have done for centuries. Cleaned up and ready for spring 2015!

 

 

 

Where did the 10-20-30 rule come from? Is it adequate?

We’ve been having an interesting discussion over on the Urban Forestry group on LinkedIn on the origins and suitability of the 10-20-30 rule for tree diversity in urban forests.  For those that aren’t familiar, the 10-20-30 rule is a guideline to reduce the risk of catastrophic tree loss due to pests.  The rule suggests an urban tree population should include no more than 10% of any one species, 20% of any one genus, or 30% of any family.

 

The first published reference to the 10-20-30 rule (often referred to as just the 10% rule) was by late Dr. Frank Santamour, Research Geneticist at the US National Arboretum in his paper Trees for urban planting: Diversity, uniformity, and common sense, which was presented at the 1990 Metropolitan Tree Improvement Alliance (METRIA) conference.  While Santamour is commonly credited with the 10% rule he notes in his paper, “I am not sure who first propounded the “10% rule”, nor am I sure that anyone would want to take credit for it, but it is not a bad idea.”

 


The other question on the LinkedIn discussion is whether the 10-20-30 rule is adequate to ensure genetic diversity in urban and community forests.  My personal is opinion is that the rule is inadequate but far preferable than the status quo in most communities.  If we consider the current issue with emerald ash borer (EAB) in North America, following the 10-20-30 rule means we would accept the loss of 1/5th of our urban canopy since both of the commonly planted ash species (Fraxinus pennsylvanica or F. americana) are highly susceptible to EAB.  On the other hand, many community tree populations the US currently include 30% or more maples, so 10-20-30 would actually be an improvement.

 

A limitation to the 10-20-30 guideline that Santamour acknowledges is that the rule does not afford protection against insects with a broad host range such as gypsy moth or Asian long-horned beetle.  However, while these pests can, and have, caused widespread damage they do not appear to threaten nearly total annihilation of an entire species or genus ala specialists such as chestnut blight, Dutch elm disease or EAB.  Moreover, a wide diversity of species is still a better defense even against generalist pests, unless you happen to get lucky and plant a monoculture of the one tree they won’t destroy.

 


One of the inherent challenges in the 10-20-30 rule is implementation.  What is the tree population in question?  Are we talking about a city? A neighborhood? A block? If there are 10 trees on a block do they all need to be different species? Some have proposed corollaries to 10-20-30 such as the “Look around rule” (or “Look around, fool!” if you prefer the Mr. T version).  This guide states if you’re getting ready to plant a tree; look around and if you already see that tree, plant something else.  The problem with diversity on a very small scale is we can end up with the ‘menagerie effect’ – one of these, one of that, one of those – that often lacks aesthetic appeal.   Ultimately this becomes a challenge for urban foresters and designers working together; how do we incorporate diversity guidelines within established design principles.

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A Note To Horse Owners

Every once in awhile I get to work with really, really cool people who do really, really cool work.  This is one of those times.  About a year ago I received a message from Dr. Stephanie Valberg, a Professor over at the University of Minnesota’s Equine Center.  It seems that she was interested in looking at a deadly disease called Seasonal Pasture Myopathy which she thought might have something to do with horses ingesting maple leaves.  Specifically, at the time she contacted me, she thought that this disease might be associated with horses ingesting tar spot, a common disease that maples get. Seasonal Pasture Myopathy is a particularly nasty disease because it is fatal in over 90% of cases, and the death is far from painless.

After doing site visits to many farms where this disease was found, she discovered something very important: Every farm had box elders in a location where horses could feed on the seed when they got hungry.  And for most of the farms, horses were also dealing with scant pickings in terms of food.  They usually had sparse pastures and not much supplemental hay.  So, in these conditions, the horses might find box elder seed attractive, or at least palatable.

After a literature search, Dr. Valberg discovered an old article showing that box elder seeds could very well contain a toxin, hypoglycin A, which might cause this disease if they were eaten.  After testing the seeds for the presence of this toxin (Done by a friend of mine, Adrian Hegeman, located here in the University of Minnesota’s Department of Horticultural Science) it was established that, Yep, box elder seeds have this toxin, and if your horse eats them, it might be in trouble.  You can find out more here.

Right now more work is going on to see if this toxin is more or less present in box elder trees that are under stress, if it is present in other parts of the tree besides the seeds, and at what time of year the toxin might be most present in the seeds.  It also looks as though some other maples may have this toxin in their seeds, most notably sycamore maple.

All in all, having the opportunity to watch this work unfold has been one of the highlights of my career.  It was like watching an episode of House unfold in real life.  And the great part is that this work has the potential to save the lives of dozens, if not hundreds or thousands, of animals.  So if you have horses, and box elder or sycamore maples in your pasture, be careful!

Imprelis damage to landscape conifers

Herbicide issues seem to be dominating my life these days. Over the past several weeks reports have surfaced around the Midwest of landscape conifers – primarily spruces and pines – that have developed rapid and severe die-back. While there are a host of insect pests and pathogens that can cause die-back in conifers, the recent cases are noteworthy in the speed with which trees expressed symptoms.

 


Photos: Andy and Carol Duvall

In many cases that have been reported the common thread appears to be the use of Imprelis, a turf herbicide developed and marketed by Dupont.  Imprelis (active ingredient: aminocyclopyrachlor) is a synthetic auxin designed to control broadleaved weeds in turf.  Ostensibly, one of the advantages of Imprelis is that has root activity in addition to foliar activity.  It appears, however, that it may have too much root activity and the internet is abuzz with photos and posts of Imprelis-damaged conifers.  http://bestlawn.info/northern/imprelis-and-dupont-trouble-t4608.html

http://www.buckandsons.com/blog/tag/dupont-herbicide-imprelis/

 

So what’s going on?  Well there are lots of blurbs coming out and lots of things being reported second and third-hand.  I suspect a few things we ‘know’ about Imprelis right now will turn out not to be the case in a few months.  Dupont has tried to shift blame to the applicators, suggesting that their rates may have been off, they applied when there was potential for drift, or that the material was mixed with other herbicides.  http://www.ksuturf.org/blog/wp-content/uploads/2011/06/DuPont-Letter-to-Turf-Professionals-061511.jpg

 

Given that reports of damage showing similar symptoms have come from Kansas, Iowa, Indiana, Michigan, and Ohio it seems unlikely that everyone is mis-applying the product.  I suspect one of a couple things may be going on.  Dupont may have underestimated the lateral extent of tree roots, especially for conifers that often have shallow, extensive root systems.  It’s also possible that Norway spruce and white pine are more sensitive to this product than whatever Dupont tested it on.

 

In the meantime stay tuned.  In case people haven’t figured it out for themselves, Dupont now recommends that applicators not use Imprelis near spruces or pines (see letter linked above). Landscapers or lawn service operators that have applied Imprelis should keep in touch with their state Department of Agriculture and their professional turf and landscape association.  Might be good to fasten your seatbelts, this could be a bumpy ride…

Mortal Kombat – garden version

Soil solarization is regarded as an environmentally friendly alternative to pesticides for controlling nematodes, weeds and disease.  Sheets of plastic (generally clear) are spread over the ground and solar energy heats the soil underneath to temperatures as high as 55C (or 131F).  Since the soil environment is usually insulated from temperature extremes, the organisms that live there are unlikely to be resistant to heat stress.

This is a practice best suited to agricultural production, where monocultures of plants have attracted their specific diseases and pests.  Decades of research have shown success in controlling pests in greenhouses, nurseries, and fields.  But there’s a down side to this chemical-free means of pest control.

It shouldn’t be surprising that beneficial soil organisms, in addition to pests and pathogens, are killed by solarization.  Studies have found that soil solarization wipes out native mycorrhizal fungi and nitrogen-fixing bacteria.  One expects that other beneficial microbes, predacious insects, and parasitoids living in the soil (but so far unstudied) would be eliminated as well.

This may be an acceptable loss to those who are producing crops; soil can be reinoculated with mycorrhizal fungi, for example.  But for those of us caring for our own gardens and landscapes, this is literally overkill.  (And consider that most of us probably have trees and shrubs whose fine roots extend over our entire property.)

So this spring, instead of solarizing your soil, consider some less drastic measures of pest and disease control. Minimize soil disruption to preserve populations of desirable microbes. Plant polycultures (more than one species) in your vegetable garden, or at least practice crop rotation.  Protect and nourish vegetable gardens with compost.  Use coarse organic mulches, which provide habitat for beneficial insects and spiders, in landscaped areas.  Above all, try to treat your soil as the living ecosystem it is, rather than a war zone.

Sudden Death Syndrome in Soy — Biggest Threat to the Entire Food Chain?

This past week we received an interesting e-mail about something called “sudden death syndrome” which we were asked to blog about.  Here’s the article we were sent.  We don’t always take requests, but we thought that this was an interesting one, so we decided to write a little post about it.  Sudden death syndrome is basically a fungal disease which affects the roots of soybeans.  Recently there has been some press out there about how Round-up ready soybeans are particularly susceptible to this disease and that the spraying of roundup itself can lead to favorable environments for it.

This is a particularly attractive disease for a number of groups because it  provides fuel to their fire.  The anti-biotech group likes it because it makes Round-up ready crops look bad, the anti-pesticide group likes it because it makes pesticides look bad, the anti-Big Ag group likes it because it makes Monsanto look even more evil than usual.  So, in short, lots of happily indignant people.

So is it true?  Is using Round-up and Round-up Ready Soybeans a sure way to condemn ourselves to a soyless future?  On a side note this is something I really care about – I am a chronic soy sauce user.  If something is good without soy sauce it then it is going to be even better with it.  Well, I spend most of Monday and Tuesday looking through scientific articles and here, in a nutshell, is what I came up with:

Sudden death Syndrome is certainly real, and it can devastate a field.  It was around before Round-up and it will be here after Round-up is gone.  The biggest factor in whether it will be a bad year for SDS is the weather.  So what about the Round-up connection?  This is something that has been looked at by researchers, and here’s what they find.  In terms of the fungus responding well to Round-up –  some studies show that it does – most that it doesn’t.  Round-up Ready varieties of soybean may be resistant or non-resistant to SDS and, of course, the non-resistant varieties won’t fare as well as the resistant varieties if SDS is present (it seems possible that this is where the whole hullabaloo started — a field full of Round-up Ready soy but which wasn’t resistant to SDS contracted the disease while nearby non-Round-up Ready soy which did happen to be resistant to SDS did fine.)

Now there are some studies, mostly in test-tubes and greenhouses, which show that Round-up could make SDS worse, but in the field, where it actually matters, there just aren’t that many studies which show a correlation between using Round-up Ready soybeans and SDS — and more studies that show that there isn’t a correlation.  What it all comes down to is that there is a possible relationship between Roundup and SDS, but, despite a lot of research (both government and industry dollars flow easily to agronomic crops), this link isn’t crystal clear and may not exist at all.