Sanitation is the First Step to a Disease-Free Greenhouse

Greenhouse Sanitation

Diseases are a major concern for greenhouse growers and can be a key limitation to profitable plant production.  Disease management in greenhouses is critical because the warm, humid environment in these structures provides optimal conditions for reproduction of many fungal and bacterial pathogens.  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.  Infected plant tissue, infested soil, and pathogen inoculum all serve as sources of pathogens that can later infect healthy plants.  Removal of any material that can harbor pathogens is the basis for disease management using sanitation practices.  This prevents spread of pathogens to healthy plants or reduces survival from one cropping cycle to another.

(Kara Keeton, Kentucky Farm Bureau)

Importance of Sanitation.  Reduction of fungal and bacterial pathogens by various sanitation practices can reduce both active and dormant inoculum (infective pathogenic tissue).  While actively growing plants can provide host tissue for pathogen multiplication and sporulation, dead plant material can harbor overwintering propagules (fungal spores and bacterial cells) for months or years.  These propagules can travel through wind/fan currents, stick to shoes or tools, or move with contaminated soil or water droplets.

Sanitation is one of the most overlooked disease management practices.  Often, growers presume that fungicides are the most important disease management tool at their disposal.  However basic cultural practices such as sanitation help reduce pathogen numbers and eliminate infective propagules that cause disease.  Poor sanitation practices allow pathogens to spread to healthy plants or to survive from one cropping cycle to another.  Elimination and reduction of pathogens can help prevent “overwhelming” of spray programs in which surviving propagules cause disease epidemics within greenhouses.

Sanitation should be considered by both conventional and organic growers. 

Water mold pathogens are often spread by contaminated soil or water.  They can also overwinter in plant debris under benches or on containers and trays that are not properly sanitized (C. Kaiser).

 

Disease Management.  Elimination and/or reduction of pathogens from greenhouses results in fewer fungal propagules.  The following sanitation practices can reduce amounts of infectious pathogens:

·        Discard plants that are heavily infected and those with untreatable diseases (e.g. root rots).  Some diseases (e.g. leaf spots) can be managed using fungicides; isolate infected plants until disease is eliminated.  Fungicides won’t bring dead tissue back to life, but using fungicides will help protect new growth, allowing plants to overcome disease outbreaks.  Contact your local Extension agent for more information.

·        If infected plants are to be treated with fungicides, prune or remove infected tissue (flowers, leaves) to eliminate sources for spore production or propagule multiplication before fungicide application. 

Leaf spot fungi often produce hundreds or thousands of spores that are carried by wind currents or on clothing.  Many leaf spot diseases can carry over from one crop to the next on weeds that are left under benches or on alternate crops on nearby benches (J. Hartman).

 

·        Discard prunings and culled plants.  Never leave cuttings in greenhouses, as pathogens may continue to multiply by producing spores or other propagules.  Do not compost cuttings or soil because incomplete composting (temperatures below 160 F may result in survival of propagules.

·        Remove weeds and volunteer plants to prevent establishment of a “green bridge” between crops.  A green bridge allows pathogens to infect alternate hosts until a more suitable one becomes available.

·        Do not reuse soil or potting media.  Do not bring outside soil into greenhouses.  Use sterilized potting mix only.

·        Disinfest pots, benches, floors, and tools to remove spores and propagules.  Use a commercial disinfectant such as Green-Shield®, 10% bleach, or 10% Lysol® concentrated disinfectant.  Note:  bleach is corrosive, so tools must be rinsed after 5 to 10 minutes of exposure.

Many soilborne pathogens produce overwintering or survival structures (in this case, the tan spherical structures) that can remain dormant for months or years (D. Hershman). 

 

·        Clean excess soil and plant debris from floors and benches.  Soilborne pathogens can remain dormant in soil for months or years, becoming infective when temperature and humidity increase or when susceptible plant material becomes available.

·        Do not drag hoses and other tools along floors, where infested soil and plant debris can stick and be moved to clean surfaces.

·        Use pathogen-free irrigation water – either municipal water or sterilized.  Install a water-treatment system if using recycled pond water.

·        Ideally, a sanitation regime should begin with an empty greenhouse.  Clean and sanitize all surfaces to insure that pathogens are not carried over from one season to the next.

·        Use foot baths containing sanitizers to prevent carrying propagules to clean areas.

 

Additional Resources

Controlling Phytophthora Root Rot in Greenhouse Ornamentals, PPFS-OR-H-9

http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-H-9.pdf

 

Managing the Greenhouse Environment to Control Plant Diseases, PPFS-GH-1

http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GH-1.pdf

 

Damping-off of Vegetables and Herbaceous Ornamentals, PPFS-GEN-3

http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GEN-3.pdf

How Much Does a Vegetable Garden Cost/Save?

OSU Master Gardener(TM): How Much Does a Vegetable Garden Cost/Save?

Great article from Gail Langellotto, coordinator of the OSU Master Gardener Program, who describes the monetary value of home vegetable gardens.  Click on the link above to read Gail's full story.  Here is a portion of the article:


"For each garden, I looked at the difference between yield and cost (difference = yield - cost). I adjusted the value of the difference to its 2012 value, using an online Consumer Price Index inflation calculator. I then divided this adjusted difference by the size of the garden, to arrive at the value per square foot of garden area.

Source	Location	Size (Square Feet)	Cost	Yield	Difference	Difference, Adjusted to 2012 Value	Value/Square Foot
Stephens et al. 1980 #1	Tallahassee, Florida	1,400	$70	$384	$314	$874.14	$0.62
Stephens et al. 1980 #2	Jacksonville, Florida	638	$83.00	$416.00	$333.00	$927.03	$1.45
Stall 1979	Homestead, Florida	600	$333.65	$495.70	$162.05	$512.02	$0.85
Doiron 2009	Scarborough, Maine	10,890	$282.00	$2431.00	$2149.00	$2297.80	$0.21
Roth 2008	Oregon	878	$318.43	$606.97	$288.54	$307.42	$0.35
Cleveland et al. 1985 #1	Tucson, Arizona	833	$45.00	$154.00	$109.00	$232.38	$0.28
Cleveland et al. 1985 #2	Tucson, Arizona	627.5	$56.00	$178.00	$122.00	$260.09	$0.41
Utzinger and Connolly Harrison 1978	Columbus, OH	150.7	$46.00	$90.00	$44.00	$154.80	$0.41

Altogether, the gardens had an AVERAGE VALUE OF $0.65 / square foot of garden area, and a MEDIAN VALUE OF $0.52 / square foot of garden area.

For a modest-sized garden, 200 square feet in size, that's a return of $104 in the first year. For larger gardens, 500-700 square feet in size, that's a return of $260-$364 in year one, alone!

In at least 5 out of the 8 observations (all but Cleveland et al. 1985, and maybe Utzinger and Connolly Harrison 1978), the costs incurred included what was needed to establish a garden, and not simply to maintain a garden. These costs are sure to decrease in subsequent years, as the cost of maintaining a garden is substantially less than start up costs.

Thus, even in the first year after establishment, the net economic benefits of vegetable gardening are positive - and these economic benefits are sure to increase in years two, three and beyond.

The consistent 'winners' in these papers included:

• salad greens
  
• tomatoes
  
• beets
  
• broccoli
  
• potatoes
  
• strawberries

These were the fruits and vegetables that yielded the most, in terms of dollars saved by not having to purchase these items. However, to truly get the best value from your vegetable garden, it is important to plant what your family likes to eat."

Boxwood Blight - Memorable Tips for Easy Identification

This weekend, the local Lexington newspaper, the Herald Leader, published a story on boxwood and boxwood blight.  Thus, I anticipate an influx of suspect samples and concerns.  Also, as weather becomes cooler and more rain is upon us, it is possible that the disease may appear in Kentucky this fall.  Below is a refresher on this devastating disease:

Boxwood blight (Cylindrocladium buxicola) was reported in southern Ohio this spring, but has yet to be found in Kentucky.  Nursery growers in the northern counties are especially concerned about movement of the disease across state lines. 



Figure 1 & 2.  Boxwood blight is most easily recognized by leaf drop.  Photos by Kelly Ivors, NC State.

 

Symptoms of boxwood blight are different from some of the most commonly observed boxwood problems.  For example, stem blight and drought damage result in foliage turning bright bronze or straw-colored while remaining intact.  Boxwood blight, in contrast, results in rapid defoliation of plants (Figure 1& 2).  Another distinguishing symptom of boxwood blight is brown stem lesions that are easily recognized after leaf drop (Fig 3).  Earliest symptoms include leaf spots, but these spots often go unnoticed unless a persistent scouting program is in place (Figure 4).  Roots are not affected.

Figure 3.  Brown stem lesions, a distinguishing characteristic of boxwood blight, are often noticed after leaf drop.  Photo permission by Kelly Ivors, NC State.

 

Avoid unhealthy plants at all costs.  Homeowners should examine plants carefully before purchase, avoiding plants with leaf or stem lesions or an unhealthy appearance.  Growers should carefully inspect incoming plants and liners before introducing them into production areas. 

Cultural practices can help prevent conditions that are conducive for the fungal pathogen.  Space plants for air circulation and rapid drying of foliage.  Overhead irrigation should be avoided.  Fungicides are not available for management of boxwood blight.  Infected plants must be destroyed by burning or burying.

Figure 4.  Leaf spots, the earliest symptoms of boxwood blight, can be detected by scouting.  Photo permission by Kelly Ivors, NC State.

 

Report suspected cases of boxwood blight immediately to your local Extension agent or specialist or to the UK Plant Disease Diagnostic Lab. 

Figure 5.  Comparison of boxwood blight to Volutella stem blight and Macrophoma blight.

 

Chrysanthemum Dieback – Rhizoctonia is Likely the Culprit

Dense canopies and frequent overhead irrigation of fall mums create ideal conditions for many plant pathogens, especially web blight and stem rot.  In greenhouses, plants grow under tight spacing and high humidity.  Furthermore, plant compactness creates microclimates within canopies.  These extreme conditions are conducive for growth of the web blight and stem rot pathogen, Rhizoctonia solani.  Unfortunately, some of these diseased plants make their way into retail centers and our front porches.

Figure 1– Stems and crowns infected by Rhizoctonia solani result in dieback in the upper canopy.  Photo by NC State.

 

Symptoms:  Stem or leaf dieback is often the first recognizable symptom.  This dieback is caused by infections of stems at the base of shoots and branches or by infection of roots and lower stems (Figure 1).  Opening up the canopy will often reveal stem lesions and/or webs or strands of fungal tissue (mycelia) (Figure 2).  Infected leaves appear water-soaked or necrotic, often becoming matted together with the web-like mycelia.

Figure 2– Under wet conditions, Rhizoctonia may spread to upper plant parts, inducing web blight symptoms.

 

Disease Management:  Both cultural practices and fungicides are required for proper disease management.  Keep foliage dry by avoiding overhead watering, by increasing air circulation (wider spacing, increased sunlight), and by practicing strict sanitation (remove diseased tissue and clean up fallen leaves).  Homeowners may use propiconazole (Green Light Systemic Fungicide), mancozeb (Mancozeb or Dithane), or captan (captan) fungicides.  See the Homeowner’s Guide to Fungicides.  Commercial growers and landscape professionals may take advantage of a wider array of fungicides, such as the active ingredients azoxystrobin, fludioxonil, iprodione, PCNB, pyraclostrobin, thiophanate-methyl, trifloxystrobin, and triflumizole.  Refer to the following publications for specific trade names:  Fungicides for Management of Diseases in Commercial Greenhouse Ornamentals and Fungicides for Management of Landscape Woody Ornamental Diseases.  Consult labels for specific information.

Apple Rots Common This Time of Year: Bitter Rot is the Most Prevalent

As apple harvent gets into full swing, many growers and backyard orchardists are encountering a variety of fruit rots.  Some of these rots are initiated by insect entry wounds or hail, and others are caused by fungal pathogens.

The most common of the fungal fruit rots is bitter rot.  

Initial infections begin as early as bloom and continue until about one month after petal fall.  Early symptoms are small, slightly sunken lesions that eventually develop concentric rings (bulls eye pattern).  Under moist conditions, spores turn a distinct salmon color.  Cutting into infected fruit reveals a V-shaped internal rot.

The fungus overwinters in mummified fruit, crevices in bark, and dead wood such as fire blight damaged tissue.  Removal of mummified fruit, cankers, and dead wood helps reduce inoculum for the following season.  Diseased fruit should be discarded immediately.  Fungicides are only effective with good sanitation, so these cultural practices are a necessary step in disease prevention and control.

Current recommendations indicate fungicide applications soon after petal fall (no later than first cover) and continue until harvest.  Fungicides  captan, mancozeb (dithane, manzate, penncozeb), polyram, and ziram are recommended on 10-14 day schedules.  Note:   Symptoms do not always occur immediately after infection, and it is sometimes late in the season before symptoms appear.  However, fruit should be protected in the early stages of development.

 

Some cultivars are more resistant or tolerant of bitter rot disease than others.  Cultivar susceptibility table available at http://www.caf.wvu.edu/kearneysville/tables/bitterrotsus.html .

More information at http://nicolewarduk.blogspot.com/2012/04/homeowner-apple-spray-schedule-low.html ,  http://www.uky.edu/Ag/IPM/appleipm/appleipm/frot.php , and http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-FR-T-2.pdf

Blueberry Mosaic Virus Detected in Kentucky

Blueberry mosaic virus was confirmed in a blueberry orchard in central Kentucky this summer.  This is the first report of blueberry mosaic in the state.  The virus has not previously been found in southern states, but it has been reported in Michigan, Indiana, New Jersey, New York, Oregon, Washington, and British Columbia. 

Formerly considered a “disorder,” blueberry mosaic has only recently been classified as a virus.  Not much else is known about it.  Highbush cultivars ‘Bluecrop,’ ‘Pioneer,’  ‘Concord,’  ‘Earlibule,’ and ‘Jersey’ are among the susceptible cultivars.  Virus symptoms have not been reported in rabbiteye blueberry.  Limited research has been conducted thus far, but it is under evaluation by a team of researchers at the USDA-ARS Marucci Center in New Jersey.

 

Symptoms

Foliar symptoms include mottling and mosaic-patterned characteristics on leaves.  Patterns range from mild to brilliant with yellow, orange, and/or red colorations (see photos).  Mosaic symptoms are not always produced each year, and environmental conditions may affect symptom development.  It is possible that during cool seasons, symptoms are more pronounced.  Thus, under ideal conditions, symptoms may appear suddenly, and it may appear that spread is rapid.

Infected plants often result in reduced fruit load.  Yield losses of 15% have been reported on ‘Bluecrop’ in Michigan.  Fruit on infected plants have been shown to ripen later than noninfected fruit, and fruit quality is low.

 

Spread

The vector (carrier) of the virus is not known.  Researchers report that blueberry mosaic is not transmissible by mechanical means (i.e. pruners).  However, the virus is graft transmitted.  Because virus particles are systemic (dispersed throughout the vascular system), once infected, all plant parts are infected, even when symptoms are absent.  Thus, cuttings should never be taken from a virus-infected plant.

As mentioned above, the vector of blueberry mosaic virus is not known.  Therefore, growers are encouraged to destroy infected plants until it is clear on how the virus spreads.  Whether an insect vector is involved is yet to be determined.

Current research indicates that the virus is slow-spreading (if at all) under field conditions.  However, in Michigan, spread is rapid. So far, the reason is unknown.

 

Treatment

There is no cure for plant viruses, including blueberry mosaic.  Growers should remove infected plants and destroy them by burning or burying.  Remove all roots within soil, as well.  Scout orchards, especially nearby plants, several times during the growing season.  Contact a local extension agent if a plant appears suspicious.

Most importantly, purchase plants from a reputable grower.  Visit nurseries before plant purchase and ask to inspect parent plants.  Furthermore, a virus-free certification is always worth the extra cost. 

 

 

Fungicide-Resistant Downy Mildew Detected in Kentucky Vineyard

This summer, a grape grower in central Kentucky reported persistent downy mildew in his vineyard.  He noted that regular applications of Abound and Pristine fungicides failed to manage the disease.  After laboratory analysis, the pathogen was deemed completely resistant to the two fungicides at the lowest recommended rates and 85% resistant at the highest recommended rates. 

 

What is fungicide resistance?

In the simplest terms, pathogens become resistant to fungicides when the chemical no longer manages disease symptoms.  However, even the most effective fungicides fail to completely eradicate a pathogen population.  There are always a few fungal spores or other fungal inoculum that survive the pesticide application.  Those survivors may be the result of ineffective spray coverage, but individual pathogens may have a trait that provides some type of resistance to the fungicide.  Think back to high school biology when we learned the theory of “survival of the fittest.”  Unfortunately, a single survivor can multiply into thousands of individuals while passing that resistance gene onto its offspring, much the way our parents passed on eye color to us. 

 

How did resistance develop?

Consider that it is highly unlikely that a fungal population will incur resistance to more than one chemical type, at least over the short term.  As a fungal population can become resistant to a single chemical, growers should rotate sprays with a different chemical group.  These chemical rotations can become confusing, and many growers do not fully understand the concept of chemical groups. 

 Chemical groups are classified by biochemical mode of action, not necessarily by active ingredient.  For example, within the strobilurin group of fungicides, active ingredients include azoxystrobin, pyraclostrobin, trifloxystrobin, and kresoxim-methyl, all of which are quinone-outside inhibitors.  Because information on biochemical modes of action can be confusing for growers, the Fungicide Resistance Action Committee (FRAC) developed numeric codes that represent these chemical groups.  Strobilurins are classified as FRAC group 11.  These codes appear on the top right side of all pesticide labels.  Thus, growers may simply refer to the coded chemical group number on labels as opposed to depending upon complex information such as mode of action.

Considering that all fungicides within the same group have the same mode of action, it is clear that if a grower fails to properly rotate fungicide groups, fungicide resistance risk is high.  Additionally, fungicide labels indicate the maximum number of applications allowed per growing season.  A maximum of four applications of strobilurins are allowed per growing season.  The grower mentioned above used Abound and Pristine fungicides consistently over a two-year period, exceeding the maximum number of applications and failing to rotate with a different chemical group.  This rapidly induced the development of a resistant population of the downy mildew pathogen.

 

Abound fungicide is classified as a FRAC Group 11 fungicide.  The chemical group code appears on the top right corner of fungicide labels.

 

How does a grower know if a resistant population developed?

Pathogen populations do not begin as 100% resistant.  In fact, resistance develops gradually.  Thus, growers should be aware of efficacy and disease control.  If a product(s) begins to become less effective over time, he should contact his local Extension agent immediately. 

 

What next?

If resistant pathogen populations develop within a vineyard, growers should immediately stop using the fungicide in question and all others in the same FRAC group.  With the assistance with an Extension agent or specialist, growers should identify other fungicides that will effectively manage disease.  In the aforementioned case, the grower stopped using strobilurin fungicides and substituted a phosphorous acid fungicide (ProPhyt, Rampart, etc.) for management of downy mildew.  If strobilurins are used for management of other diseases, tank-mix with another product (within a different FRAC group) that provides downy mildew control.

 

More Information

Fungicide resistance can appear complicated, so growers should not hesitate to seek assistance in development of a spray program.  Contact University of Kentucky Cooperative Extension agents or specialists for assistance.