Fungicide Tank-Mixes and Incompatibilities

Common Fungicides Used for Fruit Disease Management

Their Compatibilities and Incompatibilities 

·       Topsin M (thiophanate-methyl, FRAC 1)

o   Do not tank mix with highly alkaline materials such as Bordeaux or lime sulfur

o   Do not tank mix with copper

·       Inspire Super (difenoconazole + cyprodinil, FRAC 3 & 9)

o   Do not tank-mix with surfactants or foliar fertilizers

·       Rally (myclobutanil, FRAC 3)

o   Compatible with oil

o   Stable at a wide range of pH

·       Revus Top (mandipropamid + difenoconazole, FRAC 3 & 40)

o   Do not tank-mix with surfactants or foliar fertilizers

·       Topguard (flutriafol, FRAC 3)

o   Compatible with surfactants

·       Fontelis (penthiopyrad, FRAC 7)

o   Compatible with surfactants and oil

·       Pristine (pyraclostrobin + boscalid, FRAC 7 & 11)

o   Compatible with oil (except on pear)

o   Do not use Pristine + oil on pear

o   Do not use surfactants when applying by air (hops)

·       Scala (pyrimethanil, FRAC 9)

o   Not compatible with captan

·       Vangard (cyprodinil, FRAC 9)

o   Compatible with most tank additives

o   Adjust pH to 5.0 – 7.0 when tank-mixed with Rovral (stone fruit, small fruit)

·       Cabrio (pyraclostrobin, FRAC 11)

o   Compatible with most additives or adjuvants

·       Flint (trifloxystrobin, FRAC 11)

o   Compatible with most insecticides, fungicides, and foliar nutrients

·       Sovran (Kresoxim-methyl, FRAC 11)

o   Can be tank-mixed with most recommended insecticides, fungicides, plant growth regulators, adjuvants, or additives

 ·       Captan (FRAC M)

o   Do not mix with oil or within 4 days of an oil application

o   Do not mix with strongly alkaline materials (reduces fungicidal activity) such as   Bordeaux mixture or lime

o   Phytotoxic to apple when mixed with sulfur

·       Copper (FRAC M)

o   Not compatible with Topsin M

o   Do not apply under cool, slow-drying conditions

o   Do not tank-mix with phosphorus acids

o   Tank-mixing with mancozeb may cause phytotoxicity under wet or cool conditions. Spot check before use.

o   Many Bacillus products are incompatible with copper. Read label and use caution.

·       Dithane (mancozeb, FRAC M)

o   Compatible with most insecticides, fungicides, or growth regulators

·       Polyram (metiram, FRAC M)

o   Spray oils may be needed to achieve consistent control

·       Sulfur (FRAC M)

o   Do not mix with oil or use within 2 weeks of each other

o   Do not mix with Bt

o   Phytotoxic to apple when mixed with captan

o   Do not apply to sensitive crop cultivars

o   Do not use at temperatures above 80˚F

·       Syllit (dodine, FRAC M)

o   Do not mix with Bordeaux or lime

·       Ziram (FRAC M)

o   Compatible with most commonly used adjuvants

 

Above comments and compatibilities are per label recommendations, thus terminology and language may vary from one product to another.

Elm Yellows - a Sporadic Yet Lethal Disease of Elm

Elm Yellows, a lethal systemic disease of elm, was confirmed on two American elm (Ulmus americana) specimens in Franklin County in August 2013.  The disease can occur in isolated areas across the eastern portion of the US and can quickly devastate large plantings of native elm.  Elm yellows occurs only occasionally in Kentucky.  In fact, only one other incidence has been reported in the commonwealth during the past 30 years (Jefferson Co., 1990).

Symptoms of elm yellows usually appear during summer months and include bright yellowing that resembles early senescence (Figure 1).  Leaves can change hues with a few weeks, with petioles turning downward (epinasty) (Figure 2).  Leaves eventually turn brown and can remain attached to branches for several weeks (Figure 3). 



Figure 1.  Foliar symptoms of elm yellows disease include bright yellowing of leaves during summer.



Mature trees develop disease symptoms approximately nine months following infection, while young trees may show symptoms in as little as three months.  Trees usually die within a year or two after symptoms develop.  There is no cure. 

The causal agent of elm yellows is a phytoplasma (bacterium-like prokaryote) called ‘Candidatus Phytoplasma ulmi’. The pathogen inhabits phloem tissue of elm, and as the pathogen builds up in tissue, it becomes a metabolic sink for photosynthetic products.  Phloem then degenerates downstream from these sinks, causing root mortality in fine roots and subsequently in larger ones.  As this process ensues, tree canopies begin to show yellowing symptoms as described above. 

Figure 2.  Petioles droop and turn downward as elm yellows disease advances.

 

Hosts of the elm yellows bacterium are limited to elm species, particularly native elm, including the American elm (U. americana) and winged elm (U. alata).  Chinese elm (U. parvifolia) is more tolerant of infection and often remains unaffected in areas where disease has killed native elm. 

Spread of the bacterium is believed to be caused by several species of leafhoppers and possibly spittlebugs, although the white-banded elm leaf hopper has been confirmed as the primary vector.  These insects inoculate trees during summer or early autumn as they feed. 

Figure 3.  Within a few weeks of symptom development, elm yellows causes leaves to turn brown.  Leaves may fall or remain attached to trees for several weeks.

 

Control of elm yellows is not possible and control of insects is not practical.  Infected trees should be removed as soon as possible to prevent spread of disease.  Confirmation of elm yellows requires a molecular diagnostic test.  Non-elm or tolerant elm species, including Asian species and hybrids, should be used as replacement plants.

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

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.