Thursday, April 10, 2014

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

·       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.

Sunday, April 6, 2014

Untangling the Web of Copper Fungicides

Fire blight season is approaching, and delayed dormant applications of copper fungicides are commonly recommended for management of various tree fruit diseases.  But there are so many...

Below is a summary of copper formulations, their characteristics, and their limitations. 

Copper Fungicides

·       Fixed Copper

o   Safer for plant tissue than “bluestone” copper (see below)

o   May be used throughout growing season, but may cause fruit russetting

o   Low solubility in water, lower risk for phytotoxicity

o   Release copper ions slowly (with water/rain), longer residual

o   Slow drying time (rainy conditions) increases solubility, ion release, and phytotoxicity

o   Acidic conditions/additives increase solubility, ion release, and phytotoxicity

§  Adjuvants, phosphorus acid fungicides, and mancozeb lower pH

o   Use high rates during dormancy for fire blight management (until ½” green)

o   Lower rates during growing season for management of other diseases, may add lime

o   Common forms of fixed copper fungicides

§  Basic copper sulfate – Cuprofix, Basicop

§  Copper Hydroxide – Kocide, Champ

§  Copper oxychloride sulfate – C-O-C-S

§  Cuprous oxide – Nordox

·       Copper sulfate pentahydrate – bluestone

o   Dormant spray, only

o   CuSO4.5H2O

o   Highly soluble ions, phytotoxic

o   Often combined with lime to help tie up copper ions

o   No residual activity, rapid release of copper ions

o   Common brands of copper sulfate

§  Mastercop, Phyton

Tree fruit diseases managed with copper fungicides:
  •                 Fire blight (spray guide recommendations: dormant – label: silver tip to green tip)
  •                  Apple scab (dormant to pink)
  •               Bacterial canker (after harvest and late dormant)
  •                Bacterial spot (dormant/budswell, pink, and petal fall)
  •                Peach leaf curl (dormant)
  •                Cherry leaf spot (after petal fall)
  •                Black knot (dormant)
Copper is an antimicrobial; it is not selective.  Kills any exposed plant cells, bacteria, and fungi

Large numbers of copper ions (rapid release of ions) are phytotoxic to plant tissue, especially leaf tissue

Copper fungicides are not systemic and wash off with rain.  Fixed coppers have more residual activity due to slow release of copper ions.

Metallic copper equivalent is the amount of copper available for fungicidal activity (different from active ingredient).  Basic copper sulfate usually contains the highest metallic copper equivalent.

Copper can accumulate in soils, inhibit plant growth, and is toxic to microorganisms and earthworms

Tuesday, November 12, 2013

Recurring Pythium in the Greenhouse - Poinsettia Root Rot

One of our local greenhouse growers struggled with Pythium infections in pansy earlier this year.  Now, poinsettia are infected with the same root rotting/damping off fungus. 

So, why would Pythium be a recurring problem?  Simple.  Sanitation.

Sanitation is critical for greenhouse production, landscapes, orchards, and gardens.  In this greenhouse, fungal propagules are obviously spreading via debris, hoses, shoes, tools, drainage water, and more.  Also, Pythium favors soilless mixes, where there's no competition.  Growers should verify that potting mix is not contaminated and that containers are sterilized before reuse.

Moreover, greenhouses must be disinfested between crops, so that disease-causing propagules are not carried over from one crop to another.  

Once a greenhouse is infested with Pythium, fungicides are required for disease management.  A single fungicide application will not be sufficient to manage disease, so a regular schedule should be employed.  Rotate fungicides by FRAC group (mode of action), avoiding two consecutive applications of any particular group and observing maximum numbers of applications per season.  Fungicides effective against Pythium include: 
·         mefenoxam (Subdue MAXX) FRAC 4
·         etridiazole (Truban/Terrazole) FRAC 14
·         propamocarb (Banol) FRAC 28
·         dimethomorph (Stature) FRAC 40
·         phosphorus acids (Aliette, Alude, Vital) FRAC 33
·         etridiazole + thiophanate methyl (Banrot) FRAC 14 + 1


For more information on disease management of poinsettia or other greenhouse crops:

Fungicides for Management of Diseases in Commercial Greenhouse Ornamentals
Poinsettia Diseases


Thursday, November 7, 2013

Stunted Pines and Brown Needles: Diplodia Tip Blight

Diplodia tip blight is a serious disease of mature Austrian, Scots (Scotch), and Mugo pines in Kentucky. The disease is caused by the fungus Sphaeropsis sapinea.  In the landscape, tip blight is normally not observed until pines reach about 12 years old and begin to bear cones. Continuous infections (3 to 5 consecutive years) can greatly weaken and eventually kill affected pines.

Infection occurs in spring; however, disease symptoms become more obvious in mid- to late-summer and fall. Needles in early stages of development stop growing as a result of shoot infections. These stunted needles eventually die and turn straw-colored (Figure 1). Infection progresses to healthy needles and cones.

Disease Management:

·         Apply fungicides (chlorothalonil, propiconazole, or thiophanate methyl) to trees just as buds swell in spring. Apply a second spray when the candles are about half elongated and a third spray as needles begin to emerge from the needle sheaths.
·         Remove and destroy dead twigs, branches, and cones as they occur. Do not prune when trees are wet.
·         Destroy all blighted needles, twigs, and cones debris as they fall to the ground.  The fungus overwinters in debris, especially infected cones and diseased needles.
·         Trees under stress tend to be more susceptible to tip blight. Fertilize and water trees as needed to promote vigor.

 For more information on tip blight or pine diseases:

Needle Cast Diseases of Conifers

Twig, Branch, and Stem Diseases of Pine

Department of Plant Pathology, Extension Publication page

Tuesday, September 24, 2013

Skimpy Spruce – Defoliation from the Bottom Up

Rhizosphaera needle cast, the most common disease of spruce in Kentucky, causes needle drop in lower branches, resulting in a distinct thinned appearance.  The fungal pathogen Rhizosphaera kalkhoffii primarily infects spruce but can also affect some pine species. 

Figure 1 – Needles infected with Rhizosphaera turn purplish brown during summer.
Symptoms are often noticed during summer when needles on lower branches turn purplish or brown (Figure 1).  Within a few weeks, needles fall and lower limbs are left bare (Figure 2).  Small, dark fruiting bodies called pycnidia form in stomata (pores in needles) and can be used to confirm diagnoses (Figures 3 & 4).  Pycnidia can easily be recognized with a hand lens or with the naked eye. 

Figure 2 – Needle drop and thinning of lower canopy are classic symptoms of Rhizosphaera needle cast in spruce.
The life cycle of the fungus extends over a 15-month period.   Infection takes place as spores (conidia) within these pycnidia are rain splashed from needle debris onto foliage.  This infection process occurs primarily during spring, but it can continue as long as conditions are rainy, such as this past summer.  During the winter or following spring, pycnidia develop in infected needles, plugging stomata.  Needle discoloration and needle drop occur during summer of the second season, resulting in thinning of lower canopies.  If defoliation occurs 3 to 4 consecutive years, branch death is likely.  Stressed trees are more susceptible to infection by R. kalkhoffii than healthy plants. 

Figure 3 – Fungal pycnidia are often visible without a hand lens.
Disease management should consist of good cultural practices such as improved vigor and reduced plant stress, proper spacing to improve air circulation, and most importantly, good sanitation habits.  During rainy seasons or in plantings with a history of disease, fungicides may be applied two consecutive years during spring when fungi are most active.  Fungicides that include chlorothalonil, copper, or mancozeb are effective when applied during needle emergence (mid-April) and again four weeks later.  For more information, see Homeowner’s Guide to Fungicides. 
Figure 4 – Fungal pycnidia protrude from stomata.

Saturday, August 31, 2013

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.

Thursday, July 25, 2013

Downy Mildew in Grape – Secrets to Successful Disease Management

Experienced grape growers saw it coming.  New growers hadn’t a clue.  Regardless, my crystal ball told me that with months of rain would come severe outbreaks of downy mildew in vineyards. 

Grape downy mildew has reached epidemic levels in some vineyards in Kentucky and possibly the Midwest.  The pathogen that causes the disease (Plasmopara viticola) is a water mold, which warrants special considerations for disease management.  Let’s begin with a quick overview of water molds (oomycetes, to be exact). 

Water Molds

Water molds are different from true fungi.  In fact, they are not related.  Most importantly, water molds require free water to complete their life cycles.  Initial infections often occur during rainy spring weather as temperatures begin to warm.  After infection, pathogens release large numbers of “swimming” spores (zoospores) that move in films of water (damp leaves or moist soil).  This is the repeating stage of disease that leads to epidemics if wet conditions persist.  Spores are spread by splashing water and wind-driven rain.  In addition to downy mildew pathogens, many root rotting pathogens (Phytophthora and Pythium) are water molds. 
Figure 1 - Early symptoms of grape downy mildew include yellow spots on upper sides of leaves.


Downy Mildew

Downy mildew symptoms are quite distinct.  Upper leaves are the first to develop noticeable symptoms.  Yellow circular to blotchy spots can quickly enlarge and become bright yellow (Fig 1).   As disease progresses, leaf tissue becomes reddish brown, and centers of spots becomes necrotic (dead tissue) (Fig 2).  Extreme disease conditions result in a coalescing of spots into large necrotic areas.     
Figure 2 - As downy mildew spreads, leaf tissue becomes necrotic.

The most characteristic symptom of downy mildew is the “downy” fungal masses that develop on undersides of leaves (Fig 3).  If weather remains rainy or humid/foggy, pathogens will begin producing spore capsules (sporangia) on microscopic branched structures (sporangiophores).  This branching gives the disease its fluffy, downy appearance.  Sporangia can spread to healthy plant parts by wind or rain, and then open to expose infective, swimming zoospores.  This repeating cycle is dependent upon temperature and availability of free water. 

Figure 3 - The most characteristic symptom of downy mildew is the "downy" fungal masses on undersides of leaves.

Downy mildew pathogens also produce another spore type, thick-walled overwintering spores (oospores), at the end of the season.  These spores drop to the ground and overwinter in leaf debris or in soils.  In spring, they germinate just as grape begin to bloom.  Thus, early fungicide protection is critical in order to combat the initial phase of disease.  Moreover, an effective disease management program (described below) will help eliminate some of the inoculum (oospores) that before they overwinter. 

Damage Caused by Downy Mildew

Effects of infection are two-fold.  First, diseased leaves fail to properly photosynthesize, while severely infected leaves drop, leading to inadequate energy production (Fig 4).  Secondly, grape berries may become infected, leading to yield and quality losses (Fig 5).
Figure 4 - Advanced symptom development can lead to reduced photosynthesis and leaf drop.

Fruit are susceptible to infection from bloom until 3 or 4 weeks after bloom.  After that, they become resistant to infection.  Berries may not develop symptoms until several weeks after infection.  Affected fruit become soft and brown and do not mature.  Like foliar infections, infected berries become covered with downy fungal growth when conditions are wet or humid.  While fruit become resistant to infection as they mature, cluster stems (rachis) do not.  Thus, infections in these cluster stems can spread internally to berries.  Additionally, young shoots, leaves, and tendrils remain susceptible to infections throughout the growing season.
Figure 5 - Grape berries become infected between bloom and 3 to 4 weeks after bloom.  Symptoms, however, may not develop until several weeks after infection. 

Disease Management

Growers must combine cultural and chemical practices to effectively manage downy mildew in grape vineyards. 

Cultural practices are important for both conventional and organic growers.  Maintaining dry foliage is important.  Plant spacing, pruning, tucking, and other practices that improve air circulation will help foliage dry faster, and thus, conditions become less conducive for disease development.  Surface and internal vineyard drainage can also help reduce moisture levels within canopies.  Next, sanitation should not be overlooked.  To the extent possible, remove diseased leaves, fruit, and other plant parts from vineyards.  This will help to prevent fallen debris from becoming a home for overwintering pathogens.  Some species and cultivars have some resistance to downy mildew.  See page 36 of the Midwest Small Fruit and Grape Spray Guide ID-94 for a partial listing of tolerant grapes. 

Fungicides are a vital part of management of downy mildew.  Protectant sprays should begin at bud break and continue throughout the growing season.  Keep in mind though, that fungicide applications between bud break and 3 to 4 weeks after bloom are the most critical.  When selecting fungicides, remember that the downy mildew pathogen is a water mold, not a true fungus.  Therefore, not all fungicides will be effective against infection.  Refer to Effectiveness of Grape Fungicides PPFS-FR-S-18 or the Midwest Small Fruit and Grape Spray Guide ID-94 for up to date fungicide information.

Additional information on grape production and disease management can be found online at the UK Department of Plant Pathology’s website.