Disease Management for Greenhouse Strawberry in Kentucky

 

Disease Management for Greenhouse Strawberry

 

Plug production, Greenhouse:

·         Drench or dip: Aliette/Rampart (33) for Pythium root rot

·         Drench: for fungal root and crown rots

o   Switch (9+12)

o   Captan (M)

 

 

Crop production, Greenhouse:

·         At Planting (Fall)

o   Dip/drench: Aliette/Rampart (33) or LalStop K-61* or
RootShield PLUS* for Pythium root rot

o   Dip: Switch anthracnose crown rot

·         Vegetative, apply on 14-day intervals, rotate among at least 3 of fungicides listed below, adhere to maximum applications for each FRAC group.

o   Captan (M) + Elevate (17)

o   Fontelis (7)

o   Luna Sensation (7+11)

o   Luna Tranquility (7+9)

o   PhD/OSO (19)*

o   Quadris Top (3+11)

·         Vegetative phase, as needed

o   Powdery mildew, as needed: Torino (U6)

o   Pythium root rot, as needed: Aliette/Rampart (33) or LalStop K-61* or RootShield PLUS*.

·         Fruiting (mid-late Spring), apply on 7-to-14-day intervals, adhere to maximum applications per season for each FRAC group.

o   Captan (M) + Elevate (17)

o   Fontelis (7)

o   PhD/OSO (19)*

o   Quadris Top (3+11)

 

FRAC groups in parentheses.

OMRI approved with asterisk*
Biologicals that are living organisms (LalStop K-61 and RootShield PLUS) can be deactivated by fungicides. Do not apply with Switch or other fungistat.

Limited options for Pythium root rot in greenhouses; maintain strict sanitation.

Refer to efficacy guide and other information in ID-232 Midwest Fruit Pest Management Guide.

UK Plant Pathology disease management resources can be found at https://plantpathology.ca.uky.edu/extension/publications#SMALLFRUIT 

Anthracnose Diseases of Shade Trees a Problem this Spring

Anthracnose Diseases of Shade Trees

This spring has been cool and wet, leading to slow emergence of leaves on many shade trees.  This combination of favorable weather conditions and slow leaf maturity created ideal conditions for development of anthracnose disease on several common shade trees. 

In short, the term anthracnose refers to a symptom that causes dark blotching and often leaf distortion. Defoliation (leaf drop) often occurs during severe infections.  The disease often is not fatal, and a new flush of foliar growth immediately follows.  Causal fungi may also infect twigs and branches, which develop into cankers and girdle stems. 

Anthracnose diseases are not caused by the same fungi.  In fact, causal pathogens are quite host specific, meaning that the anthracnose pathogen on dogwood will not infect ash, etc.  Symptom appearance and severity differ with each host and with climatic conditions. 

The fungal pathogens that cause anthracnose diseases have similar life cycles.  Spore production occurs in spring during periods of rain; without rain, sporulation (spore production) is reduced and spore dissemination (spread) is not possible.  Anthracnose fungi sporulate in spring as deciduous tree leaves emerge.  Mature leaves are resistant to infection, but slow emergence in spring exposes tender leaves to fungal spores for an extended period of time. 

Ash anthracnose. Common symptoms include brown blotches (Fig1) along leaf edges. Leaf drop often results, and then new leaves soon emerge. Causal fungus, Discula umbrinella.

Ash anthracnose

 

Dogwood anthracnose. Leaf spots, leaf blight, and lower branch dieback may occur.  The disease is most commonly observed on trees growing in shaded locations. This disease can lead to severe cankering, tree decline, and ultimately tree death.  Causal fungus, Discula destructiva.

Maple anthracnose. Symptoms begin as leaf spots (Fig 2) and may progress into shoot blight and shoot cankers. Leaf spots with brown, somewhat angular symptoms may be confused with tar spot (spots are round and black). Symptom development and susceptibility vary with tree species, but lesions often follow veins.   Causal fungi, Discula sp. and Kabatiella apocrypta.

Maple anthracnose.

 

Oak anthracnose.  Not commonly observed in Kentucky. Irregular brown spots develop on leaf tips and along veins.  Causal fungus, Apiognomonia quercina.

Sycamore anthracnose. Young, expanding leaves develop irregular dark, necrotic blotching centered along leaf veins or edges. These dark blotches may turn tan-colored as the diseased areas of the leaves dry out. Blighting of twigs or shoots may follow. Trees produce new foliage rather quickly, but affected branches may remain crooked (lateral shoots became dominant when terminals were killed). Also affects London plane tree.  Causal fungus, Apiognomonia veneta.   

For most trees, with the exception of dogwood, anthracnose disease is not lethal.  However, repeated defoliation can be stressful to trees.  Additionally, persistent rains and disease spread can lead to infection of twigs and branches.  Good cultural practices are important to reduce disease:

• Anthracnose is favored by a moist environment. Select a planting site with a sunny eastern exposure to promote rapid foliage drying early in the day.
• Rake and destroy fallen leaves, as they can be a source of inoculum (fungal spores).  Do not compost.
• Remove dead twigs and branches, as fungi can overwinter in dead wood.  
• Reduce plant stress when possible.    
• Avoid wounding, such as bumping with mowing equipment and making jagged pruning cuts. The dogwood anthracnose pathogen can enter trees through wounds to branches or trunks.
• Maintain mulch 2-3 inches thick over the root zone and beyond the drip line (not against the trunk) to help maintain soil moisture and to protect trees from lawnmower injury.
• Protect trees from drought.  Water at least once a week during hot dry months using soakers or drip irrigation.  Avoid overhead sprinklers; wet foliage favors sporulation and infection.
• Do not transplant dogwood trees from the wild, as they may be infected with anthracnose fungi. Purchase healthy trees from a reputable nursery.
• Diagnose and treat insect and disease problems as soon as possible.
• Plant disease resistant dogwoods such as C. florida 'Appalachian Spring' or oriental dogwoods (Cornus kousa) for high risk sites, such as those with heavy shade and nearby diseased trees.
• Fungicides are often not recommended.  They can be costly and it is difficult to effectively cover large trees. Commercial nurseries, on the other hand, should protect trees with fungicides.  Dogwood that are threatened by anthracnose may benefit from early spring fungicide applications.

 

For more specifics on these anthracnose diseases, see

Dogwood Anthracnose http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-W-6.pdf

Anthracnose Diseases of Shade Trees http://www.ca.uky.edu/agc/pubs/ppa/ppa17/ppa17.pdf

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.

 

Black Rot Common on Grape

Black rot is the most common disease of grape in Kentucky.  If left unprotected, vineyards can suffer high economic losses. 

Infection occurs early in the season, usually before bloom, at temperatures as low as 50˚F.  Early symptoms develop as spots on leaves 1 to 2 weeks after infection (Fig 1).  Tan spots with darker margins often contain black fruiting structures (pycnidia) in centers (Fig.2).  Spores (conidia) from these structures cause secondary infections throughout the season.  As leaves mature, they become resistant, but newly developing leaves can become infected anytime during the season.

Fig 1.  Leaf lesions have light tan centers and darker brown margins.

Fruit infections occur early in the spring, as well.  Grapes are susceptible from flowering until 3 to 4 weeks after bloom.  Early fruit symptoms appear as light brown spots (Fig. 3).  Soon, entire berries turn dark brown and shrivel (Fig 4).  These raisin-like fruit develop black fruiting structures (pycnidia) that overwinter on the “mummies.” 

Fig 2.  Fruiting structures (pycnidia) produce spores that cause secondary infections.  They can be seen with a magnifying glass, and often with the naked eye.

Both cultural practices and fungicides are critical for control of black rot.  Fruit mummies must be removed from vineyards to eliminate sources of overwintering inoculum.  Beginning at pre-bloom, a rigid fungicide regime must be employed.  Strobilurin fungicides (Abound, Pristine, Flint) provide excellent control, but risk for fungicide resistance is high.  Rotate with triazole/SI fungicides (Bayleton, Elite, Rally) and protectant fungicides (Mancozeb, Ziram).

Fig 3.  Fruit infections begin as light brown spots.  Note:  bird’s eye rot (anthracnose) infections on fruit have dark reddish margins with light gray centers.

Commercial growers should refer to the Midwest Small Fruit and Grape spray guide for fungicide and schedule details, while homeowners can use fungicides listed in ID-21 and PPFS-misc-7.  These and other publications can be found at http://www.ca.uky.edu/agcollege/plantpathology/extension/pubs.html#Smallfruit

Fig 4.  Soon after infection, grapes with black rot disease turn dark and shrivel into hard, black mummies.  Fruiting bodies (pycnidia) that develop are the primary source of overwintering for this fungus.

Win the Battle Against Powdery Mildew

Powdery mildew is one of the most easily recognizable diseases of landscape and garden plants.  While most fungal pathogens are favored by wet weather, powdery mildew pathogens favor high humidity but not wet conditions.  Shady areas, areas with poor air circulation, and low areas that trap damp air are ideal environments for disease development.

Powdery fungal growth is an easily recognizable symptom of powdery mildew disease.

A wide range of plants are susceptible to powdery mildew:  annuals, perennials, shrubs, ornamental and fruit trees, small fruit, and vegetables.  While symptoms appear similar on most plants, powdery mildew fungi are usually host-specific.  For example, powdery mildew of dogwood cannot infect pumpkins or cucurbits, and powdery mildew of cantaloupe will not infect phlox or rose. 

Typical symptoms of powdery mildew include dusty fungal growth on surfaces of leaves and on young succulent plant tissue (Photo 1 & 2).  Powdery mildew may occur as isolated blotches or cover entire leaves, stems, buds, or flowers.  Early infections can lead to leaf stunting, curling, or other deformation (Photo 2).  Infected fruit may become disfigured or fall prematurely (Photo 3).  In the fall, small fruiting structures that resemble pepper flakes may be visible to the naked eye (Photo 4 & 5).  These structures contain overwintering spores that serve as inoculum for the following year.

Infection of young growth may result in stunted or deformed tissue.

Management of powdery mildew begins with prevention.  Plants should be properly spaced and thinned for improved air circulation and more rapid leaf drying.  Resistant cultivars are available for crabapple, dogwood, phlox, zinnia, cucurbits, and several other plants and are an excellent means of disease prevention.

Fruit infections ultimately lead to yield loss.

Fungicides usually are not warranted when cultural practices are implemented.  Early season infection, however, may require one or more applications of effective fungicides.  Homeowners have a wide range of fungicides available.  However, they should carefully read labels to confirm that the selected fungicide may be used legally on select plants or that the fungicide is suitable for edible plants.

Fungicides effective against powdery mildew include:

·         Chlorothalonil – broad spectrum protectant; ornamentals, some fruit and many vegetables

o   Bonide Fungonil concentrate or Fungonil RTU

o   Ortho MAX Garden Disease Control

o   Sevin Daconil

·         Myclobuanil – systemic; ornamentals, most fruit and vegetables

o   Spectracide Immunox (only Immunox Multi-purpose Fungicide Concentrate is labeled for use on fruit and vegetables)

·         Propiconazole – systemic; ornamentals, some fruit

o   Bonide Fungonil RTS (different from other Fungonil products, which contain chlorothalonil)

o   Bonide Infuse

o   Fertilome Liquid Systemic

·         Tebuconazole – systemic; ornamentals only

o   Bayer Advanced Disease Control

o   Bonide Rx Systemic

·         Triflorine – systemic; ornamentals only

o   Ortho Rose Pride Disease Control

Late in the growing season, powdery mildew fungi produce small, black overwintering structures that can serve as inoculum the following year.