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.

Fire Blight Damage on Flowering Pear

Homeowners continue to question me concerning management of fire blight in flowering pear, crabapple, cotoneaster, hawthorn, and pyracantha.  Shepherd’s crooks and spur dieback occurred in March or April, as pathogenic bacteria infected flowers or young shoots.  Often, homeowners do not notice damage until later in the season, and inquiries continue for weeks after damage occurred.

There is no management option during this time of year, as the fire blight bacterium is not currently active.  Hot summer temperatures suppress bacterial growth, and plants are able to compartmentalize and wall off spread.  Thus, visible symptoms are the result of early infections. 

Current recommendations indicate that pruning of blighted twigs and cankered branches should be delayed until winter when risk of disease spread is lowest.  Under certain circumstances, homeowners or commercial landscape contractors may choose to prune infected branches during the growing season.  Only young, vigorous trees should be considered, and care should be taken to prevent bacterial spread.  Always avoid working with wet plants.  Cut branches at least 6 to 8 inches below cankers, disinfesting pruners between each cut (10% Lysol disinfectant, 10% bleach, or rubbing alcohol).  Ideally, winter pruning is recommended. 

Disease management includes both cultural practices and preventative bactericides.  Because the fire blight bacterium overwinters in cankered branches, removal of diseased plant tissue before bud break (mid to late winter) is critical.  Copper applied as buds swell (late dormancy or silver tip) reduces build-up of bacterial cells, especially during warm rainy spring seasons.  Streptomycin applications are only recommended for fruiting apple and are not labeled for use in the landscape. 

See earlier posts for more information on the biology of the fire blight bacterium and for management in orchards.

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.

Black Root Rot

Black Root Rot affects a wide range of ornamentals.

Black root rot results in the decay of root systems; however, the most obvious symptoms are observed on above-ground portions of the plant. Foliar symptoms include yellowing, wilting, and necrosis (death) of foliage. Above-ground foliar symptoms are the result of root decay; as a result, the reduced root system is unable to take up sufficient water and nutrients to support foliage and stems. There is no cure for black root rot.

Learn more about black root rot from our latest fact sheet

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

Other disease-related fact sheets are available at http://www.ca.uky.edu/agcollege/plantpathology/extension/pubs.html#OrnamentalWoody

Disease-Resistant Knockout Rose Susceptible to Rose Rosette Disease

Disease-Resistant Knockout Rose Susceptible to Rose Rosette Disease

Remember when Knockout rose was the answer to our rose disease problems?  Suddenly, they were everywhere.  I, too, am guilty of mass plantings in both residential and commercial settings.  Then came rose rosette disease; Knockout was susceptible.

During the past 10 years or so, rose growers have struggled with this previously mysterious affliction.  The disease was first described in the 1930’s but it began to spread through our area in the 1980’s.  With the introduction of the Knockout series, roses became popular again.  Consequently, with more roses came more extensive disease spread. 

Rose rosette disease was first diagnosed on Knockout rose in Kentucky in 2009.  Since then, the UK Plant Disease Diagnostic Lab has witnessed a rapid increase in incidence, especially with the disease-resistant Knockout.  This year seems consistent with that trend.

Symptoms:  Disease symptoms vary with rose cultivar, but combinations of all or some of the most distinct symptoms are used for diagnosis. 

·         Stem bunching or clustering, witch’s broom

·         Elongated and/or thickened canes

·         Bright red leaves and stems

·         Excessive thorniness, small red or brown thorns

·         Distorted or aborted flowers

·         Under-developed or narrow leaves and/ or distorted canes

·         Dead or dying canes, yellow or brown foliage, dwarfing or stunting

Causal Agent:  Causal agent of rose rosette disease is a virus classified in the newly described genus Emaravirus. It is systemic and occupies all tissue with a plant, although only some plant parts may be symptomatic.  This pathogen is not spread by pruners or other mechanical means like some common viruses, but it is readily transferred onto rootstocks through grafts.  Due to high demand of Knockout roses, mass production has led to spread of diseaed roses throughout industry. 

In the landscape or garden center, disease is spread by a small mite, the rose leaf curl mite that resides in axillary buds.  Mites are transported on insects or by wind currents for up to 100 yards.

Disease Management:  Viruses become systemic in plants, and there is no cure for infected roses.  Thus, diseased plants must be destroyed so that neither the mite nor the virus is spread to healthy plants.  Mite control is difficult if not impossible, and growers may risk destroying beneficial organisms with excessive insecticide or miticide use.  Prevention is the best control for rose rosette disease.  Growers and homeowners should carefully inspect plants before purchase.  If symptoms are present, avoid purchasing roses from that supplier.  As aforementioned, destroy infected plants immediately and never hold them over in an attempt to cure.  Wild multiflora roses are ideal hosts for both the mite and the virus, so consider destroying nearby wild roses as well. 

Homeowner Grape Spray Schedule - Low Impact

Home gardeners who are overwhelmed by spray schedules may be interested in this quick publication. Note, this is a low-impact schedule, so high disease pressure will warrant revision. Contact your UK county Extension agent or refer to other UK publications for more detailed information http://www.ca.uky.edu/agc/pubs/id/id21/id21.pdf and http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-7.pdf

Sample Simplified Home Grape Low-Spray Schedule

Dr. John Strang, Dr. Patsy Wilson, Dr. Nicole Ward & Dr. Ric Bessin University of Kentucky Extension Horticulture, Viticulture, Plant Pathology, and Entomology Specialists respectively

2012

Recommendations based on ID-21. For organic options refer to ID-21. This schedule should provide reasonable control in most seasons, but is not a complete schedule to control every pest problem.  It uses a minimal number of products.

Black Rot of Grape (Clemson)

Dormant

Ø Sulforix – Anthracnose

Bud Swell

Ø Sevin – only if flea beetles are noted eating holes in the buds

New Growth (2-4” long)

Ø Mancozeb* + myclobutanil - for black rot, Phomopsis cane and leaf spot, powdery mildew & downy mildew

Ø Myclobutanil (Immunox) is systemic and won’t wash off.

New Growth (10-15” long or 7-10 days after last spray)

Ø Mancozeb + myclobutanil for black rot, Phomopsis cane and leaf spot, powdery mildew and downy mildew

Pre- bloom (Just before blooms open)

Ø Mancozeb + myclobutanil - for black rot, Phomopsis cane and leaf spot, powdery mildew & downy mildew

Bloom

Ø Mancozeb + myclobutanil - for black rot, powdery mildew & downy mildew

Post Bloom

Ø Captan + myclobutanil - for black rot, powdery mildew & downy mildew

Ø Sevin – grape berry moth control

Ø Mix all of these in the same spray tank

First, Second third and forth cover sprays (every 10 to 14 days**)

Ø Captan + myclobutanil - for black rot, powdery mildew & downy mildew

Ø Sevin – Spray for Japanese beetles only when they are present.

Ø Check label for PHI and abide by this

*May substitute Captan for Mancozeb throughout this spray schedule

**Spray schedule frequency should be shortened in rainy weather and extended in dry weather.  Early season sprays are very important because this is a protectant spray program.

Homeowner Apple Spray Schedule - Low Impact

Home gardeners who are overwhelmed by spray schedules may be interested in this quick publication.  Note, this is a low-impact schedule, so high disease pressure will warrant revision.  Contact your UK county Extension agent or refer to other UK publications for more detailed information http://www.ca.uky.edu/agc/pubs/id/id21/id21.pdf and http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-7.pdf 

Sample Simplified Home Apple Low-Spray Schedule

Compiled by Beth Wilson, Pulaski County Horticulture Agent, and

Dr. John Strang, University of Kentucky Extension Fruit Specialist

2011

For pictures of growth stages, see pages 18 and 19 in ID-21.

Recommendations based on ID-21. For organic options refer to ID-21.

Dormant (before buds swell)

Ø Fixed copper – fire blight control

Ø Dormant oil – only if you have scale insect problems

Ø These two sprays may be combined if fixed copper is used.

Green tip to half-inch green

Ø Fixed copper (if you did not spray as a dormant spray) – fire blight control

Ø Dormant oil if not used earlier – for mites and aphids

Ø Mancozeb* + Immunox (myclobutanil)  fungicides for control of apple scab and rust

Ø Fixed copper, dormant oil, Mancozeb and immunox can be combined in one spray.

Ø No insecticide needed at this point

Just before blooms open

Ø Mancozeb + Immunox – you will be on a 10 to 14 day spray schedule with this. Immunox is systemic and won’t wash off.

Ø Mancozeb must be re-applied if a significant rain (more than one inch occurs)

Ø Mancozeb has a 77 day pre-harvest interval (PHI), so you MUST stop spraying with this at least 77 days before you expect the apples to be harvested.

Ø Plus Malathion insecticide

Bloom

Ø Mancozeb – for cedar apple rust and scab control

Ø No insecticides

Ø Streptomycin – Fire blight control (every 4 days for a total of no more than 4 sprays for maximum control)

After petals fall

Ø Mancozeb + Immunox

Ø Malathion – for insect control

Ø Mix all of these in the same spray tank

Every 2 weeks after

Ø Use mancozeb as long as you can per the 77 day PHI, mix with malathion or permethrin (rotate these 2)

Ø Orchard spray – use this after mancozeb can no longer be safely used.

Ø Orchard spray contains captan (fungicide) and malathion usually, no need to mix in additional insecticide.  Add Topsin M (thiophanate-methyl), another fungicide for powdery mildew and improved sooty blotch and flyspeck control

Ø Check label for PHI and abide by this

*May substitute Captan for Mancozeb throughout this spray schedule