Two New Strawberry Viruses Detected in Kentucky.

Two New Strawberry Viruses Detected in Kentucky. The viruses (strawberry mottle virus, abbreviated SMoV; and strawberry mild yellow edge virus, abbreviated SMYEV) originated from a plug producer in Nova Scotia. In the aforementioned case,... three growers shared a shipment of plants, but only one of the growers has seen symptoms. The other two growers have not.

We encourage strawberry growers to contact their brokers to determine the source of his/her plants. Those with high risks may need to take some of the precautionary steps outlined below.

An article describing the two viruses in more detail is available at http://extension.psu.edu/plants/tree-fruit/news. Briefly, SMoV and SMYEV are transmitted by aphids. SMYEV infects only strawberry, but SMoV can also infect the weed common lambsquarters. Therefore, we encourage high-risk growers to scout for aphids and to implement a solid weed management program.  

 

 

 Finally, remember that virus diseases cannot be cured. We recommend that symptomatic plants be destroyed to prevent spread to healthy plants. If you determine that your plants originated from the Nova Scotia area, please do not hesitate to contact me for more specific information.

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. 

 

 

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.