Diseases

Diseases Common to Vegetable Plants and Ornamentals in Greenhouses

When growing vegetable plants this spring, consider the disease interaction between vegetable plants, herbs and ornamentals in greenhouses.  While it can be difficult to devote valuable space to specific crops, if possible, maintain vegetable plants and ornamentals in separate greenhouses so diseases will have less opportunity to move from vegetatively –propagated ornamentals to seed-propagated vegetables. Separate greenhouses also make it easier to use different fungicides for ornamentals vs. edible crops.

Fuchsia Rust

Fuchsia rust caused by the fungus Pucciniastrum epilobii was recently diagnosed on plants in the greenhouse. Fuchsia rust occurs throughout the United States.

The most serious losses occur during propagation; however, diseased plants at any stage of growth are unmarketable. Potted plants may recover from this disease but defoliation significantly weakens the plants and occasionally results in death.

Impatiens Necrotic Spot Virus (INSV) and Tomato Spotted Wilt Virus (TSWV)

Tospovirus is a genus that includes Impatiens Necrotic Spot Virus (INSV) and Tomato Spotted Wilt Virus (TSWV). Western flower thrips is the predominant insect vector. Thrips acquire the disease as a first instar larvae as they feed on virus-infected plants (including infected weeds showing few, if any symptoms). Once mature, the winged adult thrips are primarily responsible for viral spread. An infected thrips is able to transmit tospoviruses to at least one plant per day until its death.  Adults do not transmit the virus to their young.

Greenhouse Tomato - Impatiens Necrotic Spot Virus (INSV)

INSV and TSWV (Tomato Spotted Wilt Virus) are two members of the Tospoviruses which are vectored exclusively by Western flower thrips (Frankliniella occidentalis). These viruses have an extremely wide host range (more than 600 species of plants are susceptible). There is no cure or chemical treatment for plant viruses. Discard affected plants, eradicate weeds that may be hosts, and control thrips populations. Inspect plant material at arrival or quarantine new shipments. Do not grow vegetable transplants and ornamental bedding plants in the same greenhouse.

Lobelia - Impatiens Necrotic Spot Virus

INSV and TSWV (Tomato Spotted Wilt Virus) are two members of the Tospoviruses which are vectored exclusively by Western flower thrips (Frankliniella occidentalis). These viruses have an extremely wide host range (more than 600 species of plants are susceptible). There is no cure or chemical treatment for plant viruses. Discard affected plants, eradicate weeds that may be hosts, and control thrips populations. Inspect plant material at arrival or quarantine new shipments. Do not grow vegetable transplants and ornamental bedding plants in the same greenhouse.

Preventing Disease Transmission

The diagnosis of Tobacco Mosaic Virus  (TMV) on petunia plants this season is a reminder of the importance of having a disease prevention system in place to minimize disease spreads from infected plants to healthy plants. While propagators and wholesale growers do not intend to distribute infectious diseases such as TMV or Xanthomonas, (both transmitted mechanically), growers are advised to protect their own crops in case there are slip-ups in the production chain.

Poinsettia Diseases

Alternaria leaf spot, Xanthomonas leaf spot and Poinsettia scab are three diseases that were recently diagnosed on poinsettias and are easily mistaken for one another.  Poinsettias with leaf spots should be sent to a diagnostic laboratory for accurate diagnosis.

Poinsettia - Alternaria leaf spot

Symptoms of Alternaria Leaf spot on poinsettia are easily confused with Xanthomonas or bacterial leaf spot or poinsettia scab.  Look for small spots with a tan center.  Plants should  be sent to a diagnostic laboratory for confirmation of this disease.  Management includes reducing leaf wetness, removing diseased plants (if only a few are infected) and applying fungicides labeled for leaf spot diseases on poinsettia.

Impatiens Downy Mildew Update

As of this week, there have been several reports (growers/retailers contacting Tina) of Impatiens downy mildew in landscapes and one garden center in Massachusetts, (Cape Cod, eastern Massachusetts, Worcester County and western Massachusetts). The first reported sighting was at the beginning of August. 

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