Monday, December 29, 2008

Possible Phytotoxicity on Cordyline

These are Cordyline australis 'Southern Splendor' from a finishing operation. The main symptoms are the distorted growth and fusing together of the 'middle-aged' growth . The new growth is unaffected while the oldest growth shows tip burn. The plants were heavily infested with two-spotted spider mites (Tetranychus urticae) with obvious symptoms of yellowing and stippling present. The question from the grower was, "Is the distortion caused by the mite injury or is some other factor involved?"

Mite infestations are not known to cause such extreme symptoms so we needed to look elsewhere. The most likely cause is phytotoxicity caused by an pesticide application. The grower is looking into their rotation of miticides as mites have been a constant problem in this crop. Since they are a finishing operation (meaning they received the plants a few months earlier to grow to the final selling size) the grower may have difficulty tracking down what pesticides were applied before they took possession.

These symptoms have been seen by diagnosticians in other states, but a definitive cause of the problem has yet to be identified.

Tip burn was seen on the oldest leaves. Cordylines can be very sensitive to fluoride levels in irrigation water which can manifest as tip burn, but fluoride is unlikely to cause the other symptoms.

Two-spotted spider mites and associated injury (yellowing and stippling of older leaves) was observed.

Tuesday, December 23, 2008

Vinca minor-CMV (Cucumber Mosaic Virus)

This sample is Vinca minor from a propagation operation. The sample tested positive for CMV (Cucumber Mosaic Virus) using an Agdia immunostrip test.
CMV has a very wide host range and affects both vegetables and ornamental plants. Aphids are the primary source of infection but infection by mechanical transmission (taking cuttings, etc) is also possible. Infected plants should be destroyed to avoid spreading the virus within a greenhouse.

Monday, December 15, 2008

Aster-TSWV (Tomato spotted wilt virus)

This sample is Aster x Frikartii 'Monch' from a propagation operation showing signs of virus infection. The sample tested positive for TSWV (Tomato Spotted Wilt Virus) using an Agdia immunostrip test. TSWV & INSV (Impatiens Necrotic Spot Virus) are two related and very common viruses in greenhouse production. Cornell University has an excellent fact sheet with more information on these viruses.