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.

1 comment:

Steve Newman said...

Where the mite infestation is very important, but we see this type of distortion regularly on Cordyline that has been kept over from the previous season. I have not actually done any nutritional analyses, but it seems to be related to a boron deficiency. Use an application of 0.1 to 1 ppm using borax laundry detergent. Do not over apply boron as it will cause damage on its own.