A Double Coconut Palm Problem in Illinois?

No, it is not very, often that we receive a palm sample at the U of I Plant Clinic.  We are used to seeing corn and soybeans, as well as spruce, pine, oak, maple, and other tree problems. But, recently, we received a sample of a double coconut palm from a conservatory.

This palm has been declining since at least July (These pictures were taken in July 2011), but recently symptoms have appeared to be serious. This client submitted leaf and root samples to the University of Illinois Plant Clinic.  The double coconut sample submitted to the U of I Plant Clinic was examined for the presence of disease pathogens as well as signs of insects and none were found on the sample submitted.  The root sample that was submitted did not appear to be rotted.  The problem was concluded to be abiotic (no disease). 

I am very, fortunate to have received help from University of Florida– IFAS,  Fort Lauderdale Research and Education Center experts such as Monica L. Elliott, Ph.D. and Timothy Broschat, Ph.D.  After receiving pictures as well as soil/tissue nutrient analysis, they provided the U of I Plant Clinic with the following information:

"The leaf that has already expanded has physiological issues.  In photo “A”, there is a yellow clear line across the entire expanse of leaf about half way down from the leaflet tips – that is an indication of a one time stress during the leaf development – could be cold, could be very mild boron deficiency – hard to say exactly the problem.  These palms are very, very slow growing.  I don’t remember how many leaves they produce a year, but it isn’t very many, so a leaf is in development for months, not days.  The necrotic leaflets on the one side of the expanded leaf are physiological, not pathogenic – but it is difficult to know exactly what caused the damage.  Same for most of the necrotic leaflet tips on the younger, expanded leaf.

Picture A- showing "yellow clear line across the entire expanse of leaf about half way down from the leaflet tips"

The leaf that is emerging in photo “B”:  those spots could very well be pathogenic in origin.  Usually, when I see a halo around a lesion, I suspect pathogen and not physiological.  But, as shown, I can draw a diagonal line through those “spots”, which again is more likely to be indicative of physiological than pathogenic cause.  And, you can observe necrotic leaflet tips, which would be physiological and not pathological." -Monica L. Elliott, Ph.D.

Photo B- "showing a diagonal line of “spots”

"I had responded earlier about the soil and leaf analyses not suggesting anything nutritional, but after seeing these photos, I agree with Monica that this looks physiological.  This is not typical of phytotoxicities, which tend to result in marginal or tip necrosis on all, but the youngest leaf or if systemic, distortion, or tip necrosis of the spear leaf.  This suggests to me a possible temperature problem though it is not typical chilling injury, which affects older leaves more than the newly emerging leaf.  Perhaps cold irrigation water?  These symptoms are similar to something that was common on Dracaena marginata back in the early 1980s, but after years of working on it, we were never able to pinpoint its cause.  We were able to rule out nutritional deficiencies such as boron and calcium, which would be the most likely candidates." - Timothy Broschat, Ph.D.

  

Dear Sweet Basil, You Have Problems...Basially Yours, The U of I Plant Clinic

After working on projects and presentations, it was very, exciting to receive a sweet basil sample at the U of I Plant Clinic.  It arrived on my birthday, which made this sample even sweeter. 

This basil had been growing in a greenhouse system of 12 foot channels and 4 inch offsets with water-flow, similar to a hydroponic operation; however the root plugs of the plants appeared to be encased in a soil mixture.  These growers had first experienced problems 4 weeks ago.  Luckily, this submitter had included information with his plant sample that provided some much needed clues as to the demise of their sweet basil. 

Unfortunately, the temperature in the greenhouse had dipped down below 50 degrees F overnight, at least once.  Basil is very, sensitive to cold temperatures and should be grown at temperatures of around 55 to 60 degrees F.  We suspected that most of the necrotic areas seen on the leaves were due to cold injury; however we still needed to keep an open mind; as other issues could be lurking.

As routine, I try to rule out problems on ALL parts of the plant, even if they don't appear to be an issue at first glance.  I scanned some of the plant parts under the dissecting scope and checked for bacterial ooze under the microscope.  There were no signs of bacterial disease.

Dr. Babadoost, U of I Fruit and Vegetable Pathologist happen to peek his head into the lab and I asked him to take a look at the basil sample.  He was concerned with a fungal disease on basil, which has recently been a major issue in Illinois, called downy mildew.   For more information on downy mildew in basil, you can go to the following links:
Downy mildew wants to ruin your summer
Downy mildew poses a threat to Illinois basil crop
 

Luckily, we found no sign of any fungal diseases, such as Downy mildew, on this sample.  Dr. Babadoost and I agreed that the sample had signs of abiotic injury (most likely cold injury) as well as some insect and possible virus symptoms.  The plants had also been without water for about 15 hours and the heat was turned up to 80 degrees F (I assume to warm the greenhouse).  These factors could have also caused some plant stress symptoms.

My next stop was the office of Dr. Weinzierl, U of I Extension, Fruit and Vegetable Entomologist.  He looked at the sample and found a few leaves with possible thrip feeding.  When these leaves were examined under the scope, there were still a few thrips present.  By the way, thrips are very, small and can be very, tricky to find!  Dr. Weinzerl said that he did not recommend any treatment, as the thrip injury to the basil did not appear to be threatening the crop at this time.  Thrips can be one of those pests you don't want to have in the greenhouse, because infestations can be very, difficult to control.

The small, tan circles on leaves are thrip feeding.  The darker areas are suspected cold injury.

But, the plot thickens.......I still needed to test suspect plant tissue from this sample for a virus.  I happen to have an Agdia Inc. test strip that would test for the presence of INSV, impatiens necrotic spot virus.  This test was requested by the grower, but also, one of the few viruses that I could find know to be a problem in basil.

Two red lines on the test strip indicated that some of the plants in this sample tested positive for INSV (impatiens necrotic spot virus).  The recommendation was to rogue all of the plants that appeared to have viral symptoms immediately.  But, guess the insect vector of INSV?  THRIPS!  This may change the previous recommendation of no treatment for thrips.

The moral of the story is there could be multiple problems with a sample.  Many questions come to my mind.  How long were some of these plants infected with INSV?  Did the cold, heat, or water stress bring on the virus symptoms?  The fact of the matter is that these plants should "grow out of abiotic injury"; however, if they do not, it is possible that the plants may face further complications from the virus infection or other possible factors not seen in the sample submitted.