Russet mites on leaf tissue.

Last week a tomato sample was diagnosed with tomato russet mites (Aculops lycopersici). These conical-shaped insects, usually translucent and yellowish, cannot be seen without the aid of a 14X hand lens.

Russet mites cause damage by feeding on leaves and stems, giving them a greasy or bronze appearance. Infestation normally begins at the base of the plant and progresses upwards as lower leaves dry out. Left alone, these mites can kill plants.

Russet mite damage on tomato in greenhouse.

Fortunately, they can be controlled with miticides or sulfur. Hosts include tomato, potato, eggplant, petunia, tomatillo, and other solenaceous plant species.

We are always on the look out for test, techniques or tricks that would help up better detect, recover and/or isolate pathogens. Some methods call for the low tech approach of patience of a moist chamber and a microscope to assist in the observation. Other methods utilized various biochemical characteristics of the pathogen.  And more recently, “molecular diagnostics” using genetic methods to detect presence of specific pathogens are used in the diagnostic process.  One of the newest technique that is being used is called Loop-meidated isothermal amplification or LAMP.  This method utilized the genetic approach and it pretty cool.  I wanted to share a youtube of a training event that was put together by colleagues at Oregon State providing information on how the LAMP technique was used to detect the bacterial pathogen Rhodococcus fascians.  If you are interested, check out the video below.

Click here to view the embedded video.

A: Cercospora symptoms on a recent Pansy sample

B: Conidiophores on leaf edge

C: Cluster of Cercospora conidiophores

Damage caused by the fungus Rhizoctonia sp. on bermudagrass.

Some patches in lawns caught my eye this week.  It was interesting to note that there were several lawns in my neighborhood had patch symptoms.  Most appear to be due to rhizoctonia blight (common name of disease = brown patch, yellow patch or large patch).  I just call it brown patch.  The “smoky” halo at the edge of the damage area of the turf was evident in many of them.  I have also been getting some reports from the Dallas-Fort Worth area that this disease (caused by the fungus Rhizoctonia) was flaring up.

Now something else that I noticed was that there were several patches are not due to diseases at all.  At a few homes, including mine, we have bermudagrass in our St. Augustine lawn.  This time of the year, the bermudagrass go into dormancy – it becomes brown. The St. Augustine is still green.  Hence you get that brown spot/patchy area.  This should NOT be confused with the disease that I describe above that is caused by the fungus Rhizoctonia.

Hmm… I should head out the get a photos to post over on the Plant Clinic facebook page.  Also, for more information about the disease, I would recommend picking up Extension publication E-306 “ Warm-Season Turfgrass Disease Management in Urban Landscapes” 

With turf grasses, cooler weather also means more moisture in the soil.  Moisture is favored by most fungal pathogens. Couple with the same sprinkler program, there is now even more water in the soil. Not to mentioned that the grasses may have endured the hot summers and may be a little weaken. All these factors can contribute to successful attack by pathogens.  Check out Texas A&M AgriLife Extension Service publication E-306 by Drs. Jo and Camerino (Warm-season turfgrass disease management in urban landscapes).  This is a publication with lots of good information about turf grass diseases, more than just root rots (aka patch diseases).

Boxwood with dead branches as a result of root rot

Similarly with woody ornamentals, root and crown attacking pathogens can infect a plant (usually a stressed one) and result in the eventual death or stunting.  We have found various fungal agents such as fusarium, thelaviopsis and phytophthora causing root rot on landscape ornamentals.  A good way to figure out if you are dealing with a root rot is to look at the roots of the affected plants.  If the roots are bad looking (brown-black, sloughing off), that is a pretty strong indication that you may be dealing with root rot.  In some instances, the pathogen can also cause vascular damage – resulting in wilting prior to collapse.

Vascular system damage. On left is a healthy stem (note: whitish-green tissue). On the right is the a dying/dead branch with darken vascular tissue.

What can you do about it?  First, evaluate growing area to make sure that you are not dealing with poor drainage or excessive water situations.  If you are, try to remedy those deficiencies. Second, lay OFF  the high nitrogen fertilizers.  Many of us sometimes mistakenly think that if we can encourage the plant to be vigorous, it might just outgrow the disease.  While there is some merit to this thinking, high nitrogen will tend to encourage foliar growth.  This may put additional strain to the plant’s root system to gather nutrients and stressing out the plant even more.   Appropriate fungicides or natural supplements (such as compost or compost tea), may help to lessen the impact of the disease on the plant.  When damage is seen in the canopy of the plant, the damage in the root are pretty extensive.  Sometimes the plant can recover, sometime is does not.

Narrative and photos by L. Farris (TPDDL technician) and M. Giesbrecht (Extension Assistant)

Blotchy mottle symptoms of HLB (Citrus Greening)

Earlier this month, we were sent to Ft. Myers, Florida to observe citrus diseases in the field and learn about ongoing research projects and current management practices for disease control. The primary focus was Huanglongbing (HLB), or citrus greening, a disease that was introduced into Texas in January of this year. The trip was hosted by extension scientists at the University of Florida’s Southwest Florida Research and Education Center (SWFREC).

Citrus canker following a leaf miner infection

These scientists described their ongoing experiments with HLB and results to date and explained how they use this information to make management recommendations to commercial growers. We also had the opportunity to tour privately-owned groves. These groves perfectly displayed the results of owners who took immediate action to fight the disease and those who let it spread unabatedly.

Characteristic symptoms of the disease “greasy spot”.

There is no comparison between looking at pictures or reading descriptions of symptoms and actually seeing them up close in the field. This experience will aid us in choosing samples to test for citrus greening and has greatly increased their knowledge of HLB management.

Enjoy.

Click here to view the embedded video.

Earlier this month, I spent a week in Providence, Rhode Island at the annual American Phytopathological Society (APS) meeting.  The thrust of this year’s theme was ” Communicating Science”. It was an interesting plenary session where questions were put forth on whether the general public know what PHYTOPATHOLOGY is.  Then there was also the part where scientists are taught how to convey and articulate their work…..”get to the point already!”.  Apparently, the stereotype is that scientists harp on the details when most people rather have the general picture first.  Something for me to remember.

One of the annual activities leading up to this meeting is a video competition sponsored by the APS – Office of Public Relations and Outreach.  A winner this year is a graduate student from the Ohio State University.  It is a nice short video on “What is Plant Pathology?” .

Enjoy.

Click here to view the embedded video.

Foliage of tree that did not lose leaves.

About a week ago, I got an email in our PlantClinic box about live oak.  The gentleman had read my blog post on the annual texas live oak leaf drop (March 2011).  He had a very interesting question based on his observation of this tree.

Below is the email he sent:
After many years of watching my live oak trees lose their leaves every April – this year, one of them did not lose its leaves. Is this something to be concerned about? Was it last years drought that caused it? All the other live oaks in my yards have new bright green leaves after dropping the old ones. This one still has the old leaves. It does have new sprouts at the ends of the branches.

Was it something that he had to be concern about?  Yes and No

Yes – This plant is acting abnormal.  What could have cause this plant to not loose leaves?  Is there something that is affecting the plant that is unseen.  Yes, we had to be concern because of the unknown.

But…..

More of the foliage of the tree that did not lose its leaves this spring.

No – If the tree still looks okay and appears to be growing okay.  New sprouts at end of branches (aka new shoots) are good.  The key is to look for new bud and evidence of new growth.  If the tree is growing and appears to be okay, I would not worry too much.

How to be sure?  Well, the simplest approach is to compare the new growth of a typical plant close by and the affected plant.   Look for a shoot and measure length of the that shoot.  If all is well, the length of the shoot from a typical tree (one that dropped their leaves) and an affected tree (one that did not loose their leaves) is approximately the same, then we can conclude that both plants are still growing and seems to be fine.

Tree adjacent to the one that did not lose its leaves. This one is normal.

Let’s hope the affected tree is not showing other stress symptoms or exhibit other symptoms of concern.  One of such is super heavy fruiting (lots and lots of acorn) when it is stress and might collapse the following growing season.  Lets continue to care for the trees – avoid over watering and over fertilization, and keep our fingers cross that all will be well.   Monitor it next spring.

Mr. J. Dyell kindly share a few photos of his trees with us.

On a different note,  my diagnostician and I will be away to the Annual American Phytopathological Society meeting, held this year in Providence, Rhode Island.  So the Plant Clinic will be running with a minimal staff.  Please plan accordingly if you have to submit samples.  Processing times will be a little delayed.