Tuesday, March 12, 2013

Eastern White Pine + Drought = Problems

Eastern white pine is native to our region.  It is best grown in an area that consists of moist and well-drained soils (not clay); however it can be found in extremes such as dry soils, rocky areas, and wet sphagnum bogs.  It does prefer to have plenty of light, but will tolerate some shade.  It can be susceptible to heavy winds and branches can be lost during storms.  It had also been found to be resistant to pollutants such as ozone, sulfur dioxide and salts.  It can also develop chlorosis in soils that have a high pH.  (Manual of Woody Landscape Plants by Michael A. Dirr)

According the Jay Hayek, University of Illinois Extension Forestry Specialist, "even though eastern white pine is native to Illinois, this species is endemic only to the northern parts of the state on coarse textured soils with relatively low soil pH. Eastern white pine grows best on soils with good internal drainage (i.e., coarse loamy to fine loamy texture soils) and they are adapted to more acidic soils."

In a normal year, when we see a white pine decline, we have attributed it to "white pine decline".  For additional information, refer to this link:   http://hyg.ipm.illinois.edu/pastpest/200613a.html

So, why are we seeing so many white pines decline now in Illinois?  The main reason is DROUGHT.  However, I am seeing secondary pests/diseases on trees that have experienced drought and other stresses such as:  wet or poorly drained sites, girdling roots, deep planting or mounded mulch, alkaline soil, flooding (not this year), past hot conditions, and possibly involvement of secondary root invading fungi.

Another example of stress is trees planted too closely or incorrectly in a windbreak.  For additional information on planting windbreaks in Illinois, please refer to the Illinois Windbreak Manual:  http://web.extension.illinois.edu/forestry/iwm_complete.pdf

The eastern white pine is one of the first trees to show decline symptoms, when it is under stress.  Once the tree is under stress, it is vulnerable to various secondary disease/pest problems such as: 

Suspect Cytospora canker on Eastern white pine

Does this look familiar?  Yes, this disease is very common on spruce, but Eastern white pine can be a host for this disease.  Cytospora is confirmed by the gummy exudate on the branches, especially near the trunk.  Cytospora canker development is aided by environmental stress and wounding, which allow the Cytospora fungus to invade the tree. Fungicides are not effective. You need to help tree vitality by pruning out dead wood now, watering in periods of drought lasting two weeks, and fertilizing in the fall or early spring with a balanced tree fertilizer. If you can determine the cause of stress, of course, correct that as well.

Secondary borer hole on Eastern white pine
Often, when homeowners go out to investigate why their pine is declining, they are alarmed when they see borer holes.  Many times, these borers are not the main issue.  These secondary borers attack stressed trees and contribute to their decline.  There is not usually is not any management recommendations for these secondary borers.  If possible, reduce the stress to the tree.

Pine engraver beetle (Ips pini) holes
Pine engraver beetle (Ips pini)

We have had several reports this summer of bark beetle damage to Eastern white pine. According to Phil Nixon, University of Illinois Extension Entomologist, when a pine tree goes into decline, it is commonly attacked by bark beetles. A declining tree emits chemical compounds that the bark beetles can detect, and they fly to the tree. However, bark beetles that attack pines commonly attack the healthy trees on either side of the one in decline. In the process, they transmit blue stain fungi to the healthy trees which can cause those trees to die. In stepwise fashion, the bark beetles and fungi can kill an entire row of trees after several years. For that reason, it is commonly suggested that a pine tree in decline in a row be removed promptly to help keep the trees on either side from being attacked. Bark beetle adults emerge through pinhead-sized holes from March to October. There are usually three to four generations per year. If the tree shows symptoms of decline between March and October, one can assume that the healthy trees on either side were attacked and removing them is usually a good practice. Spraying for bark beetles is tenuous at best. They are difficult to control because they emerge at various times through the growing season. That would require several sprays per year, with limited likelihood of success.

Blue stain fungus seen in an Eastern white pine

“Blue Stain is also very common in softwoods such as Red and White Pine.  Like hardwoods,  conifers are susceptible to fungal spores floating in the air, but conifers may also become infected by bark beetles. After penetrating the bark of these trees, the beetles move into the sapwood. Here, fungal spores that have “hitchhiked” on their bodies come into contactwith the rich growing environment found there. As the staining fungi grow, discolored wood results.”-taken from http://clean-water.uwex.edu/pubs/pdf/bluestain.pdf

Unfortunately, there are no cures for these declining trees. If possible, try to provide water in periods of drought, fertilizing with an acidic fertilizer (not during drought), and waiting to see whether the tree will respond.  If you see insects on the declining trees, get some help with identification of the species to determine whether treatment is recommended. Once the tree dies, remove it to prevent secondary insect problems that could spread to healthy trees. Consider digging the roots to rule out root boring insects, girdling roots, and other problems. 

Wednesday, March 6, 2013

2012 Crop Disease of the Year at the U of I Plant Clinic was a Virus!

What was the main crop disease seen at the U of I Plant Clinic in 2012?  Well, we saw a general increase in soybean virus diseases.  More specifically, we saw a significant increase in a soybean viral disease called, soybean vein necrosis virus on many soybean samples submitted to the U of I Plant Clinic.  

Soybean Vein Necrosis Virus (SVNV)

What is a virus?  a submicroscopic, intracellular, obligate parasite consisting of a core of infectious nucleic acid (either RNA or DNA) usually surrounded by a protein coat (EM of tobacco mosaic virus) APSnet
  • Non-living pathogen
  • Unable to replicate self 
  •  Unable to transmit itself – require a vector to penetrate a cell wall (insect, seed, pollen, human, fungi, nematode, etc.)
  • We can’t see it under a microscope, but can see it under an pricey electron microscope (if available)

Some of the common plant virus vectors in Illinois are aphids, thrips, whiteflies, beetles, leafhoppers, plasmodiophorids, nematodes, and mites.   

There can be two different types of insect vector transmission: 
  • Non-persistant- feeding behavior is a stylet-born virus transmission, frequent feeding probes of short duration (seconds), ~230 viruses (this type of insect vector looses the virus rapidly if feeding on a non-infected plant
  • Persistant- feeding behavior is a circulative transmission, infrequent feeding probes of long duration (minutes to hours), ~80 viruses, (the virus multiplies within this type of insect vector)
Non-persistant insect vector                                                              Persistant insect vector
Courtesy of Oregon State University presentation

 Courtesy of Oregon State University presentation

Plant viral symptoms occur when virus RNA is incorporated in the cell and causes an "interference with the plant physiology.  Typical viral symptomology on plants can be described as mosaic, mottled, ring spots, stunt, leaf roll, curled, streaked, breaks, yellowing, reddening, or crinkled.  In some cases, the plant may be infected with a virus, and not show any symptoms at all.

If a field show symptoms of a virus, the field pattern of symptoms can sometimes mimic a typical insect (vector) distribution in a field.  For example, if you observing what you think are viral symptoms on field edges, this could be due to insect vectors that survive in fence rows.  However, viral symptoms that show up as "hot spots" within the field may be due to a wind, fungal, nematode, or infected seed pattern virus vector.

 The diagnosis of plant viruses in the field is difficult if you are relying only on plant symptomology because most viruses can exhibit similar symptoms.  In addition, other plant problems can sometimes exhibit simliar symptoms to that of viruses, such as herbicide injury.  Definite virus diagnosis is not possible without specialized testing such as Bioassays using indicator hosts, vector transmission assays, electron microscopy, detection based on coat protein or ELISA assay (enzyme-linked immunosorbent assay), or Characterization of viral nucleic acid:  PCR (Polymerase chain reaction amplication) and gels.

Picture of a hosta that has been found to be positive (2 red lines) based on an ELISA quick strip test

If you are testing a plant for a virus, a good sample is needed for virus diagnosis.  Take a representative sample of the symptomatic tissue, which may include: entire leaf, entire tuber, or entire plant.  The plant sample may need to be shipped overnight to the testing facility. If you have a question about testing facilities, you can contact the University of Illinois Plant Clinic:  http://web.extension.illinois.edu/plantclinic/

Plant viruses can survive in nature within vectors, infected debris, seed, and usually only in association with living tissue.  

When scouting for crop virus diseases, you may want to watch for moderate to high insect activity, lower than expected yields, mottled seed (soybean), no yield response to insecticide application, and presence of virus symptoms typical of virus infection.

Plant Virus Management:
highly effective when available
Not very effective in field,  greenhouse yes
Not very effective
Insecticides / vector control
Timing very difficult, with persistent viruses and very mobile vectors with many generations less effective
Tissue culture
Highly effective,  ie. potato certification programs
Coat protein technology
Highly specific and effective when available, tomato
(Stephanie Porter and Suzanne Bissonnette)