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. 

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)

For more information on plant viruses:  http://www.apsnet.org/edcenter/intropp/PathogenGroups/Pages/PlantViruses.aspx

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:

Strategy	Effectiveness
Resistance	highly effective when available
Sanitation	Not very effective in field,  greenhouse yes
Rotation	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 antisense	Highly specific and effective when available, tomato

(Stephanie Porter and Suzanne Bissonnette)

Should our Garden Club Sell Impatiens? What is the risk for Impatiens Downy Mildew in Illinois?

These are good questions. This is because many people don't understand downy mildew of impatiens (Plasmopara obducens) .  When someone buys a plant and it gets sick, they often want to blame the person/business from where it was purchased.  However, in reality, it may not be the fault of that person/business.

I think you are on the right track if you have a "reputable supplier".  This means you are confident that the pathogen that causes downy mildew on impatiens is not going to be on the plants that you are selling.  When this disease first became a problem in the U.S., it was found  in a few nurseries and not in the landscape. Since 2011, it has become a problem in landscapes!  In Illinois, we are receiving reports that this disease is a problem in the Chicago area.  Some may want to know how they can be sure that an impatiens supplier is reliable.

 Plant or finish growers of impatiens may be more at risk for downy mildew infection if:

• Impatiens production is at the same time of impatiens growing in the landscape. -This is not likely in Illinois because plant production occurs during March or April.
• Impatiens plugs or liners are from an area where infected impatiens are currently growing or impatiens downy mildew has been reported in the landscape. - This could be likely if plugs are grown in Southern States and shipped here for finishing.
• Impatiens are growing in an area where impatiens downy mildew was confirmed in the landscape in 2011 or 2012. - This could be a problem for the finish grower or end user is they planted in a landscape bed where downy mildew existed previously.

All cultivars of impatiens walleriana are susceptible to downy mildew; however New Guinea impatiens have a high resistance to this disease.

For more information:   http://www.ballhort.com/Growers/_default.aspx 
                                    http://hyg.ipm.illinois.edu/article.php?id=424
                                    http://hyg.ipm.illinois.edu/article.php?id=354

All plant diseases are best explained by referring to the plant disease triangle.   

Picture taken from apsnet.org

In order for any plant disease to occur, you need to have a susceptible host (impatiens walleriana),disease pathogen present (downy mildew), and favorable environment (impatiens downy mildew thrives in moist conditions and cool temperatures -which can occur at night). 

If you are selling impatiens from a reputable grower and the impatiens that they have provided are thought to be "disease-free", they are not likely to be spreading the plant pathogen that causes impatiens downy mildew to customers.  Based on observations of the last several years, I believe that this disease is a problem because it has become established in the landscape.  Many landscapers/growers do not understand that if they have impatiens infected with impatiens downy mildew, they need to dispose of the infected material!  If they do not, they will continue to have further infection in the same area or at a later date.  If the removal of diseased material does not take place, this disease pathogen will be lurking in yards and landscapes, waiting to infect your and your neighbor's healthy impatiens. Many landscapers and gardeners often plant impatiens in the same area, every year. Impatiens growers are quickly finding that if they have a disease outbreak of downy mildew, they will have it the following year. 

We advise that you remove all of the diseased plant material to avoid further infection of impatiens; however, it may be difficult to completely rid the planting area of this disease and this disease pathogen is known to overwinter in the soil.  I have recently been asked the question: "If I had downy mildew of my impatiens the last two years, should I plant something else?"  My answer is "Yes". 

But, as we all know, we can have a plant disease pathogen present in our landscape, but may not have a problem, because we may not have the favorable conditions required for this plant disease to develop.  We do know that we have had favorable conditions for the infection of downy mildew to occur in Illinois in 2011 and 2012.  Unfortunately, we cannot control the weather, but we can make some predictions based on previous reports of impatiens downy mildew infection in Illinois.  We know that in 2011, we started to receive reports of this disease in the landscape in September; however, this disease was new and many may not have reported earlier disease outbreaks.  In 2012, this disease was reported in July and this is when people really started to become aware of the true devastation of impatiens downy mildew in Illinois.  Most of the 2011 and 2012 reports of downy mildew infection in Illinois were from the Chicago area.

Bed of impatiens infected with impatiens downy mildew

Based on the reports of impatiens downy mildew infection and weather conditions in the Chicago area during the last two years, I believe that there is a strong possibility that we will continue to see outbreaks of impatiens downy mildew in the future in the Chicago area. However, it is much harder to make predictions about this disease in downstate Illinois; but it is possible.  

If one decides to sell impatiens, I think that I would provide a caution statement with the impatiens explaining that your hope is to provide customers disease free material (not a total guarantee), but there is a strong possibility that impatiens could be infected by impatiens downy mildew inoculum, which could be present on infected impatiens debris/soil, lurking in landscapes.  

"Growers are responding to the gardeners requests for alternative shade tolerant plants, so do not hesitant to ask what else you could offer in leiu of impatiens." - Richard Hentschel, University of Illinois Extension Horticulture Educator

Please refer to this website for alternative to impatiens:  http://flor.hrt.msu.edu/IDM/index.htm

Impatiens leaf with sporulation of downy mildew on the underside of the leaf

(Stephanie Porter)