Plant Disease Watch List

• Pine Wilt

  Pine wilt is a disease caused by the pinewood nematode, Bursaphelenchus xylophilus. This nematode is spread by the pine sawyer beetle. By itself, the beetle does little damage to a tree beyond some minor stress, but it is the primary vector of this nematode, which enters the trachea of the insect at larval stage and is spread during feeding after the insect spreads to other trees as an adult. This disease is established in Eastern Kansas but has yet to establish in most of Western Kansas at this point.

  Pine wilt disease usually kills pine trees relatively quickly, within a few weeks to a few months. Mature pine trees (10+ years old) are more susceptible than young ones. Because of this, it is not a serious threat to Christmas tree farms. However, this makes it a prime threat to windbreaks as pine trees are frequently used as windbreaks across the state.

  How do I recognize it?

  Symptoms include color change in needles from green to grayish green, then to brown. If you remove a limb, it is usually characterized by a lack of resin, as the nematodes multiply and clog up the xylem which stops resin flow. Needles do not drop immediately but may stay on a dead tree’s branches up to a year.

  What to do if I find it?

  To prevent the spread of pine wilt, it is imperative to remove dead pines promptly. They must be burned, buried, or chipped, as they may harbor insects and promote spread of the nematode. Do not use the wood for firewood, as the insects may still emerge from firewood logs. When planting evergreens, select resistant trees, such as white pine, spruces, firs, and junipers. Susceptible pines include Scots pine, Austrian pine, Mugo pine, jack pine, and red pine. No effective nematicides exist at this time.

  If you suspect a pine tree of having pine wilt, a sample of wood is necessary. Take a disk of wood or branch at least 1 inch thick and 3 to 4 inches wide and submit it to the Kansas State University Plant Disease Diagnostic Lab in Manhattan, Kansas. If a pine tree dies it is important to know whether pine wilt was the cause, as it is important to dispose of the tree properly to avoid spread of the nematode.
  
  
  
  
  For more information:

  • Pine Wilt Fact Sheet
  • Pine Wilt vs Pine Tip Blight

• Boxwood Blight

  Boxwood blight is a destructive disease caused by the fungus Calonectria pseudonaviculata, first detected in the UK in 1994. It spread to Connecticut and North Carolina in 2011 and Kansas in 2014. Since then it has spread across the United States, Europe, and parts of Canada.

  Early detection and eradication work are ongoing. In addition to boxwood, the disease attacks pachysandra, sarcococca, and other species in the family Buxaceae. Proliferation of the disease causes severe defoliation and leads to crop loss in nurseries and planted landscapes.

  Why is it important?

  Boxwood is a popular evergreen bush in Kansas because they are low-maintenance and tolerate a wide variety of environmental conditions. If allowed to spread, this disease could be devastating to the Kansas boxwood industry and landscapes.

  How to recognize it?

  Symptoms of boxwood blight include light brown leaf spots with dark borders, which coalesce and form brown patches and black streaks on green and woody stems. These symptoms cause defoliation and death of the plant. In conditions of high humidity, white growth may be visible on the undersides of the leaves.
  
  For more information:

  • Boxwood blight pest alert
  • Purdue boxwood blight page

  

• Sudden Oak Death

  In early June 2019, KDA confirmed the presence of Sudden Oak Death (SOD) in Kansas. SOD is a plant disease that has killed large tracts of oaks and other native species in California and Oregon, and infected rhododendrons have been identified in 10 states in the Midwest, including Kansas. The infected plants that have been found in the Midwest have all been traced back to a common source.

  The Kansas Department of Agriculture, Kansas Forest Service and K-State Research and Extension need your help to help stop the establishment of this disease in Kansas. We are concerned that if it establishes and spreads, the threat is twofold. Our heavy population of red oak trees will be threatened. In addition to this, our nursery industry and landscapes will be threatened, as this disease has a wide host range that includes not only rhododendrons but also azalea, lilac, viburnum, pieris, and camellia, among many others. If you suspect a tree or landscape plant to have this disease, contact your local extension office.

  KDA performed a follow-up survey in summer 2020 to determine whether SOD could be detected after its arrival in 2019. It entailed collecting host plant samples from selected wholesale and retail plant dealers and collecting water from selected retention ponds and from public waterways in counties that had received potentially infected rhododendrons. No SOD was detected.

  What does it look like?

  The common symptoms on oak trees consist of cankers on the trunk and a decline of the tree. The cankers have defined margins and a reddish-brown, “bleeding” appearance. If you remove the bark you may see a larger reddish-brown lesion on the wood.
  On nursery plants, the symptoms are slightly different. The most common symptoms are leaf scorch, foliar blight, and stem canker. These symptoms may be confused with other common problems such as sunscald.
  
  For more information:

  • K-State Research and Extension offices
  • Sudden Oak Death
  • Kansas Forest Service info about SOD and risk to Kansas oaks
  • Sudden Oak Death Host List
  • Sudden Oak Death Pest Alert
    
    
    

• Thousand Cankers Disease of Walnut

  The Kansas Department of Agriculture enacted an exterior quarantine, effective, November 20, 2014, that rescinds and supersedes the quarantine issued on July 20, 2010, regarding Thousand Cankers Disease of Walnut. Please click below for full text of the quarantine:

  Thousand Canker Disease of Walnut Quarantine

  A Thousand Canker Disease Quarantine Fact Sheet is available to further explain the details of the quarantine.

  The Quarantine also requires individuals or businesses handling “regulated articles” in Kansas to register with the Kansas Department of Agriculture. Those importing such articles must also enter into a compliance agreement. “Regulated articles” include, but are not limited to, logs, lumber, firewood, bark, mulch, burls, stumps, live plants, packing material and all other articles of walnut (genera Juglans). Exempt from the quarantine are nuts, nut meat, hulls, and processed lumber that is bark free and from states where Thousand Cankers Disease of Walnut is not found.

  Current states where Thousand Cankers Disease of Walnut is detected are: Arizona, California, Colorado, Idaho, Nevada, New Mexico, Utah, Washington (prior to 1988), Tennessee (2010), Ohio (2012), Oregon, Pennsylvania, Virginia (2011), North Carolina (2013), Indiana, Maryland (2015). 

  More information about the Thousand Cankers Disease of Walnut quarantine will be posted as it becomes available.

  Thousand Cankers Disease of Walnut Poses a Serious Risk

  Thousand Cankers poses a serious threat to the health of black walnut trees. Walnut trees are important because they produce nuts and highly desired wood.
  
  

  The Kansas Department of Agriculture, Kansas Forest Service and K-State Research and Extension need your help to help stop the introduction, and to limit the spread, of this disease in Kansas. We are deeply concerned that if it reaches the native range of black walnuts in central and eastern Kansas, we may lose this tree in our urban and native forests.
  
  Currently, the disease is known to exist in the nearby states of Colorado and New Mexico. Colorado scientists believe that the disease was brought into its urban areas by moving infected wood either as firewood or for woodworking. Wood, bark, and chips with beetles and cankers are highly contagious and should not be moved off a site for three years. Do not bring in walnut wood from out-of-state sources.

  What to Look for in a Tree

  Thousand Cankers Disease of walnut is a progressive disease that kills a tree within two to three years after initial infection.
  
  The disease-causing fungus, Geosmithia sp., is transmitted by the walnut twig beetle, Pityophthorus juglandis. Research shows that only this beetle may spread the fungus in such a way to cause the disease. Feeding on walnut trees by other beetles carrying it does not appear to cause significant damage to the tree. Branches and trunk tissue are killed by repeated infections by the fungus, as the walnut twig beetle carries the fungus into new bark cambium tissue, repeating the infection. That’s why it is called thousand cankers disease.
  
  Here are several key points to remember when surveying and sampling for thousand cankers. Dead trees require careful scrutiny of the localized area.

  • Look for declining trees. Initial symptoms are yellowing and thinning followed by death in two to three years. This is early symptom development.
  • Trees with dead leaves are highly suspect and an advanced symptom. Branches collapse in late spring and summer, and leaves die and remain attached to the branch. This flagging symptom is similar to Dutch elm disease.
  • In Colorado, twig beetles are attracted to branches with southern and western exposure. Samples should come from this area of the tree, if possible.
  • Collect a sample from branches 2 to 4 inches in diameter. Cut the branch down.

  Take a strong bladed knife or drawknife, and cut or scrape away the bark. Next, take the knife and carefully slice the tissue directly under the bark parallel to the surface, peeling away the layers. If die back is caused by thousand cankers, you will see:

  • Black cankers about the size of a dime or larger.

  • Beetle galleries in the centers of the cankers.

  
  

  You may also see:

  • Beetles about the size of a pencil lead.
  • A gray spot/mass in some beetle galleries. This is a fungus colony.
  • Small beetle entry holes in the bark above the cankers.

  
  Twig beetle entry holes.  Photo by: Megan Kennelly, KSU
  
  For More Information:

  • Thousand Cankers Pest Alert
  • Surveying and Sampling for Thousand Cankers Disease
  • Detecting and Identifying the Walnut Twig Beetle
  • Pathway Assessment: Geosmithia sp. and Pityophthorus juglandis Blackman movement from the western into the eastern United States
  • Missouri Department of Agriculture Thousand Cankers Disease of Black Walnut
  • USDA Forest Service, Thousand Cankers Disease
  • Thousand Cankers Disease
    

• Tomato Brown Rugose Fruit Virus

  Tomato Brown Rugose Fruit Virus, a recent concern for tomato and pepper growers, found in the U.S.

  Tomato Brown Rugose Fruit Virus (ToBRFV) is a newly discovered tobamovirus that has been found, but not yet established, in the United States. Its two main hosts are tomatoes and peppers, causing concern for growers of these plants. There is a Federal Order in effect to restrict the importation of tomato and pepper seeds, transplants, and fruit from countries where the virus has been found. It has been detected repeatedly in the United States since the first time it was detected here in 2019 but is considered eradicated from U.S. tomato greenhouses. However, it has been found again and has the potential to show up in additional new locations.

  ToBRFV is mechanically transmitted, meaning it can be transmitted from one plant to the next on contaminated tools and equipment, and workers handling many plants in a greenhouse. It is seedborne, so any fruit produced on an infected plant is likely to contain seeds also carrying the virus. The most likely way it has traveled so distantly is via infected seeds. It can also be moved by pollinators such as bumblebees. This virus is unusually stable and may be spread in irrigation water or even infested plant debris and soil for many years.

  Common symptoms include yellowing, wrinkling, bubbling, and mosaic pattern on leaves and a wrinkled, brown texture to the surface of any developing fruits.

  The best method of control is prevention. Purchase only certified seed. Wash hands and sterilize tools frequently when handling plants. If you do find it among your plants, dispose of any symptomatic plants and all adjacent plants. Destroy by incinerating or double bagging and trashing the plants and pots, seedling trays, and soil. Do not compost or place in trash without double bagging.