Pine wilt nematode (PWN) was identified last week by Dr. Tamla Blunt at Colorado State University’s Plant Disease Diagnostic Laboratory in Fort Collins as causing the death of a pine tree on the Redlands. Evidently, this pine tree pest was previously identified in the summer of 2012 as causing the death of another pine north of Grand Junction. The pine wilt nematode, Bursaphelenchus xylophilis, is native to the U.S. and as such, native trees have developed a tolerance to this pest.

Spread from tree to tree by long horn beetles known as Pine Sawyers in genus Monochamus, these nematodes move from the breathing pores of the beetles into the tree as the beetle feeds. The larvae of these beetles pick up nematodes as they bore their way through dead and dying trees. Trees stressed from lack of water, nutrients and a lack of general care are more susceptible to infection by these nematodes. Pine Sawyers are attracted to such trees.

Trees infected by PWN should be removed and the bark removed or the trees buried to prevent the spread of the nematodes to other trees. The beetles will not lay their eggs in trees without their bark and aren’t likely to dig into the soil to reach buried trees. More than likely, many infected trees will remain above ground with intact bark and long-horned beetles will continue to infect pine trees throughout the Grand Valley. Scots and Austrian pines are much more susceptible to the pine wilt nematode when planted in areas where average summer temperatures are above 68 degrees F. We can expect extremely high levels of mortality with Scots (aka Scotch) and Austrian pines due to these conditions. Pretty much anyone with a pine tree in their yard has one of these susceptible pines.

STAVING OFF ‘PWN’

So how should we handle the upcoming epidemic of dead PWN trees? We already have many dead trees throughout the area due to the combination of the pine wilt nematode and the two harsh winters we recently experienced. Dead and nematode pine trees need to be identified, remove and buried, burned, or debarked before the beetles can lay their eggs for the next generation of PWN-spreading pine sawyers.

A fairly simple test can be used to identify which trees are infested with these nematodes. Samples from dying branches 1 inch or more in diameter need to be collected. A sample of the branch tissue nearest to the trunk is placed in aerated water and the nematodes leaving the sample filtered out and placed on a microscope slide for identification. Trees free of nematodes can be injected with abamectin. This systemic nematocide reduces the incidence of tree death if administered soon enough. Applications of abamectin are recommended to be repeated each spring. Watering properly during our hot summer and fertilizing as needed helps keep pines healthy and less susceptible to the beetle and nematodes. Sprays of insecticide to repel and/or kill the beetle also are recommended if you expect to prevent the death of your non-native pines.

GETTING YOUR SPRINKLERS RIGHT

This past weekend I changed out the nozzles on a series of sprinklers that were not providing adequate coverage to a section of lawn. As the summer gets hotter we can expect more lawns drying up due to improper spacing of sprinkler heads, broken heads or nozzles and improper nozzles. Many times this problem can be corrected simply by changing out the nozzles using nozzles that cover more area and provide a more uniform distribution of water.

Another problem I’ve been running into involves a lack of adequate filtration for ditch water. When elm trees were dropping their loads of seed, area gardeners and farmers alike were finding there filters plugging up with these seeds. Individuals I’ve worked with were lacking an adequate self-cleaning basket strainer like the one Rich Edwards perfected. Rich was the previous owner of RE Landscape, a Grand Junction firm that provided landscape and maintenance services for many western Colorado residents and businesses. This drum-like filter is placed in the sump where the inlet for the pump is located. It has a set of nozzles that wash the filter from the inside keeping the screen free of debris and preventing it from being drawn into the irrigation system where it plugs filters, valves and nozzles. You can learn more about the FlowWater self-cleaning strainer at http://flowaterirrigation.com/. The strainer currently available has a 3-inch intake but according to Rich can be reduced to accommodate a smaller intake diameter.

Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.