Q&A

My redwood has severe dieback and is near a coast live oak with SOD. Could the redwood have SOD?

Most likely the redwood is experiencing symptoms related to cycles between drought and rainy periods. However, if there is a significant presence of California bay laurels intermixed with redwoods, there may be enough pressure from the SOD pathogen to also cause problems on redwoods, both native and exotic. Any SOD oak infections are likely directly connected to bay laurels, as both oaks and redwoods can become infected by the large number of spores produced on bay laurel leaves. The pathogen does not move from oaks to other trees.
 

Other than for copper-based sprays, what control methods are available for cypress canker?

There are several  products that have been tested for controlling cypress canker. The following paper maybe the most useful one to compare products.
Della Rocca, G., Di Lonardo, V., Danti, R. 2011. Newly-assessed fungicides for the control of cypress canker caused by Seiridium cardinale. Phytopathologia Mediterranea. 50 (1), pp. 65-73.

The most effective active ingredients for preventive treatments appear to be Azoxystrobin and thiophanate-methyl.

A good approach to slow down the disease may consist of:

1) Cutting down infected trees to reduce the chance of contagion. If only a few tips are infected, prune branches rather than take down the entire tree.

2) Cut down all Leyland cypress as it is a major vector of the disease.

3) Treat remaining healthy trees with products containing azoxystrobin (an active ingredient less toxic than thiophanate-methyl).

 

Which trees give off the most oxygen?

Assignment levels of oxygen emission are not precise and different methods can give different results. That said, it is well documented that oxygen release is proportional to the overall leaf mass, also known technically as Leaf Area Index.

There is general agreement that:

  • Pines are at the bottom of the list in terms of oxygen release because they have a low Leaf Area Index.
  • Oak and aspen are intermediate in terms of oxygen release.
  • Douglas-fir, spruce, true fir, beech, and maple are toward the top of the list for oxygen release.

If reforesting an area impacted by SOD with local acorns, what can be done to prevent spreading the pathogen during planting?

Take the following precautions when using local acorns for oak reforestation projects in areas impacted by SOD to help minimize pathogen spread.

  • Place acorns in a 10% dilution of bleach for 10 minutes then rinse twice with tap water.
  • Make sure volunteers’ shoes are free of soil, mud, and organic material.
  • Be sure tools being used are clean and free of soil, mud, and organic material.

 

How often do you administer phosphonate to oaks to help protect them from sudden oak death?

Phosphonate injection treatments to help prevent sudden oak death infection of susceptible oak species (coast live oak; California black oak, Shreve’s oak, and canyon live oak), if applied in the fall (after October 30th ), need only to be applied once every other year (biannual frequency). If your first phosphonate treatment is in the spring, then treat again in the fall (after October 30th)  and then treat once every other year.

If applying phosphonate as a bark application in conjunction with the surfactant PentraBark®, then one fall treatment each year is the prescription. If you apply it the first time in the spring, apply again in the fall after October 30th and then apply again in the fall of each year (after October 30th).

How do I determine the distance from trees on my property to P. ramorum-positive trees on SODmap?

When looking at SODmap, you may wonder if P. ramorum-positive trees are close enough to pose a threat to trees on your property. Use the free App SODmap mobile to get the answer. Just tap the App risk function and it will tell you whether  infected trees trees are within 200 m (high risk) or 1,000 m (moderate risk).  If infected trees are further than 1,000 m, risk is typically low.  Alternatively, you can use Google Earth, tapping the icon with a “ruler” on the top bar.  Click your mouse on the closest infected tree and then move the mouse to your property. Be careful to actually move the mouse all the way to an oak tree within your property. The mouse should be drawing a line when you go from the infected tree to your oak.  When you click the mouse again on top of the oak on your property, the ruler will tell you the distance. The following is suggested:

1-  As the crow flies, measure from any infected tree to any oak of interest.

2-  Repeat the measurement process using 3 different infected trees that appear to be close to your property.

3- If distance is slightly higher than 200 m (high risk) or 1,000 m (moderate risk), but your property is downhill and/or downwind, you may still consider your oaks to be at risk.