Survival of P. ramorum (SOD pathogen) in wood chips depends on a few factors:
- Were the chips allowed to become wet?
- What size are the chips?
- Is green waste present?
- What time of year was the wood chipped?
- Where in California are the chips located?
Chips that are piled wet or tarped and include infected green waste (e.g. bay laurel leaves) may support pathogen viability for over 1 year, especially in mild coastal areas. If the wood is chipped in the summer and early fall and the chips are not piled, but rather broadcast in a 1-inch layer in a dry and sun-exposed area, pathogen viability may only be supported for a few weeks, especially if in hotter interior areas.
Survival of P. ramorum (SOD pathogen) in dead hosts or non-plant substrates is extremely variable and strongly affected by climatic factors. Although a comprehensive study on this topic has not conducted, extrapolating from several studies we can say the following:
Soil becomes more infectious from late winter to early summer in the presence of rainfall, so any movement of soil away from a SOD-infested area from January to July could transport viable P. ramorum.
Keep the following in mind:
- The larger the volume of soil moved, the greater the risk.
- In organic rich soils (e.g. top layers of forest soils), pathogen survival is less than 18 months.
- If P. ramorum is present in green waste incorporated in the soil, survival can be much longer (2 years or more).
- In inert soils (e.g. potting mix), the pathogen can survive multiple years. However, for all soils, areas with less temperate climates (cold winters, hot summers) may hasten loss of pathogen viability.
From a practical perspective, if infested forest soil is picked up on tires or shoes from late winter to early summer, the pathogen will likely remain viable for about 1 year, in the absence of incorporated green waste. If soil is picked up from late summer to early fall, survival duration is much less, possibly in the order of a few months.
Leaf tip scorch symptoms on redwood trees are found from the lower to upper canopy and include healthy leaves interspersed with brown and grey leaves or portions of leaves. Grey leaves typically have black margins into the healthy tissue.
Such symptoms are typically caused by a fungus called Pestalotiopsis funerea. They are commonly associated with drought, when rainfall occurs or when there is overhead watering around the tree. Drought stress predisposes plants to being infected, so the increased moisture facilitates the infection process. Normally the fungus will only seriously affect sprouts, as branches of adult tress will regrow areas killed by the infection within a year. In nursery settings it is important to increase ventilation and avoid big differences in watering regimes to minimize symptoms.
Once bark beetles attack the main stem (trunk) of an oak, the tree is on its way out. Insecticide treatments will not save it. Oak beetles are attracted to trees that are severely compromised. They cannot attack healthy trees.
The correct approach to avoid bark beetle infestations is not to apply insecticides, but rather to identify any health issues a tree may have. As of October 2015, many trees are suffering from the prolonged drought and may need watering. Watering should be applied infrequently and never during the summer. Water-starved trees may display a thinner crown, with olive-green rather than dark-green leaves. Leaves may also be crisp when folded between your fingers. If you opt to provide water to an oak tree that is severely water deprived, make sure the water reaches a depth of about one foot below the soil surface. Also make sure the flow is low to avoid flooding the base of the tree.
The symptoms on your oak may be caused by a range of issues. If oozing is accompanied by the presence of fine sawdust, then the tree is dying. Even if it is still green you may want to consider removing it if its failure may cause harm to people or property. The fine sawdust is caused by beetles tunneling in the tree. Oaks are only attacked by beetles when dying. If no sawdust is present, then the tree’s condition may be reversible.
Unfortunately, it is difficult to determine what may be the cause of the symptoms you describe. Sudden Oak Death (SOD) can attack an oak tree if California bay laurel is within 60 feet of the oak. You can use the free SODmap Mobile App to determine if you are in a high or moderate risk zone for SOD. To find out how to do that, go to www.sodmapmobile.org. There is also a YouTube video you can watch at https://youtu.be/zE0_q3EmIfs. If the information you gather suggests that it may be SOD, then repeat the phosphite bark application (such as Agri-Fos® combined with Pentra-Bark®) in the fall between October 30th and December 15th. You may also want to consider removal of bays within 30 feet from the oak. Go to http://nature.berkeley.edu/garbelottowp/?page_id=909 to find out about upcoming treatment training sessions to learn more about treatment options. If there are no bays within 60 feet of your oak and the SODmap mobile risk is low, then it likely isn’t SOD.
If you have watered your oak, it may be a root disease such as the oak root fungus or Phytophthora cinnamomi root disease. Make sure you stop watering and expose the upper root system to the air to slow disease progression. If you have never watered your oak, then it may be a secondary disease brought on by the long drought (ex. oak die-back fungus). These are diseases that are strongly affected by the genetics of the tree and weather conditions. In this case, you may want to try watering the tree now and then once again in 2 weeks. Then water once a month starting October 15th. Do not water between July 10th and October 15th. Watering should be done using a low flow approach to ensure that the soil gets wet up to 1 foot down and that no flooding of the tree ever occurs. Unfortunately, if the secondary disease is too advanced, despite all efforts, the tree may still die.
Once an oak has the oak root fungus Armillaria (often due to excessive watering), most treatments will be ineffective. Be sure the base of the tree is free of mulch and other organic debris and slightly expose the root system at the root collar. While fertilizing may not help, try using one bark application of Agri-Fos + PentraBark. This application provides minimum nutrients, but strengthens the defense mechanisms of the tree. Of course, stop watering unless absolutely necessary. Water should never be administered from July-September.
It sounds like your tree is having problems providing enough water to the canopy to keep the foliage and cambium alive. If you are not watering it, that may be the problem. If you are watering it, your tree may have contracted a root disease. In that case, it is important to clear all organic material at least 3 feet around the stem, slightly expose the root system next to the stump to the air, avoid fertilizers, and water minimally.
The first question to ask is what type of irrigation is being used currently on the hedge. Most landscape oak root fungus problems are due to overwatering in summer months. However, Thuja orientalis (=Platycladus orientalis) is quite susceptible to Armillaria even without heavy irrigation as highly susceptible species do not require excessively high soil moisture to be killed.
Prior to any new planting, as much of the old hedge (including roots) should be removed. In addition, any other decaying wood should be removed. Replanting with plants that do not require supplemental watering is best. Some CA natives that make good hedges include: ceanothus, island mountain mahogany, manzanita, and toyon. Non-native possibilities include Leyland cypress and Japanese privet. Keep in mind though that even plant species listed as resistant to oak root fungus will die if overwatered.
Although there may be few insects flying in the winter, the wet winter season (actually fall through spring) is a prime time for production of fruiting bodies by many wood decay fungi. The combination of fresh pruning wounds (especially large wounds), high spore densities of wood decay fungi, and moist conditions (favoring spore germination) can favor new infections by these fungi. From the standpoint of reducing risk of infection by wood decay fungi, pruning in late spring or early summer is probably preferable.
In general, pruning live branches from mature oaks should be kept to a minimum. However, if it is necessary to prune coast live oak branches, as long as they are less than 4″ in diameter, the presence of SOD is not a concern. Though, it is important to prune the oak correctly.
• Make sure you prune right where the tapering of the branch ends from the main stem or even slightly closer to the stem (1/2 in. from the end of the tapering towards the stem).
• Make sure the cut is clean and allows for water to drip without accumulating.
Detailed information on “Watering Guidelines” can be found at http://cemarin.ucanr.edu/files/174267.pdf.
