Pink Rot

Pink Rot is an opportunistic disease that attacks weak or stressed palms. Palms lack the ability for secondary growth, which means they are not able to repair damaged tissue. This makes them more susceptible to diseases such as Pink Rot when damaged or pruned heavily. Various species of palms are susceptible to the disease, including many popular varieties found throughout Southern California, such as California Fan Palm (Washingtonia filifera), King Palm (Archontophoenix cunninghamiana), and Queen Palm (Syagrus romanzoffiana). The pink spores are often visible and can be found at the area of infection. This disease can attack any part of the plant including the trunk, but most often affects new growth.

Management Practices for Pink Rot

Selecting the right plant for your location is key. California Fan Palms (Washingtonia filifera) are native to the deserts of Southern Californian. They don’t do well along the coast, so don’t plant them there. Plant at the right time. Don’t plant palms in the middle of winter. Proper cultural care is crucial. Water and care for your palms properly. Avoid wounding the palm. An open wound is a perfect opportunity for Pink Rot to attack. Fungicides can be used to suppress the disease, but the cause of the stress has to be addressed to completely control Pink Rot.

Fusarium Wilt

Primarily attacks Canary Island Date Palms (Phoenix canariensis). It is a vascular disease which means it attacks the plants ability to move water and nutrients through it’s system. There are forms of Fusarium that are species specific. It’s primarily spread by pruning tools. There is no cure for the disease. It is 100% fatal; however, it is nearly 100% preventable through the use of safe pruning practices. When infected, the lower leaves die back as the palm dies from the bottom up. The fronds will often die on only one side. While this is a good indicator of Fusarium, it’s not always 100% accurate as other diseases may cause similar symptoms.

Management Practices for Fusarium Wilt

Prevention is important because there is no cure. Don’t use chainsaws to prune because they can cause large open cuts that are susceptible to disease. Prune with a hand saw instead and disinfect the blade between trees. Remove diseased palms as soon as possible since once infected, the disease is 100% fatal. Avoid spreading the soil or replanting the same species in the same location as a previously diseased tree, since Fusarium may be present in the soil. Control water runoff as it may carry the disease to a new location and infect other trees. Control trunk and root debris. Saw dust was collected in an experiment during the removal of an infected plant. They were able to grow Fusarium from the saw dust in a petri dish. Saw dust blowing around during pruning could potentially spread the fungus to adjacent palms.

Sudden Crown Drop

Sudden Crown Drop primarily affects both the Canary Island Date Palm (Phoenix canariensis) and to a lesser extent Date Palm (Phoenix dactylifera). As the name implies, this disease causes the crown, or top of the palm, to just suddenly topple over, often with little or no warning. This is potentially dangerous and people have been killed in the past from falling debris. At first look, the crown appears normal. The trunk decays internally, and it’s not until you look at the cut away sections that you can see how the disease chokes the plant. Infection is typically caused by excessive pruning.

Management Practices for Sudden Crown Drop

Once again, prevention is key since no cure is available. Management practices are similar to what was previously mentioned for Pink Rot and Fusarium Wilt including proper selection and cultural care. Do not use chainsaws or spikes. Disinfect hand saw blades between trees. A mallet can be used to tap the trunk and listen for areas of decay.

Diamond Scale

Diamond Scale is a fungal disease and not an insect as the name may imply. It primarily attacks California Fan Palms (Wasahingtonia filifera) and usually only those located in areas of marine influence. The fruiting bodies are black in color and diamond shapes. They look similar to scale, hence the name, and are found on the leaves.

Management Practices for Diamond Scale

There is no chemical control for Diamond Scale. Don’t plant Washingtonia filifera near the ocean. Use Mexican Fan Palm (Washingtonia robusta) or Guadalupe Palm (Brahea edulis) as an alternative in coastal areas.

Summary of Best Management Practices for Palm Diseases

Proper planting/transplanting is important in reducing stress to palms. Don’t plant during the fall and winter months. Don’t plant palms too deep. Practice proper cultural care methods. Don’t over-water and make sure to provide good drainage. Avoid causing wounds by not using chainsaws or spikes if possible. Practice good sanitation by properly removing and disposing of debris. Most importantly select the proper species for the location.

The above material was based on a presentation by Donald Holden. For further information please see the article “Palm Diseases in the Landscape” by Mr. Holden.  West Coast Grounds Maintenance is a commercial landscape contractor serving the Los Angeles and Orange County areas. If you have any questions we can be reached at (800) 339-2102 or by email at info @ wcgminc.com. If you would like a quote for services, please fill out the quote request form on our Contact Us page.

Here are some items that should be discussed with the general contractor prior to the start of any new construction:

• Discuss what landscaped areas will need to be protected prior to the start so that everyone is aware
• Locate any underground utilities such as irrigation lines and wiring that should be protected
• Locate other important items such as the backflow prevention device and the irrigation controller
• Discuss whether the water will be kept on to protect any existing landscape
• If the water will be off, discuss what options are available to continue irrigating
• Verify that the power will be kept on to the irrigation controller throughout construction
• Address whether sleeves will be installed under any new concrete or asphalt areas for future use
• Ask the general to note the location of any damaged sprinklers, lines, valves and/or wires

Discussing these items with the general contractor prior to the start will definitely save you some money. I don’t know how many times I’ve come on to a site where I have no idea what has been done. As I begin to test some stations I find broken lines and heads everywhere. The controller has been disconnected and there’s no power to it. There’s a new concrete handicap ramp with no sleeves installed underneath, etc., etc. etc.

So to keep it short and simple. Please give us a call before you start! Include your landscape contractor in your meetings. I guarantee you it will save you some money and headaches in the long run.

Healthy Myoporum Foilage (Click to Enlarge)

All across the Southern California coast, from San Diego to Santa Barbara, our landscapes are being attacked by a foreign invader. This enemy comes from Australia (or possibly New Zealand), is so tiny that you would probably miss it if you didn’t know it was there, and can cause some serious damage. This new pest is known as the Myoporum Thrip (Klambothrips myopori) and as you might have guessed attacks Myoporum.

There are two species of Myoporum which are popular in California and are especially susceptible including:

• Myoporum laetum – a large shrub/small tree
• Myoporum ‘Pacificum’ – a large, fast-growing groundcover

Myoporum Thrip Damage (Click to Enlarge)

These plants are popular because of their aesthetics, low maintenance requirements, and hardiness. Relatively few pests or diseases attacked these plants until recently. Now the Myoporum Thrip is causing hundreds of thousands of dollars worth of damage to our Southern California landscapes. Often used along freeways and roads you can see miles worth of these plants severely infested and in many instances completely defoliated.

Thrips feed on the foliage causing it to twist and distort. Leaf galls will also appear where the adults lay their eggs and the larvae develop. If the infestation is heavy enough it can completely defoliate the plant and cause death.

Identifying this pest is not difficult if you look closely. While very small, the adults are only 2 -2.5 mm in length, they are visible to the naked eye. They are distinguishable by their long skinny bodies. The adults are a dark brown or black color, while the larvae are a translucent to slightly orange color. You’ll know they are there by the tell-tale damage on the plant.

Myoporum Thrip Adults (Click to Enlarge)

So how do we combat this new invader? Since it’s not a native species, the Myoporum Thrip has no natural enemies here in Southern California. That’s why it has run rampant. At the moment there is no effective solution except to provide proper cultural care, which might or might not help. Imidacloprid (Merit), a systemic insecticide, may help somewhat, but it’s not entirely effective and may harm other beneficial insects. Researchers are working on biological controls to help stop the devastation. In the past they have been able to introduce natural enemies of a pest, such as parasitic wasps, that have helped control similar epidemics. For now we’ll just have to wait and see.