31.3.12

Something is Killing My Plants ! Help !


Pythium Root Rot on a Poinsettia
often indicated by wilted foliage,
where adding water worsens the problem ! 

I can speak from my own decades of experience that diseases can kill plants really fast. In some cases, diseases can kill a plant scary-fast. I've seen root-rotting fungi or plant-melting bacterial diseases melt big orchids in just 72 hours, in some cases even less. It seems that the disease always hits the plants on a weekend when I am out of town ! I mention this because we are approaching the "warm" weather, as they say here in Miami, which I call "beastly". It is this onset of warm weather, combined with higher night temperatures and higher humidity that will really foster disease development. It is important to recognize symptoms of disease onset and handle the situation NOW, not next week when you have a spare day or two.

Defining which disease is present is crucial to implementing a control program. The visual difference between a bacterial and a fungal pathogen may be subtle, but important; the control measures are very different. The chemicals used to control bacterial diseases are completely separate chemistries than those for fungi. In either case, there are resources to help with the diagnosis, and they are available online. Below is just a small excerpt ( sans photos) from a University Extension Service Bulletin about a common rose disease called Cercospora Leafspot. Such Bulletins are immensely useful for diagnosing and treating diseases and pests, they contain lots of useful photos and information, and the Bulletins are often free.      

Cercospora leaf spot is a disease often confused with black spot. Both diseases cause severe defoliation in heavily infected plants. The infection starts from the bottom of the canopy and progresses towards the tips where new growth is present. Lesions are primarily found in leaves but also in pedicels, stems, fruits and bracts. (See EDIS publication Cercospora Leaf Spot of Rose at http://edis.ifas.ufl.edu/PP268).



Symptoms of Cercospora leaf spot are circular spots usually 2-4 mm in diameter but single spots can be as large as 10 mm in diameter (Fig. 1a, 1b). The size is variable depending on the species or variety on which the lesions occur. When symptoms begin to appear, a small purplish area becomes apparent. In older lesions a small necrotic area develops and increases in size as the disease progress (Fig. 1b). At this point, the center of the spots turns tan to almost gray as the protoplast in the cells become brown and die.
In advanced necrotic lesions, groups of small tufts of conidiophores can be found. Conidiophores develop from masses of fungal tissue called stroma (Fig. 2a). Stromata are dark brown and appear as black dots over the necrotic area of the leaves. Under the microscope, cylindrical, almost straight, septate conidia can be observed (Fig. 2b).

Every state in the USA has a University Extension Service, and I feel they are hugely underused. The "Extension" Service is a tax-funded service which takes the highly technical research generated by universities and researchers, and "extends" it to the public in more readable layman terms. The recommendations are area-specific, and the diagnoses are amongst the best in the country. There are offices for the Extension Agents which serve all counties in a state, and many urban areas have several offices in one city. They are highly qualified technicians and consultants. The agents who serve the people and businesses of an area will come to your home or business at little or no charge, providing diagnostic services and advice.

Historically these "ag agents" assisted farmers and ranchers with advice and insights about how to deal with pests and diseases in farm, orchard, vegetable and animal production. They were a staple of agriculture culture, and it was their job to stay current on the problems which affect our homes, farms, landscapes, groves  and gardens. This is still true, but their field of expertise has expanded to homeowners and even municipalities. 




Bacterial Rot on Calla Lily


Anthracnose of Maple Tree












The University Extension Services can be a great asset to you in terms of disease or pest predictions, diagnosis, and treatment. They have direct access to diagnostic labs in each state or region which can identify a problem accurately, and recommend treatments you can trust. Thee diagnostic services are free or low cost, and can really save your chestnuts from being killed by a disease or pest. On a larger scale, ( no pun intended ), these agents can help identify and contain a problem before it threatens a wider area. If a newly introduced pest, such as the Giant African Land Snail in Miami, can be contained then its damage will be limited. Imagine what would happen to the Florida Everglades if it got into the million-acre wetlands and wreaked havoc on the ecosystem ? 

I often tell people to use their information options. There are people and services who can help with diagnosing problems, often for free or at low cost. I urge people to use these services often and develop a relationship with an agent who specializes in the plants you grow. Your taxes help pay for these services, so use them !

Craig Morell
Pinecrest Gardens  




1 comment:

  1. Great blog, informative and up to date. Bookmarking your page. Thanks and more power!

    ReplyDelete