NEIGHBORHOOD GARDEN FOR JUNE 9, 2012

NEIGHBORHOOD GARDEN FOR JUNE 9, 2012

*************************************************************

ABIOTIC DISEASES

BY GORGE EDGAR

A few weeks back in one of my articles I introduced the term “Abiotic”. I did not have room to properly define and explain what the term means. So today I am going to explain what Abiotic diseases are and why so many do not understand their plants.

“Plant diseases generally are classified as either biotic (caused by a pathogenic parasite) or abiotic (caused by environmental conditions such as wind, water, and temperature, or genetic disorders). More importantly, abiotic diseases also may cause symptoms that may be confused with symptoms caused by biotic diseases or pests.” (1)

Some of the common abiotic diseases include water stress (surplus or too little), hail damage, animals, herbicide damage, and genetic disorders. Don Janssen in his article “Abiotic Diseases” says, “Hot weather, inadequate moisture, drifting of herbicides, freezing temperatures, transplant shock, compacted soils, mower injury, and lack of nutrients are examples of factors that can cause abiotic disease problems. Abiotic diseases are caused by factors other than living (biotic) agents.”

He goes on to write, “To diagnose abiotic disease problems it is important to evaluate the characteristics of the site, past weather condition, and the care practices. In some cases, more than one abiotic factor may contribute to the poor health of a plant. Plants that are growing under stressful conditions may also be more prone to certain biotic disease problems, such as fungal cankers.”

“A good understanding of the growing requirements of plants and selecting the right species for the conditions of the site can help prevent abiotic stresses. Unfortunately, weather extremes cannot be controlled and are common.” (2)

Paula Flynn, Department of Plant Pathology at Iowa State University published an article on September 12, 2003, titled “Biotic vs. Abiotic-Distinguishing Disease Problems from Environmental Stresses”. She writes, “Unfortunately, the damage caused by various living and nonliving agents can appear very similar. Even with close observation, accurate diagnosis can be difficult. For example, browning of leaves on an oak tree caused by drought stress may appear similar to leaf browning caused by oak wilt, a serious vascular disease, or the browning caused by anthracnose, a fairly minor leaf disease.”

“When the cause of a plant health problem is not readily diagnosed, it’s important to take a systematic approach and carefully consider site conditions, weather condition, care of the plant, and the known biotic disease agents of that plant. The first important step is to determine the identity of the plant and its requirements for healthy growth.”

“There are a few clues to look for that will help you distinguish between abiotic and biotic disease problems.

· Abiotic damage often occurs on many plant species. Drought stress or chemical drift will likely cause damage on several types of plants in a yard or garden. In contrast biotic disease problems are more limited to a certain species. The fungi that cause tomato blight do not cause damage on sweet corn for example.

· Abiotic damage does not spread from plant to plant over time.

· Biotic diseases sometimes show physical evidence (signs) of the pathogen, such as fungal growth, bacterial ooze, or nematode cysts, or the presence of mites or insects.” (4)

JayDee Gunnell and Jerry Goodspeed, Horticulture Agents, Cooperative Extension Service at Utah State University have listed the “Top 10 Abiotic Diseases of Wood Ornamentals” in an article by that name that I found on line. Most also apply to other plants. They are:

“1. Iron chlorosis, (A common nutrient deficiency in alkaline soils),

2. Planting depth, (Planting too deep reduces available oxygen to the roots & causes trunk decay),

3. Circling and girdling roots, (Constricting roots that reduce proper flow of water and nutrients),

4. Mechanical damage, (Practices that result in physical damage of plant tissue),

5. Packaging material, (Foreign materials left on plants that ultimately restrict growth),

6. Excessive irrigation, (Practices that deplete oxygen from the root zone),

7. Summer scorch. (When plants cannot physically translocate enough water to leaf margins),

8. Herbicide damage, (Practices that cause spray or drift that damages non- target plants),

9. Winter damage, (Fluctuations in temperatures that ultimately damage plant tissues), and

10. Salt damage. (High levels of salt reduce the plant’s ability to uptake water (chemical drought)” (3)

Remember what Don Janssen wrote, “A good understanding of the growing requirements of plants and selecting the right species for the conditions of the site can help prevent abiotic stresses.”(2) And what Paula Flynn wrote, “When the cause of a plant health problem is not readily diagnosed, it’s important to take a systematic approach and carefully consider site conditions, weather condition, care of the plant, and the known biotic disease agents of that plant.” (4)

References: (1) NebGuide G2045 Abiotic Diseases of Sugarbeets in Nebraska by Harveson and Yonts, January 2011

(2) Abiotic Diseases by Don Janssen, former UNL Extension Educator in Lancaster County. This resource appeared in the Lincoln Journal Star Newspaper Sunday edition in July 2007.

(3) “Top 10 Abiotic Disorders and Cultural Problems of Wood Ornamentals” by JayDee Gunnell and Jerry Goodspeed, Horticulture Agents, Cooperative Extension Service at Utah State University. (extension.usu.edu/files/publications/publication/Horticulture_

PlantProblems_2010-02pr.pdf)”

(4) Biotic vs. Abiotic-Distinguishing Disease Problems from Environmental Stresses” by Paula Flynn, Department of Plant Pathology, Iowa State University (http://www.ipm.iastate.edu/ipm/hortnews/2003/9-12-2003/stresses.html)