Plant Pathology - Abiotic  Distress

A young pepper in distress from cool temperatures.

Recently, we enumerated the common causes of plant diseases in a post entitled  Plant Pathology. Now,  in keeping with the morbid greyness of November, we'll briefly review the character and sources of  "non-disease-related" problems.

Every gardener has encountered a sick looking plant. Some morning you cheerfully get up, grab a cup of coffee and then look at your flower box on the windowsill or maybe step into your sun porch to greet the newest pepper sprouts or marigolds and discover that overnight one, or some, suddenly are, to put it gently, 'failing to thrive.'   

What happened? Who did this? Don't jump to conclusions.

A  first reaction might be to think that some sneaky microbial pest has contaminated your private green domain. The plant  appears "sick," i.e. in some kind of  distress, but it may not be diseased; and the symptom appearing in front of you may be signaling a problem actually orginating in a different part of the plant. The plant's distress might not be caused by some other living thing at all...

Abiotic factors account for a lot more plant problems than you might think. Some experts attribute abiotic issues  as accounting for about 50% of plant problems while a few contend that it might be as much as 80%!  Many abiotic problems are readily remedied (or entirely avoided) by applying simple, good gardening practices - maintaining moisture levels, cultivating regularly to promote aeration and drainage, thinning plants, weeding etc. Some abiotic problems,  such as nutrient deficiencies, are harder to diagnose and require more time to correct; and some, like drought or monsoons, may not have readily available solutions. In my admittedly limited experience, containers, i.e. pots of any size or shape, seem to be prone to abiotic problems: they heat up and dry out fast,  salt residues from old fertilizers or hard water build up and soil fertility declines because soils or nutrients are not  replenished on a regular basis.  So - if you use a lot of containers, it's important that you be alert to the range abiotic problems that might develop.

Types of Abiotic Problems

Abiotic factors fall into several rather distinct, but unsexy,  categories:

Mechanical - These typically are simple breakages or abrasions that are usually caused by wind, hail, dogs, cats and other animals including small children.  [Tiny punctures in leaves or missing leaf tissue, however,  suggests some kind of  pest has been free loading.]

Beans showing some yellowing leaves.
Photo: NYSAES Geneva, NY

Chemical -  Nutritional deficiencies and toxicity frequently show up with disease-like symptoms. Too much of a good thing like fertilizer,  or, as in cases like road salt or pesticides - just a little too much of a bad thing, can cause yellowing (chlorosis) to varying degrees; but yellowing  can also  indicate  viral and bacterial  infestations.

How toxicity shows up depends upon whether a chemical is  absorbed by a plant  or comes into  direct foliar contact with some part of it, e.g. via careless spraying.  In the former case, symptoms may be general in nature, e.g. wilting or poor new shoot development; in the latter, leaf discoloration along with dead spots can rapidly occur.


[See earllier posts:  Macronutrients and Micronutrients about plant nutrition and how to recognize possible deficiences.]

Environmental - Plants, like many of us, typically do not respond well to sudden changes in their environment.  Temperature extremes, lighting,  air quality, oxygen and moisture levels will manifest themselves in various ways such as wilting, leaf drop, lack of flowering, inferior fruit, slow growth etc.  Note: oxygen and moisture levels can be related -- saturated soil that does not drain well will leave roots suffocating and that in turn can cause leaves to wilt, develop marginal browning and eventual dropping.  [And, of course, with respect to roots attacks by parasites and nematodes can also induce similiar symptoms.]  

Factors to Consider in Evaluating Problems

A wilted plant in a dried out pot is clearly distressed and easily resurrected by restoring the soil's moisture level, but a plant showing yellowing leaves as in the bean plants depicted above requires a more  systematic analysis to determine the cause.  Yellowing  leaves can be arise from a variety of factors:  nutrition, environment, parasites, fungi, bacteria,  viruses etc.

So after getting over the shock that your beloved rutabaga looks under the weather, switch on your situational awareness circuit and look at the unhappy specimen in front of you with an open mind and  begin thinking about  at leas some of the following before deciding on a  course of action:

• Does the symptom appear to be confined to just one plant, or are other plants also affected? 

• If more than one plant seems afflicted, is the symptom confined to a small area in your garden involving just a few plants or does it appear in a wider area? [Abiotic problems tend to be uniform in character and, in a garden setting, usually show up aross a wide area and are not limited to just one or a few plants. In fact, different types of plants may be affected.  Keep in mind, however,  that if you see multiple symptoms, there is a good chance that you may be dealing with multiple problems. ]

• If lately  you've been suspicious about the health of a plant, does the symptom seem to be changing over time?  

• Is the symptom spreading on this plant or are other plants showing lesser or greater degrees of the symptom?  [If yes, this implies a biotic cause.]

• Is just a specific variety of plant affected? [If yes, this also implies a biotic cause.]

• What part of the plant is affected?  Look at the whole plant -  check its stems, leaves, roots, blossoms, fruit. 

• Where is  the symptom located:  low or high on the stem.  

• Does the symptom appear to be confined to leaves, stems, blossoms or just to the tissue between leaf veins? 

• Consider the plant's setting. 

• Is the soil compacted,  loose, wet or dry;

• How much sunlight does the plant really get;

• Is the plant crowded? [Did you forget about thinning to the recommended spacing...]

• Has the weather been hot or cool?

• Are leaves or fruit touching the soil or other plants?

• If you are thinking that an insect or similar  pest is responsible, look on the underside of leaves and on stems for egg or spore clusters or  frass.  Snails (mullusks) may have left slime trails in their  retreat to a secure, remote daytime location.

• Finally, do you remember anything about  last year's garden problems?   Is what you are seeing  similar to anything that occured last year? Both abiotic and biotic problems tend to recur especially in small gardens.   

Be Your Own Plant Dr.

For gardener's who would like to minimize their reliance on the Internet and use a book to solve their plants' problems, I recommend "What's Wrong With My Plant (and how do I fix it?"   by David Deardorff and Kathryn Wadsworth (Timber Press, 2009).  The book served as one of the texts for my Master Gardener training program. The first half follows a decision tree format employing exceptionally  clear illustrations  -   you start with a symptom and then choose the next refining step from a choice of equally clear illustrations with accompanying text.

The second half of the  book discusses the diseases and disorders in detail as well as organic remedy options.  Deardorff is a plant pathologist at the U. Hawaii and serves as a consultant to the U. of Washington's Extension Service. The co-author is a professional photographer.  Both hardcover and paperback editions are available.


And remember:

"My green thumb came only as a result of the mistakes I made while learning 

to see things from the plant's point of view." - H. Fred Ale

What's in Your Garden Soil? - Nematodes

Nematode loa loa removed from eye.
Source: dated.org

I missed Halloween for this post; but given that it seems  horror movies are released year round, mentioning parasitic nematodes along with the beneficial ones seems okay to do. Most of us probably  have heard about diseases stemming from parasitic nematodes,  but hopefully have not suffered from ascariasis, trichinosis, hookworm or worse. we'll try  just to focus on what's in our garden's soil and not our guts...

Nematodes, named after their phylum, Nematoda, ["nema" means  "thread-like"] are unsegmented round worms that live in all the environments that other earthly lifeforms do.  They actually constitute the most numerous of animal lifeforms. In fact, for pratical purposes, nematodes are inseparable from other lifeforms... If you know what nematodes exist in a particular environment, you can predict what  other lifeforms will be also be found there.

According to the Wikipedia entry, about 25,000 species so far have been identified with probably tens of thousands more awaiting discovery.   They are typically described as being  just a "tube within a tube" with  a front and back end.  Their front ends are adopted for their feeding preferences. 'Herbaceous' types,  like  root feeders, insert long microstylets  into plant cells to syphon nourishment; fungal  feeders use shorter stylets to puncture cell walls; and  bacterial eaters have more recognizable mouth-like openings for collecting their lunches as they wiggle through  soil.  Most nematodes reproduce sexually, but a few are harmaphroditic; and many  are able to enter a dormant state to survive extreme environmental surprises like drought or extreme cold.

Cross section of typical  nematode.
Source: Biology Stack Exchange

Because nematodes closely co-exist with other lifeforms in their environments, their minescule wiggles are sufficient to meet their daily needs. Their greater travels depend upon outside factors such as wind, water or physical transport by some other agent -- animal, insect, garden tool or tractor tire for dispersal.

Soil nematodes are very small ranging in size between  1 mm and 50 ml; but some, like the parasitic ones that attack vertebrates,  can be large. One parasitic nematode that abides in the placenta of sperm whales   reaches 30+ feet!  

Minor carrot damage from root piecing nematodes.

Parasitic  nematodes can affect plants in several ways.  Some appear in foliar tissue (leaves); others burrow into roots or stems; while others just attach themselves externally to roots. Gardeners have probably encountered the effects of these latter pesty varieties on their cabbages and carrots. Small infestations of these "herbaceous" feeders cause carrots to respond with those little bumps, called 'root galls'.  Bigger infestations of this type of nematode (e.g. the NRK nematode - our local favorite) show up as "root knots" on cruciferous veggies like cabbage and broccoli, and they also can  cause serious crop damage to  legumes  like soy beans. Various root knot nematodes affect more than 2,000 agricultural  crops and ornamentals.

N.B. - Root knot nematodes also affect many common weeds such as lambsquarter, purslane, 

and dandelions -- Better keep weeding!

Severe root knot.

If you think that you have a root knot problem like the one pictured to the right, take a look at this visual assessment technique from Cornell Extension. You can probably use it as an initial guide for sizing up your  situation. Cornell's Plant Disease Diagnostic Clinic for a small fee will analyze soil samples for nematodes and other pathogens. There are also  commecial services that will analyze soil samples and identify what you've got.  Beneficial nematodes can be purchased to improve your soil if it turns out that you have a nematode deficiency or infestation.  Suppliers offer both  tailor made and  standard  mixes for particular crops and soils.

What Good Nematodes Do

Because nematodes occur naturally in the environment, their uses in pest control and sustaining soil health make them  important components in  organic farming practices.

Grasshopper demised by its parasetic nematode.
Photo: U. of Fl.

Nematodes in soil are particularly important  for protecting healthy young plants by controlling a lot of plant pests and pathogens. They also   increase soil fertility   by  making more nutrients available for plant use through their digestive processes. Among these is the ammonium cation (NH4+). Because ammonium is very soluble in water, it is easily taken up by plants - although too much of it, like all good things, is toxic. NH4+ is critical for plants. They convert it  into organic compounds like amino acids.  Animals, like us, and other creatures  depend on plants to supply us with these compounds.  Both plants and  us omnivores should be grateful for these beneficial nematodes. So, continue to tread lightly on your garden soil.

Although there are lots of potential nematode bad guys even in healthy soil, these are generally outnumbered by beneficial nematodes. Among the ranks of beneficial nematodes are the predatory   fellas that devour bacteria, fungi, protozoa along with other nematodes. Unfortunately, getting rid of an infestation of the bad dudes  using chemicals also  eleminates the good guys too. A balance of beneficial versus parasitic nematodes in healthy soil actually stimulates plant growth. Healthy plants simply  outgrow any nutrient challenge posed by low levels of parasite activity.  Finally, by their wiggling through  soil nematodes also promote soil fertility by redistributing both  good and bad bacteria and fungi.

What's a Normal Nematode Load in Soil? 

The US Dept. of Agriculture reports that a healthy census is around 100 nematodes in a teaspoon of dry garden soil. Given their microscopic size, this is a surprizingly low number.  But nematode populations can rapidly expand, e.g.  a rotten apple on the ground might contain 90,000+ nematodes while it still  vaguely resembles an apple.  Even this remains a low number compared with the  abounding nematode populations found in  sea beds that can reach 1,000,000 per square foot!

Good Gardening Practices 

Backyard gardeners can employ a number of techniques to minimize harmful nematodes. Among these are

Clean equipment and boots.
Source: Northville Dairy

• Using certified seeds and choosing nematode-resistant or tolerant varieties;

• Cleaning tools and equipment;

• Weeding as well as removal of infected stock;

• Rotating crops and allowing some areas to remain fallow during  growing seasons;

• Using cover crops and green manure along with compost both to keep up soil nutrient levels. 

Now stop worrying about what you might be walking on,  and remember to:

"...trust dirt. I don't trust diamonds and gold." - Eartha Kit

Vegetable Gardening Book Suggestions for the Holidays 

Sometimes I think my library is getting dated; and because it's nearing the gift giving season, I thought I would come up a list of relatively newer books about vegetable gardening that might be suitable for stuffing into  albeit very large holdiay stockings.

You will quickly notice that the titles in the below list are not spankingly brand new 2018 or 2019 books. Like any good book, they remain in print or readily available from used book dealers because they continue to  serve gardeners well. I compiled my list  from examining a number of  "best" book lists from various gardening sites that I trust, personal familiarity with some titles and the personal recommendations from gardener friends.  Most of the entries appeared on at least two lists, and a few titles appeared three or more times.

I did not use either Amazon or Barnes & Noble lists as sources although I did use these sites to view  sample pages of some titles.  The books are available from these sources, but if you do become motivated to give one or more to a friend, I  suggest that you also check used book sources such as abebooks.com, alibis.com or  bookfinder.com etc. for lower prices. Happy shopping...

• Brie Arthur - Foodscape Revolution: Finding a Better Way to Make Space for Food and Beauty in Your Garden. St Lynn's Press, 2017. 

• Susan Ashworth - Seed to Seed: Seed Saving and Growing Techniques for Vegetable Gardeners. 2nd ed. Seed Savers Exchange, 2002. [If you are unfamaliar with Seed Savers, find out about it now at seedsavers.org.]

• Mel Bartholomew - All New Square Foot Gardening: The Revolutionary Way to Grow More in Less Space. 2nd ed. Quarto Publishing Group, 2013. [Many a backyard gardener consider this to be their 'best' vegetable growing  bible. Actually, any edition will do.]

• Andrea Bellamy - Small Space Vegetable Gardens. Timber Press, 2014. [Don't have a yard or can't get to a community plot, then how about using a roof top, patio or windowsill - great ideas here.]

• Eliot Coleman -  Winter Harvest Handbook:  Year Round Vegetable Production Using Deep-Organic Techniques and Unheated Greenhouses. Chelsea Green Publishing, 2009. [n.b. Coleman  authored the classic, New Organic Grower (now in its 3rd edition). This one assumes you have a lot space for gardening.]

• Derek Fell - Vertical Gardening: Grow Up, Not Out for More Vegetables and Flowers in Much Less Space. Rodale Inc., 2011.

• Brad Halm & Craig McCrate - High Yield Vegetable Gardening: Grow More of What You Want in the Space You Have.  Storey Publishing, 2015.

• Toby Hemenway - Gaia's Garden: A Guide to Home Scale Permaculture. 2nd ed. Chelsea Green Publishing, 2009. [In case you are not familiar with the term, 'permaculture' is about establishing and using techniques that promote sustainable and self-sufficient agriculture.]

• Craig Le Houllier - Epic Tomatoes: How to Selet and Grow the Best Varieties of All Time. Storey Publishing, 2015. 

• Wendy Kiang-Spray - Chinese Kitchen Garden: Growing Techniques and Family Recipes from a Classic Cuisine. Timber Press, 2017. [This is specialized and (warning) includes recipes; but I like Chinese food and Timber Press is very selective in its offerings.  To learn a little more about the author and the cuisine, checkout her blog: greenishthumb.]

• Ron Kujawski and Jennifer Kujawski - Week-by-week Vegetable Gardener's Handbook. Storey Publishing, 2010. [Not on any list, but this is a personal recommendation. I reviewed it in February 2018, and now find myself referencing it regularly.]

• Bret Markham - Mini Farming: Self-sufficiency on 1/4 Acre. Skyhorse Publishing, 2010. [This might tempt you to buy that vacant lot next door...]

• Tara Nolan - Raised Bed Revolution: Build it, Fill it, Plant it - Gardening Anywhere. Cold Springs Press, 2016. [The author, a Canadian, founded Savvy Gardening that promotes innovative approaches to both ornamental and vegetable gardens.]

• The Organic Gardener's Handbook of Natural Pest and Disease Control: A Guide to Maintaining a Healthy Garden and Yard the Earth Friendly Way. Rodale Inc., 2009.

• Barbara Pleasant - Home Grown Pantry: A Gardener's Guide to Selecting the Best Varieties & Planting the Perfect Amounts For What You Want to Eat Year Round. Storey Publishing, 2017. [The author is a regular contributor to Mother Earth News and winner of three Golden Globe awards from the Garden Writers' Association.]

• Rodale's Ultimate Encyclopedia of Organic Gardening. Rodale Inc., 2009 ["Rodale's own  gardening bible has been a mainstay for organic vegetable growers since J. L. Rodale published the original in 1959.]

• Edward C. Smith - Vegetable Gardener's Bible. 2nd edition. Storey Publishing, 2009. [A Vermonter, Smith has been writing for 30+ years and gardening for more. He also has a "bible" on container growing published in 2011.]

• Jessica Walliser - Container Gardening Complete. Cool Springs Press, 2017. [The author is a regular contributor to Savvy Gardening, a women's owned company out of Canada covering  all aspects of gardening.]

And remember: 

"The more that you read, the more things you will know. The more things that you learn, the more places you'll go." - Dr. Seuss