| VISIBLE ABOVE GROUND - | ROOT SYMPTOMS - |
| Stunting | Galls or Swellings |
| Chlorosis | Stubby Roots |
| Mid-day Wilting | Lesions or Dark Spots |
| Leaf Drop | Stunting |
| Small Fruit | "Dirty Roots" |
| Yellowing | |
| Curling and Twisting of Leaves and Stems | |
| Patches of Poor Growth in Field | |
| Lack of Response to Treatment For Other Problems | |
| Premature Maturity | |
| Delayed Maturity | |
| Reduced Yield | |
| "Unthriftiness" | |
This table contains above and below ground damage symptoms and signs resulting from nematode feeding and root penetration.
Persons familiar with crop damage will note that many of these symptoms and signs are not specific for nematodes but could also result from other causes, such as poor nutrition or irrigation, or other pathogens.
The point of this table then, is to illustrate that there are no specific symptoms or signs that can be relied on to diagnose a nematode problem.
Having made this point, clicking on the highlighted words in the table will lead you to pictures of plant damage in which we know the cause was nematodes.
Viewing these symptoms and signs in the field should raise suspicion of a nematode problem which can then be diagnosed through sampling.
Some of the more indicative symptoms for nematodes include mid-day wilting, patches of poor growth, and lack of response to treatment for other problems.
Because nematode feeding and movement is disruptive of plant vascular tissue, it is often difficult for plants to take up enough water on a hot day to keep from wilting. When water stress becomes less severe in the evenings, plants are able to catch up and look perfectly healthy the following morning.
Frequently, nematodes are not evenly distributed across a field resulting in patches of poor growth interspersed with healthy looking plants.
Because nematode damage resembles that caused by other problems, if efforts have been made to assure optimum levels of irrigation and fertilization and other pathogens and insects have been considered, it's a good time to sample for nematodes.
"Unthriftiness" is a symptom common to many nematology texts. I haven't been able to find it in a dictionary. Let me know if you do. It appears to be a word coined by nematologists to indicate the crop is not doing well for no particular reason.
"Dirty Roots" is a condition referring to citrus nematode. Soil sticks to a gelatinous substance which is released by citrus nematode during egg laying and is not easily removed when the roots are washed with water.
A reduction in root growth is commonly caused by ectoparasitic nematodes, sometimes without any other recognizable symptoms. However, in many cases, roots appear short, stubby, and malformed. The feeding on root tips often causes swelling and cessation of elongating growth. Feeding on root tips of the taproot may stop elongation of the taproot or cause the formation of a multiple tap or storage root that is forked. Feeding of many nematodes at points where lateral roots emerge results in lateral- and feeder-root stunting or destruction. (From: McKenry, M.V. and P. A. Roberts. 1985. Phytonematology Study Guide. University of California, Division of Agriculture and Natural Resources. Publication 4045.)
Necrotic lesions can be induced by root lesion nematodes (Pratylenchus) on the roots of many host plants. These lesions are visible as a darkening or browning of roots at sites of invasion and underlying feeding sites within the root cortex. In later stages, more general necrosis and root rot may occur so that plants eventually have poorly developed, often brown colored root systems. The lesioned cortical tissue will often slough off, and the portion of the root distal to the lesion will die. Although lesion symptoms are indicative of root lesion nematode damage, the root lesion nematode does not produce lesions on some hosts whereas on other plants similar lesions can be induced by other disease organisms and soil factors. (From: McKenry, M.V. and P. A. Roberts. 1985. Phytonematology Study Guide. University of California, Division of Agriculture and Natural Resources. Publication 4045.)
An integral part of the root knot nematode symptom is the presence of root rotting and wilting organisms such as Rhizoctonia and Pythium, which cause rotting and the complete breakdown of galled tissue. This is particularly common in the soft fleshy roots of many field and vegetable crops - for example, tomatoes, cucurbit crops (melons, squash, cucumbers, etc.), sugarbeets, lettuce, and okra. Plants whose root systems have more secondary thickening and appear woody seem to be less susceptible to secondary rotting infection; examples are cotton roots and roots of many perennial tree and vine crops. (From: McKenry, M.V. and P. A. Roberts. 1985. Phytonematology Study Guide. University of California, Division of Agriculture and Natural Resources. Publication 4045.)
