Scouting Tobacco in North Carolina

Troubleshooting Tobacco

Tobacco is a valuable crop; thus any problem should be quickly identified and a solution determined. Accurate identification of tobacco problems involves at least five steps.

  1. Conduct an unbiased assessment of the field.
  2. Determine the pattern of plant symptoms in the field.
  3. Characterize plant injury symptoms.
  4. Note the crop growth stage.
  5. Obtain field history information.
It is important to know when the problem appeared, how fast the symptoms developed, if the symptoms are getting more severe, and if the symptoms appear to be spreading to other plants. Generally, diseases start in small areas and spread to other leaves, plants, or areas as the season progresses. Many insect problems appear throughout a field within a short period. Others may spread from localized spots. In either case, the problem or damage increases as insects grow or reproduce. Many chemical injuries appear almost at once. If a symptom appears almost overnight and is evident over a large portion of the field, it is almost always chemically related.

Unbiased Assessment
The biggest mistake one can make is to enter the field with a preconceived idea about the problem. It is important to enter the field with an open mind and let the crop indicate the cause of the problem. (See Table 1 for symptoms and damage patterns of common tobacco problems.)

It is also important to realize that an answer does not always result from the first visit. Usually the visit will eliminate all but one or two possible problems. Plant and soil analyses along with the cooperation of several specialists may be needed to determine the exact cause of the problem.

Table 1. Symptoms and Damage Patterns of Common Tobacco Problems
Symptoms Pattern Possible Cause
One to Four Weeks After Transplanting
Feeding scars, tunneling just below soil line Uneven stand, in patches or throughout Wireworms, Sod webworm, Whitefringed beetle
Plants cut off or girdled near soil surface, without necrosis Uneven stand, often worse near borders Cutworms
Plants girdled, necrotic; may have dark brown lesions near soil surface Uneven stand Soil-borne disease
Roots brown or black, plants stunted Uneven stands in streaks or patches Fertilizer salts injury from fertilizer applied before transplanting
Shanks of plants swollen and soft Uneven stand Fumigant injury
Circular yellow spots beginning on lower leaves that turn necrotic with blue-gray fungal growth on underside Localized in low or shaded areas of leaf Blue mold
Slow-growing plants with no visible lesions on stalk or roots Uneven stand Pretransplant incorporated herbicide injury
Stunted plants that wilt on hot, dry days, ofent resulting in firing of lower leaves; roots are swollen and galled Localized Root-knot nematode
Four to Eight Weeks After Transplanting
Stalks develop black lesions near soil line; root system is brown to black; wilting also occurs; pith is brown or black and may be separated into discs Localized Black shank
Wilting beginning first on one side of the plant; roots are brown to black; vascular area in pith is discolored Localized Granville wilt
Stunted growth with pale yellow leaves; lower leaves yellow first and tend to "fire up" Localized in sandy areas Nitrogen
Stunted growth with uniform yellowing over the plant; bud leaves yellow first; lower leaves do not "fire up" Localized in sandy areas Sulfur deficiency
Eight to Twelve Weeks After Transplanting
Stalks develop black lesions near soil surface; root system is brown to black; wilting occurs; pith is brown or black and may be separated into discs Localized Black shank
Wilting beginning on one side of the plant; roots are brown to black; vascular area in pith is discolored Localized Granville wilt
Leaf spots with concentric rings appearing first on older leaves; severity increases on plants with root injury; humid weather also increases severity Generalized Brown spot

Patterns in the Field
The first step in diagnosing a tobacco problem is to determine the pattern of symptoms in the field. Field patterns can be used to narrow the scope of potential problem causes by eliminating some possibilities and indicating others. Erratic stands, for example, are usually caused by insects, nematodes, or soil-borne diseases. The lack of a pattern is just as important as a distinctive pattern.



Figure 2. Cold injury is often seen between the lateral veins of tobacco leaves.


Cold injury, for example, leaves damage, which is usually seen 7 to 10 days after cold temperatures and is spread randomly through a field (Figure 2). This damage, which is often seen between the lateral veins of tobacco leaves, can be confused with atrazine injury. The symptoms are similar; however, chemical injuries normally occur in regular patterns that can be related to soil carryover, direct spraying, or drift (Figure 3).



Figure 3. Herbicide injury.

Streaks of dead or slow-growing plants down the row may indicate fertilizer salts injury caused by band application in the row before transplanting (Figure 5). Fertilizer salts injury may also occur when fertilizer is broadcast before transplanting, in which case damage will appear in irregular patches. Sometimes nutrient deficiencies may appear in alternate rows, which indicates equipment malfunctions, or in different areas of the field, which can be related to soil variability. Stunted plants in alternate rows may indicate sprayer overlap. If plants are injured by spray drift, the foliar symptoms will decrease in severity with increased distance from the drift source.



Figure 5. Injury caused by fertilizer salts.


Plant Symptoms
The symptoms seen on tobacco plants and the damage pattern in the field are important clues to be used in determining the cause of poor growth. Often the above-ground symptoms are related to root problems. For example, wilting and the death of leaves, usually beginning at the tips and extending to the base of the leaf, are symptoms of root problems. Plants to be examined for root problems should be dug rather than pulled from the soil. Many roots, particularly diseased or injured ones, may be left in the ground if a plant is pulled up. Diseased roots are dark brown or black, healthy roots white. Roots injured by fertilizer salts are similar in color to diseased roots (Figure 6). Root-knot nematodes cause a characteristic swelling, which is easily identified, on parts of the roots.



Figure 6. Damage to roots from fertilizer salts.


The vascular system should also be examined. This is done by splitting the stalk lengthwise with a knife. Healthy tissue will be white, whereas diseased tissue is dark colored or black. The whole plant should be examined for the presence of insects or mold. The leaves should be examined carefully.

Wilting is a symptom of diseases, such as black shank and Granville wilt, that attack both the vascular system and roots. The pith of a stalk cut lengthwise may appear black if the plant is infected with black shank. If the vascular region (just beneath the bark) is black, this may be a symptom of Granville wilt.

The outside of the stalk near the soil line should also be examined. Some organisms may girdle the stalk of young seedlings. Wireworms and other soil insects may attack the stalk just below the soil line. Occasionally, the base of young plants may be injured during pulling and transplanting; these symptoms are similar to those caused by soil diseases.

Holes in leaves may result from chewing insects but may also be caused by hail or wind damage or by chemical burn. Careful examination will reveal that holes in hail-injured leaves are actually tears. Leaves injured by chemicals may be necrotic (dead or burned), twisted, cupped, or curled. In general, chemical injuries and foliar diseases will produce a specific pattern of damage in the field. Many foliar diseases usually appear first as yellow spots and progress to dead areas within the leaf. The spots may also enlarge with time. Table 1 lists symptoms and damage patterns associated with many commonly seen tobacco problems.

Crop Growth Stage
The causes of plant injury differ during the growing season. For example, wireworms and cutworms attack recently transplanted tobacco, and the resulting injury occurs early in the season. Problems associated with poor root growth also occur during the first month of the season. In general, chemical injuries from soil carryover or misapplication also are seen early in the season. Chemical injuries from drift may occur any time. It may be of help in diagnosing problems to know the spraying schedules for the crops surrounding the tobacco field. Nutrient deficiencies usually occur after the first month.

Field History
For each field, all survey and scouting information should be combined into a field history. This means you must keep accurate records of what you find on each visit. These histories will help you build a long-range pest and crop management plan and see trends in pest populations.

Knowing the background of a field is often as important to the accurate diagnosis of a field problem as being able to recognize specific injury symptoms. A field history should include information about the crop planted previously as well as the practices employed in growing the present tobacco crop. Table 2 lists some of the important factors that should be included in a field history.

Table 2. Factors to Include in a Field History
Previous Crop(s) Tobacco Crop
Fertilizer used Transplanting date
Chemicals used Weather conditions
Liming Variety
Pest and agronomic problems encountered Fertilizer used
Chemicals used
Equipment used
When did the problem first appear?
Are the symptoms getting worse or better?


Tobacco Pest Management            Scouting for Weeds

Scouting Tobacco in North Carolina