Topping tobacco in the button stage (soon after the flower begins to appear) rather than later increases yield and body if suckers are controlled. When tobacco plants are not topped for three weeks after reaching the button stage, yields are reduced by 20 to 25 pounds per acre per day, or about 1 percent per acre per day when normal yields range from two thousand to 2,500 pounds per acre. In addition to improve yield and quality, early topping has other advantages:
- It usually allows topping to be completed before harvest begins, helping spread the workload away from the peak harvest period.
- It reduces the possibility of plants blowing over in a windstorm.
- It stimulates earlier root development, which increases fertilizer efficiency, drought tolerance, and alkaloid production.
- It helps to reduce buildup of certain insects because eggs and larvae are removed with the floral parts.
Sucker control is facilitated by managing tobacco in such a way as to reduce sucker pressure and maximizing the effectiveness of chemical applications. Using a reasonable nitrogen fertilizer rate and striving for a uniform crop are two of the most important things that tobacco producers can do to facilitate sucker control and management.
Proper Use of Contacts (Fatty Alcohols)
The purpose of contact fatty alcohol application is to provide sucker control between early toping and the time at which the upper leaves are large enough to be sprayed with flumetralin without causing leaf distortion.
You should make the first contact application as soon as 50 to 60 percent of the plants have visible button. A good general rule is to apply a contact solution that chemically tops five to ten percent of the small, late plants in a field. If no chemical topping occurs during the first application, the solution is too weak or application was too late. Timing of chemical application is important because neither contacts nor flumetralin will adequately control suckers long than one inch.
Coverage of leaf axils and stalk rundown are essential for contact applications. Contacts should be applied with 3 nozzles per row, at low pressure and with 50 gallons per acre delivery volume. The suggested ratio for the first application of C8-C10 contact alcohol products is two gallons in 48 gallons of water; this makes a four percent solution. A five percent solution is suggested for the second or third application; this is two and half gallons in 47.5 gallons of water.
Contacts are more effective if applied three to five days apart when humidity is low and leaf axils are fully exposed – that is, generally between 10 a.m. and 6 p.m. on sunny days, except when the plants are wilted and temperature exceed 90oF. Also, none of the products should be applied to plants that are wet with rain or heavy dew or that are severely stressed by drought. Rainfast period for contact alcohols is one hour unless stated different on the label of the contact you are applying.
Another major advantage of contact alcohols, especially where two or three applications are made, is that they shorten the period for the systemic chemical to control suckers after topping. Systemic chemicals containing only MH tend to “give out” six to seven weeks after application. When the harvest season lasts for 10 or more weeks, sucker regrowth often occurs. Flumetralin, another systemic-acting chemical, controls suckers longer than MH does, but its control is further extended when preceded by one or two applications of alcohol contact.
Proper Use of Flumetralin
Flumetralin should be applied like a contact solution but not until the plants are in the elongated button to early flower stage. The objective is to apply flumetralin so that it touches the small suckers like contact solutions do because, unlike MH, flumetralin does not move to sucker buds through the leaves.
Flumetralin must first wet the suckers like a fatty alcohol contact before it can stop cell division like a systemic. Flumetralin should be applied like a contact solution: only to the same rows to which the crop was planted. For example if you transplant 4 rows spray 4 rows.
Even though the flumetralin label allows for application of up to one gallon per acre, the general recommendation has been for application rates of two quarts per acre. Increasing flumetralin rates from two quarts per acre to three quarts or one gallon in a single mechanical application has not consistently improved sucker control, primarily because control is so dependent on coverage of all leaf axils, which is not improved by increasing flumetralin rates.
However, application of two quarts of flumetralin followed by one quart of flumetralin seven days later improves sucker control compared to three quarts of flumetralin applied in a single application. This would indicate that increasing rates of flumetralin above two quarts per acre is only advantageous if the flumetralin is applied in a split application.
It is likely that split applications reduce the number of missed leaf axils–the main cause of poor sucker control when MH is not used.
Like other sucker control products, flumetralin does not completely control sucker longer than one inch. Rainfall within two hours after application could reduce effectiveness of flumetralin, but reapplication will also increase the potential for soil residue carryover. Therefore, do not reapply if flumetralin wash off occurs.
MH
Unlike fatty alcohol contacts and flumetralin, MH is absorbed by leaves and moves within the plant to small sucker buds. Good absorption and systemic movement depend on having good crop growing conditions. Therefore, MH should never be applied on drought-stressed crops or on those wilted by too much rain, high temperatures, or both.
If soil moisture is adequate but afternoon temperatures will be high enough to cause partial wilting, MH should be applied only during the morning, starting when the leaves are just slightly wet with dew. Afternoon spraying generally is not suggested except on cool, cloudy days when soil moisture is good.
MH is absorbed more effectively by younger, upper leaves than by older, lower leaves. Therefore, MH should be applied to the upper third of the plant using the three-nozzles-per-row arrangement.
Most MH labels stipulate that it must not be applied before the upper leaves are eight inches long to reduce possible stunting, a discoloration called “bronzing,” or both. These abnormalities are sometimes observed when MH is applied on leaves longer than eight inches. Growth distortion of upper leaves treated with flumetralin also occurs, but less frequently than that associated with MH. Research suggests that the likelihood of discoloration and stunting from MH applications is greatly reduced when applications are delayed until upper leaves are 16 inches long.
MH residues can also be reduced when the interval between application and harvest is maximized. The MH label states that you should wait at least seven days between MH application and harvest, with the anticipation that rainfall during this period will wash off some residues. If tobacco is ready for MH application and harvest, make every attempt to harvest first, then apply MH. It will most likely be at least seven days before the crop will be ready for another harvest. This will ensure MH-free first primings.
Field Diseases
Black Shank. Black shank is caused by a soil-inhabiting fungus (Phytophthora nicotianae) that belongs to a group of the most destructive fungi that attack plants. These fungi thrive in high-moisture areas. The black shank fungus produces three types of spores, including a swimming spore that infects tobacco roots and sometimes infects stalk stems at leaf scars (where leaves fall off). Some leaf infection can be observed after rains that splash soil onto the leaves.
The symptoms of black shank are well known to tobacco growers. Once infection occurs, death usually follows quickly. In highly resistant varieties, the symptoms on the stalks are usually confined to near-ground level. When stalks are split, the pith often appears blackened and separated into discrete discs. Discing can occur because of other factors; likewise, not all plants suffering from this disease exhibit this symptom.
Brown spot. Brown spot is caused by an airborne fungus (Alternaria spp.). It may be considered an “opportunistic” disease-causing agent. It does not usually become a problem in varieties tolerant to this disease if good cultural practices are followed. However, during periods of extended rainfall late in the harvest season, it can become destructive. Brown spot is a disease of senescent (old) tissue.
Granville wilt. Granville wilt appears first as a wilting on one side of the plant. As the disease progresses, the entire plant wilts and dies. When plants survive they are usually stunted, and their leaves may be twisted and distorted. The stalk usually becomes dark, especially at the ground level. At this stage, Granville wilt may be easily confused with other diseases, such as black shank. A diagnostic characteristic of Granville wilt is the streaks that extend up the stalk just beneath the outer bark.
Relatively high soil temperatures and adequate to high moisture levels in soil favor Granville wilt bacteria. In fact, wet seasons greatly increase infection by these organisms. Infection may not be noticed immediately because wilting symptoms may not appear until plants undergo a moisture stress. Thus, it is not unusual to observe symptoms of Granville wilt several weeks after infection actually occurs.
Granville Wilt Management:
- Rotate with fescue, small grains, or soybeans. Control weeds.
- Use varieties with high levels of resistance.
- Destroy stalks and roots immediately after harvest.
- Avoid root wounding.
- Manage nematodes.
- Fumigate in the spring.
Target Spot. The fungus that causes target spot lives in many North Carolina soils. Saturated soils and leaf moisture favor sporulation of the fungus and germination of the spores into the tobacco leaves.
Target spot symptoms are quite similar to those of brown spot. With target spot, the centers of the lesions rapidly become very thin and papery and shatter if only slight pressure is applied. The concentric rings that
characterize brown spot lesions may look similar to those caused by target spot. Target spot may occur on leaves at any plant position and, where conditions favor the problem, may cause considerable destruction. Target spot, like brown spot, is favored by frequent rainfall and high humidity.
Removing the lower leaves and ensuring adequate nitrogen are recommended management tactics. Quadris is a local systemic product that can be used for target spot. Use Quadris at 6 to 12 fluid oz./acre. Eight fluid oz./acre has given consistently good results. Drop nozzles are highly recommended for Quadris application in the field to ensure uniform coverage of the foliage.
