The proper management of
pests can improve tobacco quality and yield while reducing costs. This
guide is designed to help scouts and growers learn how to check for pests
and to know when treatment is economically justified. No pesticide recommendations
are included. Refer to the latest edition of the North Carolina Agricultural
Chemicals Manual or contact your county Agricultural Extension agent for
1 Tobacco Pest Management
What is Integrated Pest Management (IPM), and how can it help me produce
a profitable tobacco crop? This is a logical question asked by growers
when Integrated Pest Management is discussed. Integrated Pest Management
is a systematic way of controlling pests that combines tried and true methods
with new technology. The objectives of Integrated Pest Management
are to consider all appropriate methods of lowering pest levels (rather
than relying solely on chemicals), to use pesticides only according to
need, and to help produce crops more profitably.
Most growers realize that pests and poor growth can lower crop yield and quality, thus reducing profits. Less clear to many growers, but just as important, is that profits may also be lost when money is spent unnecessarily to control pests. If they wish to avoid unnecessary losses, growers must know not only the pest level in each of their fields but also the level, or economic threshold, at which the cost of the damage a pest is likely to do outweighs that of controlling the pest.
Integrated Pest Management is designed to help growers protect their crops at the lowest possible cost. A successful IPM program is composed of three elements.
1 . The crop must be checked, or scouted, regularly and systematically
2. The grower must be aware that pests must reach a certain level, the economic threshold, before control measures are justified economically.
3. Pest control decisions should be based upon scouting results and economic thresholds.
Field scouting is designed to detect the presence and concentration
of pests. This procedure is not casual or spontaneous. To scout
tobacco properly requires checking fields on a routine schedule using predetermined
methods. The information gathered while scouting may be used to help
make immediate pest control decisions. Scouting observations may
also become part of the field history, which can be used to make long-term
cultural decisions (like crop rotation plans). A tobacco scouting
calendar appears on the inside front cover.
An important aspect of scouting is the accurate identification of pests. Lumping insects into the general category of worms or identifying weeds only as grasses is a mistake. Knowing precisely which insect, weed, or disease is in a field is important. When control decisions are made, this information allows the grower to design a specific treatment plan instead of wasting money on a "shotgun" approach. Identifying diseases and weeds will also help when planning rotations and selecting varieties.
Avoid the temptation to make pest control decisions for several fields based only on information from one or two fields. Pest levels can vary greatly from one field to another, even though the fields appear similar.
Each field should be checked closely, or scouted, once a week. On each of these scouting trips, the grower should take samples, or stop at predetermined locations in the field and examine plants. The chart tells how many stops should be made, or samples taken, per field and how many plants should be examined per sample.
When stopping to take a sample, look first for any pests that might jump or fly off the plant (for example, flea beetles). Look for pests on both sides of the leaves of the five plants to be examined at each stop. Most pests will be found in the top half of the plant, but don't ignore the lower half. Do not look for a particular pest; take note of all pests found on a plant. Once you have finished checking the fiveplant sample, look around the area and make note of any problems.
Occasionally a field should be checked again in less than a week. For example, if a high number of small hornworms (less than 1 inch long) are found, but the field does not contain enough large hornworms to be at threshold, then it should be scouted again in two or three days. Similarly, a second scouting trip within a week is called for if aphids are found on a large number of plants, but the aphid colonies are just below the size at which the plants could be counted as infested.
There are several points to remember when scouting tobacco:
1. Before entering a field, look at its shape and determine an overall sampling pattern to cover the whole field. Once in a field, the spots where samples are taken must be selected randomly. Devise a routine to identify the exact spot at which the next stop will be made. Decide, for example, that once you get to the general area of the next sample you will take the sample two rows over from your present position and 10 plants down. Take a sample in that spot unless there is a skip in the row. In that case, take a sample at least two rows over from where you would have stopped had there not been a skip in the row.
2. Do not use the same pattern or enter the field at the same location
each week. It is very easy to fall into the habit of entering the field
in the same place each week, perhaps because there is a convenient place
to park nearby. Develop three or four patterns and rotate their use (Figure
3. Do not sample within four rows or 20 feet of the field edge. Do, however, make general observations along field edges as some problems can begin in this area.
4. Do not wait for a spot with obvious damage to begin sampling or skip a spot because it has obvious damage. Decide where to stop beforehand and take a sample of whatever is found at that location.
5. When walking a field, watch for dying or stunted plants. If any are observed, try to identify the reason. If the cause is not readily apparent, dig up a plant (including roots) and take it to the county Extension agent for diagnosis.
6. On each field visit, it is always useful to record some general comments
on field conditions, pest levels, agronomic problems, etc. Note localized
problems that may not have shown up in any of the samples. Always be alert
for agronomic or unexplained problems. Contact the county Extension agent
for help with problems that are difficult to diagnose.
|Field Size (acres)||Number of Stops, Plant To Examine/Stop|
|Less than 3||8 stops - 5 plants/stop|
|3 to 8||10 stops - 5 plants/stop|
|More than 8||Add 2 stops for each additional 4 acres or divide the field into 2 or more smaller fields. More samples may be taken if desired, which may be helpful in borderline cases. Examine 5 plants/stop.|
The number of pests or level of crop damage at which it pays to spend
money on a pesticide treatment is the economic threshold for a pest. Most
tobacco growers already do a good job of watching their crop and monitoring
the activities of pests. When pests are found, however, some growers have
trouble deciding whether a pesticide treatment is justified. This is where
thresholds can help. Some growers do not realize that the first sign of
pests in tobacco is not necessarily the proper time to consider control.
One might think that if pests are present they must be damaging the crop or interfering with its growth, thus causing a loss. Actually, pests can sometimes build to relatively large numbers before it pays to control them. For example, undamaged leaves of a tobacco plant may grow larger or the plant may add weight to compensate for some insect damage. Also, the crop may simply out compete a low level of weeds. Treating for a pest that will not reduce the quality or yield of the crop is a waste of money.
Another point to consider is that natural control agents are almost always working against an increase in pest levels. In other words, the existence of a pest does not guarantee the pest will ever reach damaging levels. There is no point in spending money to control a pest that may never build to damaging levels. Waiting to see if there will be enough pests to warrant treating is one of the ways Integrated Pest Management works to save growers money.
Keep in mind that although the thresholds given in this manual have worked very well, they were developed as guidelines for average conditions. In unusual situations, such as during periods of drought stress or when multiple pests are present, lower thresholds should be used.
Pesticide Selection and Application
Once a pest exceeds the economic threshold, the grower must determine
the best and least expensive way to prevent unacceptable losses. If a pesticide
treatment is needed, I the pesticide and its rate and method of application
must be customized to the pest. This is probably the surest way to save
money. High pesticide rates are not needed if the correct pesticide is
chosen and the method of application delivers the needed amount of chemical
to the pest. To apply pesticides properly, sprayer pressure and volume
must be correct; the right nozzle type, arrangement, and number must be
used; and the sprayer must be accurately calibrated.
Specific pesticide recommendations are not included in this guide. When deciding on a pesticide, talk to your local Extension agent and consult the North Carolina Agricultural Chemicals Manual or Tobacco Information before talking to your chemical supplier.