Losses due to insects were greater in 2008 than what they were in 2007 (from about 1.5% in 2007 to about 4.6% in 2008). Insect pressure from populations of tobacco budworm and hornworm caused some problems during the season. Other insects causing some problems in 2008 were mainly Japanese beetles and aphids. Growers sprayed an average of 6 times per acre for insect control in 2008.
Thrips are responsible for the transmission of tomato spotted wilt virus (TSWV) in tobacco. Thrips are very tiny insects, barely visible with the naked eye. Although there are many different kinds of thrips found on tobacco, only three of those species are capable of transmitting the disease. One of those, Frankliniella fusca (the tobacco thrips), is the most common thrips found on tobacco.
Transmission of the disease seems to be most common during a fairly short period of time early in the season. Insecticide applications to control the thrips seem to provide very little help in controlling the disease. By the time that the insecticide kills the thrips, they have already transmitted the disease. The application of Admire or Platinum insecticides prior to transplanting does provide some suppression of the disease. However, the suppression of TSWV by Admire and Platinum does not appear to be directly related to thrips control.
Host-plant resistance work is being conducted by Clemson University researchers. In the future, this may provide the best control strategy for this disease.
For several years now, we have been seeing fewer green aphids and more red aphids, with the latter being more difficult to control. Some taxonomic work suggested that the aphid that we have had on tobacco for the past few decades was not the green peach aphid, Myzus persicae. A new species, the tobacco aphid (Myzus nicotianae), was described. We have now come full circle. Other taxonomists have looked at the situation and come to the conclusion that these are both the same species, the green peach aphid. The green peach aphid does come in both a red and green color form, with the red generally being more difficult to control.
Aphids secrete a sugary substance known as honeydew. Honeydew is sticky, and a perfect site for the development of sooty mold. Once honeydew and sooty mold are present on the leaves, they are nearly impossible to get off. As aphids molt, they leave their cast skins behind. I have received numerous calls from growers (by the way of the county agents) who complained of getting poor control of aphids with Orthene. When I examined the situation, what I found was tobacco leaves covered with cast skins, honeydew, and sooty mold. There were no live aphids. Orthene will kill the aphids, but it will not (nor will anything else) get rid of the cast skins and damage.
Tobacco that has been damaged by aphids will carry that damage all the way to the warehouse floor. Leaves will be thinner, black, and stuck together. The result is a mess. The tobacco is of very poor quality and, justifiably, brings a lower price. The way to avoid aphid damage to your tobacco is to control the aphids before they build up to such high numbers.
The red form of the green peach aphid is more difficult to control than the green form. In the past, research has shown that, of materials labeled for use against aphids on tobacco, only Orthene and Thiodan did an adequate job of control. That situation has been complicated by the fact that the tobacco companies do not want Thiodan residues in the tobacco. Some have said that tobacco will be spot-tested for Thiodan residues on the market floors and, if certain markets are exhibiting Thiodan residues, they will shift their buying to other markets. We no longer include Thiodan in our recommendations. In the Spring of 1996, Admire received its first label for aphid control on tobacco. More recently, Platinum has been labeled on tobacco. Both Admire and Platinum will give excellent control of the red and green forms of the green peach aphid.
For more information on tobacco insect control in the plant bed, greenhouse,and field, read the 2009 Growers' Guide. For more information about insect management, contact Francis P. F. Reay-Jones, 843-662-3526, ext. 208, firstname.lastname@example.org.