Thrips in Peanuts and Their Impact on Tomato Spotted Wilt Virus (TSWV)

There have been a lot of questions recently about thrips control in peanuts.  In general, thrips will not hurt peanut yields except in EXTREME situations.  Peanut seedlings are relatively vigorous compared to most of the crops grown in Mississippi. Foliar insecticide applications, though rarely needed, should be based on plant injury rather than thrips numbers. 

In relation to other crops, peanuts are more similar to soybeans in terms in their tolerance to thrips injury than they are to cotton.  Cotton seedling growth is relatively slow and low numbers of thrips can cause severe injury in cotton.  In contrast, soybean seedling growth is more vigorous than cotton and more thrips are needed to cause similar levels of injury to what would be seen with a few thrips in cotton.

Similarly, peanut seedlings are more vigorous than soybean seedlings in terms of growth rate. As such, even more thrips are needed in peanuts to cause similar levels of injury to what would be observed in soybean.

The bottom line is that peanuts are very tolerant of thrips injury and in most situations will outgrow thrips injury pretty fast without an impact on yield. Because of that, foliar insecticide applications are rarely needed to control thrips in peanuts.

The biggest question has been about thrips control and tomato spotted wilt virus.  It is true that thrips vector TSWV in peanuts and a lot of other crops. However, there is no relationship between foliar thrips control and TSWV. If anything, research from the University of Georgia has shown that foliar insecticide applications can increase the incidence of TSWV. The reason for this is that some insecticides are irritants and cause the thrips to move from plant to plant more, thus spreading the virus more rapidly in sprayed peanuts. 

 Basically, you cannot spray your way out of TSWV!

Integrated Management of TSWV

If you have already planted, it is too late to implement a full-scale TSWV management plan.  TSWV management starts before the season and integrates multiple strategies.  Variety selection is the most important factor for TSWV management. Fortunately, most of the varieties that are available and planted in Mississippi have good tolerance to TSWV. 

Impact of Variety 

The table below is from the Georgia Peanut Rx program.  The numbers basically reflect the level of risk to the diseases listed. So the higher the number, the greater the risk of having the particular disease.  You will notice that all of those varieties we plant in Mississippi have 10 TSWV points. This means that they all have good resistance to TSWV and we should be in good shape from that standpoint.

 Table 1.  Peanut varieties (Source The University of Georgia).

Impact of Planting Date

Another important factor is planting date.  Peanuts planted earlier than May 1 tend to have higher levels of TSWV than peanuts planted during May.  The table below is similar to the previous table and shows the points for TSWV. Basically, peanuts planted in May have a lower risk of TSWV than peanuts planted in April. These dates are based on Georgia’s growing conditions and may vary some in Mississippi.

 Table 2.  Impact of planting date on the severity of TSWV (Source, The University of Georgia).

Thrips Management and TSWV

 The other important factor is selection of an at-planting insecticide.  As mentioned earlier, the occurrence and severity of TSWV is not correlated with thrips management and all thrips management practices are not created equal in terms of managing TSWV.  The at-planting options are listed below in Table 3.  All of these options are fairly equal in terms of thrips management, but there are some differences in management of TSWV. 

For instance, Admire Pro sprayed in furrow at the time of planting provides good thrips control, but is not a great option for TSWV management.  The caption below is in the notes section of the Admire Pro label and you can see that this particular insecticide can actually increase the incidence of TSWV.  You can click on it to get a larger view.

In contrast, research from the University of Georgia showed that Phorate (Thimet 20G) is the only at-planting insecticide that will effectively reduce the incidence of TSWV. Even with Phorate, the reduction in the incidence of TSWV is only low to moderate.

 Table 3.  Some at-planting insecticides options for peanuts.

Conclusions

In conclusion, the interactions between peanuts, thrips, TSWV, and the environment are very complex. In general, thrips management does not lead to a reduction in TSWV. Management of this disease, like other viruses, relies on an integrated approach.  Similarly, there is no fungicide or other chemical that can be sprayed to minimize the impact of TSWV.  Fortunately, the varieties that we are planting in Mississippi have good resistance and tolerance to TSWV and that is probably the most important component of TSWV management.

 A very good resource about peanut production and where we got a lot of this information is from the University of Georgia Peanut website:

  http://www.ugapeanuts.com/

There are multiple tools available for thrips management ranging from at-planting insecticides to foliar sprays.  Keep in mind that all of the options available are very good for thrips control, but may impact other pests. Some of these insecticides can actually increase the severity of TSWV. Another concern is that most of these, especially the foliar sprays will eliminate natural enemies and can flare spider mites, a much more serious situation to have to deal with in the future.

 If you have any questions or concerns, feel free to contact any of us at any time.