“The way mites and thrips are managed is very different and too many growers waste insecticide because they are treating for the wrong critter,” he adds.

In seedling cotton, thrips damage tender leaves and terminal buds with their sharp mouthparts and feed on the escaping juices. Leaves may turn brown on the edges, develop a silvery color, or may become distorted and curl upward.

Light thrips infestations tend to delay plant growth and retard maturity. Once cotton plants are 4 to 6 weeks old, they usually outgrow thrips damage and begin to recover.

In most areas, plants recover and suffer no yield loss, if infestations remain light throughout the first few weeks after cotton emergence.

Heavy infestations may kill terminal buds or even entire plants. Damaged terminal buds result in abnormal branching patterns. 

If late infestation persists, plant maturity may be delayed with resulting yield loss. In some areas of northeast North Carolina and southeast Virginia, this is almost an annual occurrence.

In this area, often called ‘thrips central’, thrips over-winter as hibernating adults in sheltered areas, as larvae on plants, or as pupae in the soil.

The larvae usually feed for approximately 6 days before pupating in the soil. Approximately 4 days later, new adults emerge which soon feed and lay eggs.

Most thrips species complete five or more generations per year in the area.

Persistent heavy populations of thrips in the area, which is a heavy production area for both cotton and peanuts, has created a relatively new problem with tomato spotted wilt virus, which is vectored by thrips.

Managing tomato spotted wilt virus (TSWV) starts with the understanding of how thrips spread the virus. If an adult lands on a plant that is infected with TSWV, that insect cannot spread TSWV. The only way it can be spread it is when thrips feeds on an infected plant immediately after the insect hatches from an egg.

Kennedy stresses that only tobacco thrips and western flower thrips can transmit TSWV from one plant to another. Once the insect is infected, it can spread the disease from plant to plant for the rest of the pest’s life.

“What that means in practical terms, is that the grower doesn’t have to worry about TSWV being spread within a field, unless there is a reproducing population of western flower thrips or tobacco thrips in that field,”Kennedy says.

Tobacco thrips tend to move around from the field to border areas and they reproduce in either, seemingly with little preference of one over the other. Western flower thrips tend to stay in a field, especially if the crop is flowering.

Since TSWV can only be transmitted when emerging larvae feed on plants, the real threat to movement of the virus in a field comes from populations of western flower thrips that stay in a cotton field or a vegetable field and reproduce there.