Unfortunately, thrips have reared their ugly little heads again this year and have caused some considerable damage, particularly to carored peaches. I have had several reports of thrips causing severe “russetting” damage from early feeding and now were are getting into the stage for “silvering” type damage (see example below). With the severity and extent of the damage we have seen in certain places, I just wanted to alert everyone to this potential problem and provide some advice on how to mitigate it.
The key species of thrips found in southeastern peach orchards are the Western flower thrips. These thrips are small, slender, winged insects with amber or yellowish-brown to dark brown females that are approximately 1 mm long, and the males are smaller and light yellow. Thrips have rasping mouthparts that are used to pierce into plant tissues and ingest the sap. Western flower thrips populations begin to increase in abundance in orchards just prior to peach bloom and have up to 5 generations a year, with several different generations active in orchards at any given time. However, Western flower thrips are generally only a threat to peach production during bloom or just before harvest.
During bloom, the adults and larvae feed on flower parts, as well as developing fruitlets beneath the shuck which results in russeting or shallow brown scars (see image below).
As the fruit develops and begins to color prior to harvest, adults move from other host plants (usually weeds or grain crops) to the peach trees to feed on new leaves and ripening peach fruit. At high populations, thrips will feed on young, succulent leaves, causing the leaves to wrinkle and curl as they mature (see image below).
In addition, adults and larvae will feed on the cells of the fruit skin, which causes “silvering” of the fruit (see image below).
We generally haven’t seen a lot of russetting damage in the past, so it is definitely concerning to see as much as we have this year. Sadly, with the russetting damage, there is nothing we can do right now, but in the impacted blocks, it would be a good idea to monitor for thrips next spring during bloom. According UC IPM, in the previous impacted blocks, begin monitoring for thrips at bloom by examining blossoms from trees by tapping a shoot with five to ten blossoms against a sheet of paper. They note that first instar nymphs are white in color and often difficult to see, so be sure to check carefully. To effectively monitor the populations, check a minimum of 50 trees in each orchard for thrips. If 2 or more adult thrips are present or if any nymphs are found, a treatment is likely warranted. I generally do not recommend methomyl (e.g. Lannate) because of it’s toxicity against beneficial insects, but if you have had severe russetting this year and find thrips at bloom, it might be worth trying a Lannate LV (3 pt/acre) at petal fall to knock down their populations. However, additional chemical options are mentioned below.
Right now, we are primarily seeing the curling leaves and silvering of the fruit. Sadly, in general, there are not a lot of options to manage Western flower thrips in peaches. While we obviously cannot fix the damage that already occurred, by monitoring the fruit we can assess whether a chemical application is needed to stop further damage from taking place.
Visually inspect the fruit and count the number of adult thrips on 10 fruits per 5 sites in an orchard, particularly focusing on fruit from lower 1/3 of canopy. If there are 5 adult thrips per 50 fruits plus considerable silvering, then a chemical treatment may be needed.
With varieties that being picked and/or are going to be harvested soon, our best options for thrips management are going to be Delegate WG (7 oz/acre) or SpinTor 25C (8 fl oz/acre), which both have 1 day PHI for peaches and nectarines (7 days for plums). Another option would be Exirel (20.5 fl oz) which has a 3 day PHI.
With varieties that still have time before harvest, there are chemistries that can help suppress thrips populations, but also have longer PHI periods. Additional options include Assail 30SG (8 oz/acre) which has a PHI of 7 days, Transform (2.75 oz/acre) or Brigade WSB (32 oz/acre) which both have PHIs of 14 days. And if there is a variety that is a way off from being harvested, but there is a risk of mites and thrips, Agri-Mek SC (4.25 fl oz) has been shown to suppress thrips, but also has a PHI of 21 days. Please make sure to always read the label prior to making any application to check current rates and restrictions.
Thrips quickly and readily develop resistances to insecticides. If pressure from thrips becomes severe enough to warrant insecticide applications, it is important to rotate the classes, utilizing different Modes of Action.
That is a lot of information to throw at you all, so If there is anything I can help with or clarify, please let me know.
Good luck everyone! And here’s to a great rest of the season! (fingers crossed)
TL:DR
Thrips management options:
| Trade Name* | Rate/acre | PHI (days) |
| Delegate WG | 7 oz | 1 |
| SpinTor 25C | 8 fl oz | 1 |
| Exirel | 20.5 oz | 3 |
| Assail 30SG | 8 oz | 7 |
| Transform WG | 2.75 oz | 7 |
| Brigade WSB | 32 oz | 14 |
| Agri-Mek SC | 4.25 fl oz | 21 |
