Mid-season management of grape berry moth

Spray after the July 4 weekend to protect against the second generation of grape berry moth.

Grape berry moth damage on fruit
Controlling berry moth infestation in July can maintain berry quality and yield. Photo by Rufus Isaacs, MSU Entomology.

Background

Prevention of mid-season infestation by berry moth is important for reducing issues at harvest-time. Accurate timing of sprays is essential for effective control. Controlling generation two (July) and three (August) is key to minimizing problems at harvest and reducing the cluster rots that can be associated with berry moth-infested clusters.

Grape berry moth can be a challenging pest to manage in vineyards during the mid-season. This is partly due to their extended egglaying activity and the need for timing sprays accurately, as well as the challenge of effectively penetrating the dense canopy in order to achieve adequate cluster coverage. This article will discuss three key factors for mid-season berry moth control: timing, insecticide selection and coverage.

2020 timing predictions

We have been tracking development of wild grape (Vitis riparia) across Michigan for the last several weeks, and we have now recorded wild grape bloom in all major grape growing regions. These dates are used as the starting point for the Michigan State University Enviroweather grape berry moth growing degree day (GDD) model. It is best to use wild grape bloom dates from your own farm, but if you don’t have that you can use the dates in Table 1 below as a guide. You will need this date for the biofix to run the model and determine when the next (second) and late-season (third) generations of grape berry moth are likely to begin laying eggs in your area.

From the conditions in 2020, we estimate that egglaying of this pest for the second generation will start on or just after the July 4 weekend in southwest Michigan. Please check the model for your own site with your own wild grape bloom date to be sure.

Predicted 2020 timing of the start for grape berry moth egglaying and egg hatch of larvae. For the following week, sprays targeting eggs can be started just after the July 4 holiday in southwest Michigan. Other regions have not yet reached enough growing degree days (GDD) and are not predicted until after July 6.

County (weather station)

Wild grape bloom

Predicted start
of generation two egglaying (810 GDD47)

Predicted start
of generation two larvae (910 GDD47)

Berrien (SWMREC)

June 2

July 4

After July 6

Van Buren (Lawton)

June 4

July 6

After July 6

Allegan (Fennville)

June 5

After July 6

After July 6

Ottawa (Holland)

June 11

After July 6

After July 6

Grand Traverse (Old Mission)

June 12

After July 6

After July 6

Product selection

For insecticides with activity on grape berry moth eggs such as insect growth regulators and diamides (Intrepid, Intrepid Edge, Altacor), applications should be made starting at 810 GDD (base 47 degrees Fahrenheit), and later in the season at 1,620 GDD for generation three. Intrepid (12 ounces per acre) or Intrepid Edge (12 ounces per acre) applied at this timing provide long-lasting control of grape berry moth eggs and larvae, giving two to three weeks of protection. Altacor (4.5 ounces per acre) has a wider range of activity and provides two weeks protection while also controlling Japanese beetles. These products are relatively resistant to high heat too, making them a good choice for the predicted weather conditions.

For insecticides that target larvae, waiting until the predicted egg-hatch at about 910 GDD47 (usually four to five days later) is advised, so the insecticides are able to control the young larvae when they hatch and try to get into the berries. For this timing, broad-spectrum insecticides such as Altacor (4.5 ounces per acre), Delegate (5 ounces per acre) and Verdepryn (11 ounces per acre) can also be used since they have activity against young larvae. Imidan (2 pounds per acre) is also effective against grape berry moth but should be applied in water that is pH 5-5.5 for maximum activity. There are also multiple biologically based insecticides that can reduce grape berry moth infestation. These include Grandevo (3 pounds per acre), Venerate (6 pounds per acre), Spear-Lep (2 pounds per acre) and products containing B.t. such as DiPel and Javelin (1.5 pounds per acre).  

There are many pyrethroid-containing insecticides registered on grapes for controlling this pest. They have high activity but relatively short residual control. For most of these insecticides, their duration of control is reduced by high temperatures and ultraviolet. With the predicted weather for the next few weeks, pyrethroids are unlikely to provide a week of good control, so this should be taken into account when considering the options. Products with UV blockers may last a little longer, however the clusters are usually in the shade already but won’t protect against the high temperatures. Within the pyrethroids, bifenthrin is unusual in being relatively unaffected by high heat conditions, so products such as Brigade, Bifenture and Brigadier that contain bifenthrin as the active ingredient would be a good options for growers considering a pyrethroid insecticide to control grape berry moth during the upcoming hot conditions.

If you manage a vineyard that had significant damage last year, or where larval damage has been widespread already this spring, it is likely you are facing high grape berry moth pressure again this season. In these situations, a cover spray applied two weeks after the 810/910 GDD timing later July is recommended to maintain protection before the third generation of grape berry moth in August.

Coverage

Getting the most out of the treatments in July requires using enough water volume to make sure the clusters are well covered. Using a spreader-sticker will help ensure that the tiny spaces within the canopy are covered. One spray applied with excellent coverage on all rows will be more effective than two partial applications that give berry moth places to hide. It is also important to focus the nozzles and the applications onto the clusters. Spray going into the air is not helping you control this pest, so adapt the fans, airflow and nozzles to ensure excellent cluster coverage for any applications targeting this pest. 

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