Insecticides for control of blueberry maggot

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Adult emergence of the blueberry maggot has already begun over much of the blueberry production region of Michigan. For most blueberry growers, who either have resident populations in their fields or grow in proximity to abandoned or wild blueberry plants, the focus for this point on through harvest is to protect their fruit from infestation. Control of blueberry maggot has been achieved for many years using broad spectrum insecticides. These kill the adult fly on contact and prevent the insect surviving to the point of being able to lay eggs into the fruit. Guthion is highly active against blueberry maggot with long residual activity and has a seven day pre-harvest interval. The organophosphates Malathion and Imidan are also effective, with shorter pre-harvest intervals and potential for use closer to harvest. Carbamates such as Sevin and Lannate and the pyrethroids Asana, Mustang Max and Danitol are moderately active on adult fruit flies. As a general rule, our trials in fruit crops against maggot flies using two-week spray schedules have shown lower activity from the pyrethroid chemical class than from the organophosphates. Their performance would be expected to be higher in fields with fewer days between applications.

There are several new insecticide products that include blueberry maggot on their labels. These include the neonicotinoids Provado and Assail that are also active on Japanese beetle and aphids. Our small plot trials of these products have shown that they are effective for protection of fruit from maggot infestation. Additionally, in large-scale trials over four years in Michigan blueberry farms we found no blueberry maggot infestation in fields treated with Provado during July and early August. The spinosyn-containing compounds SpinTor (non-organic formulation), Entrust (organic formulation), and Delegate (BBM suppression) are labeled for blueberry maggot control, but require ingestion by adult flies to be active.

In field trials with high pest pressure and two-week application intervals, their performance has been rated as good (see table). Performance would be expected to be higher in fields with lower pressure and with less time between applications, and because these products are sensitive to being washed off, reapplication would be needed after rain or overhead irrigation. These spinosyn-containing products are active on flies and moth larvae (worms), but cannot be relied upon for control of aphids or beetles.

GF120 NF Fruit Fly Bait (spinosad) is registered for control of the blueberry maggot and is listed by the Organic Materials Review Institute (OMRI) for use in organic production. Because the primary route of entry of the insecticide into the insect is through ingestion, applying this product during the fruit fly pre-oviposition period is important for optimal performance. GF120 must be applied with specialized equipment, and is designed for low-volume application by air or by ground. Field efficacy data are encouraging for this product, but we have limited experience with this novel formulation in large-scale trials in Michigan and it is not active on Japanese beetle or aphids that might occur at the same time.

Surround WP is an alternative and organically-approved kaolin clay product for fruit fly control. The activity of Surround for fruit fly control is based on creating a protective barrier between the plant and the pest that 1) reduces host recognition of the pest, and 2) prevents adult oviposition (i.e.; egg laying). Because it is not toxic to adult flies like conventional insecticides, complete coverage of the plant is critical. Multiple applications are typically needed to attain initial coverage of the bush with the kaolin, and further sprays may be necessary afterwards to maintain coverage after wash-off from rain or excessive wind. Field trials indicate that when adequate coverage is maintained, excellent fruit protection can be achieved. However, the white residue on the plant makes this unsuitable for fruit destined for the fresh market, particularly because the residue in the calyx cup of the fruit is so challenging to remove.

Blueberry maggot fly populations are generally distributed unevenly through blueberry plantings. Monitoring for blueberry maggot across your farm can help identify hot spots where this pest requires control. By monitoring edge and interior traps for this pest, growers can also understand whether there is only a border infestation and pressure from the surrounding habitat that can be managed using border applications.

Compound trade name Chemical class Optimal spray timing for blueberry maggot Residual activity Effectiveness rating**
Guthion, Imidan Organophosphates Within 7 days of the first fly being captured 14+ days E
Malathion Organophosphate Within 7 days of the first fly being captured 5-7 days G
Lannate, Sevin Carbamates Within 7 days of the first fly being captured 5-7 days G
Asana, Danitol, Mustang Max Pyrethroid Within 7 days of the first fly being captured 7-10 days G
SpinTor, Entrust*, Delegate, GF120 NF* Spinosyns Immediately after the first fly has been captured 7-10 days F-G
Provado, Assail Neonicotinoid Within 7 days of the first fly being captured 10-14 days G-E
Surround WP* Particle FilmProtectant Multiple applications before fly emergence As long as thorough coverage of the canopy is maintained G

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