Blueberry insect pest activity picks up with the warmer weather
Scouting this week indicates increased fruitworm and aphid activity.
With fields past petal fall and small fruit sizing, fruitworm management should be the focus of grower’s IPM programs for the next few weeks. Blueberry fields were scouted yesterday (June 6) in Van Buren and Ottawa counties, revealing fruitworm activity that indicates that growers with a history of these pests should be protecting berries from these insects.
Cherry fruitworm moths were caught at all of the farms we scouted and the flight is peaking at the farms we checked in Ottawa County and past its peak in the Van Buren County sites we scout. We expect the flight for cherry fruitworm to continue to decline at southern Michigan farms in the next 7 to 14 days. Cranberry fruitworm flight has picked up at all the sites we visit, and moths were caught at all those sites. Cherry fruitworm eggs were first observed at the Grand Junction farm last week (May 31) and we observed eggs at all the farms we monitored this week.
Guthion, Imidan, Asana, Danitol, Sevin and Assail are all rated as being excellent insecticide options for control of fruitworms. Lannate can provide high activity, but has shorter residual control. There have also been recent registrations of the reduced-risk insecticides Delegate, Rimon and Avaunt that are registered for fruitworm and provide good levels of control. These also will control other pests: Delegate is labeled for control of fruitworms, leafrollers and for suppression of gall midge, maggot, and thrips; Rimon for fruitworms, spanworm, leafrollers and maggot; and Avaunt for fruitworms and spanworm, with activity also expected on plum curculio.
For any insecticide applied for fruitworm control, maintaining good coverage of the clusters is important to get residue to the parts of the berry where fruitworms are found such as in the calyx cup where eggs are laid. Because the larvae move over such a small distance before they enter the berries, it is important to use sufficient water and to consider spray additives (spreader-stickers) that will help spread the material across the berry surface. This is especially important for insecticides that need to be eaten by larvae for activity such as B.t. and Intrepid.
We have compared the level of fruitworm control at three one- to nine-acre fields in four commercial blueberry farms in southwest Michigan (two in Ottawa and two in Van Buren counties) over the past few years. At each farm, three fields with a history of fruitworm infestation were compared that received one of three programs comprised of insecticide applications at bloom, petal fall, and 7 to 10 days after petal fall. The three programs were (rates are all per acre)
- A) Confirm at 16 oz, Guthion at 1.25 lb, Guthion at 1.25 lb,
- B) Confirm at 16 oz, Asana at 9.6 oz, Asana at 9.6 oz or Mustang Max at 4 oz, and
- C) Intrepid at 8 oz applied using the degree day model, Intrepid at 8 oz 10 to 14 days later, and Assail at 5.3 oz 7 to 10 days later
All three programs were very effective at protecting fruit from fruitworm damage. Single berry damage (indicative of cherry fruitworm damage or the early stages of cranberry fruitworm feeding) was lowest in Program C, but this was not significantly different between programs: A) 1.1 percent damaged berries, B) 0.7 percent damaged berries, and C) 0.5 percent damaged berries.
Similar results were seen for multiple berry damage, which is a sign of advanced cranberry fruitworm feeding. No multiple berry damage was found in any fields treated with the IPM program and very low levels of multiple berry damage were seen in the other programs. The percentage of berries with cranberry fruitworm damage was well below 1 percent in all fields and there was no significant difference among treatments.
We also have seen an increase in the number of blueberry aphids at the farms we scout. We observed single aphids and colonies with 5 to 10 individuals. Growers and scouts should continue checking fields for aphids, and with the high levels of rain this spring, there will be many vigorous young shoots for supporting aphid colonies. To scout for aphids, examine two young shoots near the crown on 10 bushes and record the number of shoots where aphids are found. Also record the number of shoots with parasitized aphids. Be sure to sample weekly from as wide an area in the field as possible to have a better chance of detecting whether aphids are present. Although natural enemies, such as parasitic wasps, lady beetles, lacewings and hover fly larvae, can keep this pest in check, aphids can transmit blueberry shoestring virus, so growers may want to consider using an insecticide to control aphids if there are blueberry varieties that are susceptible to shoestring on the farm.
A very low amount of feeding by leafrollers, much less than 1 percent of clusters with damage, was observed at the Grand Junction and West Olive farms. The number of these pests observed should diminish as growers apply insecticides to control fruitworms. Growers and scouts should continue to check fields for feeding damage by leafrollers during the next two weeks. To scout for these pests, examine 10 shoots on 10 bushes on the field border and 10 shoots on 10 bushes in the field interior. Look for leaf or flower clusters that have feeding holes or webbing in the cluster. Leafrollers are generally not economically important in Michigan and they are normally very well controlled by insecticide applications targeting fruitworms.
Spotted wing Drosophila
CFW = cherry fruitworm, CBFW = cranberry fruitworm, BBA = blueberry aphid, SWD = spotted wing Drosophila, BBM = blueberry maggot, JB = Japanese beetle
Dr Isaacs’s work is funded in part by MSU’s AgBioResearch.