West central Michigan small fruit regional report – August 12, 2014

Spotted wing Drosophila continues to show up in all berry crops, but in low numbers compared to 2013 populations. Although no fruit infestations have been reported in blueberries, growers should stay alert and apply insecticides only if flies are present.

We had another week of excellent weather conditions with some scattered rain showers, but almost no impediments to continue with the harvest of blueberries, raspberries and strawberries. In general, daily temperatures remained without change with only a slight increase in the average daily maximum temperature in relationship to the previous week. Maximum daily temperatures during the past seven days averaged 82 degrees Fahrenheit, and minimum temperatures averaged 58 F. There was little precipitation in the area with a minimum accumulation of approximately 0.80 inches of rain – a necessary supplement to crops with additional irrigation.

Blueberry harvest has continued without major problems, although there is a lack of labor for hand-picking. This has resulted in an increase in the amount of fields that are machine-harvested.

Regarding phytosanitary problems, these are limited to a few cases of fruit rot infections, mainly Alternaria, which required fungicide treatment. However, there is some evidence of a potential outbreak of leaf rust due to the prevailing weather conditions. There are a few options for leaf rust control at this time. Michigan State University Extension plant pathology specialist Annemiek Schilder recommends Sonata, which has a zero-day pre-harvest interval, or Abound.

Raspberries and day-neutral strawberries are also being harvested. Fruit rots are the main concern in both berries, but spotted wing Drosophila (SWD) have started showing up on harvested berries across west central Michigan. Careful monitoring and timely applications of control measures are critical to prevent a buildup of SWD population in those fields.

Currently, our SWD monitoring network indicates that the flies remain at low densities in all berry crops, but mainly in blueberries. So far, the maximum number of flies trapped in a single trap in a field that showed high infestations in 2013 has been 11 individuals. However, 60-70 percent of the trapped individuals were males. That decrease in the size of the observed SWD populations has made it easy for growers to control without using large amount of insecticides.

In general, most growers are having effective SWD control and no fruit infestations have been reported. Early detection combined with a good selection of appropriate insecticides and low SWD populations have substantially reduced the economic impact of SWD during this season.

One key element in the control of SWD is monitoring. Checking the SWD traps as often as possible during harvest and giving them the proper maintenance is critical. If you are using the TRECE lure for SWD monitoring and are feeling that the lure is not working properly, try installing a check trap baited with the mix of brewer yeast and sugar. However, it might be possible that the “lack of attraction” of the TRECE lure could be the result of a low population of flies at the target site. If no flies are trapped, check the fruit for SWD larvae infestations to verify whether or not your monitoring devises are failing.

At this time, it is important to remain vigilant and follow our recommended protocol for dealing with this pest:

  • Monitor with traps baited with a yeast and sugar solution or the TRECE commercial lure.
  • Apply insecticides as soon as flies are detected in the traps.
  • Sample the fruit in search of worms before and after any insecticide application using a salt or sugar solution to evaluate the effectiveness of your SWD control program.

Remember to make sure you take into consideration weather conditions at the time of the application and during the expected protection period. Check the weather and if the daily temperatures or rainy conditions may affect the durability of the insecticide you applied, repeat the application with a different insecticide. For insecticides and doses, see “SWD Management Recommendations for Michigan Blueberry.”

Contact your nearest MSU Extension county office or Carlos Garcia at 616-260-0671 or garcias4@msu.edu for assistance.

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