After several years of declining productivity and market uncertainties, some Michigan growers are taking action to turn their business around to improve farm profitability and maintain employment. One action already having an impact in west central Michigan is the removal and replanting of old, diseased and blueberry stem gall wasp infested fields (see photo). Although this action has been in many growers’ mind for a long time, only a few took this drastic measure in the past two years. Increased expenses for insect and disease management combined with a decrease in profitability is making it very difficult to justify maintaining and operating those unproductive fields. In 2019, grower’s expenses per acre averaged $206 for spotted wing Drosophila management alone and $254 for disease management. However, growers with blueberry stem gall wasp infested fields had to add another $100 to manage this pest, according to “Blueberry IPM End of Season Survey” from Garcia et al. in 2020.

Michigan’s low productivity is also the result of a large percentage of old blueberry fields with many fields more than 50 years old. In addition, these fields are low-density plantations (less than 1,400 plants per acre) and are planted with old varieties that in many cases are virus and nematode infested. Dagger nematodes are commonly found in blueberry fields and as indicated by Fred Warner from Michigan State University Plant & Pest Diagnostics, they are vectors of tobacco ringspot (TRSV), the causal agent of necrotic ringspot, and tomato ringspot virus (ToRSV) in blueberries. These viruses can be very harmful to the plant’s health and cause significant yield losses over time. These plantings are also very heavily infested with the blueberry stem gall wasp. This is especially important for fields planted with Jersey, a mid-season variety planted in 5,800 acres across Michigan making up 27% of the 21,700 acres planted in Michigan, according to the Michigan Fruit Inventory of 2018. An additional 6% is planted with Rubel, an old variety with limited use in the bakery and food industry.

Under these circumstances, average yields are low in comparison with the most productive fields in other regions of the USA and abroad. In 2019, Michigan’s blueberry yield averaged only 4,200 pounds per acre compared to over 15,000 pounds per acre in areas like Washington and Oregon, according to USHBC, 2019. These significant yield differences impact Michigan’s ability to compete in the market. This difference is highlighted with data from the 2016 USA harvest season where the total acreage harvested was 92,800. Michigan’s harvested area was 20,300 acres which constituted 22% of all harvested area. However, the production was only 19% of the total volume produced within the USA.

In comparison, Washington harvested 13,400 acres (19% of the total USA harvested acreage) but produced 20% of the 593,610,000 pounds produced in the USA, according to the USDA Non-citrus Fruit and Nuts Survey, 2017. More yield per acre reduces production costs for 1 pound of blueberries and increases farm profitability. Thus, in the light of market uncertainties and extensive damage from the blueberry stem gall wasp and blueberry shoestring virus, it is perfectly appropriate to remove and replant old, unproductive and damaged fields.

Removing and replanting blueberry fields at a time when blueberry profitability is declining is difficult. However, in 2019, the USDA Farms Services Agency (FSA) expanded the Tree Assistance Program (TAP) to offset the cost of the removal and replanting of blueberries in Michigan. Growers need to take advantage of this cost-sharing program offered to blueberry growers by the USDA FSA. This program pays for up to 60% of the removal/replanting of blueberry stem gall wasp infested fields.

For those interested in removing/replanting undesirable fields, follow these basic guidelines to make a successful transition to a high technology production system.

First, renovation is not advised at this time, especially if the fields is infected with shoestring virus and a high infestation of blueberry stem gall wasp is present. The new growth coming from the crown still will be shoestring infected and the gall wasp will start attacking the new growth.

Second, removal and shredding or complete elimination of old plant residues including roots is necessary to start anew especially if the field is heavily virus infected or gall wasp infested.

Third, disk and turnover the soil to expose and reduce insects and nematodes that might be present in the soil. It may also help to bury deep in the soil blueberry gall infested plant residues.

Fourth, take soil samples to analyze nematodes, nutrients and pH in the laboratory. For instructions on where to send soil samples for nutrient and pH analysis please visit the MSU Soil and Plant Nutrient Laboratory website, and for nematode samples please visit the MSU Plant & Pest Diagnostic website.

Fifth, take this opportunity to level the field, correct or install a new irrigation system and adjust the soil pH and incorporate required amendments.

Sixth, leave the field fallow for one year or plant a cover crop such as Rapeseed ‘Dwarf Essex’, oilseed radishes or grasses to reduce the presence of nematodes and other undesirable pest problems. It is also important at this time to practice proper weed management as many weeds can serve as hosts to nematodes and diseases.

Seventh, select the variety. Based on your own experience and on some partial results of experimental trials at MSU, select varieties that have demonstrated some level of resistance to blueberry stem gall wasp and fruit rots, especially Anthracnose.

In 2017, MSU’s Rufus Isaacs evaluated the susceptibility of commercially available cultivars to blueberry stem gall wasp damage for several years. Based on his varietal evaluation plots at the MSU Trevor Nichols Research Center in Fennville, Michigan, he classified those varieties as:

• Highly susceptible: Jersey and Liberty (27% and 3% of Michigan’s planted surface)
• Resistant: Bluecrop and Elliott (19% and 26% of the Michigan’s planted surface). Aurora, new released variety, is also resistant but in Michigan it is planted in less than 1% of the planted surface, according to Patrick Edger.

Although this is not a complete recommendation for variety selection, these varieties are the ones tested for blueberry stem gall wasp susceptibility by MSU until now. There is a series of highly productive new varieties developed by local plant breeders, MBG Marketing and international companies like Fall Creek. However, before selecting some of their new varieties, communicate with growers that already are experimenting with the new materials. We have seen some of these new varieties planted in west central Michigan already showing diverse degrees of susceptibility to the blueberry stem gall wasp.

If you have questions regarding blueberry stem gall wasp susceptibility of varieties you are planning to use for replanting, do not hesitate to ask the MSU blueberry plant breeder expert, Patrick Edger (edgerpat@msu.edu) for advice. You may also call your local MSU Extension office for information and advice.