- Apples:
- Monitoring and managing apple maggot
- Grapes:
- Herbicide drift on grapes
- Honeyberries:
- Honeyberry field day recap
Apples:
Monitoring and managing apple maggot (less common in commercial orchards)
Image: An apple maggot trap is red like a ripened fruit, which attracts apple maggot adult flies, which can be enhanced with a lure that gives off fruity scents. Traps are used to monitor apple maggot adult flies, but are not effective at controlling them by themselves.
Apple maggot is a pest (Rhagoletis pomonella) is a pest that is less common in commercial orchard, but still relevant for many, and can lead to fruit distortion and fruit drop in severe cases when left unaddressed.
The USA National Phenology Network usually maintains an apple maggot forecasting tool on its website displaying data for the current day and a six-day forecast. However, growers should be aware the current forecast stopped updating on June 5th of this year and is not accurate at this time.
The tool is based solely on degree day (DD) calculations. The key lists important milestones for first generation apple maggot flight, which is usually an issue for home growers and orchards with minimal pest management programs. For example, at around 774-899 DD accumulations, adults can be expected to emerge in seven days or less, and emergence and activity is expected to happen around 900-2000 DD.
At this time, the Cornell NEWA program connected to the UMN Horticulture Research Center (HRC; 1292 DD as of 07/09/25) weather station indicates the first adults have emerged and are potentially active within the HRC.
More on trapping and monitoring:
If you didn’t set up a trap this year, it may still be helpful to install one now to continue to monitor apple maggot activity. Apple maggot can be trapped with yellow cards (less specific), but more effectively using round red balls, which is attractive to apple maggots, specifically. It requires an adhesive to help catch insect pests.
Apple maggots can be identified by the white spot on their thorax and white stripes, or banding on their wings. They’re about ¼ inch long, which is smaller than a typical house fly.
A lure that mimics ripening fruit can additionally be added to round red balls to more effectively attract apple maggot. These traps are available from commercial Integrated Pest Management (IPM) suppliers like Great Lakes IPM, but can also be found on online marketplaces or even some garden centers.
Insecticides for apple maggot can be applied 7 to 10 days after the first trap catch (biofix date). To learn more about pesticide management for apple maggot, refer to the Midwest Fruit Pest Management guide section, “Apple third and summer covers- insect pests” starting on page 38.
Grapes
Herbicide drift on grapes
Images: Different herbicides lead to a range of symptoms in grapes including the fanning displayed on the left and shoe-stringing— a condition with the appearance of fabric puckering, or a tightened cupped look as seen on the right photo (left photo credited to a Minnesota grower from Morrison County and right photo from a grower located in Washington County).
The complications of off-site drift
Grapes might be the canary in the coal mine when it comes to their sensitivity to herbicide drift, as they show more dramatic symptoms than other crops.
Experiencing drift—whether it originates from within or outside of a vineyard—can be frustrating, challenging, and even devastating for severe situations.
It often takes a communal approach to ensuring good herbicide practices in surrounding areas to prevent drift from entering vineyards. An online resource like DriftWatch can provide some help in putting vineyards on the map. Open communication with neighboring farms and highway departments can help improve transparency around spray applications taking place outside of the vineyard. We recognize that these conversations can be challenging and may not always fall within what’s realistic or appropriate in every situation.
Growers who have detected drift in Minnesota always have the option to immediately report their findings to the Minnesota Department of Agriculture (MDA) to open an investigation, which can help inform the MDA of the greater problem and assist in litigation.
While useful, this process has limitations and may not resolve all aspects of the herbicide drift problem. If you are interested in learning more about filing a drift complaint to the MDA, refer to their web page, “Pesticide drift complaint process and timeline.”
Additional steps to prevent herbicide drift for new vineyards and vineyard blocks, include selecting growing sites that are not adjacent to row crop fields, or planting a buffer strip of trees on vineyard edges with neighboring row crop fields.
On-site drift (misapplication)
To prevent injury from on-site herbicide applications, be careful about which herbicides you apply at any given time of the year, along with grapevine ages, and the weather condition present when spraying.
Certain herbicides should only be applied in vineyard blocks with mature grapevines, as they can injure younger grapevines with less woody growth (see herbicide infographic in next section). Some herbicides are systemic, whereas other herbicides are more local and can actually be used for managing grapevine suckers— the shoots that emerge from the grapevine base. To learn more about ground and weed management for grape production, view Growing grapes in Minnesota: Chapter 10.
Identifying herbicide drift damage
Herbicide symptoms can vary depending on the herbicide involved. Additionally, the amount, concentration, droplet form (i.e., particle vs vapor), and weather conditions at the time of drift can relate to the severity of damage.
Growth regulator herbicides (Auxin):
Some herbicides are formulated using auxin (plant growth regulator; PGR) as an active ingredient. This includes products like 2,4-D and dicamba, as well as picloram, triclopyr, and clopyralid. Auxin based herbicides often cause drift damage near agricultural fields where it is used for row crop production.
Volatilization can be an issue for growth regulator herbicides like dicamba and 2,4-D. A more recent update to dicamba occurred in February of 2024 when three major dicamba formulations are no longer registered for use in over-the-top soybean production.
This includes XtendiMax® (EPA Reg. No. 264-1210), Engenia® (EPA Reg. No. 7969-472), and Tavium® (EPA Reg. No. 100-1623). These dicamba products remain registered for other uses, including corn, small grains, pastures, and turf. In Minnesota, however, dicamba use of any kind is restricted after specified dates in June, based on the Minnesota growing region.
Dicamba 2025 update (Minnesota Department of Agriculture)
2,4-D is also used in agriculture for 2,4-D tolerant crops, which can lead to issues with drift. Just like dicamba, it has multiple formulations, some of which are more likely to volatilize than others. The table below lists 2-4D symptoms, which can lead to vine death in severe cases.
2,4-D Herbicide (Minnesota Department of Agriculture)
ALS inhibitors:
Inhibition of acetolactate synthase (ALS) is a different mode of action in herbicides trisulfuron-methyl, imazapyr, and chlorsulfuron. Grapes are moderately sensitive to ALS inhibitors, but symptoms are typically less severe than auxin herbicide damage.
EPSP synthase inhibitors (Glyphosate):
Glyphosate is a well-known herbicide that can cause injury in grapes and works by inhibiting EPSP synthase, an enzyme that plays a key role in creating plant proteins and other biochemicals.
Glyphosate is registered for use in vineyards, but can still cause on-site drift with misuse. Applying the product with a weed wick or shield can help prevent issues. In general, glyphosate drift symptoms are less severe and less systemic than symptoms caused by auxin-based herbicides.
While symptoms can vary within different herbicide categories, some trends exist, which can be referenced in the chart below.
Table: Herbicide drift symptoms for three major herbicide categories.
*Symptoms referenced from UC IPM’s herbicide injury symptom tool.
Drift symptom vocabulary:
Chlorosis
A pale or yellow leaf color due to a lack of chlorophyll.
Epinasty
When leaves have a downward bending appearance due to the upper leaf growing faster than the bottom side.
Leaf feathering
Abnormal growth on leaf edges that cause a feathered appearance on leaf margins.
Leaf strapping
An unusual, stretched-look to a leaf, relative to its width.
Leaf stacking
When leaves growth unusually close to a stem due to shortened internodes, making the foliage look compressed.
Mottled chlorosis
Parts of a leaf appear chlorotic while other parts look normal.
Shoe-stringing
Distorted leaf appearance that looks both elongated and cupped, almost like the fabric puckering that can happen when a thread’s tension is too tight within a piece of fabric.
Additional resources
University of California IPM’s Herbicide symptoms search engine
Preventing herbicide drift and injury to grapes (Oregon State Extension)
UMN Herbicide infographic
The University of Minnesota Extension Fruit Program presented a new infographic that categorizes various herbicides based on them being a pre- vs post-emergent herbicide, vine age, and whether the vines are bearing fruit.
This document is currently available for download using the following link: Herbicide options for vineyards.
*This table was created from information sourced from the Midwest Fruit Pest Management Guide.
Honeyberries
Honeyberry field day recap
Check out this week’s article covering the first Upper Midwest Honeyberry Academy. This article goes through an introduction to honeyberries, or haskap, and describes a number of events and speakers who presented throughout the day.
Article: First Upper Midwest Honeyberry Academy hosted in Stillwater, MN
Thank you to our farm and ag professional partners for contributions to the UMN Fruit Update series. Unless otherwise credited, photos were taken by Madeline Wimmer or sourced from the UMN Extension system.
This article may be shared for educational purposes with attribution to the University of Minnesota Extension. For other uses, please contact UMN Extension for permission.
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