Weekly Fruit Update - June 30, 2021

Photo: Minnesota SweeTango growers attend a (rainy!) field day at Ferguson's apple orchard on Saturday, June 26. Photo: Annie Klodd

 

Author: Annie Klodd, Extension Educator - Fruit and Vegetable Production

In this week's update: Japanese beetle and SWD, strawberries, raspberries, apples, grapes. Plus info on upcoming apple and grape events.

Japanese beetles trickling in

The Minnesota Japanese Beetle (JB) Trapping Network monitors Japanese beetles (JB) at 5 site across Minnesota. The team has increased the number of sites as the insect's geographic range has expanded.  

Densities of adult JB are highly variable across the state this week. Trap count numbers this week were highest in Rosemount and Chanhassen, relative to Forest Lake, Hastings, and Taylors Falls.

Source: FruitEdge (fruitedge.umn.edu/japanese-beetle/japanese-beetle-trapping)

 

Small JB populations do not necessarily mean it is time to start spraying. Mature plantings can tolerate more Japanese beetle feeding than newly established plants.

As of yet, there is no official economic threshold for when to begin spraying for JB, but UMN researchers continue to conduct the on-farm research needed before thresholds can be established. University of Wisconsin-Madison entomology specialist Dr. Christelle Guedot reports that even 30% defoliation on grapevines has not led to yield reduction in recent trials. For more on current JB research, read Managing Japanese Beetle and Variety Preferences in Apple.

Do not set out traps for JB control. Traps have been well-documented to attract more beetles than they kill, making the problem worse. Commercial growers mainly rely on insecticides for this pest. Exclusion netting is quite effective, but not widely adopted.

For management options, read Japanese Beetles: Choices for Conventional and Organic Insecticides.

Spotted wing Drosophila (SWD) counts low, rising

The Minnesota SWD Trapping Network run by the UMN Integrated Pest Management Program checks SWD traps weekly at several Minnesota fruit farms. So far in 2021, trap counts are low at most monitoring sites but are rising. Trap count numbers are significantly higher at the Houston Co. site (see chart below).

 

You can track the weekly trap counts, updated on Tuesdays or Wednesdays, at this link.

Photo: A Scentry trap for monitoring spotted wing Drosophila

Strawberries

June-bearing strawberry season comes to a close this week for many farms. At the same time, the day-neutral strawberry season is ramping up.

Good work to everyone this strawberry U-pick season. It was a very short season, averaging about 10 days. But between keeping everything watered and managing strong numbers of U-pick customers, it was a busy couple of weeks.

As one customer of Rod's Berry Farm said, "The berries were small this year, but tasted good! They were adorable and perfectly shaped. I ate several pounds." 

Renovation: The best time to start renovation is immediately after completing the harvest season. I confirmed with Dr. Jim Luby, long-time UMN strawberry breeder, that growers should go ahead with renovation now even though it is a couple weeks earlier than normal. 

For step-by-step guidance on renovation, please see Follow These Steps for Strawberry Renovation from July, 2020.

Good question! A grower last week asked a great question about the use of 2,4-D to control weeds in strawberries at the beginning of renovation. While it may seem counterintuitive, several formulations of 2,4-D are labeled for over-the-row application in strawberries during renovation only. His question was "I am reading my 2,4-D label and I don't see that it's labeled for strawberries. Should I apply it during renovation?"

• Be sure you are using one of the 2,4-D products that is labeled for use in strawberries. Not all of them are.
• The reason 2,4-D can be applied after harvest without injuring strawberry plants is because the plants are not actively growing after harvest. 2,4-D targets actively growing plants.
  
• Once you mow and new leaves begin forming, it is too late to use this chemical. 
• Use the 2,4-D amine or choline salt formulations, and only if the label includes strawberries. Do not use 2,4-D ester or it could damage the plants. The grower I spoke with had read the label on his 2,4-D and noticed that it was a 2,4-D ester - thankfully, he caught this before applying it. 
• For more information on 2,4-D choline salt and what product names to purchase, read this article from Michigan State University.
• Obviously, no one is required to use 2,4-D, especially if you are aiming for more organic practices. Mowing and hand-weeding are used to help control weeds in strawberries during renovation as well. The most important thing is to remove weeds before they go to seed.
  

Now that day-neutral strawberries have begun producing fruit, they should be harvested about every 2 days on average. This helps prevent SWD infestation and ensures quality fruit. Maintain regular fertigation with nitrogen, and include other nutrients only if a foliar test report indicates a need. If growing tabletop strawberries (which several Minnesota and Wisconsin farms have started since 2019), test the pH of your fertigation water; citric acid can be used to amend the pH if needed. Strawberries grow best in a soil or media pH between 6.0-6.5. Feel free to contact Extension with questions (kloddann@umn.edu). 

Raspberries

Summer-bearing raspberries are in-season in many MN locations. Since SWD populations are still low, the need to spray insecticides in minimal at this time. 

Some raspberry growers, including myself, have noticed ripe fruit on fall-bearing (primocane) raspberries. This is several weeks early. Dr. Bernadine Strik at Washington State University pointed out to me that these ripe berries are not growing from true primocanes; they are technically on lateral shoots growing from the stubs of last year's cut floricanes. That explains it!

Apples

Codling moth and apple maggot trap counts remained low at the Preston and White Bear Lake orchard sites this week. Both insects were found at a density of just 0-1 per trap. Since the first generation of codling moth is currently active, growers may find higher counts in traps on their own farms; therefore, on-site monitoring is important for making spray decisions. At Saturday's SweeTango field day hosted by Ferguson's Orchard, owner Tom described how their orchard uses mating disruption to reduce codling moth populations.

Disease pressure on apples has remained low for several weeks now due to dry weather. Many orchards have not sprayed fungicides in 3-4 weeks because low leaf wetting hours have not necessitated it. Powdery mildew infection may occur with recent rainfall and humidity, so keep an eye out for that. 

Information on Japanese beetles can be found at the beginning of this article.

Interested in cider apples or selling to cideries? Attend our on-farm field day at Milk & Honey Ciders next Friday, July 9th from 1-4pm. Registration is required so that we can bring the right number of cider sampling supplies and handouts. Register here: https://forms.gle/7K5je3Hi4SHfq6bj7

Grapes

Attend next week's Cold Climate Grape Webinar for a discussion of: drought/heat impacts on grapes, current pest concerns, how to decide when to spray what. Plus we will be doing something fun this time: 

Send us your photos of vineyard problems, and we will diagnose them. If it's something we can't diagnose from a photo, we will talk about that, too. Photos of weird leaves, plants, and clusters are welcome. 

Register for the webinar here: https://extension.umn.edu/event/cold-climate-grapes-mid-season

What to do this week: As mentioned above, make a decision about if and when to spray for Japanese beetles and other insect pests, based on economic benefit and density of pest infestation. Weigh the cost of the application against the impact the pest has on grapevine yield and/or health. Often, small infestations are insignificant and not worth the cost or environmental impact of the spray. For instance, Minnesota growers very rarely need to spray for grape berry moth; growers should not spray for grape berry moth unless at least 5-10% of the clusters are infested (source). This is extremely uncommon in Minnesota and Wisconsin.

Additionally, use the weather forecast to help time your next fungicide application. The dry weather this season has allowed growers to space out applications, as disease pressure has been minimal. We did receive some much-needed rain last week. Rainfall and humidity at this time in the season can stimulate powdery mildew infection, so keep an eye out for this and apply a fungicide effective on powdery mildew. The most critical time for management is pre-bloom to 4 weeks post-bloom. We will discuss this more in next week's webinar (link).