Nov 8, 2022
Michigan blueberry growers absorb latest tips

Production strategies were in focus at Michigan State University’s (MSU) first annual Blueberry Field Day in August at the Trevor Nichols Research Center near Fennville, Michigan.

The educational sessions included a presentation by MSU small fruit educator Carlos Garcia on major weather factors affecting pesticide use. Garcia said high temperatures and low relative humidity will cause pesticide droplets to evaporate quickly, drastically reducing their volume before reaching the target.

click to enlarge

“This may reduce the amount of product deposited on the insect habit, which will, in turn, reduce the amount of pesticide deposited and that’s needed for an effective pest control,” Garcia said. “It may also create pesticide drift that will be lost in the environment.”

Daily temperatures during the application affect the persistence of the insecticide on the target surface, he said. Insecticides are negatively affected by high temperatures greater than 85˚ F, he said.

Environmental relative humidity at the time of application affects the volume of the spray deposited on the target. He said low relative humidity reduces droplet size and the amount of spray deposited on the target. High humidity increases the survival rate of small insecticide droplets reaching the target site, which positively affects the spray volume and pesticide efficacy.

Wind velocity also “affects the deposition of insecticide on the target site and increases the potential for losing a portion of the application volume as drift.”

Ana Heck, an MSU apiculture Extension educator, explained how she is part of an effort to develop and deliver programming and education for small scale beekeepers, growers and pesticide applicators. Heck discussed program updates, colony health resources and examples from the MSU Extension Apiaries.

In-field presentations

Field day participants moved to nearby blueberry fields for presentations that included reviews of irrigation approaches, spotted wing drosophila (SWD) strategies, samba wasp trials for biocontrol of SWD and soil health requirements, among others.

Sushila Chaudhari, assistant professor in MSU’s Department of Horticulture, addressed weed control in blueberry fields. She reported on results of a trial gauging the performance of Florpyrauxifen-benzyl, a relatively new active ingredient that belongs to WSSA (Weed Science Society of America) Group 4 or HRAC (Herbicide Resistance Action Committee) Group O. Florpyrauxifen-benzyl is a synthetic auxin which kills susceptible plants by causing disruption of growth processes.

Florpyrauxifen-benzyl (Loyant, Corteva Agriscience) provides adequate control of red sorrel and horseweed in blueberry fields, according to a 2021 trial conducted by Chaudhari. Two sequential applications and a later-season application caused higher injury as compared to an early-season application, she said. Similar trials were conducted this year.

Florpyrauxifen-benzyl is a post-emergent herbicide that shows activity in pigweeds, horseweed/marestail, fleabean, lambsquarters, sowthistle, prickly lettuce, horse nettle, field bindweed and sheperspurse, and some grasses and sedges.

It is currently labeled for selective post-emergence grass, sedge and broadleaf weed control in rice in the states of Arkansas, Florida, Louisiana, Mississippi, Missouri, South Carolina, Tennessee and Texas.

“It’s a new product, not registered at this time in blueberry,” Chaudhari said. “We are collecting the data to see if it can be used in blueberries or not. It’s registered in rice, but not in any specialty crops.”

Chaudhari led Michigan’s work that is in the second year of the trial.

“It’s being done through the IR-4 Project,” she said. “The trial is being conducted at five different locations throughout the U.S. – one here, one in New Jersey, North Carolina, Oregon and California.”

The crop protection industry focuses their efforts on major crops, leaving specialty crop growers with fewer tools for effectively managing pests. The IR-4 Project develops data necessary for the registration of safe and effective pest management solutions with the Environmental Protection Agency. 

“(Florpyrauxifen-benzyl) does have good activity for several of the broadleaf weeds that are problematic in our specialty crops,” Chaudhari said. “That’s why we were interested to see if this crop could be registered for managing weeds.”

Researchers are studying how safe the product is on the crop, and its ability to control weeds without affecting the plantings. The product is exempt from minimum residue limits due to its limited toxicity.

“We just need to conduct only efficacy research and its impact on the crop,” she said. “The decision is going to be made on all of the data being collected in the five locations. We want to see what is a good timing and rate for this application, and do we need to use a shielded (spray) boom because we don’t want to conduct direct application of the herbicide to the blueberry bushes, to avoid injury.”

Researchers conducted two application timings in Bluecrop, one in June and one in July. The June date was selected to be after the bloom.

“It has been seen previously that if you apply this auxin product when the blueberries are blooming it can cause damage and yield reduction,” she said.

Two rates were applied, 16 ounces per acre and 32 ounces per acre.

“At the high rate, we have seen some injury, especially when applied without using any boom,” Chaudhari said. “Injury symptoms appeared mainly on new shoots as shoot and leaf curling, and leaves showing red color. The injury was seen mainly in the new shoots that were coming.

“So, 16 ounces is a good rate,” she said. “The late application is causing more injury. It does have a good activity on horse nettle, and that is one of the big weeds in our blueberries. Maybe every grower will not want to use this, but if we have it on the list those who have the highest level of horse nettle would benefit most. I also see the activity on poison ivy, but that was only one plant.”

Attacking fruit rots

 Timothy Miles is assistant professor-Extension specialist for diseases of blueberries, grapes, hops and other berry crops in MSU’s Department of Plant, Soil and Microbial Sciences.

Click to enlarge

He said fungicide resistance is a significant challenge for blueberry growers. Alternaria fruit rot is widely considered the most common and severe postharvest rot of blueberry, although it can be seen in the field on overripe fruit. Anthracnose (ripe rot) is a serious preharvest and postharvest disease. Botrytis fruit rot is typically a minor disease but can become severe. Other fruit rots are less common. Losses result from unmarketable fruit.

“We work on diseases that are actively managed within a single growing season,” Miles said. “In blueberries, these are mostly mummy berries, blossom blights – anything that will kill or blight the blossom like botrytis or anything that will kill a blossom.

“Then I work on fruit rots, which can occur before bloom all the way to harvest,” Miles said,

There are steps to take before planting; viruses are a problem in blueberries, and getting control of the plants is important, he said. MSU has a diagnostic clinic to test for different viruses.

“That can help with clean plant material if people want to test it,” he said.

Miles’ lab also is looking at “mystery diseases we haven’t been able to quite figure out. Stem blights tend to be one of those. That’s basically a bush die-back.”

Researchers have a recent grant from the Michigan Blueberry Commission (MBC) to look at some of these die-back issues.

“We’re finding it’s not going to be a simple as we thought,” he said. “There are probably 10 or so players you can isolate on a dying blueberry bush.”

 MSU also is involved in a partnership with the MBC and the diagnostic clinic that can reimburse for blueberry samples across the state.

“It tripled, at least, the number of blueberry samples we get in on an annual basis,” Miles said. “It’s been great for me because it allows me to find new problems and things like that.”

Miles said the clinic addresses more than diseases.

“There are entomologists there. There is an herbicide person. So, if you have a weed that’s resistant to herbicides, they can test for that,” he said. “There’s a general pathologist that can look at these stem blight things. It’s kind of a nice, integrated clinic. So, if you have issues, they can help solve them.”

The MBC also added support for a block grant from the Michigan Department of Agriculture and Rural Development.

“It has been an anthracnose trial that we’ve been doing for about three years to reevaluate a lot of the pesticides we have in our fruit management guide,” Miles said. “We test a pesticide for a number of years and when we feel that it’s working we will rate it. It’s been about 25 years before most of them have been rated. We’ve been trying to make some slight changes on what fungicides are working on the crops.

The main disease in Michigan is anthracnose in blueberry, said Miles, who conducted a trial focused on the fruit rot at MSU’s Southwest Michigan Research & Extension Center.

“I would say our main fruit rots are probably anthracnose and botrytis, although we might also attribute Alternaria as being an issue in the past, but that’s almost like a spoilage thing.”

The focus of most fungicide programs has been anthracnose. Fortunately for growers, this was probably a pretty light year for anthracnose. It was dry from about bloom to almost all the way to harvest which is good.

“We do a lot of trials for mummy berry,” Miles said. “There’s a zero-tolerance policy for mummy berry, so that’s why we worry about it. It also starts the management season and is one of the first diseases you might control.”

Herbicides kill weeds by disrupting specific plant processes and they are classified based on their modes of action. If herbicides with the same mode of action are used repeatedly, resistant weed populations may develop.

— Gary Pullano, Senior FGN Correspondent

Top photo: Michigan State University (MSU) small fruit educator Carlos Garcia, far left, and Sushila Chaudhari, far right, assistant professor in MSU’s Department of Horticulture, were among the presenters at the inaugural Blueberry Field Day. Photos: Gary Pullano

Second photo: Jackie Perkins, manager and research technician in the lab of Michigan State University professor and Extension specialist Rufus Isaacs, discusses the use of Samba wasps to control spotted wing drosphila in blueberries.

Bottom photo: Timothy Miles, assistant professor-Extension specialist for diseases of blueberries and other crops in MSU’s department of plant, soil and microbial sciences, discusses fruit rots in blueberries.

Current Issue

see all current issue »

Be sure to check out our other specialty agriculture brands

produceprocessingsm Organic Grower