For this week’s episode, I’m in over my head. I’m out of my element. But I know that last year’s spring was long and cold and wet…so I know we will be seeing higher rates of fungal infections in blueberry. I saw a lot of mummy berry in our early blooming varieties in Durham. It was a real bummer. Because the weather was so gnarly during bloom last year, and I know that prime time for mummyberry infections happens during bloom, I’m sure I wasn’t the only one who was bummed out by all those shriveled grey blueberries. I think I need to understand this disease a little better. I really need help and I turned to a couple of experts in the area to explain this to me.
Ann Hazelrigg, University of Vermont
Mummyberry is a fungal disease of blueberry and we really had a big problem with it last year because it really likes cool wet conditions in the spring. If we have the same conditions this spring, I expect a lot of new infections because there will be a lot of inoculum or spores in the field.
It’s a fungal disease that overwinters on these mummified berries underneath bushes. Right around the time that forsythias bloom, these mummies produce a fruiting body called an apothecia that can produce millions of spores. These spores, during wet cool conditions, are carried by wind and rain splash to the new shoots. They cause a shoot blight. It can be kind of tricky to determine if the injury you’re looking at is caused by frost, shoot blight can look like frost damage and it can look like another fungal disease called botrytis, which is not as impactful.
But anyway, the spores from these mummies go to the shoots where they can cause shoot blight and then, it’s an interesting disease because it has two different spore types. A second spore type is produced on these blighted shoots. They are often carried by wind currents but often by bees to the flowers. That’s when the berries get infected, through these flower infections from this other kind of spore. At first, infected berries look just fine. As the season goes on these infected blooms produce fruit that starts shriveling. They look a little off color. That’s when you know you’ve had a mummyberry infection.
Anna: Ok, so walk me through a couple seasons here. Maybe people noticed some damage last year. What are they seeing? At what point are they deciding I really need to do something?
Ann: Well, that should have been a decision they made last year. If a grower had a severe infection last year, they should be ready for it this year. They will have a lot of overwintering mummies. Small backyard growers with only a few bushes were able to pick off those affected berries. That’s not really something a commercial grower can do.
One thing we can do is try and disrupt those mummies by raking under the bushes. Typically those apothecia – those fruiting bodies - are coming out when forsythia are blooming. In Burlington, that’s right now. So maybe too late this year. That’s something they can do before apothecia form. Another really good approach is to bury those mummies. We recommend putting on a 2” layer of mulch, especially if they had a really bad year before, and that covers up those mummies. Another thing people can do earlier in the season is use urea to burn out those mummies.
Anna: And that urea application is something that’s applied to the ground.
Ann: Right. Applied to the ground.
So those are the things people should be doing now, then watching as leaves are coming out, watching for that shoot blight. You can protect new tissue from infection using fungicides. You would be using fungicide to protect plants during that shoot blight phase and again during the blossom blight phase.
Anna: All right so there are lots cultural practices to reduce disease pressure and fungicides to protect plants during periods of severe disease pressure. You can find a list of resistant varieties in the New England Small Fruit Management Guide as well as a list of crop protection products registered for use in blueberry. Ann mentioned that you may need to treat affected plants pretty frequently – at least weekly – before and during bloom.
Now, we certainly avoid using insecticides during bloom to avoid non-target effects on our pollinators. Please do yourself a favor and listen to my conversation with Frank Drummond about pollinators in wild blueberry. His description of how native bees do their work is a delight. So we avoid insecticides during bloom but we’ve always felt pretty confident that our fungicides have minimal effects on these insects. However, it sounds like there might be synergistic effects on bee offspring when multiple chemicals are brought back to the hive or the nest of social and solitary bees. I turned to my colleague here at UNH Extension to unpack some of this information.
Cheryl Smith, University of New Hampshire
Anna: I rely pretty heavily on my colleagues here at UNH couple of colleagues around here who are long-term extension folks with lots of knowledge and ‘history’. Cheryl is one of those people and also one of those people who probably look a little younger than she actually is and she probably gets a lot of that “oh you probably started when you were a baby if you’re even thinking about retirement. That’s crazy how UNH lets babies work there.” Well for Cheryl, that’s kind of true. She did start at UNH when she was a ‘baby’. She got her PhD here at UNH with Bill MacHardy studying apple scab, a fungal disease of apples that has a lot in common with mummyberry in blueberry. They’re both fungal pathogens and they both overwinter on the orchard floor so many of the cultural practices and chemical approaches are similar.
Cheryl: Ok so pull those table back up…so I went through the guide and pulled all the product that are the most efficacious then we’ll look back at the
Anna: I’ll spare you from hearing how the sausage is made here but we kind of struggled to answer the question of how fungicides might impact pollinators by using the Cornell pesticide decision making guide. In a nutshell our conclusions were that fungicides are definitely not as great a risk to pollinators as insecticides. That’s pretty obvious.
If bees are bringing home fungicides as well sublethal amounts of insecticides, their offspring might be challenged to detoxify all of these chemicals at once. We’re talking about honey bees bringing home nectar and pollen to their hive but we’re also talking about native, solitary bees who bring home pollen to their little tunnel they’ve built in the ground or in a stem for their babies. This is where the synergistic effects of these combinations of chemicals come into play.
There are concerns in three scenarios. Bees are bringing home fungicides plus commonly used organophosphates and pyrethroids for insect pests of blueberry. However, these chemicals wouldn’t be used in blueberry during bloom and probably wouldn’t be used on-farm until later in the season for blueberry and even for neighboring crops. For early season mummyberry fungicide programs, I’m not too worried about tank mixes or other chemicals applied to blueberry this time of the year.
The second concern is if bees are bringing home fungicides as well as neonicotinoids they’re picking up from other plants in the landscape. These products vary in their toxicity to bees but, again, detoxification can get challenging when there are multiple chemicals in the mix.
The third concern is regarding synergistic effects of fungicides and commonly used organophosphates used for controlling Varroa mites in managed honey bees. This concern, of course only applies to managed honey bees and not native bees. On their own, these miticides are toxic to mites and not to bees because healthy bees are capable of quickly detoxifying those toxins. The risk of using miticide is greatly outweighed by the benefit here. Varroa mites are the number one cause of honey bee hive losses and these enormous parasites transmit disease and suck out bee fat body. Think of fat body as insect livers. Very important for detoxifying chemicals…and we find ourselves in chicken egg situation here because fungicide exposure is only a problem when the bees are exposed to multiple chemicals and the chemicals are there to reduce risk of mite parasites that deplete bee’s detoxification abilities. What to make of this?
Cheryl: So I guess I’d look at it and say, if you have hives and its during bloom, think about what fungicides you are using or not use fungicide at all.
Anna: OK so best practice is to maintain all the best cultural practices and to only use any pesticide if you really need. If you need to use pesticide, make sure you are using the most efficacious approach and rotate products to avoid resistance developing in the fungus.
Back to my conversation with Cheryl and I will note that she refers to shoot blight as primary infection and blossom blight as secondary infection. If you have a copy of the small fruit guide handy you could follow along as we go through the efficacy table:
Cheryl: So if someone had a mummyberry problem last year, I would probably tell them to go in with Indar.
Anna: and that’s a FRAC 3?
Cheryl: Right. It’s very efficacious for primary and secondary infections, but I know there are label restrictions on how many times you can use it in a season. You wouldn’t want to rotate it with Inspire Super because it’s got a group 3 in it. Technically you’re not really rotating. Then you look at something like Luna Tranquility which is very efficacious and you could rotate it with something like Indar. Now, you’ve also got something like Double Nickel. There’s a possibility of rotating something like that in there too. Is it as good, no. But its pretty good.
Anna: I’ll interrupt this conversation to mention that Double Nickel is a biopesticide, actually a bacterium, which basically works to outcompete pathogens in plants and prevents infections. Cheryl mentioned that tank mixes of Double Nickel and Cueva have been pretty successful with fireblight management in apple so definitely a major player in fighting plant disease.
Cheryl: Back to the chart, going down the list. You’ve got Orbit and Tilt but there’s another group 3, so you’re really not rotating.
Anna: Now what is Regalia?
Cheryl: Regalia is a plant activator, it’s the extract of giant hogweed.
Anna: And how is that supposed to work?
Cheryl: You’ve got to get that on as soon as new growth starts because it’s a plant activator. You can’t put it on say a few days before you expect an infection because its got to turn on the plant’s defense mechanisms. I think it’s got an every two week label recommendation. I’d want to get that on early and get in two applications, maybe three applications before you’d really need it. It’s labeled in blueberry and its got pretty good efficacy in blueberry.
So thinking in terms of safety, you’ve got fenhexamid (Decree/Elevate). Captevate is fenhexamid plus captan. So if someone wanted to control this using the lowest risk material they could use fenhexamid, but it’s really not that effective.
Anna: So another thing to consider when you are considering pollinator protection here is that establishing pollinator habitat is another tool in your arsenal. These habitats provide pesticide-free safe zones, rich with overwintering habitat and flowering plants full of nectar and pollen. If we’re concerned about mixing chemicals in the food bees are bringing home, it certainly couldn’t hurt to make sure they’ve got plenty of clean healthy pollen over the course of the season. There are more benefits to consider, which I discussed during a conversation with Rufus Isaacs, an entomologist and fruit specialist at Michigan State University. Which was rudely interrupted by a lagging zoom call, a quintessential occurrence in this the spring of 2020:
Rufus Isaacs: Yeah, we’ve got some farms that had opportunity to put pollinator habitat in. They might have a low spot where you’re much more likely to get frost damage in the spring, so you’re not going to grow blueberries there. Any area that’s perhaps difficult to acidify to the right pH. Some areas where they move harvest machinery around, little corners of fields. It’s been hard to get big areas but there are some opportunities to fit patches in. Our NRCS through Farm Services, there’s an opportunity for receiving payment for a minimum of two acres. Multiple farmers have been able to find space around the farm to establish a couple acres of pollinator habitat.
So something we need to highlight when we’re talking about these plantings. They’re designed to start blooming after blueberries have finished blooming. Here in Michigan they’re starting mid-June and providing flowers for bees to visit through July and August and all the goldenrod in September. We’re not trying to boost bee’s nutrition during blueberry bloom. Partly because we want them to visit the blueberry flowers and partly because it’s hard to find annually blooming plants that will bloom that early. Trees and shrubs will do it but most of what we’re planting is from seed. This is for bees like bumble bees that will visit blueberries and do very well there but they need food for the rest of the summer. If they don’t have it, they won’t make as many queens or as many workers and they won’t persist in the landscape. I see it as a long term landscape where these insects always have something they can feed from.
I also don’t see this practice as replacing honey bees. People still bring in honey bees. We’ve found that those planting provided the extra, maybe 20%, in berry size and yield that you would get from having really good pollination, over and above what the honey bees were able to provide.
It’s just like with integrated pest management. We’re not just relying on one approach to getting the flowers pollinated. We’re trying to put different things into the farm so that each year we get reliable pollination and a good yield, rather than relying on one thing that works most years.
Anna: Something I’ve been thinking about when it comes to these kind of crappy springs we’ve been having, can you talk about pollinator habitats when it comes to resiliency in extreme weather situations?
Rufus: It’s funny that you should mention that because, when we were doing the work I mentioned earlier, we had two years where the bee population increased and we were able to measure yields. In the year where it was more normal weather, we got an increase of about 10-15% yield. In one year, we had a really warm spring and then a frost. The yields across the state were down, but if you look at the percent increase in yield that we got from having wildflower plantings – and especially if you look at the price of blueberries that year because the supply was down and the price went up – it was actually much more of an economic benefit on those odd years when supply is shorter. I think that speaks to resiliency too. You’re more likely to get a decent yield on those odd years when you’ve got this backup of wild bees doing the work.
Anna: Those bumble bees! Man they are little flying tanks! A side note here as well - I remember asking Rufus a few years ago about unexpected benefits from his wildflower work in terms of farmer adoption and he mentioned another project with sunflower plantings were also very popular among deer hunters for their ability to attract wildlife small and large! I’m including some resources from Cathy Neal on the Extension website with some guidance on how to establish wildflower plantings in the northeast but the best advice from Cathy is perseverance! Plantings will take a year or two to establish so power through those weedy years!
Before I conclude here, I do have to point out some other potential fungal pathogens that could be in the mix. Phomopsis is one would also benefit from cool wet springs. So you may need to seek the help of your neighborhood Extension plant pathologist to correctly identify any pest problem, you know two here – thanks to Ann Hazelrigg of Vermont and our very own Cheryl Smith of New Hampshire - but every state has a few of them so reach out to Extension if you have any questions! Thanks to Rufus Isaacs of Michigan State University and a special thanks to Jason Lightbown who wrote and performed our theme music.