To keep everyone up to date with research while keeping everyone safe from Covid-19 by avoiding group gatherings, we hosted our first Virtual Cranberry Mini-Clinic. We had 75 participants, and we will be hosting more in the future. An unexpected benefit is that everyone on their marshes can attend a virtual clinic without leaving the marsh unattended for a day. When we can gather again, we will likely supplement our face to face meetings with virtual meetings like these.

Tom Lochner thanks everyone for patience and flexibility as we learn this new way of communicating. Updates include the WSCGA’s work-from-home plans, along with DATCP coordination to enable nutrient and pesticide trainings. Other work with DATCP has included getting truck weight limits increased. We will also be watching agricultural emergency spending, payroll protection, and other federal programs. Please contact Tom with issues and ideas!

Dr. Jed Colquhoun responded to some questions regarding moss control: there are no silver bullets. His hope is that we will experience drier weather, which will help with moss control. However, this does not seem to be the case in the near future given the historically high-water levels we currently have in Dane County (1 in a 3 billion probability). Dr. Colquhoun has tested various copper-based fungicides, fertilizers, and herbicides to control moss, however the effectiveness of these treatments is only 25 to 40% moss suppression at best, and only for a few weeks as moss can quickly regrow from spores or its root system. In addition, the products tested can only be applied while cranberry vines are dormant. If vines have broken dormancy at all, they can sustain persistent injury.  A Massachusetts newsletter reported they have a cranberry label for a product against moss–but this does not work on sphagnum mosses, and it is not labeled for use in Wisconsin. Dr. Colquhoun and his team will continue their research on moss control and other escapees. 

Allison Jonjak, new Cranberry Outreach Specialist with Extension, introduces herself–which you can read more about here: https://fruit.wisc.edu/2020/04/24/allison-jonjak-new-cranberry-outreach-specialist-uw-madison-division-of-extension/ 

Dr. Shawn Steffan talked about spray windows for sparganothis fruit worm control. The best control strategy is to spray early when 10 to 25% of the eggs have hatched. This happens about 1000 degree days (DD; starting in March 1^st) for the 10% and 1140 DD for 25% egg hatch. This period is the ideal spray window to kill the most sparganothis, and research shows that spraying during this period is 60% more effective at controlling sparganothis than later sprays. 

Dr. Steffan will continue his research on mass propagation of nematode bioinsecticide. Nematode bioinsecticides have been very effective thus far, especially at controlling flea beetle larvae months. The next step will be to scale up and have growers and pest control professionals keep their own cultures. Dr. Steffan also provided an update on pheromone mating disruption. A product aimed at cranberry and sparganothis fruitworm and black-headed fireworm is currently undergoing testing for registration for sparg. He hopes to continue a trial with sparg this year–that would be the 2nd year with good sparg data, which would be enough information to get sparg on the label. Another year of data for cranberry fruitworm would be required, and Dr. Steffan is hoping his new lab technician will be onboarded by June 7 to run these trials. 

Dr. Jyostna Devi Mura, new Plant Physiologist with the USDA-ARS, introduced herself–and you can find her intro here: https://fruit.wisc.edu/2020/04/27/introducing-dr-jyostna-mura-usda-ars-cranberry-physiologist/

Dr. Christelle Guédot will continue her research on pollinator gardens and chemical ecology identifying compounds which could potentially attract cranberry and sparganothis fruitworm. She will continue work with Dr. Steffan on degree days (DD) trials, with the goal of providing growers with practical information on insect pest control. Dr. Guédot also shared information about two new products, Exirel and Comoran. Comoran contains both Assail and Rimon, and Jack Perry has been happy with the effectiveness of the product. It has a good price per acre, compared with tank mixing the two products. New insecticides are coming down the pipeline. One broad-spectrum insecticide needs to be finalized with Ocean Spray and with other handlers, but it is already registered on cranberry. Dr. Guédot also reminded growers they can not use Belay anymore, and to check the pesticide management guide and with handlers for the latest information. If you have questions on this, please reach out to Dr. Guédot.

Dr. Amaya Atucha covered the topic of potassium (K) fertilization. There are always questions about potassium applications early in the year to alleviate “crunchy” vines—but this is a myth. K fertilization has no effect on alleviating crunchy vines and growers should not be applying it right now. Whether and when to apply K: the first place to start is your tissue analysis levels. If tissue analysis results show K level in the 0.4 to 0.75 ppm range, K should be applied to replenish what as extracted by the fruit, as a maintenance strategy. If you have 300 barrels/ac, you’re removing 30-35 lb of K (roughly 40 lb of potassium oxide K₂O) in berries, so you do not need to apply more than what you’re removing. If you’re getting consistent good yields and your tissue results are in the normal range, don’t overapply K as it will create imbalances with other nutrients. Dr. Atucha mentioned that research performed at UW-Madison in the late 90s on K fertilization across more than 15 marshes in the state, showed that no decline on yield of fruit size even when no K was applied for 4 years. This shows us that we may not need to apply K every year. If you’re not comfortable applying zero potassium, a safe way forward may be the maintenance calculation. 

In terms of soil K concentrations, 40 to 60 ppm of K in the soil should provide enough to support vine growth and fruit production. If you want to increase your soil test levels, you need 15 lb of K₂O/ac to increase 1 ppm (based on the top 3″ of a sandy soil). 

Regarding the question whether higher yielding cultivars need more potassium, Dr. Atucha says there is not a lot of research on this, but if you are harvesting more berries per area, you will have to fertilize with more K because you are removing more of it. 

Dr. Atucha also addressed the question are early spring applications of K beneficial? She has not seen anything in the literature supporting this. The timing of potassium application should coincide with fruit growth. Fruit set to pea size berry should be the optimal window for K applications. Similar to early season potassium, there is no research supporting late season application. Fall K applications have NO effect on setting buds for next year, nor do they increase increases color development in berries.

Regarding potassium fertilizers, the most commonly used are potassium chloride, potassium sulfate, and potassium-magnesium sulfide. K-mag is well known as well. All products are effective at providing the needed potassium, so we have no preference for one over the other, aside from price. 

Dr. Atucha also addressed a question on leaf drop. She said that last year’s leaves are photosynthetically active and provide carbohydrates to support new growth during early spring. However, once we make it to bud break to roughneck, the new tissue becomes efficient at producing carbohydrates really fast, and that by roughneck older leaves are not as critical in providing carbohydrates for fruit set. Research shows that removal of old leaves by roughneck has minimal impact on fruit yield or fruit size. Her recommendation is, even if you are having leaf drop, you do not need to apply more fertilizer. Instead, keep an eye on new growth. If it remains green, you are fine. If new growth is slow or yellow, you may need to apply nitrogen. If new growth looks fine, then you do not need to apply fertilizer. Regarding tracking plant growing degree days (GDD) and bud cold hardiness, Dr. Atucha pointed out that GDDs in plants are not the same as Degree Days (DD) for insects, and that there is not a good correlation between GDD and bud sensitivity to freeze or frost events. Dr. Atucha’s team hs been working on correlating bud cold hardiness with GDDs, but they have not found a good correlation between GDD and bud cold hardiness. 

This article was posted in Cranberry and tagged Cranberries, fertilization, insect control, Weed Management.