On April 19^th, we had 56 cranberry growers join us at the Wisconsin Cranberry Research Station for the annual Spring Mini-Clinic. Livestream locations, hosted by Whittelsey Cranberry Co. and Bartling’s Manitowish Cranberry Co. had 17 and 24 attendees each, allowing lively discussion without long drives. Five topics were covered: a bud dissection practicum, looking back while looking forward: a Casoron review and current weed management research, current dissolved oxygen work, grower polls/discussion, and Wisconsin State Cranberry Growers’ Association Updates. Bud dissection, Casoron, dissolved oxygen, and selected polls are recapped here.

Bud Dissection Practicum

Growers who were able to access their vines brought 2-4 buds from their earliest variety for dissection practice. Microscopes on site gave growers the opportunity to strip the upright of leaves, make a longitudinal slice, and examine the state of the bud. Work pioneered by Dr. Amaya Atucha have provided growers with guidance for plant part identification and an easy index for cold damage evaluation.

Physically inspecting a bud is more instructive than looking at pictures, so make time this week to practice. If you are inspecting for cold damage, bring the buds inside and wait 24-36 hours at room temperature before dissecting and checking for brown, necrotic tissue. If you do not have a microscope, a magnifying glass or loupe are nearly as useful. (Apple growers can do these inspections with eyes alone, but to see cranberry flower primordia, especially in dormant or not yet swollen buds, magnification is very helpful.

Looking back while looking forward: a Casoron review and current weed management research

Casoron has been the backbone of cranberry weed management programs for decades, so its mechanism of action and details around most effective use patterns deserve a thorough review. First discovered in the 1950’s, Casoron has not had any reports of herbicide resistance. It exhibits pre-emerge activity only.

Casoron, an HRAC 29, inhibits root and shoot meristem division and growth, as well as inhibiting seed germination. It can be absorbed by roots and leaves—but while it can move from roots to leaves, it will not move from leaves to roots. Casoron doesn’t display “symptoms” on treated weeds, as the treated weeds simply don’t emerge, or simply stop growth. No coloration or growth patterns are visible.

Cranberry plants tolerate Casoron because applications are made when cranberries aren’t actively growing. Plants are capable of processing Casoron into a less-toxic form, though at high rates this natural protection mechanism can be overwhelmed.  Casoron applications are safest for cranberries when cranberries are still dormant and temperatures have not risen appreciably. Casoron’s average half-life Is 60 days, which means an application provides between 2 and 6 months of weed control depending on soil characteristics. (Casoron will last longer in heavy soils.) Casoron has low mobility in the soil, but high volatility losses can happen in hot and wet conditions. To avoid volatile losses, apply granular Casoron, incorporate it via irrigation or rainfall, and make applications when temperatures are low.

To incorporate Casoron, ½ to ¾ inch of water should be applied after a Casoron application to incorporate the active ingredient into the weed zone. Watering-in prevents losses from volatility, and ensures the active ingredient will come into contact with weeds. Many growers apply Casoron on a day when they expect to frost protect at night, counting on water from frost protection to incorporate the application. This is a good practice—volatility will be low on a cool day preceding a frost protection night.

A grower perception is that beds should kept “wet, so that Casoron keeps working.” Best practice is to keep beds at the proper moisture for cranberry growth, regardless of whether Casoron has been applied. Too little water would result in weeds not taking up Casoron, but too much water results in dilution, or driving the Casoron deeper than the germination and growth zone. Another risk of excess moisture is puddling—puddling can concentrate Casoron in areas which then results in vine injury.

Casoron is the only known herbicide which controls “volunteer” or “sport” cranberry plants. Colquhoun et al evaluated rates of Casoron, Danitol, and Callisto on cranberry emergence, and found the results in Figure 3. Casoron at 30 lb/a produced good control in this greenhouse study, which implies including Casoron at least every 2 to 3 years in your rotation will protect cranberry vine variety purity.

Dissolved Oxygen work in Wisconsin

When under flood, cranberry plants are subjected to a number of stressors, including reduced photosynthesis, no transpiration, no nutrient uptake, and the potential to shift from aerobic to anaerobic carbohydrate consumption. Various anatomical changes can take place as an adaptation mechanism—but some of these are not yet well understood in cranberry (for example, the results of ACC synthase and ethylene production). Negative impacts of flooding are influenced by the dissolved oxygen content in the flood water, the flood duration, the flood water temperature, and clarity. Plant age and cultivar may also play roles. Under anaerobic conditions, the plant consumes more carbohydrates per unit of energy produced, resulting in early depletion of carbohydrate stores. Low carbohydrates result in low fruit set later in the season.

both winter & spring floods: time of application, depth, duration, water and air temperature, ice layer thickness, and light penetration. Work is also being done to characterize carbohydrate levels available in the plant across growing periods. (Figure 5)

Work was done at the Wisconsin Cranberry Research Station to characterize dissolved oxygen during a winter flood. Dissolved oxygen reduced from 13mg/L (on day 1 of the flood) to 5.16mg/L on day 8 of the flood, on which the Marsh Manager elected to drain the flood. The critical dissolved oxygen level for cranberry plants before damaged is observed has been shown to be 4mg/L of dissolved oxygen.

Dissolved oxygen has also been measured in spring floods and found to be highly temperature dependent. It was noted that small puddles tend to read low in dissolved oxygen, corroborating poor vine health in areas prone to ponding.

Dr. Mura’s current work focuses on the questions of

1. What critical Dissolved Oxygen levels reduce carbohydrates in plants in winter and spring floods?
2. What levels of carbohydrates are critical for cranberry production?
3. Is excess ethylene production under anaerobic respiration protecting plants, or is it causing leaf drop?

Selected Grower Poll Results    

Diazanon 600, produced by Loveland, has been discontinued and to the best of our knowledge, prior inventory is sold. Diazanon 500 and Diazanon 50W still currently have inventory available, but Adama does not intend to produce more to resupply inventory. If growers have an expected need for Diazanon products, plans should be made to purchase sooner rather than later.

Growers faced with controlling red-headed flea beetle without Diazanon available plan to use (most popular) Venom, (second most popular) nematodes/biological, and (all tied) not sure, Imidan, Sevin, Confirm, Altacor. 

Department of Agriculture, Trade, and Consumer Protection has released a Special Pesticide Registration for Stinger in cranberry. If you are making a Stinger application, you need to have a physical printed copy of the Special Registration on hand as an extension of the label. That label can be found here: https://datcp.wi.gov/Documents/SPRStingerCranberryLabel.pdf

Growers’ planned pre-bloom insect control, from most popular to least popular, were: Fanfare, Orthene, Delegate, a pest flood, Intrepid, with various combinations of Orthene, Fanfare, and Delegate comprising the least popular tier.

Thank you to those who made time to attend the Mini-Clinic in person, and please reach out if you have any questions or suggestions for next year!

This article was posted in WFN, Vol. 1-4 and tagged Allison Jonjak, Cranberries, cranberry mini clinic, Jed Colquhoun, Jyostna Mura, mini clinic.