As the cranberry vines have emerged further from dormancy, the winter injury has become much more apparent. While there are a lot of different products being used to try to help ease the winter stress, there is not a lot of research behind their use and efficacy. When we asked Carolyn DeMoranville for her thoughts, she told us that potassium (K) is the nutrient that is associated with improved plant turgor/hydration, so products containing K have been the classic choice. The cation exchange complex in the soil holds Ca, Mg, and K. So, adding Ca and or Mg along with the K is intended to maintain a good balance.
Some growers are choosing to add some nitrogen early in the season. Remember that when N is applied pre-bloom, it is rapidly taken into the plant and moved to the new leafy growth. Adding too much N at this stage can lead to excessive growth, so start small.
Insect Management. Cranberry weevil numbers are remarkably high on a few bogs. 10’s and 20’s can be swept at bogs that have a history of high numbers. If you are NOT finding them, you don’t have them. Many bogs have low or no weevil numbers, a few have the usual 2-4, but weevil bogs that already have the fabulously high counts (25-75) warrant a spray. Green spanworm can be found, but no bog has treatable numbers, and many bogs have NO spanworm. The threshold is 18 and only 1 or 2 have generally been found. Green spanworm is actively feeding now if you have them and will be wrapping up its caterpillar stage in just a week or two.
Interestingly, a few bogs have cutworms this year. Humped green fruitworm and False armyworm, both fat green caterpillars, are being found in low numbers on a few bogs. Again, nothing treatable but more cutworms seen this spring than in many years. The threshold is 4.5 per sweep set and only a very few 1s have been found.
By far, the most common thing in the sweep net continues to be tiny collembola. It’s really important to know that they are NOT a cranberry pest. They eat detritus in the bog (trash). These tiny springtails come in many colors (yellow, green, gray and black) and can distract us from the real pests. They are abundant in some sweep sets, come in many colors and sizes (small and really small), but the general shape is always the same. They are little round blobs that jump when you poke at them.
If you are looking for tiny black bug, it is out now as a little yellow nymphs. They are the same size as the collembola and hard to differentiate. The collembola ping when you touch them, but the black bug nymphs run fast when you touch them. Tiny blunt-nosed leafhoppers which are also little yellow nymphs right now, have also hatched and on bogs where no broad spectrum (Fanfare, Diazinon) has been used in several years. 99% of what you see will be collembola but be aware that these other pests are out there. All are very small and yellow.
A dark adult leafhopper is being picked up in low numbers at a few sites. It is a Constricted Leafhopper and is NOT a pest. It is similar in size and color to the adult blunt nosed leafhoppers that we may see in July, but the real blunt nosed leafhoppers are small yellow nymphs right now.
The Insect and Disease Clinic II is WEDNESDAY May 21st 7:30-9:30 AM at the Cranberry Station, and we’ll have pictures and specimens of these troublesome pests. If you suspect a problem, bring the contents of your net in a plastic bag and we can check it under the microscope! 2 credits and FREE. Check in with Marty (martys[at]umass[dot]edu (martys[at]umass[dot]edu) or 508-265-6921) or just show up!!
The current insect management choices are as follows:
Avaunt eVo (indoxacarb) can be used against weevil if the population is not resistant. It will also hit spanworms and cutworms. Avaunt will NOT hit black bug and leafhopper.
Actara (thiamethoxam) can be used against weevil and works well. It will NOT manage any other pests.
Assail, Arvida (acetamiprid) can be used against black bug and leafhopper, should help with spanworms and cutworms, but will NOT manage weevil at all.
Fanfare (bifenthrin) is the cheapest and most effective option – it hits all insects. However, it has extremely high aquatic toxicity and you MUST hold your water for 3 days. Fanfare can only be used once if you are delivering for export fruit. It can be used twice if you are domestic but check with your handler.
Disease Management. This is the time to manage upright dieback using a chlorothalonil application. Time the application for when the bud has broken dormancy and new growth has begun (elongation period prior to roughneck). Chlorothalonil is the compound of choice.
The first fungicide application for Fairy Ring control is also timed for budbreak. A combination soil drench of Indar and Abound is recommended. Please see the Chart Book for details.
Many disease issues are related to or worsened by poor drainage! Between frost irrigation and rain, beds can be saturated. Take measures to improve your draining if you can.
If you suspect Phytophthora root rot or have any other disease diagnostics or management questions, please reach out (Leela Uppala 508-970-7644).
The Insect and Disease Clinic II is WEDNESDAY May 21st 7:30-9:30 AM at the Cranberry Station, including another raffle for a jug of rampart if you bring in a phytophthora sample (20-40 uprights with roots in a plastic bag) to test yourself via immunostrip!
Weed Management. Lots of preemergence herbicide is being applied! It is now too late for Spartan. Casoron is a volatile herbicide. Ideally it is meant to volatilize into a gas in soil where it remains in the pore spaces between soil particles. If you apply when the soil and/or air temperatures are too warm you will have rapid losses, so ideally it should be applied when those temps are under 60°F and immediately incorporated by irrigation to move it into the soil.
For dodder management, Kerb and QuinStar have good crop safety and have a little flexibility on timing. They can be used preemergence or early post-emergence (after the dodder germinates and is seeking a host to attach to).
Many growers continue to have questions about what the best timing for grass management my answer is always “it depends”. There is no single perfect timing because there are so many different grass weeds out there. Remember that the clethodim products (Select Max, Intensity One) work on ACTIVELY growing grass – those that are getting bigger and adding biomass. For poverty grass, that stage doesn’t happen until much later in the season (July), but for other grasses it can be happening now. Feel free to call me with any questions about timing, identification, or any other issues (Katie 508-970-763).
Sheep sorrel, aka red sorrel (Rumex acetosella), is flowering now, and is suddenly very visible everywhere because the flower stalks are taller than the cranberry canopy. This is a perennial plant but it is not usually very competitive with established cranberry plants. It is generally only found in new plantings or in areas where vines are thin and is considered more of a nuisance than a truly problematic weed issue.
At this time of year, there are not effective herbicide strategies you can use. The historic recommendation for sheep sorrel is to use Casoron. If you have patches in established beds, consider mapping those areas now so you can spot treat with Casoron next spring (since Casoron works before weeds emerge). Also, too late for this year, but an early spring preemergence application of Spartan may also control red sorrel (again, too late for this year but make a note for next year). Mesotrione (Callisto) is NOT effective postemergence for this weed. It is possible that earlier applications may be more effective – by the time you notice sheep sorrel (now) it is already well into making flowers/seeds! For many weeds, herbicide efficacy DECREASE as plant size/stage increases.