Natalie Hoidal & Marissa Schuh
Uff da, more rain when most of the state doesn’t need it. Soils are waterlogged, and fields on some farms flooded. Despite the challenging summer that has alternated between heat advisories, air quality alerts, and torrential rain, a lot of crops are doing better than might be expected. The next week looks like a reprieve from what has been typical this summer, with cooler temperatures, clear skies, and fewer chances of rain.
A note about berries
While we typically don’t discuss fruit in this newsletter, berry crops can be a great addition to vegetable farms. We’ve been keeping tabs on berries in Minnesota, and noticing that you-pick berry operations are packed full of customers and selling out in record time. The co-ops are selling mostly local vegetables this time of year, but all of the berries are from California and Michigan. It seems like there is an opportunity for vegetable growers to add some fruit to their operations, and berries can pair nicely with vegetable crops (we think of apples and grapes as whole separate industries, but berries are often marketed in similar ways to veggies). As we head into winter, keep an eye out for some upcoming courses and opportunities to learn more about adding berries to your vegetable farm.
Crop updates
Cole crops
It’s been a great year for leafy cole crops like kale and collards, but the humidity has caused problems for head forming cole crops like cauliflower and broccoli. In addition to the two diseases that are now widespread in humid years, Alternaria and black rot, we’re seeing quite a bit of brown bead and lumpy, loose heads in both cauliflower and broccoli. This is to be expected; August harvested broccoli and cauliflower are often a bit dicey. Hopefully Fall weather will be a bit drier for the next successions of these crops.
Garlic
Garlic is being cured. As you get ready to sort and select next year’s seed garlic, it is important to be ruthless when selecting next year’s seed stock. We saw high levels of aster yellows as well as all kinds of other garlic viruses this year. Based on the severity of the infections we saw, a lot of these issues likely arrived in seed, as opposed to being introduced by insect vectors this year.
An potentially underrated sorting tool? Your sense of smell. Garlic infected with aster yellows often has a distinct smell (great to talk about in a written medium!). The best way to calibrate your sense of smell is to find some garlic that clearly has Aster yellows based on visual symptoms, and start smelling it. Once you’ve figured out the smell, you can start sniffing all of your garlic to cull bulbs that you might miss based on visual symptoms alone.
Discolored garlic bulbs resulting from aster yellows infection. Photo: University of Minnesota.
If you’re looking for garlic seed, SFA maintains a directory of garlic seed sellers whose garlic has tested negative for garlic bloat nematode: https://sfa-mn.org/garlic-directory/
Vine crops
Winter squash and pie pumpkins are ripening this week, as are melons. We reposted our brief guide to harvesting melons, pumpkins, and squash, so take a few minutes to review the guide if you need a refresher.
Powdery mildew is showing up in vine crops. Depending on harvest timing and how susceptible your variety is to this disease, you may manage this disease with fungicides. Powdery mildew evolves resistances to fungicides relatively quickly, see the Midwest Vegetable Production Guide for information about what products work consistently in our region.
Peppers
Peppers are finally rolling in, though growers are reporting reduced yield and quality. There may be a couple of factors at play….
Peppers generally experience poor fruit set. As many as ⅔ of the flowers on a given fruit are likely to not produce a viable fruit, even under optimal conditions. When conditions are less than optimal, we see that number jump.
Plants experiencing stress from insects or diseases can have delayed fruit set. In our short growing season, a delay in fruit set can translate into significant yield reductions.
High temperatures can cause flowers and buds to abscise, or fall off. Yield reductions can occur at temperatures as moderate as 80 degree F during the day, 70 degrees at night. Nighttime temperatures are considered more detrimental than daytime temperatures, and we’ve had plenty of nights above 70 this summer.
Exposure to far-red radiation can reduce fruit set in peppers. This is mostly a concern for greenhouse growers with artificial lightning, but wildfire smoke exposes us (and our plants) to more far-red light than we normally see. This potentially reduces yields.
Plants and fruit with spots? Bacterial spot might be your culprit.
This has been a big year for bacterial spot in peppers. We see a little bit of this disease every year, but this year's constant rainfall, humidity, and temperatures above 75F have caused this disease to flare up on many farms.
Bacterial spot in a bell pepper. Photo: Dan Egel, Purdue University.
Bacterial spot lesions on leaves start small, then get larger and combine into larger, dead areas of the leaf. Photo: Dan Egel, Purdue University.
Once the symptoms above show up on plants, you are limited in what you can do. Copper can be used preventatively but its efficacy is mixed.
At this point in the season, the best we can do is start working on cultural practices to reduce chances this disease shows up again.
Dispose of unmarketable peppers outside of production areas
Chop up and integrate crop residue
Rotate out of solanaceous crops for 2-3 years
Work on broadleaf weed control (more air flow, fewer potential plants to harbor the pathogen)
If you’ve experienced losses from this disease a few times, consider also…
Working with your transplant source to reduce the chance that this disease starts in the greenhouse
Trial some resistant varieties
Increase plant spacing to reduce transmission
Tomatoes
After a slow start, tomato production is finally ramping up in fields. We’ve had some discussions recently about the best time to harvest tomatoes, and there is some debate about how much early harvest impacts the flavor of tomatoes.
Why harvest early? If your tomatoes are splitting (very common when we have so much rain), or rotting on the plant, it’s a sign that you’re likely waiting too long to harvest. Early harvest prevents splitting, in some cases helps you avoid the progression of disease onto the fruit, and helps keep the tomato field clean and critter free. The more overripe tomatoes in a field, the more birds, squirrels, and other creatures you’ll see.
So, how ripe is ripe enough? In general, any tomato that has started to turn even a little bit (some people call this “first blush”) will e able to ripen fully. There is some evidence that while the sugar content of fruit ripened in storage / off the vine may be comparable to vine ripened tomatoes, there are certain aromas or volatiles that differ when fruit ripen off the vine. Some people really notice the difference, while others hardly notice. There seem to be varietal differences as well. It also likely depends on your market: if you’re selling to a grocery store, you’ll likely want to harvest earlier so that the fruit can handle delivery, storage, and sitting on a shelf. If you’re selling directly to customers at farmers markets or through a CSA, you’ll likely want to harvest a bit closer to full maturity to give your customers that full tomato flavor. It really depends on your customers, and how long you want your tomatoes to last. The image below shows a spectrum of tomato ripening, and rough guidelines for when you might harvest for wholesale vs. fresh market vs. eating off the vine. (It might be hard to tell but the tomato in the photo is orange, not red).
Tomatoes for different markets may be harvested at different times. Image: Natalie Hoidal, UMN Extension.
Potatoes
Potato harvest is ramping up. A couple of weeks ago we discussed potatoes being harvested early as “young” potatoes; now we’re seeing more standard / mature potatoes come to market. *If* the forecast holds true, later this week might be a great time to dig potatoes. We’ll hopefully have warm days and dry weather to allow for field curing. Remind your customers that potatoes should not be stored in the fridge. While they prefer humid conditions (95% relative humidity), the ideal storage temperature for potatoes is 40-50 degrees F. Every year we get a question or two from a farmer whose customer stored their potatoes in the fridge, resulting in cold damage. Cold damaged potatoes look pretty bad, and customers sometimes think farmers sold them rotten potatoes, so communicating ahead of time helps to prevent this from happening.
Sweet corn
Sweet corn harvest is in full swing. We have had conducive conditions for corn earworm migration so far this August, so continue your spray program or be ready to talk to customers about wormy corn.
A bunch of soil health opportunities
This fall, our team is hosting a bunch of field days and field trips focused on soil health. We hope you’ll join us for one or more of these opportunities!
Preparing your high tunnel for winter: Flipping beds and planting a winter cash crop or cover crop
Practice (hands-on) cleaning up beds after a cash crop, and prepping the soil for the next crop. Learn about cover crops that perform well in high tunnels (free seed may be available), and winter cash crops like spinach that can be grown in unheated Minnesota High tunnels.
Led by Natalie Hoidal, Adria Fernandez and Dana Jokela (Johnny’s Selected Seeds)
Cost: Free Date: September 2nd Time: 10am - 12pm
Registration: z.umn.edu/HTfielddays
Succession planting and advanced high tunnel management field day
Learn about the basics of succession planting, managing a 2-acre farm with reduced tillage methods, and how to take your high tunnel to the next level of management for higher yields and a longer season. This field day will take place at Farm Farm in Princeton, MN; a 2 acre low-till farm managed by Jimmy and Heather. They have high tunnels with a mix of standard crops like tomatoes and greens, as well as some tropical crops like ginger. They have invested in automatic roll up sides and vents, automated watering, and they heat their tunnel on cool nights in the spring and fall to extend the growing season.
Both inside the high tunnels and in their fields, they use careful succession planting, which allows them to be profitable and efficient on a small scale. In late September, when many farms have slowed down, they are still actively growing many vegetables. While many Minnesota farms have a 16-week growing season—or 16-week community supported agriculture (CSA)—Jimmy and Heather are able to offer a 31-week CSA.
Cost: Free Date: September 30thTime: 2pm - 3:30pm
Registration: z.umn.edu/FarmFarmFieldDay
Soil health bus tours! Sustaining the soil and growing profitable fruit & vegetable farms
Join UMN Extension and partners to visit urban, suburban, and rural farms growing
fruits and vegetables at various scales. Learn about soil health practices, unique growing challenges, and conservation support programs.
Dates: September 22, October 10, November 14, 9am-3:30pm
Registration and descriptions of each tour: z.umn.edu/vegetablebustours
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