Authors: Natalie Hoidal & Marissa Schuh
While the growing season is still a few months away, now is the time to plan and order supplies. Read on for information about varieties, trellising systems, insects, and a common cucumber pathogen.
Navigating varietal terminology
There are so many cucumbers available to growers, and so much variation in performance, cost, and management between varieties. While we will not discuss specific varieties here, it’s important to understand the reproductive biology of the varieties you choose. There cucumbers available today have three distinct types of reproductive biology: they are either gynoecious, parthenocarpic, or monoecious.Gynoecious
A gynoecious variety has primarily female flowers. This has a few implications: 1. Gynoecious varieties tend to produce more fruit overall per plant. 2. They tend to produce earlier (cucumbers often produce male flowers first, so a variety that only produces female flowers will set fruit earlier). 3. They often produce fruit in a more concentrated window - this is great for mechanical harvest or wholesale markets, but may be less ideal for a smaller farm that requires more consistent supply over the season. Succession planting can also address this. 4. Since the flowers are mostly female on gynoecious plants, you need to provide a pollen source. A gynoecious variety (unless it is also parthenocarpic - see below) requires a pollenizer / non-gynoecious variety planted alongside it. Approximately 10-15% of the plants in a given plot or tunnel should be pollinizers to supply adequate pollen.
Parthenocarpic
Parthenocarpic varieties do not require pollination to produce fruit. Some parthenocarpic varieties are also gynoecious, others are not. Parthenocarpic varieties are well suited to high tunnels since it can be tricky to provide sufficient pollination in tunnels. This is especially important if you are using insect barriers to keep cucumber beetles and other insect pests out of your tunnels. Most parthenocarpic cucumbers will be entirely seedless, though it is possible for seeds to show up if there are pollenizing varieties nearby.
Monoecious
Monoecious varieties produce both male and female flowers. As such, they do not require an additional pollenizer variety. They set fruit slightly later than the gynoecious varieties, but they produce for a longer period of time, which is ideal for farmers with continuous markets.
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| Floral biology significantly influences earliness, yield, and management. Photo: edurafi2, Wikimedia |
Grafted cucumbers
Grafting is likely not worth the time and expense for field-grown cucurbits. However, growers should consider grafting for tunnel grown cucumbers. Unlike tomatoes, which are grafted primarily for vigor and disease resistance, cucumbers are grafted almost exclusively for cold tolerance. This has been practiced by farmers in Japan and Korea for decades, but is just beginning to gain popularity in the US. By using a cold tolerant rootstock, like Cobalt, Tetsakabuto, or white skin figleaf gourd, you can plant earlier in the season than you would with ungrafted cucumbers. Earlier planted cucumbers will also finish earlier, making them a good crop to follow with spinach or other fall greens. While grafted cucumbers are not yet commonly available, our Extension colleagues from across the region recommended reaching out to Tri-Hishtil and Re-DiVined. If you’re already purchasing grafted plants from another supplier, ask them about grafted cucumbers, as they may be able to provide them You can also graft cucumbers yourself; see this guide from Purdue University for instructions.
Trellising cucumbers provides many benefits including higher yields, less disease pressure, and easier harvesting. Most Minnesota cucumber growers trellis their cucumbers, but in states where cucumbers are grown on a larger scale, they are more often grown directly on the ground. There are two primary systems for trellising cucumbers; both have benefits and drawbacks.
Choosing a trellising system
Trellising cucumbers provides many benefits including higher yields, less disease pressure, and easier harvesting. Most Minnesota cucumber growers trellis their cucumbers, but in states where cucumbers are grown on a larger scale, they are more often grown directly on the ground. There are two primary systems for trellising cucumbers; both have benefits and drawbacks.
Basic trellis
A basic trellising system for cucumbers consists of some sort of netted structure, supported by posts. Vines can either be woven through the net structure or clipped. Net structures vary; common materials include mesh or nylon nets, wires along the top and bottom of poles with string woven in between, or cattle / hog fencing. Some growers have free or steeply discounted access to cattle fencing from neighbors. These fences are also re-usable and easily sanitized, but keep in mind that a metal trellis is more likely to overheat and cause damage to your plants. Nylon or mesh nets are theoretically re-usable, but many growers find that the time it takes to untangle vines from the nets is not worth the effort. If you are using a mesh or nylon net, it should be supported on the top and bottom with a thicker wire running along the length of the trellis system. The net should be attached to the wires at all points where cucumbers are planted to support the weight of the climbing plants. Posts are most commonly metal t-posts, but growers with permanent trellis systems also use 4x4 wooden posts. A permanent trellis system can also be used for tomatoes and peas in future years. These basic trellis systems are most common for field grown tomatoes, but are also suitable for tunnels.
Cucumbers grown with this basic trellis system should have all side-shoots within 2 feet of the ground removed to encourage climbing. This also allows for better airflow at the base of the plants.
Cucumbers grown with this basic trellis system should have all side-shoots within 2 feet of the ground removed to encourage climbing. This also allows for better airflow at the base of the plants.
Pruned trellis
A pruned trellis system is much like a tomato pruning and trellising system. Cucumbers are pruned to a single leader, which is clipped or tied to a hanging string. This system requires a strong support system: growers either use 4x4 posts along the length of the tunnel with a strong wire running across the top, or they attach the strings to purlins (metal pipe structures) across the ceiling of their tunnels. If you plan to attach your trellis strings directly to the purlins, make sure that your greenhouse roof is reinforced and specifically designed to hold the weight of trellised plants (this is not necessarily standard for all tunnels, and these tunnel designs are more expensive). The most common system is the “umbrella system”, where a single leader vine is allowed to climb the string until it reaches the top wire, and then 2-3 buds are allowed to develop; the vines coming from those buds hang down and produce fruit. This system allows for easy harvest and produces high yields.Make sure to use varieties specifically adapted to greenhouse production if you are using this method.
Growing cucumbers on the ground
While not common in Minnesota, some very large growers do not trellis their cucumbers at all. The primary benefits of not trellising are labor reductions (at least before harvest) and ease of mechanical harvesting. However, at the scale of most Minnesota growers, this is not preferable. Fruit that touch the ground may be more prone to insect and disease pressure, and trellising allows for easy weed management between rows.
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| For very large growers who harvest with machines, it is common to grow cucumbers directly on the ground without a trellis. Photo: Stephen Ausmus, USDA ARS |
For more comprehensive information about growing cucumbers in high tunnels, see Purdue’s recently published guide: https://extension.entm.purdue.edu/publications/ID-521/ID-521-W.pdf
Insect management: Cucumber beetle
Cucumber beetles are the most obvious and devastating insect pest of cucumbers. There are two species, spotted and striped, with striped being the bigger problem. Striped cucumber beetles have one generation a year, though they often feel like an ever-present problem.
Preventing Cucumber Beetle Damage
Exclusion is one major route of dealing with cucumber beetles.- In the field, floating row covers can be placed as seedlings emerge and plants start to grow, just make sure to remove them as flowers appear to allow pollination.
- In the hoop house or greenhouse, research at Purdue has shown insect exclusion screens can keep cucumber beetles out of the hoop house. A screen size of 0.8 x 1.0 mm is able to keep beetles out while also allowing for ventilation.
- Trap crops, or cucurbit cultivars that are highly attractive to pests, can be used to reduce feeding on the crops actually want to harvest.
- Research in Missouri and the Northeast has found blue hubbard squash to be a good trap crop.
Good sanitation will (hopefully) help reduce next year's numbers.
- Removing or destroying crop residue will make it harder for cucumber beetles to find a spot to overwinter.
Deciding when to Treat
When action should be taken depends on plant age. Scout at least weekly, increasing frequency once you find beetles. For recently emerged plants with one true leaf, treatment should be considered if there are 2+ cucumber beetles per plant on one quarter of the plants. Once plants have 2 or more true leaves, Minnesota research suggests that treatment should be considered once beetles have defoliated 25% of leaves.Organic Products
Organic growers will have to rely heavily on the techniques listed above, as the organic pesticides available are limited in both their availability and efficacy. Some growers report that Kaolin clay reduces feeding. Research in Massachusetts found that Surround (kaolin clay) did reduce beetle numbers, and research in New York found Surround helped reduce defoliation in zucchini.
For a full list of products effective against cucumber beetle, see the Midwest Vegetable Production Guide. For a deep dive into cultural controls for cucumber beetles, see Managing Cucumber Beetles in Organic Farming Systems.
Conventional Products
Seed treatments are effective at protecting young plants in the first few weeks of life. Consider whether a seed treatment is truly necessary though. Seed treatments offer 2-3 weeks of protection, and if you are holding the transplants indoors longer than that, the seed treatment won’t be effective once plants are outside.
When managing cucumber beetles beyond the seedling stage, use the threshold above. Also note it is important to time sprays to reduce risk to pollinators. Honeybees tend to be most active early in the day, so spraying in the late afternoon will help.
For a full list of products effective against cucumber beetle, see the Midwest Vegetable Production Guide.
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| Cucumber beetles have two notable talents: feeding and making more cucumber beetle. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org |
Disease management: Angular Leaf Spot and a Look-Alike
Cucumbers short growing season often means they have less disease issues than other cucurbits. Angular leaf spot is common in Minnesota cucumbers. This bacterial disease is known to be seedborne, and can also survive in infected plant tissues. This disease doesn’t attack the fruit directly, instead causing parts of the leaf to turn yellow, dry out, and sometimes fall out. This can lead to yield reductions.Water is an important part of angular leaf spot biology, as it is how bacterial diseases move around. Avoid working with cucumbers when the plants are wet. The bacteria can survive as long as plant tissue is present, so prompt residue destruction and rotation are also critical.
Note that angular leaf spot is often confused with downy mildew. Downy mildew is not seen every year in Minnesota, but when it does appear, it can kill cucumber plants in 1-2 weeks. Both diseases cause distinct, angular yellow areas on the upper surface of the leaf, but only downy mildew causes fuzzy grey spores on the leaf’s underside. If you believe you are seeing downy mildew, reach out to Natalie or Marissa.
As angular leaf spot is bacterial, copper may provide some control. For more information on chemical control options, see the Midwest Vegetable Production Guide.
There are other diseases that often affect cucumbers in Minnesota. You can read about them on the University of Minnesota Extension website.
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