Spot the symptoms

Powdery mildew appears as white and powdery spots, mostly on the upper side of the leaves. The disease appears first on the older, lower leaves of lettuce heads (Fig. 1). As the disease advances, hyphae and “powdery” conidia cover the leaves, resulting in slower plant growth and yield reduction. The conidia represents the symptom and sign of the pathogen due to its visibility to the naked eye. Conidia on the plant surfaces germinate, penetrate the tissue and form haustoria. Infected lettuce leaves turn chlorotic and eventually take on a brown, dried appearance. Occasionally, survival structures, cleistothecia, will emerge as visible dark brown spots.

Photo: Rosa Raudales

Know the enemy

Golovinomyces cichoracearum (formerly known as Erysiphe cichoracearum) is the name of the fungus that causes powdery mildew on lettuce. This pathogen is distributed worldwide. This type of powdery mildew affects most types of lettuce species (e.g. lettuce butterhead, crisphead, romaine, etc.) and related crops (e.g. chicory). Other strains of this same pathogen cause diseases on greenhouse ornamentals in the Asteraceae family.

This fungus is an obligate parasite, which means that it requires plant tissue in order to complete its life cycle. Resting structures such as cleistothecia and thick-walled mycelium in crop residues are suspected to be the main survival stages between crops. Therefore, removal of infected plants and debris becomes very important for preventing disease spread.

Spore dissemination is favored by air flow in the greenhouse. Spores disperse to very long distances. The time from when a spore lands on the surface of a leaf to the time it produces new conidia can be as short as 72 hours but is most likely to occur between 5 to 7 days. Unlike other fungal diseases, free moisture on the leaves will inhibit germination of spores.

Powdery mildew thrives in dry and warm environments but can also persist in cooler periods. Once infection has begun, the mycelium continues to spread on the plant surface regardless of the moisture conditions in the atmosphere. Maximum germination of conidia occurs at 96 to 98 percent relative humidity (RH).

Photo: Leanne Pundt

Reduce the risk of disease and control the problem

Maintain adequate ventilation. Maintain low relative humidity levels by properly timing ventilation and heating. Maximum spore germination occurs at RH higher than 96 percent. Spatial distribution between lettuce plants is important to increase air flow between plants and also for uniform coverage for spraying fungicides.

Remove infected plants. Scout plants and remove symptomatic plants quickly. Collect symptomatic plants in a plastic bag to avoid spore dispersal. Sanitize all greenhouse equipment and production areas to avoid the presence of plant residues with the disease re-infecting the greenhouse. After each crop cycle, remove all excess plant debris. Inspect new plant material such as seedlings, cuttings or transplants coming into the greenhouse.

Use resistant cultivars. Keep resistant varieties of lettuce in mind that are less susceptible to powdery mildew. These varieties include Jericho, Sandy, Red Salad Bowl, Loma and Regal Oak. You can visit vegetablemdonline.ppath.cornell.edu to stay up to date on resistant varieties.

Choose the right fungicide. Preventative fungicides are recommended if powdery mildew has been an issue in the past or the environmental conditions favor the disease. Corrective fungicides should be applied at first sight of powdery mildew. Rotating out fungicides helps avoid the risk of the powdery mildew becoming resistant to the chemical or antagonistic organism. Attention to spray distribution and coverage is also important for control. Table 1 includes a summary of products available for control of powdery mildew.

Cora (cora.mcgehee@uconn.edu) is a graduate student in Plant Science at the University of Connecticut. Rosa is an assistant professor at the University of Connecticut (rosa.raudales@uconn.edu) with a M.S. in Plant Pathology and a Ph.D. in Horticulture.

Acknowledgements. This project is supported, in part, The Connecticut Department of Agriculture via the Specialty Crop Block Grant Project# AG151260.

Disclaimer: Reference herein to any specific commercial products by trade name does not necessarily constitute or imply its endorsement, recommendation, or favoring by the University of Connecticut. The data presented here shall not be used for advertising or product endorsement purposes.

When I was asked what sort of internal company events a produce grower could organize to increase employee buy-in of their products, I mentally threw my hands up in the air. What can’t they do! I mean, it’s food. Everyone likes food. Given the popular (and necessary) nature of your product, are you maximizing your employee potential when it comes to marketing?

As produce growers, you have an amazing opportunity at your fingertips to leverage the personal marketing reach of your employees. There’s almost nothing more powerful than food to bring people together, and word-of-mouth referrals and reviews reign supreme. Put the two together, and you’ve seriously expanded your organic marketing efforts with marginal impact on your budget.

Product knowledge (PK) training is central to any business that has a product to sell. You can’t expect to reach your goals if your employees don’t fully understand, and relate to, the product you sell. How they value your produce product will also impact the quality of the job they do growing it. But standard PK meetings are boring, and do little to excite employees about your offerings. Here are a few ways you can get creative with internal marketing.

Launch parties

Similar to what you might see for a grand opening, staging an internal launch event for a new product is a great way to get the entire team excited. Launch parties are also a great way to ensure all staff gets to sample the new offering, be exposed to new packaging, and learn about different ways to use the produce. Provide a product sheet to all employees so they are aware of any specific promotional language you’ll be using for company marketing and advertising.

Seasonal taste tests

Set up seasonal taste tests so that employees can get to know how your produce tastes as it develops, and when it’s in its prime. Or learn how certain growing practices are helping — or hurting — flavor and quality. Doing so can create a sense of inclusion and pride in your produce. Set up these events just like one would at a public event tasting. Tomato tastings are a popular model, and attendees get to vote on their favorite flavors.

Employee chefs

I’m assuming you’d prefer your employees purchase and use your produce instead of someone else’s. So why not incentivize them to be creative with yours? Relevant content development is a crucial part of modern marketing, and recipes and produce go hand in hand. Teaching your customers how to use your produce in creative ways should be an integral part of how you market your product. By having recipe and cooking contests with your employees, you not only create a way for them to participate in, and influence, company culture and marketing – but you can also promote their recipes to customers.

Hold a monthly recipe contest. The previous month’s winner gets to join in on the team of judges. The month’s winning employee chef receives some sort of bonus incentive (cash, a paid day off, whatever works for your business). Then, you use the winning recipe as marketing content for customers. Even better, shoot a video of your winning employee chef preparing their winning dish. A turn in the spotlight is always great for employee morale.

Cook & learn

Exposure and education are key to employee happiness and development. If you can’t often let employees out to visit vendors or other operations, consider bringing experts to them. If you are working with a local or celebrity chef to promote your produce, bring them in-house for special demos just for your staff. This is a great opportunity for employees to learn more about how to use your produce and ask food prep and cooking questions.

Leverage social media

Now that your employees have tasted and used your produce in their own kitchens, what are you doing to leverage their individual social media reach? It’s no secret people like to take pictures of their food. Wouldn’t you prefer your employees were taking pictures of your food? There’s no shame in rewarding employees for preaching your brand message online to their own personal network — given the message is relevant. Consider offering small cash payments or other benefits to employees who share images and information with social media. Make sure everyone understands how to properly name, tag and write about your products when they do post them. You can even include sample post language on your employee product sell sheets.

Grow side benefits

Planting the seed of intellectual curiosity is a big side benefit of deepening your employee’s product knowledge. Many produce growers will need to turn to internal education and training programs to meet demand for qualified labor and knowledgeable growers. Growing employees from within starts with employees who become interested in what you do and how you do it. That interest can sprout at the entry level of your labor pool. Be sure not to leave anyone out when you’re holding any of these internal events.

I realize all this internal marketing seems like a lot of extra work. It is. But ask yourself — what could your company be missing by not earning employee buy-in?

Leslie (CPH) owns Halleck Horticultural, LLC, through which she provides horticultural consulting, business and marketing strategy, product development and branding, and content creation for green industry companies. lesliehalleck.com

Genetics: There are several names for the greenhouse cucumber (Cucumis sativus) including European, Dutch, English or burpless cucumbers (Fig. 1). Aside from generally being long and slender, there are several ways in which greenhouse cucumber varieties differ from field-grown cultivars. First, they are generally considered to have a milder flavor and less bitterness. Second, the skin on fruits is very thin and, as a result, peeling is not required prior to eating. Third, fruits are also parthenocarpic, or seedless. Beit Alpha is another type of greenhouse cucumber that is popular. They are similar to the European/Dutch cultivars in that they are mild-tasting and seedless and, though the skin is thicker than standard European varieties, it is still thin enough not to require peeling. However, they are smaller than the European/Dutch cultivars when mature and harvested, when fruits are 6 to 8 inches long.

Production systems: The most common production systems used for cucumbers are those systems used for other vining or high-wire crops, including Dutch buckets or a gutter system with slabs or bags of substrate.

Propagation and young plant production: Greenhouse cucumbers are propagated by seed. The seed for greenhouse cucumber varieties is expensive, approaching $1 per seed, due to the fact that the genetics are gynoecious and parthenocarpic (seedless). Seeds may be sown directly into 4-inch blocks of stone wool, coconut coir, or other substrate that will be transplanted into production systems. The air temperature should be maintained at 84° F for the first few days for optimal germination. After the radicle has emerged, lower temperatures to mid-70s° F. Supplemental lighting can be used to keep seedlings compact. Once transplants have three to four true leaves, they are ready to transplant.

Nutrient solution: Greenhouse cucumbers are a heavy-feeding crop. Complete nutrient solutions with an electrical conductivity (EC) between 2.0 and 3.0 mS/cm and a target pH between 5.5 and 6.0 should be used. The ratio of nitrogen to potassium (K) should be around 1:1.5; elevated levels of K are used for this heavy-fruiting crop. Avoid elevated nutrient solution and root-zone EC, as the high concentration of salts can damage roots and cause root rots to occur.

Temperature: Cucumbers are warm-growing compared to other greenhouse and hydroponically grown crops. Daytime air temperatures should be maintained between 75 and 80° F, but should not exceed 85 to 90° F. Temperatures during the night should not drop below 65° F.

Light: Cucumbers are, generally speaking, a high-light crop. There are some varieties that will perform better under lower-light conditions, but all will respond positively to increased light intensities. Supplemental light can be used to enhance growth and productivity, but only if the investments in lights and operating costs are economical.

CO2: Cucumbers benefit from carbon dioxide (CO2) enrichment in the greenhouse. Supplemental CO2 from liquid injection or burners up to 1,000 ppm can boost productivity, especially during periods where ventilation is reduced.

Pollination: Since nearly all the cucumber cultivars grown hydroponically are parthenocarpic and form fruits without ovules being fertilized, no effort to pollinate flowers is required.

Pruning and training: As with other vine crops, cucumbers require pruning and training. As with tomatoes, “suckers,” the shoots arising from leaf axils, are removed to maintain a single, primary stem. Cucumbers also produce tendrils, which should be removed. If left on the plant, they will wrap around other plants and infrastructure, causing problems. Fruit thinning should also occur for standard-sized cucumbers. If more than one fruit is allowed to develop at each leaf axil, the fruit load will be too great and the quality of individual fruits will be diminished.

Cucumbers need trellising since they are a vine crop, and there are several methods that may be used.

The drape method is where the stem is trellised on twine up the suspended wire, then allowed to drape down over the wire and grow toward the ground.

The umbrella method is similar to the drape method in that the stems are trained up to the wire. However, once stems grow above or over the wire, they are pruned back to the send leaf after the wire and two main stems are allowed to grow and drape over support wires, growing down toward the ground.

The V-cordon method is somewhat similar to the drape method, in that the vine is trellised up to the wire and then grows back down toward the ground. However, the high-wire is not directly above the plants in a V-cordon. Instead, the wire runs a few feet out from the plant into the aisle, requiring stems to be trellised at an angle. With one row leaning into an aisle and the other row running toward the other aisle in a double aisle, it allows more light to be intercepted by each individual plant by reducing the shading from neighboring plants.

Some growers are also staring to use the lean-and-lower method (Fig. 2), similar to what is used for tomato. As plants near the support wire, the trellis each stem is trained to is lowered so the growing point is below the support wire, and then moved down the wire several inches.

Pests: Spider mites, thrips, whiteflies and aphids are some of the most common insect pests of greenhouse cucumbers. One of the most distinctive signs of an infestation is the mottled, chlorotic cucumber leaves resulting from spider mites. At first glance, it could appear like high-light damage or a nutrient deficiency, but this occurs when spider mites feed on leaves and cause stippling all over them.

Diseases: Cucumber mosaic virus can have detrimental impacts on crops. Since aphids can transmit this disease, keep aphids under control and your plants virus-free to avoid outbreaks. Powdery mildew is the most common disease in cucumber production. Look for those varieties that have some resistance to powdery mildew and start control measures early to avoid the development of hot spots.

Physiological disorders: Fruit abortion occurs when there are too many fruits on the plant at any one time and there is insufficient vegetative growth to maintain the crop load. Fruits may also abort when there is a sudden change in crop culture or the environment.

Harvesting: Growers can harvest from cucumber plants for approximately 12 weeks, though this will vary with cultivar, environment and culture. For standard-sized European cucumbers, fruits are usually harvested when they are between 12 and 14 inches, with the USDA requiring a minimum fruit length of 11 inches. Frequent harvests up to three to four times per week are necessary to keep plants balanced between vegetative and reproductive growth, as well as to maintain fruit quality.

Postharvest care: While the thin skin of greenhouse cucumbers is a positive attribute with respect to flavor and convenience, it creates challenges for postharvest; the thin skins allows more water loss from fruits compared to thicker-skinned field cultivars. To minimize water loss and extend postharvest quality, individual fruits should be shrink wrapped. For Beit Alpha cucumbers with the slightly thicker skin, multiple fruits may be placed on a polystyrene tray that is then shrink-wrapped, or they can be placed inside a plastic bag with ventilation holes. While fruits can be stored at room temperature, they can also be cooled to extend product life, but temperature should not get below 50 to 55° F to avoid chilling injury. Cucumbers may yellow in response to ethylene, so exposure should be minimized throughout the postharvest chain.

Christopher (ccurrey@iastate.edu) is an assistant professor of horticulture in the Department of Horticulture at Iowa State University.

It’s an interesting time to work in horticulture, and many young people are taking notice. Fruit and vegetable production is a task that’s now being carried out in warehouses and greenhouses as well as in fields. Production technology is developing at an incredible pace, reducing labor needs, improving food safety and changing horticulture as we know it. It’s also attracting a different group of potential produce growers.

According to a 2017 National Young Farmers Coalition survey of “3,517 past, current and aspiring farmers under 40 years across the U.S.,” 75 percent of respondents said that they did not grow up on a farm — wow! When you look at the controlled environment agriculture industry, I wouldn’t be surprised if many of those younger folks also fall into this category and are new to growing commercially. While one group may be known more as “farmers” and the other group “growers,” there are many similarities, and they share one common goal — growing high-quality fruits and vegetables efficiently.

These new-to-the-industry folks, along with experienced growers who are following in their family’s footsteps, are evolving along with the market and creating a more forward-thinking, innovative produce industry. In this month’s cover story, we delve into the family-focused history and future of Big Marble Farms, a year-round Canadian greenhouse cucumber operation. Although CEO Ryan Cramer says he “grew up in a cucumber crop,” he did more than step into an existing role in the family business — he, alongside his father and uncle, created a new, high-tech greenhouse operation in 2009 with the future in mind. “You’ve got to be always moving forward,” Cramer says. “That’s a common thing. You always have to be constantly innovating and adapting to the changes — constantly becoming more efficient and looking for ways to produce better.” Read more about Big Marble Farms here.

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Twitter: @Karen_GIE