Agronomy

Description

As a crop that originated in Central America, snap beans are also known as green beans. Stringless snap beans debuted during the 1890s. Before that time, all snap beans had a fibrous string that traced each pod’s seam, and they were called string beans. Stringless varieties have had growing popularity since their introduction. In some cases, however, consumers may still like string beans. Snap beans can be categorized based on several features. For example, their growing habits may be described as bush, runner or half-runner types. Pods may have round or flat characteristics, and the pod color can also vary.

Site Selection

Snap beans prefer well-drained, fertile planting areas. Sites with good air filtration are also preferred. Even with less desirable soil, however, snap bean production could still be possible. In areas with poor drainage, the problem should be resolved. Otherwise, the risk for soil-borne disease and root respiration problems can increase. Soil pH level should range from 6.0 to 6.5. Make soil pH adjustments as necessary because pH level will dictate the extent to which snap bean plants can use fertilizers applied.

Fertility

Conducting a soil test can inform whether the selected snap bean planting site requires input applications to address soil pH or fertility needs. Snap beans may also serve as a rotational crop because the plants can fix nitrogen and contribute to enhanced soil fertility.

With respect to fertilizer needs, nitrogen requirements for snap bean production will depend on the variety. Generally, less nitrogen would be necessary for blue lake varieties, which need an estimated 15 pounds of nitrogen per acre, than non-blue lake varieties, which require an estimated 45 pounds of nitrogen per acre. For phosphorus and potash, producers should compute the specific application rate based on soil test results. Given that snap beans have a relatively short maturation time period, apply fertilizers at planting. Soil zinc, iron and manganese deficiencies can create challenges for snap bean production, so use soil test results to also monitor these micronutrient levels.

Variety Selection

As mentioned earlier, snap bean varieties can have several defining characteristics. Select varieties with attributes that fit the market’s needs. With respect to growing habit, most varieties grow as bush beans or runner beans. As the name suggests, bush beans have a relatively short stature — generally, they grow to 1- to 2-foot heights — and they’re compact. Because they typically set all pods at once, harvest occurs generally just once. In runner beans, they flower and develop pods during an extended time horizon. As bean plants that can grow to 6- to 7-feet heights, runner beans, also known as pole beans, must vine up a trellis. Some pole bean vines may grow as tall as 10 feet. Half-runner beans represent a compromise between bush and runner bean varieties. On average, half-runner bean vines grow to 3-foot lengths.

Bush and runner snap beans can form round or flat pods. Blue lake types are those with round pods, and Kentucky wonder types refer to bean varieties that produce flat pods. From a color perspective, most snap beans have green pods. However, other possible colors include yellow, which are also known as wax beans; purple; and streaked.

Possible Green Bean Varieties

Planting

Snap beans grow well when temperatures range from 60 degrees F to 70 degrees F. Production is possible, however, with 50 degree F to 80 degree F temperatures. Because of their sensitivity to cool weather and frost, avoid planting snap beans if either cold temperatures or frost pose a risk. As a general rule, begin planting snap beans when the soil warms to the appropriate temperature. Generally, the ideal soil temperature is at least 55 degrees F. Then, in two- to three-week intervals, producers can continue planting snap beans to lengthen the growing season and extend fresh snap bean marketing opportunities.

Growing snap beans begins with directly seeding the selected variety. To thwart disease risk, choose seed that has had fungicide treatments. Treated seed is especially preferable if producers plant snap bean seed into cool soils. For all bean varieties, planting depth typically ranges from 1 inch deep to 1.5 inches deep. Seed size and soil type will dictate the specific planting depth. Row and in-row spacing will vary by snap bean type. Row spacing typically ranges from 30 inches to 36 inches for bush beans but 36 inches to 48 inches for runner beans. With respect to in-row spacing, the distance averages 1.75 inches to 2.5 inches for bush beans and 6 inches to 9 inches for runner beans.

For bush beans, constructing raised beds, covering them in black plastic and using drip irrigation may support high yields and result in a cleaner bean harvest. Growers raising trellised beans have reported similar results.

Like other specialty crops, snap beans may grow in high tunnels. For snap beans, high tunnel production would enhance earliness and boost fruit set. Producers who choose high tunnels for snap bean production can plant seeds four weeks to six weeks before they would otherwise. To manage temperatures, high tunnels may need daily ventilation, especially when temperatures begin to rise. Constructing low tunnels to cover snap bean plants within a high tunnel may provide added protection from cold weather. When choosing a high tunnel site, look for soils that have good drainage and fertility and sites that would provide full sun and year-round irrigation access. Other considerations include microclimates, crop rotations, disease pressure and bed configurations. Within high tunnels, drip irrigation systems tend to work well. High tunnel production may also involve less pest pressure. Within a high tunnel, use a 12- to 15-inch row spacing, and plant bush bean seeds every 2 inches to 3 inches.

Cultural Management

Runner beans need a trellis structure. To build a trellis, producers may install stakes 15 feet to 20 feet apart. Then, they can string 10- to 12-gauge wire between posts near the top and bottom of each post. After creating a cross-cross pattern between the wires with twine, runner beans will have a structure that they can climb and that will give them support. Other possible trellis frameworks include the teepee and A-frame structures.

Water Management

Some research suggests that irrigation can promote snap bean yields. Georgia trials indicated a 25 percent to 50 percent yield improvement in well-irrigated snap beans relative to dry land snap beans. Depending on the stage of the growing season, weekly moisture needs may peak at 1.5 inches to 2 inches. If snap beans confront a water shortage during blossom-pod set or other critical growth periods, then plants may drop their blossoms and pods and yield more poorly.

To know whether the soil lacks adequate moisture, consider monitoring soil moisture levels. Typically, snap beans don’t wilt, so recognizing plant-level moisture needs may be challenging. In plants experiencing moisture stress, however, their foliage may develop a bluish cast. If providing irrigation to snap bean plants, then avoid applying too much water. Plants exposed to excess water may develop a root rot infection.

Sprinkler irrigation systems that either use center pivots or traveling guns are irrigation options for snap bean growers. Drip irrigation systems represent another alternative if growers can provide the necessary management.

Weed Control

A good defense to weed infestations involves adopting management practices that encourage a snap bean canopy to develop quickly. Several cultural weed management strategies focus on ensuring that a canopy will develop quickly. Those include choosing weed-free snap bean seed, preparing a clean seedbed, fertilizing and watering as appropriate, planting seed at the correct row spacing and addressing diseases and insects. Until snap beans have grown to have a good cover, diligently remove weeds.

Mechanical and chemical practices are also possible weed control mechanisms for snap beans. Mechanical control refers to using plowing or disking during field preparation. Cultivating, mowing, hoeing and hand pulling would also help to address weed populations. Cultivation practices may be best suited for planting areas experiencing minor weed issues.

With respect to herbicide use, herbicide selection will depend on weed type, soil attributes, a herbicide’s strengths and weaknesses and herbicide application requirements. Note that residual herbicides may lose their effectiveness after cultivation has occurred.

Insects and Diseases

Problematic insects for snap bean producers can target seeds, plant roots and young seedlings; foliage; or pods and seeds. Addressing pests that feed on marketable plant components should be a priority.

Pest monitoring needs will vary throughout the growing season. On a weekly basis, check snap bean plants for insect damage before blooming. After the plants have bloomed, increase the monitoring frequency to twice per week. Pests for which growers can scout include corn earworms, stink bugs, European corn borers, caterpillars, beetles, spider mites, whiteflies, thrips, lesser cornstalk borers, grubs, wireworms and seedcorn maggots. Snap bean losses may also be attributed to aphids and leafhoppers.

Various diseases can cause problems for snap bean seedlings and foliage. Diseases that may affect snap bean varieties include Pythium damping-off, Rhizoctonia damping-off and tip blight, Southern blight, bean rust, anthracnose, Pythium cottony leak and white mold. Depending on the growing stage influenced by a disease, prevention or control strategies may include adopting a proper crop rotation, choosing well-drained planting sites, selecting the right varieties, deeply turning the soil and applying fungicides.

Virus and nematode risks may also influence snap bean production. Common bean mosaic, Southern bean mosaic and yellow bean mosaic viruses may all infect snap beans. Control methods may include rotating crops, cleaning adjacent vegetative cover, choosing certified seed and selecting virus-resistant varieties. Nematodes can target snap bean roots. Crop rotation and fumigation can address nematodes.

Harvest and Storage

Snap bean maturation varies by bean type. As a general rule, bush beans require between 48 days and 60 days to mature compared with the 58 days to 70 days for runner beans. High-quality snap beans would be straight, well-formed, brightly colored, tender and firm, and they should have a fresh appearance. Bush snap beans usually set pods at the same time. Harvest when they have reached the mature-green stage, characterized by tender pods and the correct bean size for the given variety. For some varieties, harvest when seed development is one-third complete. If beans are harvested after the mature-green stage, then pods may be tough and fibrous, but mature stringless varieties are less likely to have toughness and stringiness characteristics.

If growing runner beans, then harvest may occur for an extended period. On average, growers establish three- to five-day intervals for harvesting, and harvests occur five times on average per crop. By regularly harvesting mature beans, the plants continue to flower, and immature pods continue to develop.

After harvest, snap beans benefit from immediate cooling because of their perishability. Field heat must be removed. Storage life may extend to eight days to 12 days provided that producers harvest snap beans at cool ambient temperatures, quickly transport snap beans to coolers programmed to the correct temperature and provide a humid environment during storage. Storage temperatures should range between 41 degrees F and 45 degrees F.

The relative humidity level recommended for snap bean storage is 95 percent to 100 percent. After harvest, water loss in snap beans represents an issue to manage. If snap beans lose 10 percent to 12 percent of their weight, then they also lose their marketability. Another key to postharvest handling involves quality control. Snap bean inspections should screen the harvested material for pod size, weed debris, worms and insects. Such inspections will ensure that producers market a high-quality product.

Sources

Cantwell, Marita and Trevor Suslow. Bean, Snap: Recommendations for Maintaining Postharvest Quality. University of California. Davis, 95616.

Delahaut, K.A. and A.C. Newenhouse. 1997. Growing beans and peas in Wisconsin. University of Wisconsin. Madison, WI 53706.

Drost, Daniel and Reagan Wytsalucy. 2014. High Tunnel Green Bean Production. Utah State University. Logan, UT 84322.

Hawkins, Gary L., George E. Boyhan, Stanley Culpepper, Esendugue Greg Fonsah, Kerry A. Harrison, William C. Hurst, David B. Langston, Changying Li, Daniel D MacLean, Alton N Sparks and Paul E. Sumner. 2013. Commercial Snap Bean Production in Georgia. University of Georgia. Athens, GA 30602.

Midwest Vegetable Production Guide for Commercial Growers. 2015. Midwest Vegetable Production Guide for Commercial Growers.

Orzolek, Michael D., George L. Greaser and Jayson K. Harper. 2002. Snap Bean Production. Penn State Extension. University Park, State College, PA 16801.

Rowell, Brent and John Strang. 2011. Snap Beans. University of Kentucky. Lexington, KY 40506.

Rutledge, Alvin D. 1995. Commercial Bush Snapbean Production. University of Tennessee. Knoxville, TN 37996.