ASHS 2024 Conference

Soils host weeds, pathogens, and insects that can cause crop damage and reduce yield. Many methods have been developed to reduce these pressures within the soil, including soil solarization, chemigation, anaerobic soil disinfestation, and soil steaming. We have utilized soil steaming to reduce weed seeds and soil infestation in high tunnel and field tomato (Solanum lycopersicum) production. While it successfully reduces most weed species and southern blight (caused by Athelia rolfsii) in tomatoes, the emergence of nutsedge (Cyperus spp.) in soils with established populations can increase after steaming. Our research goal was to evaluate the efficacy of various soil preparation methods prior to steaming to allow the steam to penetrate the soil and target nutsedge directly. Except where noted, the field was first chisel plowed, disced, and then shaped into 2-foot-wide by 6-inch-tall beds. We compared 8 preparation methods for controlling nutsedge: a no-till control, herbicide control using S-metolachlor and halosulfuron-methyl, 6-inch-tall bed size, 12-inch-tall bed size, chisel plowed row, black plastic mulch, 4-inch-deep trenches on no-till, and 6-inch-deep trenches on no-till. Four trenches were cut into the soil with a soil trencher for each plot. Four replicates were included in a completely randomized design. Half of each bed was steamed until temperatures reached 160 °F, 4 inches deep, except for the herbicide beds and mulched beds, which were left unsteamed. Four sets of temperature probes were placed 12, 8, 6, and 4 inches deep in the soil and temperatures and used to monitor temperature changes in steam soils over time. Nutsedge coverage was visually estimated by placing a 1 by 6-foot rectangular PVC frame in each row over a representative section. 12-inch-tall beds had nearly 100% nutsedge coverage, while 6-inch-tall beds had nearly 50%. Herbicides reduced nutsedge coverage to 29%, and the plastic mulch reduced coverage to 8%. The steamed no-till, 4-inch trench, 6-inch trench, and chisel-plowed beds had no nutsedge emergence through the trial. The 6-inch-tall beds had lower temperatures at 6 and 8 inches deep than the other methods, which could account for the observed increases in nutsedge emergence post steaming. The time-consuming nature of soil trenching would make it impractical for most horticultural production settings; however, the chisel plow and no-till could be readily adopted. Determining effective methods to prepare the fields for soil steaming to reduce or eliminate nutsedge will make soil steaming a more viable method for organic farmers facing nutsedge pressures.

Cereals and other non-legume cover crops can help vegetable farms to reduce nitrogen leaching to ground water during rainy winter periods. A cover crop’s carbon to nitrogen ratio is an important metric that can help farmers better understand the nitrogen release dynamics from soil-incorporated cover crops. Cover crops with a lower C:N ratio (15:1) typically mineralize nitrogen when they are incorporated into the soil, whereas those with a higher C:N (25:1) usually immobilize nitrogen. But farmers need simple, reliable, field-based methods to predict a cover crop’s C:N ratio. Therefore, we evaluated the relationship between the Feekes growth stage scale and the C:N ratio of rye (Secale cereale L., ‘cv. Merced’) and triticale (X Triticosecale Wittmack, cv. ‘Pacheco’) cover crops in the Central Coast region of California. Over a hundred field samples of rye and triticale shoots were collected at various developmental growth stages from organic and conventional vegetable farms and planting date trials, across multiple soil types, planting times, row spacings, and plant densities. The Feekes scale was correlated with the C:N ratio of cover crop shoots of rye (r2=0.63) and triticale (r2=0.76). The transition from Feekes 9 (when the ligule of the flag leaf is visible) to Feekes 10 (‘boot’ stage) is roughly when the C:N ratio went from below to above 20:1. Regression plots were developed that illustrate the relationship between the Feekes scale and the C:N ratio. These results have practical implications for a new ground water protection regulation (Ag. Order 4.0) in California’s central coast region that incentivizes winter cover crops that are grown until the C:N ratio is 20:1 or more.

Snap bean production has decreased by ~30% recently due to an increase in imports and changing consumer preferences towards more fresh and frozen products. A major production concern is weed species that escape control, since they cause yield losses and can contaminate harvest loads. Coupled with changing weather patterns, snap bean processors and growers will have to adjust to these and future challenges. Field surveys were conducted to identify associations among crop/weed management practices and environmental factors on snap bean yield and weed density. From 2019-2023, snap bean fields throughout the major U.S. production regions were surveyed for weeds at harvest. Management records for each field were obtained from growers. Information on soil and weather conditions of each surveyed field also was obtained. In total 358 production fields were surveyed in the Midwest (Illinois, Iowa, Minnesota, Wisconsin), Northeast (Delaware, Maryland, New York. Pennsylvania), and Northwest (Oregon, Washington) regions. To determine associations among management and environmental variables on crop yield and weed density, the machine learning algorithm random forest was utilized. The models had 24 and 22 predictor variables for crop yield and weed density, respectively, and both were trained on 80% of the data with the remainder used as a test set to determine model accuracy. Partial dependence plots were used to visualize the change in response variables based on the most important predictors. The crop yield model had pseudo-R2 values of 0.56 and an accuracy of 74%. Higher average temperatures during early season growth, higher soil organic matter content, and planting midseason (June-July) predicted an increase in average crop yield. Meanwhile, excessive precipitation early in the season, high sand content of the soil, high temperatures at crop flowering and row cultivation predicted a decrease in crop yield. The weed density model had pseudo-R2 values of 0.55 and an accuracy of 81%. While row cultivation was associated with lower snap bean yield, it corresponded to a decrease in weed density, suggesting row cultivation had less-than-ideal selectivity between the crop and weed. Moreover, multiple spring tillage operations prior to planting predicted an increase in average weed density, implying that excessive tillage may favor emergence of weeds in snap bean. Over the coming decades, climate change-driven weather variability is likely to influence snap bean production, both directly through crop growth and indirectly through weeds that escape control practices that also are influenced by the weather.

Weed management is one of the biggest challenges vegetable growers face. Plastic mulch, herbicides, tillage, and hand-weeding are common ways vegetable growers manage weeds. These methods can be labor intensive, require specialized equipment, and cause environmental harm. Tarping is an alternative weed management method. Silage tarps or high-tunnel plastics are commonly used tarping materials; these are multi-functional tools that can be used for several years. Tarping facilitates stale seedbed weed management techniques by modifying the soil microclimate and promoting weed germination. After weed germination, opaque tarps can terminate weeds via occultation (lack of sunlight), whereas clear tarps terminate weeds by creating extreme temperatures. More information is needed for the type and timing of early-season tarp application for optimal weed control. The research was conducted at the Iowa State University Horticulture Research Stations in Ames, IA. This study examined three types of tarps: black, white, and clear, at three different durations: two, four, and six weeks prior to planting compared to a non-tarped control. Clear tarp and control treatments were cultivated at the time of tarp removal prior to planting. Soil temperature was recorded at 5 centimeters depth for 6-week tarp treatments. Early-season clear tarping did not elevate temperatures enough to terminate the majority of weeds. However, black and white tarps created a weed-free planting bed. Average soil temperatures underneath the clear tarp were the warmest (21.8ºC), followed by black tarp (15.1ºC). White tarp treatments (11.7ºC) had a lower average soil temperature than treatments with no tarp (14.8ºC). Two weeks following tarp removal, six-week clear tarp treatments had a higher percent weed cover than black and white tarp treatments measured using Turf Analyzer, a digital photo analysis software. Differing soil temperatures did not significantly impact soil microbial biomass carbon. The two-week white tarp had significantly higher soil microbial biomass nitrogen than all other treatments except four-week clear tarp. There was no effect of tarp type or duration on onion crop yield. These results indicate that the use of white and black tarps can be a feasible alternative weed management method in North Central vegetable production systems.

Propagation greenhouses produce a wide range of crops, each presenting unique responses to light quality and quantity. With dynamic LED lighting solutions now available and proven to be viable over large acreages, propagators can tailor their lighting protocols to each crop with regards to zone management, photoperiod, spectrum and intensity. The effects of light quality and quantity on plant morphology and growth are well documented and while the exact impact is not generalizable across all crops and varieties, certain themes hold true. For example, high levels of blue light are generally associated with compact plants and thick, waxy leaves. In contrast, high levels of far-red light can cause etiolation in multiple species through the shade avoidance response but enhances photosynthesis and growth when combined with red light. Given the high importance of crop morphology in propagation, dynamic Dynamic LED lighting has been used to develop advanced lighting protocols in the propagation of fruit, vegetable and ornamental crops. In the production of cucumber transplants, applying high levels of blue light and a long photoperiod effectively slows the growth of cucumber transplants at the end of the propagation cycle, a strategy which proved useful to a propagator looking to delay transplant delivery per the client’s request. Concretely, the combination of high blue levels and a long photoperiod slowed crop growth, prevented tendril development and restricted plant stretching. Further, the use of high-blue treatments over young leafy greens effectively reduced plant height by 2-3 cm and produced stronger plants. Another trial focused on the production of strawberry tray plants found that a balanced light spectrum produced more stolons (i.e., daughter plants) while a blue-enriched spectrum produced significantly more leaves. In the production of ornamentals, dynamic lighting can be used to reduce the greenhouse’s reliance on plant growth regulators (PGRs), enhance leaf or petal coloration and trigger bud formation. In red-leafed varieties, controlled light-induced plant stress through spectral and/intensity adjustments have proven effective at stimulating the production of red pigments and enriching the leaves’ hue. Results from various commercial and research trials demonstrate benefits of dynamic LED lighting in the propagation of horticultural and ornamental crops alike. This presentation presents data from the aforementioned case studies among others.

Food- and nutritional-security are among the highest concerns for Hawaii residents. The state imports about 85% of the consumed food and there’s roughly two-week worth of food locally at any given time. Local food production is costly due to high inputs cost. Algae extracts are known to supports plants' flowering and fruiting, increasing plant nutrient uptake, enhancing resistance and recovery from plant stress events, and increasing nutrient use efficiency and fertilizer assimilation. Three different algae extracts (Afrikelp, Acadian, and Kelpak) were evaluated for their effect on growth and yield of bush bean, bell pepper, and tomato in a randomized complete block design (RCBD) with 5 blocks. The algae extracts were applied 5 times during each growing season. The algae extracts were applied at dilution rate of 1:100 with a week between applications for the bush bean crop and two-week intervals for bell pepper and tomato crops. The results showed a highly significant (p < 0.01) increase in the three crops yield under all algae extracts compared to control (water only) treatment. The results also showed there was a significant (p < 0.05) difference between the algae extracts with highest yield recorded under Afrikelp extract compared to Acadian and Kelpak. The yield increase reached between 150-300% compared to control treatment.

Onions are a globally popular kitchen staple, not only for their flavor, but also their nutritional value. According to the Agricultural Marketing Research Center, onions are the fourth most consumed fresh vegetable in the United States. To bring this valued crop to our kitchen tables, quality onions must be produced in high quantities to meet consumer demands. Since they are especially susceptible to weed competition due to their minimal canopy cover, weed management is an important consideration for onion production. One weed management tool is soil tarping. This study evaluated the impact of two types of tarping (solarization and occultation) and duration of tarping (6-, 4- and 2-weeks) on weed control in Patterson and Candy onion production. Field experiments were conducted during the 2023 growing season in Brookings, South Dakota. Solarization was conducted using clear tarps secured with sandbags and buried edges. Tarps were placed in April and May at respective weeks before removal on May 30. Immediately following tarp removal, each plot was tilled, and rows of onion transplants were planted. Occultation was evaluated using white side up and black side up silage tarps, both applied at respective weeks before removal and onion planting. Each treatment plot filled a twenty-four by ten-foot area. A randomized complete block design with four blocks and ten treatment plots per block including a control with no tarp was established. Response variables for data collection included weed type, height, and biomass as well as onion yield. All tarping treatment plots resulted in less weed pressure than the control at tarp removal. Broadleaf weed count collected during the growing season was different among tarp treatments (p=0.03). Data collected June 12 showed 6-week clear tarp to have 67% less broadleaf weed count per acre than the control, and 74% less than the 4-week black tarp. There was no difference in onion yield due to tarping treatment. This may have been due to biweekly weeding events that evened out treatment effect on weeds over the growing season. There was, however, a difference in yield between Candy and Patterson onion cultivars (p=0.02). Candy averaged a marketable count of 19 of 48 planted onions while Patterson averaged a marketable count of 36 of 48 onions planted. Soil tarping may be an effective option for farmers to reduce early season weeds in onion production, however, it should be used alongside other management strategies to obtain a viable yield.

Sales of compact vegetable bedding plants for the home-gardening market segment are increasing. However, production guidelines for these new crops are limited. Our objective was to assess the effect of fertilizer use and controlled-water deficit (CWD) on plant growth during production, and after-production effects on fruit yield. ‘Siam’ tomato and ‘Basket of Fire’ pepper plants were grown in a greenhouse for 4 and 6 weeks, respectively, using 10-cm containers. Half of the plants received a water-soluble fertilizer once a week, and the other half were irrigated with tap water only, relying on the starter fertilizer charge in the substrate (EC = 0.9 mS·cm−1). Plants were irrigated when the substrate volumetric water content (VWC) reached 0.15, 0.30, 0.45, or 0.60 m3·m–3. After the experiment, plants were transplanted into 20-cm containers, top-dressed with controlled-release fertilizer (CRF), and grown for another 10 weeks to evaluate carryover treatment effects. Plants that did not receive fertilizer were shorter and had a lower shoot dry mass (SDM) than those that were fertilized, regardless of species. Shoot height of tomato followed a quadratic trend in response to CWD, which peaked at 0.45 m3·m–3, whereas SDM linearly increased with increasing VWC. No growth responses to CWD were measured for pepper. However, plants of both species that did not receive fertilizer looked chlorotic and had a lower chlorophyll concentration than those that were fertilized (15 and 32 µmol·m–2 for tomato and 15 and 27 µmol·m–2 for pepper, respectively). Plant greenness increased after applying CRF, suggesting that applying fertilizer right before shipping could increase quality of these plants when grown with limited or no fertilizer to control growth. After the carryover phase, differences in plant growth were maintained, and differences in yield was measured between fertilized and non-fertilized plants (56 and 48 fruits for tomato and 153 and 112 fruits for pepper, respectively). Our results show that growth and yield of compact tomato and pepper plants are affected to a larger extent by fertilizer use than by substrate VWC.