Lisa W. DeVetter

Mulches Reduce Weeds, Maintain Yield, and Promote Soil Quality in a Continental-Climate Vineyard

Weeds reduce vineyard productivity by competing with grapevines for water and nutrients. To manage weeds, growers commonly apply herbicides and/or cultivate, which compromise soil quality. With the expansion of continental-climate viticulture, such as in the Midwest, there is a need for sustainable weed management strategies that maintain grapevine productivity, fruit quality, and soil quality. Our objective was to evaluate four weed management strategies in a Midwestern vineyard. Data were collected from an established vineyard in Iowa planted with Maréchal Foch grapevines (an interspecific hybrid). Treatments were established in a randomized complete block design. Treatments were replicated four times and included: (1) cultivation, (2) herbicide application, (3) straw mulch, and (4) a living mulch of creeping red fescue (Festuca rubra L. Pennlawn). Weed control, grapevine productivity, fruit quality, and soil quality were measured from 2004 to 2010. Straw and living mulches provided greater weed control than cultivation and herbicides. Grapevine yield was unaffected by the treatments, although pruning weights were reduced in cultivated and living mulch plots. Excluding titratable acidity and pH, no differences in fruit quality were detected. Straw mulch plots tended to have more phosphorus and potassium in analyzed soil samples. Water-filled pore space and water content were also higher in plots mulched with straw. Both types of mulched plots had higher organic matter, total organic carbon, and stable aggregate content. Biological activity, measured as soil enzymatic activity and earthworm counts, was enhanced in mulched plots. Our results demonstrate that straw and living mulch reduce weed populations, maintain grapevine productivity, improve several indicators of soil quality, and are viable weed management strategies for continental-climate viticulture.

Blueberry Producers’ Attitudes toward Harvest Mechanization for Fresh Market

The availability and cost of agricultural labor is constraining the specialty crop industry throughout the United States. Most soft fruits destined for the fresh market are fragile and are usually hand harvested to maintain optimal quality and postharvest longevity. However, because of labor shortages, machine harvest options are being explored out of necessity. A survey on machine harvest of blueberries (Vaccinium sp.) for fresh market was conducted in 2015 and 2016 in seven U.S. states and one Canadian province. Survey respondents totaled 223 blueberry producers of various production sizes and scope. A majority (61%) indicated that their berries were destined for fresh markets with 33% machine harvested for this purpose. Eighty percent said that they thought fruit quality was the limiting factor for machine-harvested blueberries destined for fresh markets. Many producers had used mechanized harvesters, but their experience varied greatly. Just less than half (47%) used mechanical harvesters for fewer than 5 years. Most respondents indicated that labor was a primary concern, as well as competing markets and weather. New technologies that reduce harvesting constraints, such as improvements to harvest machinery and packing lines, were of interest to most respondents. Forty-five percent stated they would be interested in using a modified harvest-aid platform with handheld shaking devices if it is viable (i.e., fruit quality and picking efficiency is maintained and the practice is cost effective). Overall, the survey showed that blueberry producers have great concerns with labor costs and availability and are open to exploring mechanization as a way to mitigate the need for hand-harvest labor.

Floral Morphology Differs Among New Northern Highbush Blueberry Cultivars

Variation in floral morphology and timing of bloom are common among cultivars of northern highbush blueberry (Vaccinium corymbosum L.). These differences can affect the ability of commercial pollinators to effectively pollinate and fertilize ovules, which can impact fruit set, berry size, and ultimate yields. New northern highbush blueberry cultivars may exhibit differences in flower morphology, which could impact pollination and fruit set. Evaluation of new cultivars compared to standard industry cultivars is of specific importance in predicting potential pollination constraints by honey bee (Apis mellifera), one of the primary pollinators in North America, and in developing optimal hive stocking densities. Three new cultivars (‘Blue Ribbon’, ‘Top Shelf’, and ‘Cargo’) were compared to an industry standard (‘Duke’) for floral morphology and relative bloom phenology. All new cultivars had significantly smaller flowers as compared to ‘Duke’; however, ‘Top Shelf’ flowers exhibited a unique characteristic whereby many flowers (81%) had partially fused petals. Reduced flower size of new cultivars suggests floral morphology may be a constraint to effective pollination by honey bees and/or these cultivars will require higher honey bee stocking densities for effective pollination. However, the partially unfused petals in ‘Top Shelf’ may provide improved exposure to the stamen and pistil, which could increase accessibility to pollinators like honey bee and promote pollination and fruit set.

Contribution of a Winter Wheat Cover Crop to the Maintenance of Root Lesion Nematode Populations in the Red Raspberry Production System

One of the primary production challenges red raspberry (Rubus idaeus) growers in the Pacific northwestern United States confront is root lesion nematode [RLN (Pratylenchus penetrans)]. In this perennial production system, red raspberry serves as a sustained host for RLN. When a red raspberry planting is slated for removal in the fall, a new red raspberry planting quickly follows in the same field the following spring. The primary crop that occurs in rotation with red raspberry is a winter wheat cover crop to provide soil coverage and protection during the winter. The objectives of this research were to determine if winter wheat (Triticum aestivum) provides a green bridge for RLN in continuous red raspberry production systems and to determine if modified winter cover cropping practices can be used to reduce population densities of RLN before replanting red raspberry. Four trials were established in fields being replanted to red raspberry and the following modified winter cover cropping practices were considered: cover crop planting date (at fumigation or 2 weeks after fumigation), termination date (cover crop kill with herbicide 2 or 6weeks before incorporation comparedwith the industry standard of incorporation immediately before planting), and the additional application of methomyl. ‘Rosalyn’ and ‘Bobtail’ winter wheat planted as cover crops in these trials were demonstrated to be maintenance hosts for RLN (ranging from 10 to 947 RLN/gwinter wheat root across trials) allowing them to be a green bridge for RLN to infect the following red raspberry crop. Altering winter wheat cover crop planting date, termination date with herbicide, or methomyl application did not affect RLN population densities in the subsequent red raspberry crop. Although planting an RLNmaintenance host may be of concern to growers, the advantages of reduced soil erosion and nitrate leaching associated with cover cropping outweigh the perceived risk to the subsequent red raspberry crop.