Common groundsel (Senecio vulgaris) is an increasingly important weed in strawberries (Fragaria ×ananassa), a crop in which open space within and between rows is susceptible to infestations. Cultivation, hand hoeing, and registered herbicide are only partially effective in controlling common groundsel, and tolerance or resistance to herbicides is common in this species. Field and greenhouse studies were conducted to identify and select herbicides for controlling common groundsel in newly planted strawberries. Herbicides applied to strawberries within 1 week after planting in 2000 were: terbacil and simazine alone and tank mixed with napropamide; pendimethalin, dimethenamid, metolachlor, ethofumesate and sulfentrazone. Based on selectivity and efficacy observed in this preliminary experiment, sulfentrazone and flumiclorac were selected for further evaluation in 2001 and 2002. Strawberry tolerance of sulfentrazone and flumiclorac 1, 3, 6, and 18 weeks after application (WAA) was similar to that of the registered herbicides terbacil and napropamide, but injury was greater than in hand weeded plots. Plants sprayed with 300 g·ha–1 (4.3 oz/acre) sulfentrazone produced yields similar to terbacil treated plants, but with less plant stunting. Tolerance of newly planted `Allstar' and `Jewel' was affected by the interaction of soil pH and sulfentrazone rate. Plant stunting 3 WAA increased with sulfentrazone rate, reaching 68 and 61% in `Allstar' and `Jewel', respectively, with the highest rate [400 g·ha–1 (5.7 oz/acre)] and high soil pH (7). `Allstar' grown in low pH (5) and treated with sulfentrazone (400 g·ha–1) showed only 8% stunting, whereas `Jewel' was not stunted 3 WAA at the same rate and pH. Both cultivars recovered (50% less stunting) from the severe injury observed when sulfentrazone was applied to high pH soils. However, at low pH both cultivars were stunted more at 6 WAA than at 3 WAA. Plant diameter for both cultivars was 25% higher when they were grown in the lower soil pH. Fruit yield was not affected by the sulfentrazone rates evaluated (0 to 400 g·ha–1). Sulfentrazone was active at four stages of common groundsel growth: preemergence (PRE), cotyledon (COT), early post (EPOST) seedlings at the four-leaf stage, and late post (LPOST) seedlings at the10-leaf stage. The calculated 50% growth reduction (GR50) value for PRE and COT stages was 50 g·ha–1 (0.7 oz/acre), whereas the GR50 for EPOST and LPOST stages was 100 g·ha–1 (1.4 oz/acre). Sulfentrazone controlled common groundsel when applied PRE and COT, but at EPOST and LPOST stages sulfentrazone did not provide complete control, although plant height was reduced 80% to 90% compared to untreated plants. Results indicated that common groundsel is controlled in the field with 150 and 300 g·ha–1 (2.1 and 4.3 oz/acre) of sulfentrazone applied before seedling emergence. The least strawberry injury occurred when sulfentrazone was applied immediately after transplanting at 150 and 300 g·ha–1, although crop tolerance was reduced under conditions of high soil pH (>6.5) and varied with cultivar.
Rodrigo Figueroa, Douglas Doohan, and John Cardina
Steven B. Polter, Douglas Doohan, and Joseph C. Scheerens
Terbacil at 0, 0.8, 1.6, 3.2, and 6.4 oz/acre (0, 0.06, 0.11, 0.22, and 0.45 kg·ha-1) a.i. was applied immediately after planting, at the thee-leaf stage and at the six-leaf stage to greenhouse grown strawberry (Fragaria × ananassa) cultivars Jewel, Mira, and Allstar. Strawberry was most tolerant of terbacil when the herbicide was applied before leaf emergence. `Mira' was more tolerant of terbacil than was `Jewel'. `Jewel' and `Allstar' exhibited similar levels of tolerance. In a second experiment terbacil at 4.8 oz/acre (0.34 kg·ha-1) was applied to the soil, to the foliage, and to the foliage followed by a water rinse. Injury was greatest when terbacil was applied directly to the strawberry foliage rather than to the soil, but was minimal when foliage was rinsed after application. In a final experiment terbacil at 4.8 oz/acre was applied to greenhouse-grown `Jewel' strawberries at the thee-leaf stage followed by a water rinse 0.5, 1, 2, or 4 hours after application. Rinsing the foliage of strawberry plants after application significantly reduced leaf injury. Delaying the rinse up to 4 hours did not lead to increased injury. Over all, the results from our study indicate the potential for using terbacil as an effective herbicide on newly established strawberries, especially if the compound is rinsed from leaves (if present) after treatment.
Steven B. Polter, Douglas Doohan, and Joseph C. Scheerens
Field experiments were conducted in newly planted strawberry (Fragaria ×ananassa) with terbacil applied at rates of 0 to 6.4 oz/acre a.i. either 4 days after planting but before appearance of new growth, or at the three-leaf stage. Irrigation of 0.4 inch was applied to half of the plots immediately after application of terbacil. Injury was greater when terbacil was applied before new growth than when applied at the three-leaf stage. Injury symptoms increased linearly with terbacil rate. Irrigation immediately following terbacil application reduced injury relative to non-irrigated plots. Weed control was reduced when terbacil was applied at the three-leaf stage than when applied before new growth. Irrigation did not reduce weed control. Herbicide injury symptoms were not detected the spring following terbacil application. Fruit yield was not affected by herbicide and irrigation treatments applied the previous year. The combination of low rates of terbacil, 0.8–1.6 oz/acre a.i., followed by irrigation to remove the herbicide from foliage is a safe option that growers can use to improve weed control and reduce hand weeding costs in the planting year.
Annette Wszelaki, Sally Miller, Douglas Doohan, Karen Amisi, Brian McSpadden-Gardener, and Matthew Kleinhenz
The influence of organic soil amendments (unamended control, composted dairy manure, or raw dairy manure) and weed treatments [critical period (CP) or no seed threshold (NST)] on diseases, growth parameters, yield, and postharvest quality was evaluated over 3 years in a transitional organic crop rotation of tomato, cabbage, clover, and wheat. More growth, yield, and postharvest quality parameters were affected by amendment treatments in cabbage than in tomato. Significant differences in yield among amendment treatments were found in 2001 and 2003 in cabbage, with higher marketable and total yields in amended vs. control plots. Soil management effects on cabbage varied annually, though amendments were required to maximize crop growth, as head weight, size, and volume and core volume of treatment plots exceeded the control plots in 2002 and 2003. Few differences were found between weed treatments, although in 2001 cabbage heads from the NST treatment were larger than heads from the CP treatment. Similar results were found in tomato in 2003. Also, the CP treatment had a higher Area Under the Disease Progress Curve than the NST treatment in tomato in 2003. Overall, disease pressure was highest in tomato in 2001. But disease levels within years were mostly unaffected by amendment treatments. In cabbage, disease was more common in 2002 than in 2003, although head rot was more prevalent in compost-amended plots in 2003 than in manure-amended or control plots. Tomato postharvest quality parameters were similar among amendment and weed treatments within each year. Soil amendment may enhance crop yield and quality in a transitional-organic system. Also, weed management strategy can alter weed populations and perhaps disease levels.