Douglas J. Doohan

Crop rotation and tillage system effects on weed seedbanks

Abstract We characterized the size and species composition of the weed seedbank after 35 yr of continuous crop rotation and tillage system treatments at two locations in Ohio. Spring seedbanks were monitored during 1997, 1998, and 1999 in continuous corn (CCC), corn–soybean (CS), and corn–oats–hay (COH) rotations in moldboard plow (MP), chisel plow (CP), and no-tillage (NT) plots where the same herbicide was used for a given crop each growing season. There were 47 species at Wooster and 45 species at Hoytville, with 37 species occurring at both locations in all 3 yr. Crop rotation was a more important determinant of seed density than was tillage system. Seed density was highest in NT and generally declined as tillage intensity increased. Seeds accumulated near the surface (0 to 5 cm) in NT but were uniformly distributed with depth in other tillage systems. At both locations there was a significant interaction between tillage and rotation for estimates of the total seed density. Seed density was highest in NT-CCC, with 26,850 seeds m−2 at Wooster and 8,680 seeds m−2 at Hoytville. At Wooster total seed density in CCC plots was 45 and 60% lower than in COH plots for CP and MP. In NT the total seed density was 40% greater in CCC than in COH. At Hoytville total seed density in CCC plots was 72% lower than in COH plots that were CP or MP, whereas seed density was 45% higher in CCC than in COH plots that were in an NT system. There were more significant differences in seedbank density for any given species for crop rotation than for tillage treatments. Seed densities of three broadleaves (shepherds-purse, Pennsylvania smartweed, and corn speedwell) at Wooster and four broadleaves (yellow woodsorrel, redroot pigweed, Pennsylvania smartweed, and spotted spurge) at Hoytville were more abundant in COH (140 to 630 seeds m−2) than in CS (10 to 270 seeds m−2) or CCC (< 1 to 60 seeds m−2), regardless of the tillage system. At both locations Pennsylvania smartweed seeds were more abundant in COH (260 and 630 seeds m−2) than in other rotations (10 to 20 seeds m−2). Relative importance (RI) values, based on relative density and relative frequency of each species, were lower in CS than in CCC for common lambsquarters and five other weeds at Wooster; RI of giant foxtail was 80% lower in COH than in CCC at Hoytville. The data show how species composition and abundance change in response to crop and soil management. The results can help to determine how complex plant communities are “assembled” from a pool of species by specific constraints or filters. Nomenclature: Redroot pigweed, Amaranthus retroflexus L. AMARE; shepherds-purse, Capsella bursa-pastoris (L.) Medicus CAPSA; common lambsquarters, Chenopodium album L. CHEAL; spotted spurge, Euphorbia maculata L. EPHMA; yellow woodsorrel, Oxalis stricta L. OXAST; Pennsylvania smartweed, Polygonum pensylvanicum L. POLPY; giant foxtail, Setaria faberi L. SETFA; corn speedwell, Veronica arvensis L. VERAR; oats, Avena sativa L.; soybean, Glycine max (L.) Merr.; corn, Zea mays L.

The Challenges of Specialty Crop Weed Control, Future Directions

The process of labeling new herbicides for specialty crops has always been difficult. Progress in solving specialty crop weed control problems will likely be more challenging in the future. Major crops like corn, cotton, rice, soybean, and wheat are planted on millions of hectares, and most of these crops are treated with herbicides. In contrast, specialty crops (i.e., minor crops, e.g., container ornamentals or lettuce) are planted on 122,000 ha or less; thus, the potential value of herbicide sales is limited in these crops by the low number of hectares planted per crop. High crop value, small hectarage per crop, and generally marginal herbicide selectivity results in a high potential of liability for herbicide registrants and little incentive to label herbicides in these crops. The Interregional Project Number 4 (IR-4) program facilitates the registrations of pesticides on minor crops. Work needed to support pesticide tolerance in a given crop is conducted by IR-4 and cooperators. However, to develop new crop tolerances, the IR-4 process requires new herbicides. The success of glyphosate-resistant soybean has resulted in a less profitable herbicide market for all crops. In response, most primary pesticide manufacturers have reduced the size, or even eliminated herbicide discovery programs. As private industry slows or stops herbicide development, there will be fewer new minor-crop herbicides. Many questions face minor-crop weed scientists. For example, what are other practical solutions to control weeds in minor crops besides herbicides? Should research focus on development of competition models and decision thresholds or on weed removal tools such as robotics? What funding sources are available for minor-crop weed scientists? Are grant programs at the Federal level prepared to increase support for minor-crop weed research? Will university administrators replace retiring specialty crop weed scientists, knowing that their funding sources will produce little overhead? These questions require a response from all parties interested in specialty crop weed control. Nomenclature: Corn, Zea mays L., cotton, Gossypium hirsutum L., lettuce, Lactuca sativa L., rice, Oryza sativa L., soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.

Response of Five Vegetable Crops to Isoxaflutole Soil Residues

Field experiments were conducted in 2001 and 2002 at two sites in Ohio to characterize the effect of isoxaflutole herbicide applied the previous year to field corn on processing tomato, bell pepper, cabbage, snapbean, and cucumber. Isoxaflutole was applied preemergence to field corn in 2001 at 0, 53, 70, 105, and 210 g ai/ha. There were no rotational crop cultivar by herbicide rate interactions at either site. Generally, there was a higher level of visible injury on crops at the Fremont site. Isoxaflutole residues at either site did not affect processing tomato yield. Bell pepper yield was reduced 33% when rotated into 210 g ai/ha rate plots only at Fremont. Snapbean marketable yield was reduced by isoxaflutole carryover from 70 and 210 g ai/ha rates resulting in 0.39 and 0.0 t/ha at Fremont. Similarly, isoxaflutole soil residues from 105 and 210 g ai/ha resulted in 14 and 24% visible injury on cucumber but did not reduce marketable yield. Site differences in soil characteristics and precipitation in the application year may have contributed to observed differences in crop response. Nomenclature: Isoxaflutole; bell pepper, Capsicum annuum L. ‘Aristotle’ and ‘Paladin’; cabbage, Brassica oleraceae L. var. capitata ‘Red Dynasty’ and ‘Huron’; corn, Zea mays L. ‘Pioneer 34B29 LL’; cucumber, Cucumis sativus ‘Vlasset’ and ‘Dasher 2’; processing tomato, Lycopersicon esculentum Mill. ‘Peto 626’ and ‘Heinz 9437’; snapbean, Phaseolus vulgaris L. ‘Strike’ and ‘Hialeah’. Additional index words: Herbicide carryover, herbicide soil residues, rotational crops, vegetable crops. Abbreviations: ANOVA, analysis of variance; CEC, cation exchange capacity; DAE, days after emergence; PRE, preemergence; SOM, soil organic matter.

Comparison of survey methods for an invasive plant at the subwatershed level

Invasive plant survey methods that are practical and economical are needed to describe established colonies and detect nascent invaders. We compared results from random and roadside surveys of Alliaria petiolata (Bieb.) Cavara & Grande across a 5730-ha subwatershed. The random survey included 150 1-ha plots; the roadside survey examined 0.1-mile increments (10-m deep) along paved roads (totaling 1104 0.16-ha plots). In the random survey, agriculture was the dominant land use (49% of sampled area), and most A. petiolata patches were in wooded, shaded riparian, and waste areas (34%, 34%, and 29% of patches, respectively). In the roadside survey, right-of-way land use was dominant (38% of sampled area), and most A. petiolata patches were in right-of-way, wooded, and shaded riparian areas (53%, 22%, and 19% of patches, respectively). According to generalized linear model analysis, survey methods did not differ in the overall probability of finding A. petiolata (P=0.17 and 0.11 for random and roadside surveys, respectively). Shaded riparian, wooded, and mixed-species right-of-way land uses were the dominant habitat for A. petiolata in both surveys, but only the random survey indicated waste areas as significant habitat. Alliaria petiolata occurred mostly as small patches in roadsides, but as large patches in random plots, suggesting faster spread in the roadside. Results indicated that disturbed lands along roadsides were important for invasion and spread of A. petiolata; therefore, the roadside survey was a useful, practical method for detecting nascent invasions and management planning. The random sampling lacked a land use bias, and provided data that could be generalized across the subwatershed; however, this method required at least four times more person hours to complete than the roadside survey for a similar amount of area. Although roadside sampling did not provide a completely reliable assessment of target plant populations within the landscape, it may provide an adequate approximation, depending on the specific goals of the survey. Concurrent surveys would provide the most complete information.

Dose Response of Glyphosate and Dicamba on Tomato (Lycopersicon esculentum) Injury

Abstract Field studies were conducted to determine the response of sublethal glyphosate and dicamba doses to processing tomato flowering loss and marketable yield. Dose–response studies for both herbicides were conducted on four commercial processing tomato lines (two different lines within each study) and plants were sprayed at either the vegetative stage or the early bloom stage. Both glyphosate and dicamba caused higher yield losses when sprayed at the early bloom stage. A 25% yield loss was observed with 8.5 and 7.5 g ae ha−1 for glyphosate and dicamba, respectively, at the early bloom stage and 43.9 and 11.9 g ae ha−1 for glyphosate and dicamba, respectively, at the early vegetative stage. Overall, these tomato cultivars were more sensitive to dicamba than to glyphosate. We conclude that glyphosate and dicamba drift could have serious implications on tomato yields especially if the drift occurs during flowering. Nomenclature: Glyphosate; dicamba; tomato, Lycopersicon esculentum Mill.

Common Groundsel (Senecio vulgaris) Seed Longevity and Seedling Emergence

Abstract Common groundsel is an alien annual weed that has become increasingly troublesome in many crops in Ohio. Understanding the periodicity of seedling emergence and longevity of seeds buried in the soil may help growers devise more efficient strategies to control common groundsel. Studies were conducted to determine the dormancy status of common groundsel seeds over 24 mo, and to describe the effect of tillage and fertilizer on the pattern of seedling emergence and the rate of depletion of seeds from the soil seed bank. Common groundsel seeds were collected (June 2000 and 2002) from sites along a 700-km transect from Kentucky to Michigan (39°1′ and 43°36′N, respectively). Seeds were cleaned and placed in nylon mesh bags for burial in a common garden. Every month for the following 24 mo, replicate bags from each location were exhumed. Germination was tested under alternating temperatures of 20 and 10 C, for 14 and 10 h day/night, respectively. Germination response at each sampling date was similar regardless of seed source, but differed for the 2000 to 2002 and 2002 to 2004 experiments. Laboratory germination of seeds buried was initially high (98%) and declined rapidly to about 20% by midwinter. Germination increased to about 60% during the second summer, followed by a slow decline to 40% during winter and another rapid decline before the third summer. The rapid declines in germination were preceded by low soil temperatures (<5 C) and the germination peaks corresponded with periods of high soil temperatures (∼ 20 C). Results suggested that common groundsel follows a cycle of dormancy and nondormancy corresponding to decreases and increases, respectively, in soil temperature. During 2 yr of deep burial in undisturbed soil, 94% of the seeds germinated or died, suggesting that common groundsel seeds may not persist more than a few months in regularly disturbed soils. Nomenclature: Common groundsel, Senecio vulgaris L. SENVU

Sensitivity of sweet corn (Zea mays L.) and potatoes (Solanum tuberosum L.) to cloransulam-methyl soil residues

Abstract Field experiments were conducted in 1999 and 2000 at three sites in Midwestern USA to characterize the sensitivity of sweet corn and potatoes to cloransulam-methyl soil residues the year following application to soybeans. Cloransulam-methyl was applied pre-emergence to soybeans in 1999 at 0, 1 X , 2 X , and 4 X the recommended rate. In 2000, there was a cultivar-by-herbicide interaction for sweet corn injury at some but not all sites. Generally, the sweet corn injury was apparent at 7 days after emergence (DAE) and peaked at 28 DAE. Sweet corn and potato injury was more severe at sites with coarse soil texture and low soil organic matter. There was evidence of differential tolerance by different potato varieties. Results suggest that cloransulam-methyl residue the year after application to soybean is high enough to injure most sweet corn and potato cultivars.

Selectivity and Efficacy of Clopyralid on Strawberry (Fragaria X ananassa)1

Field experiments were conducted in 2001 through 2003 in Wooster, OH, to determine strawberry (Fragaria X ananassa) plant response to clopyralid applied after plant renovation in established plantings. Clopyralid applied at a rate of 200 g ae/ha or greater controlled at least 82% of common groundsel (Senecio vulgaris) 6 wk after treatment (WAT). Maximum total fruit yield (marketable plus unmarketable fruits) occurred at a clopyralid rate of 200 g/ha, and higher or lower rates resulted in reduced yield. Application of clopyralid at 400 g/ha tended to reduce the canopy of the strawberry crop, especially in comparison to rates lower that 200 g/ha. Overall, clopyralid applied POST at 200 g/ha did not reduce fruit yield when applied after strawberry renovation, and effectively controlled common groundsel plants that were entering the reproductive stage. Nomenclature: Clopyralid; common groundsel, Senecio vulgaris L. #3 SENVU; strawberry, Fragaria X ananassa Duch. Additional index words: Herbicide tolerance, postrenovation application.

Response of processing carrot to metribuzin on mineral soils in Nova Scotia

Metribuzin was examined as an alternative to linuron and prometryn when prometryn-treated processed carrot in Atlantic Canada in the 1990s could not be exported to the United States, where prometryn was not registered for this crop. Field studies demonstrated that 280 g ha-1 metribuzin applied after the three-leaf crop stage resulted in only minor injury and no yield loss for both a metribuzin-tolerant (Caro-Choice) and -sensitive (Dominator) cultivar. Metribuzin applied either pre- or post-emergence controlled two Matricaria species, chickweed [Stellaria media (L.) Vill.] and shepherd’s-purse [Capsella bursa-pastoris (L.) Medik.], equivalent to approved prometryn and linuron treatments. Controlled environment studies were conducted to examine the effect of crop growth stage, temperature and soil pH on metribuzin injury to carrot. Differential tolerance between the two cultivars occurred only up to the three-leaf stage. Under controlled environment conditions, carrot injury to metribuzin increased threefo...

Grafting Imparts Glyphosate Resistance in Soybean

Abstract Grafting is a widely-adopted cultural method to incorporate desired traits of rootstock with those of the scion and has been used successfully to address many biotic and abiotic stresses, including drought/waterlogging, insects, and diseases. However, it is not known if a herbicide resistance trait can be transferred across a graft union. Using Roundup Ready® (RR; glyphosate-resistant) soybean grafted with conventional (CN; nontransgenic and glyphosate-sensitive) soybean, we show that grafting is capable of transferring glyphosate resistance from RR rootstocks to CN scions. Grafts of CN/CN (scion/rootstock), CN/RR, RR/CN, and RR/RR were treated with potassium salt of glyphosate at 0.28, 0.84 and 1.68 kg ae ha−1. The CN/RR plants survived glyphosate treatment at 0.84 and 1.68 kg ha−1 while CN/CN plants were killed, indicating that glyphosate resistance is systemically mobile across the graft union. Intraspecies transfer of glyphosate resistance was unidirectional from root to shoot, since RR/CN plants were killed by glyphosate. The glyphosate resistance trait is conferred by CP4 5-enolpyruvylshikimate-3-phosphate synthase (CP4-EPSPS); therefore, we further examined whether CP4-EPSPS played a role in the phenomenon. CP4-EPSPS was detected in the CN scion of CN/RR plants by enzyme-linked immunosorbent assay (ELISA) but only 0.001% of that detected in RR leaf. This concentration is unlikely to have contributed significantly to the glyphosate resistance observed in CN/RR plants. Amino acid systemic trafficking and/or tissue specific glyphosate resistance are more likely the reasons for this phenomenon. These results show that grafting a transgenic herbicide-resistant rootstock to a nonresistant scion can confer resistance to the entire plant. Nomenclature: Glyphosate; soybean, Glycine max (L.) Merr. Resumen El injertar es una práctica cultural ampliamente adoptada para combinar caracteres deseados de un patrón con aquellos del injerto y ha sido utilizada exitosamente para lidiar con muchos estreses bióticos y abióticos, incluyendo sequía/inundación, insectos y enfermedades. Sin embargo, no se sabe si el carácter de resistencia a herbicidas puede ser transferido a través de la unión del injerto. Usando soya resistente a glyphosate (RR) injertada con soya no resistente a glyphosate (CN), nosotros demostramos que los injertos son capaces de transferir la resistencia a glyphosate de un patrón resistente a tejido convencional injertado. Injertos de CN/CN (injerto/patrón), CN/RR, RR/CN, y RR/RR fueron tratados con sal potásica de glyphosate a 0.28, 0.84 y 1.68 kg ae ha−1. Las plantas CN/RR sobrevivieron al tratamiento con glyphosate a 0.84 y 1.68 kg ha−1, mientras que las plantas CN/CN murieron, lo que indica que la resistencia a glyphosate es móvil sistémicamente a través de la unión en el injerto. En vista de que glyphosate mató a las plantas RR/CN, la transferencia intra-específica de resistencia a glyphosate fue unidireccional desde la raíz al tejido aéreo,. El carácter de resistencia a glyphosate es conferido por CP4 5-enolpyruvylshikimate-3-phosphate synthase (CP4-EPSPS), por lo que examinamos si CP4-EPSPS jugó algún rol en el fenómeno observado. por medio de un ensayo de inmunoabsorción ligado a enzimas (ELISA), se detectó CP4-EPSPS en el injerto CN de plantas CN/RR, pero solamente un 0.001% de los niveles detectados en hojas RR. Esta concentración es poco probable que haya contribuido en forma significativa a la resistencia a glyphosate observada en plantas CN/RR. Tráfico sistémico de amino ácidos y/o resistencia a glyphosate en tejidos específicos son probablemente las razones que explican este fenómeno. Estos resultados muestras que injertar tejido sin resistencia a herbicidas sobre un patrón resistente puede conferir resistencia a toda la planta.