Nathan L. Hartwig

Cover crops and living mulches

Abstract Cover crops and living mulches bring many benefits to crop production. Interest in winter annual cover crops such as winter rye and hairy vetch for ground cover and soil erosion control has been increasing in the last 30 yr in some areas. The integration of cover crops into a cropping system by relay cropping, overseeding, interseeding, and double cropping may serve to provide and conserve nitrogen for grain crops, reduce soil erosion, reduce weed pressure, and increase soil organic matter content (Hartwig and Hoffman 1975). Hairy vetch has increased availability of nitrogen to succeeding crops, increased soil organic matter, improved soil structure and water infiltration, decreased water runoff, reduced surface soil temperature and water evaporation, improved weed control, and increased soil productivity (Frye et al. 1988). More recent research with perennial living mulches, such as crownvetch (Hartwig 1983), flatpea, birdsfoot trefoil, and white clover (Ammon et al. 1995), has added a new dimension to the use of ground covers that eliminates the need to reseed each year. Cropping systems with the use of ground covers have been worked out for vineyards, orchards, and common agronomic crops, such as corn, small grains, and forages. Legume cover crops have the potential for fixing nitrogen, a portion of which will be available for high-nitrogen–requiring crops such as corn. In areas where excess nitrogen is already a problem, the use of ground covers may provide a sink to tie up some of this excess nitrogen and hold it until the next growing season, when a crop that can make use of it might be planted (Hooda et al. 1998). Even legumes tend to use soil nitrogen rather than fixing their own, if it is available. It is these possibilities that provide the incentive for looking at the effect of various kinds of cover crops on soil erosion, nitrogen budgets, weed control, and other pest management and environmental problems. Nomenclature: Crownvetch, Coronilla varia L. ‘Penngift’; birdsfoot trefoil, Lotus corniculatus L.; corn, Zea mays L.; flatpea, Lathrus sylvestrus L.; hairy vetch, Vicia villosa Roth; white clover, Trifolium repens L.; winter rye, Secale cereale L.

Effect of Row Spacing and Herbicides on Burcucumber (Sicyos angulatus) Control in Herbicide-Resistant Corn (Zea mays)'

Abstract: Experiments examining burcucumber management in glufosinate-resistant (GR) and imidazolinone-resistant (IMI) corn were conducted in 1997 and 1998 in southeastern Pennsylvania. GR corn was planted in 38- and 76-cm rows, and postemergence (POST) treatments of glufosinate and glufosinate plus atrazine were applied to corn at the V4 or V5 growth stage. In a second study, IMI corn was planted in 76-cm rows, and 15 preemergence (PRE) and POST herbicide programs were evaluated. Herbicide treatments included RPA-201772, CGA 152005, simazine, imazethapyr plus imazapyr, imazamox, chlorimuron plus thifensulfuron, nicosulfuron plus rimsulfuron plus atrazine, CGA 152005 plus primisulfuron, and combinations with atrazine. Burcucumber germinated throughout the growing season, with greatest emergence occurring in early June, gradually decreasing to minimal emergence by mid-July. Glufosinate alone controlled burcucumber 79 to 90% 7 weeks after planting (WAP) regardless of application timing or row spacing. By 10 to 13 WAP, control was 82% or less due to lack of residual control and new burcucumber emergence. Row spacing had little effect on burcucumber emergence or control and appears to have little impact on burcucumber management in corn. In general, PRE herbicide programs were less effective than POST programs, although PRE treatments containing atrazine equaled some POST herbicides. POST-applied chlorimuron plus thifensulfuron, nicosulfuron plus rimsulfuron plus atrazine, and CGA 152005 plus primisulfuron controlled burcucumber greater than 80 and 90% in 1997 and 1998, respectively. Imazethapyr plus imazapyr and imazamox applied POST controlled burcucumber 66% 10 WAP. Adding atrazine to POST herbicide programs did not increase control, with the exception of imazethapyr plus imazapyr. Nomenclature: Atrazine; chlorimuron; glufosinate; imazamox; imazapyr; imazethapyr; RPA-201772 (proposed name, isoxaflutole), [5-cyclopropyl-4-(2-methyl-sulphonyl-4-trifluoromethyl-benzoyl)isoxozole]; nicosulfuron; primisulfuron; CGA 152005 (proposed name, prosulfuron), {1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3,-trifluoropropyl)-phenyl-sulfonyl]urea}, rimsulfuron; thifensulfuron; burcucumber, Sicyos angulatus L. #3 SIYAN; corn, Zea mays L. Additional index words: Cultural control, herbicide-resistant crops, weed emergence. Abbreviations: EPOST, early postemergence; GR, glufosinate resistant; HRC, herbicide-resistant crops; IMI, imidazolinone resistant; MPOST, midpostemergence; POST, postemergence; PRE, preemergence; WAP, weeks after planting.

Effect of Tillage, Row Spacing, and Herbicide on the Emergence and Control of Burcucumber (Sicyos angulatus) in Soybean (Glycine max)1

Abstract: An experiment was conducted in 1998 and 1999 in southeastern Pennsylvania to examine the effect of tillage and soybean row spacing on burcucumber emergence and growth. A second experiment evaluated postemergence (POST) soybean herbicides on burcucumber control. In the tillage and row spacing study, a glyphosate-resistant soybean variety was planted in no-till and reduced-tillage systems in 38- and 76-cm row spacings. In the POST herbicide experiment, chlorimuron, glyphosate, CGA-277476, thifensulfuron, and several combinations of these herbicides were applied at two different POST application timings in 38-cm row soybean planted in a reduced-tillage system. In the tillage and row spacing study, burcucumber emergence was greatest starting in late May through mid-June and mostly ceased by early July, regardless of tillage system or row spacing. Although there was no difference in germination period in either tillage system, preplant tillage increased the number of emerged plants by 110% in 1997 and 70% in 1998 compared to the no-till system. Row spacing had no effect on burcucumber emergence or biomass production. In general, most POST herbicide programs controlled burcucumber, and there was no difference between early POST and mid-POST application timings. Chlorimuron at 13 g ai/ha, chlorimuron plus thifensulfuron, glyphosate, glyphosate plus chlorimuron, and glyphosate plus CGA-277476 provided 87% or greater control of burcucumber 12 wk after planting. These herbicides reduced burcucumber density and biomass by more than 56% in 1997 and 96% in 1998. Nomenclature: CGA-277476 (proposed name, oxasulfuron), 2-[[[[[4,6-dimethyl-3-pyrimidinyl]amino]carbonyl]amino] sulfonyl]benzoic acid, 3-oxetanyl-ester; chlorimuron; glyphosate; thifensulfuron; burcucumber, Sicyos angulatus L. #3 SIYAN; soybean, Glycine max (L.) Merr. Additional index words: Cultural control, emergence period, herbicide application timing, herbicide-resistant crops. Abbreviations: EPOST, early postemergence; GDD, growing degree days; LPOST, late postemergence; MPOST, mid-postemergence; POST, postemergence; WAP, weeks after planting.

Effect of establishment date and crop competition on burcucumber fecundity.

Abstract An experiment examining the effect of burcucumber emergence date and corn competition on burcucumber fecundity was conducted in 1997 and 1998 in central Pennsylvania. Burcucumber seedlings were transplanted in the field in approximately 10-d intervals starting in late May through mid-August with or without competition from corn. Burcucumber plants grown without competition from corn produced 716 g dry matter and 4,500 seeds plant−1 in 1997 and 607 g dry matter and 1,800 seeds plant−1 in 1998. Biomass was greatest for plants established in late May, whereas seed production was greatest for plants established in mid-June. Although seed numbers were reduced in comparison to the May and June establishment periods, plants established as late as August still produced seed. Burcucumber established in corn produced 96% less dry matter and seed than the plants in a noncompetitive environment in both years of the study. Although the growth and seed production of burcucumber grown in corn was drastically reduced, plants established in mid-July still produced seed. Nomenclature: Burcucumber, Sicyos angulatus L. SIYAN; corn, Zea mays L.