Field Crops Research 128 (2012) 48–54 Contents lists available at SciVerse ScienceDirect Field Crops Research jou rnal h om epage: www.elsevier.com/locate/fcr Interactions between maize dwarf mosaic and weed interference on sweet corn Martin M. Williams II a,∗ , Jerald K. Pataky b a Global Change & Photosynthesis Research, USDA-ARS, University of Illinois, 1102 S. Goodwin Ave., Urbana, IL 61801, USA b Department of Crop Sciences, University of Illinois, 1102 S., Goodwin Ave., Urbana, IL 61801, USA a r t i c l e i n f o Article history: Received 12 October 2011 Received in revised form 13 December 2011 Accepted 14 December 2011 Keywords: Competition Development Growth Stress tolerance Yield a b s t r a c t Maize dwarf mosaic (MDM) and weed interference are two economically important stresses to sweet corn; however, a fundamental understanding of the extent to which the crop is affected by combinations of these stresses is lacking. The objective of this study was to quantify the extent to which MDM incidence and weed interference influence the sweet corn canopy, phenological development, and yield. In field research, five levels of MDM incidence (0, 25%, 50%, 75%, and 100% of the plant population) were estab- lished in two sweet corn hybrids that also were grown in the presence or absence of wild-proso millet. During the vegetative phase of crop growth, the crop’s ability to tolerate these multiple stresses was largely additive. For instance, incidence of MDM decreased crop growth and delayed development by as much as five days, and wild-proso millet added to those detrimental effects by an extent that was deter- mined by the severity of weed interference. In contrast during the reproductive phase, MDM incidence and weed interference interacted in their effect on the crop. Moreover, differences in hybrid responses to the multiple stresses indicated that the benefit of improved crop tolerance to weed interference was not lost when the crop is infected with MDM. Use of hybrids with high levels of MDM resistance and improved competitive ability with weeds reduces the risk of losses from MDM and weed interference, two commonly occurring stresses in sweet corn. Published by Elsevier B.V. 1. Introduction Maize dwarf mosaic (MDM) is the most prevalent viral dis- ease of sweet corn (Zea mays L.) in the continental U.S. and is caused by Maize dwarf mosaic virus (MDMV). Sugarcane mosaic virus (SCMV) causes Sugarcane mosaic (SCM) and frequently co-occurs with MDM in sweet corn. Both pathogens overwinter in the south- eastern U.S. and are vectored by dozens of species of aphids. Once transmitted to sweet corn, the viruses infect systemically causing symptoms to occur on newly developing plant tissues. The most prominent symptoms are a mosaic or mottled pattern on leaf sur- faces. The disease stunts plant growth, delays silking up to four days, and causes up to 70% yield loss (Gregory and Ayers, 1982; Mikel et al., 1981a,b). Yield losses from MDM are the result of a com- bination of a reduction in photosynthetic rate due to chlorophyll loss, and an elevation in respiration rate due to virus replication (Gates and Gudauskas, 1969; Tu and Ford, 1968; Tu et al., 1968). Little is known about corn canopy responses to the viral diseases, such as the dynamics of the crop’s ability to compete for light. Resistance to MDM and SCM is mostly qualitative (i.e., resis- tant or susceptible phenotypes) although some intermediate ∗ Corresponding author. Tel.: +1 217 2445476; fax: +1 217 3335251. E-mail address: mmwillms@illinois.edu (M.M. Williams II). phenotypes occur occasionally. A single gene or extremely closely linked genes on the short arm of maize chromosome six convey resistance to both MDMV and SCMV although modifier genes also appear to influence resistant and susceptible phenotypes (Jones et al., 2007). For brevity, infections by MDMV and SCMV hereafter will be referred to as simply MDM. Nearly two-thirds of all com- mercial sweet corn hybrids have no resistance to MDM (Pataky et al., 2011). Symptomatic plants also occur sporadically among MDM-resistant hybrids when plants are infected at very early growth stages (e.g., 2–3-leaf stages). Yield losses up to 10% have been observed in MDM-resistant sweet corn hybrids in response to inoculation at early growth stages that results in a low incidence of systemically infected, symptomatic plants (Kerns and Pataky, 1997). The preponderance of MDM-susceptible sweet corn hybrids and the limited use of MDM-resistant hybrids creates the potential for sporadically occurring, severe, localized epidemics of MDM in sweet corn. Weed interference is common in North American sweet corn production. Based on recent surveys of Midwestern sweet corn growers, nearly all sweet corn fields have weeds that escape con- trol and a majority of fields harbor weed communities sufficiently large enough to cause yield losses (Williams et al., 2008a). Although no single weed species is problematic in every field, wild-proso millet (Panicum miliaceum L.) has become prevalent throughout the upper continental U.S. and southern Canada. A weedy race of 0378-4290/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.fcr.2011.12.005