Competitive Effects of Volunteer Corn on Hybrid Corn Growth and Yield

Transgenic volunteer corn is a competitive weed in soybean that decreases soybean yield at densities as low as 0.5 plants m−2, yet the competitive effects of volunteer corn in corn have yet to be quantified in the peer-reviewed literature. In order to quantify competition between volunteer corn and hybrid corn, seed was harvested from transgenic hybrid corn. The seed was then hand-planted at two locations (Lafayette, IN and Wanatah, IN) into 3 by 9 m plots of hybrid corn at five densities: 0 (control), 0.5, 2, 4, and 8 plants m−2. Volunteer corn competition reduced leaf area and biomass of hybrid corn plants. Hybrid corn grain yield at Lafayette, IN, was reduced by 23 and 22% due to competition with volunteer corn growing in densities of 8 plants m−2in 2010 and 2011, respectively, but when volunteer corn grain yield was combined with the hybrid corn grain yield, there was no reduction in total grain yield. This study demonstrates that the competitive effects on the grain yield of the hybrid corn will be offset by the grain yield of the volunteer plants. However, because the unpredictable locations and densities of volunteer corn plants present challenges to machine harvesting, future studies should examine what proportion of the volunteer crop is actually harvestable.

Occurrence of Beet western yellows virus and its aphid vectors in over-summering broad-leafed weeds and volunteer crop plants in the grainbelt region of south-western Australia

During the summer periods of 2000, 2001, and 2002, presence of Beet western yellows virus (BWYV) was assessed in tests on samples from at least 12 broad-leafed weed species and 5 types of volunteer crop plants growing in the grainbelt region of south-western Australia. In 2000, BWYV was detected in 2 of 35 sites in 2% of 1437 samples, whereas in 2001 and 2002 the corresponding figures were 3 of 108 sites in 0.04% of 8782 samples, and 1 of 30 sites in 0.08% of 2524 samples, respectively. The sites with infection were in northern, central, and southern grainbelt districts, and in high and medium rainfall zones. The hosts in which BWYV was detected were the weeds Citrullus lanatus (Afghan or wild melon), Conzya spp. (fleabane), Navarretia squarrosa (stinkweed), and Solanum nigrum (blackberry nightshade), and the volunteer crop plant Brassica napus (canola). Small populations of aphids were found over-summering at 28% (2000), 4% (2001), and 17% (2002) of sites, mostly infesting volunteer canola and Raphanus raphanistrum (wild radish). They occurred in high, medium, and low rainfall zones, but were only found in central and southern grainbelt districts. The predominant aphid species found was Brevicoryne brassicae, with Acyrthosiphon pisum, Brachycaudus helichrysi, Hyperomyzus lactucae, Lipaphis erysimi, Myzus persicae, and Uroleucon sonchi present occasionally. The importance of these findings in relation to the epidemiology and control of BWYV in the grainbelt is discussed.

Duration of Control from Preemergence Herbicides for Use in Nonburned Grass Seed Crops

Legislatively mandated reductions in open field burning have increased grass seed growers reliance on herbicides to control seedling grasses in established stands of perennial species. In nonburned fields, a dense flush of seedling weeds and volunteer crop emerges with the onset of fall rains, and additional germination of some species occurs throughout the fall, winter, and spring. Because rainfall patterns in western Oregon are erratic during late summer and early fall, the choice of when to apply preemergence herbicides is difficult. Herbicides applied too early may dissipate before the rains arrive, whereas herbicides applied too late may not prevent germination and seedling establishment. Pendimethalin was least affected by a 3- to 4-wk exposure on dry soil waiting for rain, followed in order of increasing sensitivity by oxyfluorfen, metolachlor, and trifluralin. Most treatments controlled California brome less effectively than perennial ryegrass. Duration of 85% or greater control of subsequently oversown perennial ryegrass averaged 69 d for 2.2 kg/ha pendimethalin, 11 d for 0.42 kg/ha oxyfluorfen, and 4 d for 2.2 kg/ha metolachlor, and duration of 50% or greater control averaged 98, 33, and 18 d for the same treatments. Doubling of herbicide rates doubled the duration of control in 15 out of 27 cases but increased the duration only an average of 75% in the other 12 cases. Average time to doubling of weed populations over those occurring when herbicides and weed seeds were applied on the same day was 12, 10, and 11 d after application for pendimethalin, oxyfluorfen, and metolachlor, respectively. The similarity of these periods suggests that the major difference in performance of these herbicides with time was how close to complete control they had initially achieved. Pendimethalin was the superior preemergence herbicide for controlling California brome and perennial ryegrass in these established stands, but oxyfluorfen and metolachlor also were useful if applied near germination.

The biology of Canadian weeds. 101. Helianthus tuberosus L.

Helianthus tuberosus L., Jerusalem artichoke, is a native perennial tuber-producing weed. In Canada, its range extends from the Maritimes to the Pacific coast, but it is primarly found in southern Ontario and Manitoba. A cultivated form has been grown commercially in Ontario and western Canada for use as a human food source, for livestock feed and for the production of a variety of chemical products such as ethanol. As a weed, H. tuberosus competes vigorously with grain and field crops, but does not readily invade arable land except as a volunteer crop. The high carbohydrate content of H. tuberosus tubers, coupled with multiple regenerative strategies featuring seeds and tuber-bearing rhizomes, can lead to rapid population increases under favorable conditions.Key words: Helianthus tuberosus, Jerusalem artichoke, weed biology