Hairy Nightshade Critical Interference Period in Potatoes

Field research trials were conducted in Idaho at the Aberdeen Research and Extension Center in 2006 and 2007 to determine the critical interference period of hairy nightshade in potatoes. ‘Russet Norkotah’ variety was planted both years in plots three rows wide by 12 m long. When the potatoes had emerged, one- to two-leaf hairy nightshade plants that had been germinated and grown in the greenhouse were transplanted at a 2 m−1row density and allowed to grow for 10, 20, 30, or 40 d after emergence (DAE) before removal, or the potatoes were maintained weed-free for 0, 10, 20, 30, or 40 DAE before transplanting. Potatoes were harvested from the center row at the end of each growing season and yield and grade was determined. Russet Norkotah is a small-canopied potato variety and often does not completely close canopy in Idaho. Russet Norkotah U.S. No. 1 and total tuber yield were similar to weed-free yield when hairy nightshade transplanting was delayed up to 22 or 24 DAE, respectively, or planted at emergence and allowed to remain for only 6 or 11 d, respectively. Otherwise, yield decrease was 5% or greater. Therefore, the critical weed-free period for Russet Norkotah potato U.S. No. 1 or total tuber yields was 6 to 22 or 11 to 24 DAE, respectively.

Cured Dairy Compost Influence on Weed Competition and on ‘Snowden' Potato Yield

Potatoes are an important global food crop typically produced in high-input systems in temperate zones. Growers that have access to compost may use it to improve soil health and increase tuber yields, but compost may also increase weed competition by increasing early-season water availability and weed growth. A field study at the Michigan State University Montcalm Research farm in 2010 and 2011 investigated the impact of compost on weed competition in potato. Potatoes were grown in field plots with 0, 4,000, or 8,000 kg carbon (C) ha−1of compost under weed-free conditions, and in competition with common lambsquarters, giant foxtail, and hairy nightshade. Compost did not increase biomass or seed production of any weed species. Giant foxtail and hairy nightshade at 5.3 plants per meter of row reduced potato yield by 20%; common lambsquarters reduced yield by 45%. The yield reduction by giant foxtail and hairy nightshade was due to a decrease in tuber bulking, whereas yield reductions from common lambsquarters were a result of lower tuber set and bulking. Potato yield increased 5 to 15% in compost compared to non-compost treatments; tuber specific gravity decreased by 0.3% in composted treatments. Across weed densities, elevated soil potassium levels in the 8,000 kg C ha−1composted treatment may have increased potato yield and decreased tuber specific gravity.

Interaction between Preemergence Ethofumesate and Postemergence Glyphosate

Greenhouse and field experiments were conducted to determine whether PRE-applied ethofumesate increased POST spray retention and weed control with glyphosate. In greenhouse studies, ethofumesate was applied PRE at rates from 0 to 224 g ai ha−1followed by POST treatment with either water or glyphosate (840 g ae ha−1) to which a red dye had been added. Plants were immediately washed and spray retention determined spectrophotometrically. Common lambsquarters retained more glyphosate solution compared to water, regardless of PRE ethofumesate rate. Increasing the rate of PRE ethofumesate increased the POST spray retention of both water and glyphosate. PRE application of ethofumesate increased POST spray retention of water by 114% and glyphosate solution by 18% compared to no ethofumesate treatment as determined by nonlinear regression. Ethofumesate rates of 90 g ha−1increased POST spray retention to at least 95% of the total observed response. In field studies, common lambsquarters, redroot pigweed, and hairy nightshade densities were all reduced by ethofumesate, although the duration of ethofumesate effect varied by species and ethofumesate application timing. PRE ethofumesate had no significant effect on hairy nightshade density until after POST glyphosate was applied, whereas common lambsquarters densities were most affected by PRE ethofumesate early in the season. Late-season redroot pigweed density was reduced by ethofumesate regardless of application timing.

Preemergence Herbicides for Potential Use in Potato Production

Field trials were conducted in 2009 and 2010 near Paterson, WA and Ontario, OR to evaluate weed control and potato tolerance to PRE-applied pyroxasulfone, saflufenacil, and KSU12800 herbicides. Pyroxasulfone at 0.09 to 0.15 kg ai ha−1and saflufenacil at 0.05 to 0.07 kg ai ha−1applied PRE alone or in tank mixes with several currently labeled herbicides did not injure potatoes at either site in both years. KSU12800 at 0.15 kg ai ha−1injured potatoes from 18 to 26% for a period of about 4 wk after emergence at Ontario both years. In addition, KSU12800 at 0.29 and 0.45 kg ha−1injured potatoes from 17 to 38% at 17 d after treatment (DAT) at Paterson in 2009. Pyroxasulfone at 0.15 kg ha−1controlled barnyardgrass, hairy nightshade, and redroot pigweed 96% or greater, but control of common lambsquarters was variable. Saflufenacil at 0.07 kg ha−1provided greater than 93% control of common lambsquarters, hairy nightshade, and redroot pigweed at both sites in 2010. KSU12800 at 0.15 kg ha−1controlled common lambsquarters, hairy nightshade, and redroot pigweed 99% or more at Ontario, but only 87 to 93% at Paterson in 2010. These herbicides did not reduce yield of U.S. no. 1 tubers or total tuber yields compared to standard labeled herbicide treatments when weed control was adequate.

Common Lambsquarters and Hairy Nightshade Control in Potato with Dimethenamid-p Alone and in Tank Mixtures and Comparison of Control by Dimethenamid-p with S-metolachlor and Metolachlor

Dimethenamid-p was labeled for preemergence use in potatoes in 2005. The herbicide provides hairy nightshade control; however, a tank-mix partner targeting common lambsquarters must be used in order to provide satisfactory control of that weed. S-metolachlor and metolachlor, also labeled for use in potato, are in the same chemical family as dimethenamid-p and questions have arisen as to whether or not these herbicides provide the same or different levels of hairy nightshade control. The objectives of this study, therefore, were (1) to compare preemergence control of common lambsquarters and other weeds in potato with dimethenamid-p applied at 0.72, 0.94, or 1.12 kg ai ha−1alone or in two-way tank mixtures to determine appropriate tank-mix partners, and (2) to compare hairy nightshade control by dimethenamid-p with control by S-metolachlor or metolachlor. Two-way tank mixtures of dimethenamid-p with ethalfluralin, EPTC, flumioxazin, metribuzin, pendimethalin, or sulfentrazone generally improved season-long common lambsquarters control compared with dimethenamid-p applied alone at 0.72, 0.94, or 1.12 kg ha−1. When compared with control by dimethenamid-p alone at 0.72 or 0.94 kg ha−1, control by dimethenamid-p at either rate tank-mixed with ethalfluralin or EPTC was not improved as much as control by combinations of dimethenamid-p at those rates with the other tank-mix partners. Hairy nightshade control by three-way tank mixtures of S-metolachlor or metolachlor with various combinations of metribuzin, ethalfluralin, EPTC, or pendimethalin ranged from 60 to 86% and was not as great as the 93 to 98% control by dimethenamid-p at 0.72 kg ha−1combined with the same tank-mix partners. U.S. No. 1 and total tuber yields of comparative two- and three-way tank mixtures were generally increased when weed control was improved.