Chemical weed control in potatoes

Nine herbicide treatments were applied to potatoes grown at three locations in each of 3 years. The locations were characterized by widely different soil types—silty clay loam, sandy loam, and muck—and by differences in rainfall and temperatures during the growing season. None of the herbicide treatments applied pre-emergence gave adequate weed control at all locations and/or in all years. EPTC at 6 lb per acre (6.72 kg/ha) gave excellent weed control on both mineral soils but not on muck. Metabromuron at 4 lb per acre (4.48 kg/ha gave excellent weed control only on the low organic matter sandy loam. Propachlor at 6 lb. (6.72 kg/ha) and 2 lb amiben plus 3 lb propachlor (2.24 plus 3.36 kg/ha) gave variable control. Four herbicides: 1 lb paraquat (1.12 kg/ha), 2 lb linuron (2.24 kg/ha), 6 lb dinoseb (6.72 kg/ha) and 6 lb dinoseb plus 2.25 dalapon (6.72 plus 2.52 kg/ha) applied at potato plant emergence, when weeds were in the 2–6 leaf stage, also gave variable control but as a group generally gave better control than the pre-emergence herbicides, particularly on muck soil. The effectiveness of herbicides applied at potato plant emergence was less affected by soil type than those applied pre-emergence but was affected by the degree of weed emergence. On muck soil, weeds generally emerged well before “at emergence” herbicide treatments were applied. Tuber yields were not directly affected by the herbicides, but were reduced where weed control was inadequate. Tuber specific gravity and chip color were unaffected by the herbicides.     

Pre and postemergence herbicides for weed control in castor crop

Weed management is among the main factors limiting cultivation of castor (Ricinus communis) in extensive fields, particularly when labor is scarce or expensive. This experiment evaluated the efficiency of weed management programs using preemergence (clomazone, pendimethalin, and trifluralin) and a postemergence herbicide (chlorimuron-ethyl) applied at 20 days after emergence in castor plants cv. BRS Energia under rainfed conditions in Apodi, Brazil. No phytotoxicity was observed on the castor plants, and the postemergence herbicide significantly increased castor seed yield to 1466 kg ha⁻¹ complementing the weed control of preemergence herbicides treatments in which seed yield was 1207 kg ha⁻¹. Seed yield on weedy and weed-free treatments was 760 and 1971 kg ha⁻¹, respectively. Weeds were kept under a satisfactory control up to 40 days after emergence. This program resulted in reasonable weed control because the preemergence herbicides controled monocotyledon weeds, while the postemergence herbicide controlled broad leafed species being selective to castor plants.     

Comparison of various weed control programs for potatoes

All weed control programs resulted in satisfactory weed control. Costs of controlling weeds ranged from $10 to $93/ha. Cultivation alone was the cheapest method of controlling weeds. Controlling weeds by using herbicides alone with no cultivation resulted in the highest weed control costs but tended to give the best weed control at harvest. Herbicides saved one to two cultivations. EPTC (S-ethyl dipropylthiocarbamate) gave slightly better control of green foxtail [Setaria viridis (L.) Beauv.] and slightly poorer control of broadleaf weeds than trifluralin (α,α,α,-trifluoro-2,6-dinitro-N, N-dipropyl-p-toluidine). Cultivation helped control weeds but had no other apparent beneficial or adverse effect on potatoes. The correlation coefficient between total tuber yield and dry weight of weeds was ?0.97 at Grand Forks, North Dakota and ?0.85 at Casselton, North Dakota.     

Selectivity and weed control efficacy of pre- and post-emergence applications of clomazone in Southern Brazil

During the 2006/07 and 2008/09 growing seasons in Southern Brazil, we evaluated crop selectivity and weed control efficacy of clomazone on rice when applied alone or in a mixture with other pre- and post-emergence herbicides (BRS Querência variety). All herbicide treatments caused some degree of rice injury during both years; however, in no case was the injury still visible 21 days after application. Rice injuries were observed when application rates exceeded the recommended dose, and particularly when the herbicide was applied pre-emergence. Density reduction and panicle sterility served as measures of rice injury. Echinochloa crus-galli was the primary weed; it reduced rice yields by approximately 50% compared treated plots. In both growing seasons, clomazone herbicide (400 g ai ha⁻¹) controlled the weed 87.0%–99.6%, and it provided 8.06 t ha⁻¹ to 9.44 t ha⁻¹ of rice yield.     

Postemergence directed application of bentazon + metribuzin for broadleaf weed control in Russet Burbank potatoes

Field studies were conducted to evaluate potato (cv. Russet Burbank) injury and weed control with mid- or late-postemergence directed applications of bentazon at 0.56, 0.84, or 1.12 kg ha^?1 + metribuzin at 0.28 kg ha^?1 + petroleum oil concentrate (POC) at 2.3 L ha^?1. Potato injury was 5% or less when bentazon + metribuzin + POC was applied as a postemergence directed spray. Hairy nightshade, redroot pigweed, and common lambsquarters control were excellent with all rates of the bentazon + metribuzin + POC mixture tested at either application time. In weed-free trials, neither U.S. No. 1 nor total tuber yield was reduced compared to the untreated control by any rate of the bentazon + metribuzin + POC mixture applied as a directed spray. Thus, postemergence directed applications of bentazon + metribuzin + POC show excellent potential for broadleaf weed control in Russet Burbank potatoes.     

Interrelations between nitrogen and phosphorus fertilization and early blight control of potatoes

Three different rates of soil-applied nitrogen were combined in all possible combinations with different schedules of fungicidal sprays for early blight (Alternaria solani) control in field experiments for three consecutive years. The nitrogen was applied with a constant rate of phosphorus. Yield response to fungicidal sprays was more pronounced when potato plants had received nitrogen and phosphorus. Both spraying and fertilizer application reduced the percentage of leaflets infected by early blight. However, the effect of the fungicide was greater than that of fertilizers. Estimates based on the cost and price assumptions indicated that $1.00 investment in the optimum number of fungicidal sprays at the adequate rate of fertilizer returned $8.34, $9.71 and $1.89 in 1970, 1971 and 1972, respectively.     

Broadening weed control with imazamethabenz combinations

Broad-spectrum weed control by use of imazamethabenz (AC 222 293) in herbicide combinations was investigated in the greenhouse. Imazamethabenz at rates ranging from 0·1 to 0·4 kg a.i./ha effectively controlled wild oats (Avena fatua L.). Additional control of redroot pigweed (Amaranthus retroflexus L.) was achieved when imazamethabenz, plus octoxynol surfactant, was applied in combination with MCPA (amine or ester) or commercial MCPA mixtures (bromoxynil/MCPA and cyanazine/MCPA). Only inclusion of propanil/MCPA in the combination reduced wild-oat control by imazamethabenz at the lower rate (0·1 kg/ha). Control of green foxtail (Setaria viridis (L.) Beauv.) was also obtained by use of fenoxaprop-ethyl in combination with imazamethabenz (plus octoxynol). Three-way mixtures of imazamethabenz (or plus octoxynol), MCPA alone or mixture, and fenoxaprop-ethyl may provide practical control of grass and broad-leaved weeds in the field.     

Effects of the nematicide 1,3-dichloropropene on weed populations and stem canker disease severity in potatoes

The soil fumigant 1,3-dichloropropene (1,3-D) has been used in the UK for the control of potato cyst nematodes (PCN), Globodera pallida (Stone) and Globodera rostochiensis (Wollenweber), but its potential herbicidal activity has not been extensively investigated in this country. Field and glasshouse studies were therefore conducted to evaluate the potential of 1,3-D for the control of weeds in potatoes, and observations were made on the severity of potato stem canker, caused by the fungus Rhizoctonia solani Kühn [teleomorph: Thanatephorus cucumeris (Frank) Donk]. Autumn application of 1,3-D at 211.5 L active substance (a.s.) ha⁻¹ significantly suppressed the number of germinating weeds and the percentage of weed ground cover by 83% and 79%, respectively, relative to controls. There were also species-specific significant decreases (field pansy, Viola arvensis, in particular) in the number of weed seeds germinating in field soil in the glasshouse post-1,3-D treatment. The effect of 1,3-D declined in time and single (autumn or spring) or combined application produced a slight, but not significant, reduction in the number of weeds germinated on potato ridges relative to those recorded in untreated soil. The severity of stem canker on potato plants was not significantly reduced by 1,3-D but both mean number and weight of stems per plant were significantly increased compared with plants from untreated plots. These studies demonstrated that 1,3-D, in addition to giving PCN control, has efficacy against weeds; implications are the potential for reduced herbicide input in the crop rotation with accompanying economic and environmental benefits.     

Biochemical and molecular control of cold-induced sweetening in potatoes

The benefits of being able to process potatoes directly into chips or fries from cold storage (2 to 4 C) include less shrinkage, retention of dry matter, decreased disease loss, extended marketability, and the elimination of the need for dormancy-prolonging chemicals. Unfortunately at low temperature, potato tubers undergo a phenomenon known as cold-induced sweetening where the rate of conversion of starch to reducing sugars (i.e., glucose and fructose) is accelerated. As raw potatoes are sliced and cooked in oil at high temperature, the accumulated reducing sugars react with free amino acids in the potato cell forming unacceptably brown- to black-pigmented chips or fries via a non-enzymatic, Maillard-type reaction. Potatoes yielding these unacceptably colored products are generally rejected for purchase by the processing plant. All commercial potato cultivars presently used for the production of potato chips and fries accumulate excess free reducing sugars when exposed to cold stress. If a “cold-processing potato” was available, energy savings would be realized in potato-growing regions where outside storage temperatures are cool. In regions where outside temperatures are moderately high, increased refrigeration costs may occur. This expense would be offset, however, by removal of the need to purchase dormancy-prolonging chemicals, by a decreased need for disease control and by improvement of long-term tuber quality. The primary goal of this review is to describe recent research of a biochemical and molecular nature that relates to the underlaying mechanisms regulating post harvest, cold-induced sweetening in potato tubers. No attempt was made to outline the extensive research conducted on the genetic manipulation of carbon metabolism between starch and free sugars during photosynthesis and/or during potato development in relation to source/sink interactions.     

Disease and sprout control in individually film wrapped potatoes

Potatoes (Solanum tuberosum L. cv Russet Burbank) were individually wrapped in Cryovac D-955, a biaxially oriented shrink film, and stored at 24°C. The wrapped potatoes were either treated with a fungicide (thiobendazole), or the film itself was coated with an antimicrobial agent (silicon quaternary ammonium salt) to control diseases that may appear during storage and marketing. Under film wrapped conditions, disease control using a fungicide or antimicrobial agent was not completely successful; however, the marketable qualities of the potatoes were not affected. Disease spread under film wrapped conditions was minimized if the potatoes were disinfected in chlorine (0.5% sodium hypochlorite) and wrapped after they were dried. In another study dormant and post-dormant potatoes were individually film wrapped after they were treated with maleic hydrazide (MH) (pre-harvest treatment) or isopropyl N-(3-chlorophenyl) carbamate (CIPC) (postharvest treatment) for sprout control. Under film wrapped conditions, MH decreased sprouting in the dormant potatoes but not in the post-dormant potatoes. CIPC inhibited sprouting in the post-dormant film wrapped potatoes but was less effective in the dormant potatoes.