CC201 discusses soybean weed control including methods and types of weed control

Burnside, O. C.

Robinson, L. R.

English

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnHistorical Materials from University of Nebraska-Lincoln Extension ExtensionApril 2014CC201 Soybean Weed ControlL. R. RobinsonO. C. BurnsideFollow this and additional works at: http://digitalcommons.unl.edu/extensionhistThis Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted forinclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University ofNebraska - Lincoln.Robinson, L. R. and Burnside, O. C., "CC201 Soybean Weed Control" (2014). Historical Materials from University of Nebraska-LincolnExtension. 3077.http://digitalcommons.unl.edu/extensionhist/3077UNIVERSITY OF NE LIBRARY JUN 1 7 19x}) SOYBEAN WEED CONTROL cc 201 ~~ L. R. Robison and 0. C. Burnside '~~ ~ ~~ ~'<> ~.,~ -z<S # ---~ ~§} Soybean acreage in Nebraska increased from 165,000 acres~in 1959 ~~~ Introduction 786,000 acres in 1966. Soybeans complement corn and sorghum product~ b'Y pro-viding the farmer an additional crop he can produce using much of ~ same equip-ment. Soybean growers are improving production methods but there ~s much to be learned about how to fit together the pieces of the crop production puzzle . Lossess and Problem Weeds in Soybeans Of the three classes of soybean pests (disease-insects-weeds ) , weeds have been by far the most important. Losses from weeds in soybeans in the Unit ed States due to reduced yield and quality and the cost of soybean weed control exceeds 300 million dollars each year. In Nebraska, this loss is about ll million dollars or $14 per ac~ea uring soybeans at $2.75 per bushel). ~~~~ In Illinois, six giant foxtail plants per foot of row~\ ed soyb /1-fll\:yields lo% and 50 plants per fact of row reduced yields 28%. Simi~ r searc tn~l­aware indicated one morningglory plant per foot of row reduced ~ s about 2~~c In Nebraska, l bu/A decrease in soybean yields occurred for every -lP~~~~eeds produced. co\.\.l~ \\.:. 1\ '{ Problem weEds in Nebraska soybeans are foxtail, pigweed, crabgrass, lambs -quarter, velvetleaf, smartweeds, cocklebur, sunflower, jimsonweed, and shattercane . Fortunately, mechanical, cultural and chemical weed control methods are available which, when used in combination, will usuall y provide adequate weed control. Weed Control Methods l. Mechanical weed control (a) Seedbed preparation: Seedbed preparation involves an important series of production operations. Weed control measures often are considered the series of operations following planting. Seedbed preparation frequently determines crop success or failure as poorly prepared seedbeds seldom produce good soybean stands and often do not destroy existing weeds . EXTENSION SERVICE, UNIVERSITY OF NEBRASKA COLLEGE OF AGRICULTURE AND HOME ECONOMICS AND U. S. DEPARTMENT OF AGRICULTURE COOPERATI NG E. F. FROLIK, DEAN J. L. ADAMS, DIRECTOR Tillage opera tions should provide a f irm, mellow seedbed for soy?eans. There is little if any benefit from ear l y spring tillage operat i ons so far as stimul ating weed seed germina tion and weed con-t rol is concerned. The final operati on should be timed so that weeds are destroyed when soil temperature i s conducive to rapid soybean emergence and growth. The important thing is to provi de a favorable envi ronment for rapid germination and uniform stand establishment . (b) Rotary hoe: Properly used, the rotary hoe i s an effective weed control tool. Too often weed control failure results f r om de l aying the rotary hoeing until weeds can be seen and l/2 inch or more tall---this i s :too l a t e . Most annua l weed seeds germinate in t he upper inch of soil. Larger seeded crops such as soybeans usually a r e planted deeper and ar e rooted deeper than most annual weeds. The main purpose of the rotary h oe i s to di s turb the weeds without apprec i ab l y disturbing the crop. Timing i s critical and should be geared to the stage of weed growt h rather than t o soybean growth except that you should try to avoid rotary hoe ing soybeans in the "crook" stage . Rota r y h oe operations should begin when most of the weeds have germinated and are in the "white " stage but not yet emerged . Weeds are easily killed at this stage, but once emerged and greater than l/4 inch t all they cannot be effectively destroyed with arotary hoe. Usually weeds will be in the "white" stage five days a fter soybean emergence . The grower should walk into the field and dig in the top soil--weed seedlings are easily seen. A timely rotary hoe ing often gives 80 to 9o% weed control. De l aying rotary hoeing three or four days after weeds emer ge will reduce weed control effectiveness 50% or more . The rotary hoe sh ould be operated at 8 to 12 miles per hour and be heavy - ~enough to give sha llow soil penetration. Do not worry about breaking off a f ew soybean plants . If the soybean stand is reduced lo% a good rotary hoe ing j ob i s being done and soybean y i e l ds will not be reduced. Timely operation of the r ot ary hoe i s sometimes interrupted or de layed due to r ainf all, but the f armer should be an opportunist and be ready when soil moisture i s l ow enough so that the rotary hoe can be oper ated without the soil "balling-up." In general, two r otar y hoeings should be enough. Stop rot ary hoe ing after soybeans are 4 inches t a ll. It i s practically useless to rotary hoe after weeds are established; furthermore, the l arger the .soybeans the greater the injury . Properl y u sed, the rotary h oe is the most effective and economica l weed control method availab l e to the soybean producer. -2-(c) Cultivation: Cultivation is still the most widely used weed control method for soybeans grown in rows wide enough to cultivate. Cultiva-tion is the only method of controlling perennial weeds such as milk-weed, hemp dogbane, or clammy groundcherry. Many annual weeds are also missed by presently available herbicides (e.g. smartweed, velvet-l eaf, cocklebur, sunflower, and jimsonweed). Cultivation is aimed at burying surviving weeds in the row and controlling weeds between rows. Again, timeliness is important. The longer weeds compete, the greater the soybean loss, and larger weeds are more difficult to destroy by cultivation than small ones. Do a thorough job--missed weeds cause trouble at harvest time. Combine losses may be increased lo% in weedy soybean fields. 2. Cultural weed control (a) Soybean variety: Do not pick up a stranger--you may get taken. University testing programs determine and suggest which varieties are best adapted to Nebraska conditions. Suggested varieties generally will provide better weed competition than untested imports because of environmental adaptation . Check the suggested varieties before buying seed; do not get shortchanged. (b) Seed quality: Bargain seed generally reduces your profits. Seed low in germination with poor vigor or contaminated with weed seeds is an invitation to weedy soybeans. Why plant your weed problem? Uniform soybean stands--without skips and open spots--provide crop competition to weeds. Can a farmer afford anything but the very best seed availabl e? (c) Row spacing : One significant production practice that has the potential of boosting soybean yields and helping in weed control is that of narrow row planting. In soybeans, narrow rows generally mea n 20-inch spacing or less. Narrow rows aid in weed control by \ providing greater competition and earlier shading of weeds. Nebr-aska research on 10-, 20-, 30-, and 40-inch row soybeans indicates it took 36, 47, 58, and 67 days, respectively, for soybeans to cover the ground. Weeds must be controlled if narrow rows are to help rather than hinder your efforts of increasing crop production. Unfor-tunately, crop competition and shading are not adequate weed control measures by themselves so mechanical and chemical weed control methods must be utilized. The more weed control methods used the more effective and dependable will be your weed control. Herbicides now available do not give consistent or adequate control of some common Nebraska weeds. Cultivation must also be used. This means a farmer should plant his soybeans in row widths he can rotary hoe and cultivate. ~nother factor to consider is the adaptation of machinery to other row crops being grown. One can hardly afford separate equipment for several different row spacings. -3-(d) Planting rate and date: Planting rate should be 8 to 12 seeds per foot of row. Thi s will be adequate to a llow germination loss and soybean plant loss due to rotary h oeing and still give s ix to eight established plants per foot of row . High planting ratesJ within reason) provide greater competition to weeds--too l ow a rate leaves too many open spaces for weeds to fill in. Seeding dates may vary from year to year and will differ according to location in the state. Soybeans are usually planted May 10 to June 5 but plantings as ear l y as May 5 to May 15 are being considered by some farmers. Soybean planting dates will generally be similarJ or slightly after) corn. If soi l temperature conditions are unfavorable for rapid soybean germination and emer-gence) weed problems increase. 3 . Chemica l weed control Gene r a lly) herbicides for se l ective weed control in soybeans need to be supplemented. Cultivation is especially needed where resistant weeds and/or perennials are present in the soybean fields. Herbicides may not be e conomical in fields were weeds do not pose a serious production problem or cultivation has provided effective weed c9ntr9l. Band applications of herbicides should be cons idered to reduce herbicide cost. (a) Preemergence Herbicides for Nebraska (l) Amiben: Amiben (amiben ) should be used preemergence at 2 to 3 lb/A. Use the higher rate on heavier soil types. Amiben is mostly a s~ctiveJ translocated) root-absorbed herbicide) but also may be absorbed to some extent through the l eaves . To be most effective) Amiben should be incorporated into the soil. The most common incorporation method i s rainfall. Mechanical incorporation with a rotary hoe or some other tillage implement will improve weed control in case rainfall does not occur within two or three days after application. Amiben will control most annual broadleaf and grassy weeds. Weeds such as cocklebur) morninggloryJ jimsonweed) shattercaneJ and sunflower are not controlled. Also missed are such common perennial weeds as clammy groundcherryJ common milkweed) and hemp dogbane . Amiben is quite water soluble and in years of excess rain-fall may leach through the soil profile and give little weed control . Amiben generally gives weed control for four to six weeks before being dissipated . Generally) soybeans are quite tol erant to Amiben. Beating rains right after application may cause a hard crust to form on the surface of some soils through which soybeans have difficulty emerging. Amiben reduces the emergence pressure of soybeans and further aggravates the emergence problem. Rotary hoeing to break the crust may be nec-essary. -4-(2) Treflan: Treflan (triflura lin) sh ould be used preplant at l/2 to l lb/A. Use the lower rate on sandy soi ls. Treflan is highly volatile and must be incorporated immediat e l y aft er , or in conjunction with, application for best results. Thoro~gh soil inc orporation by di sking two times at right angles 3 to 6 inches deep with a t andem disk or incorporator is beneficial for weed control. Harrowing or rotary hoe ing in Nebraska will not provide adequate inc orporati on . Treflan will provide season l ong control of most annua l grassy weeds but is weak on broadl eaf weeds with the exception of pigweed and l amb s -quarters. Tolerant weeds include cocklebur, common ragweed, jimson-weed, smartweed, sunflower) and velvetleaf. Sha ttercane can be controlled with Treflan at l lb/A in conjunction with cultivation. Treflan may be applied and incorporated two to three weeks before planting . Soybeans are quite toler ant to Tre flan but planting soybeans more than 2 inches deep in Trefl an treated soil may result in severe soybean injury. To avoid pos s i b l e Tre flan carryover in the soil) do not exceed manufacturer's recommended applica tion r ate . (b ) Other Preemergence Herbicides Available for Use on Soybeans (l) Alanap : Use Al anap (NPA) preemergence at 4 lb/A. Use lower rate on sandy soils . Alanap is absorbed through the root system after seed germina tion. The sodium salt form (Alanap - 3) i s soluble and l eaches r eadily. Weed control from three to s i x weeks may be expected. Rain-fall or mechanical incorporation of Al anap is needed to get weed con-trol. Alanap shoul d not be used on shallow planted soybeans due to injury pos s ibilities . Alanap controls mainly broadleaf weeds. (2 ) Ramrod: Apply Ramrod (CP-31393 ) preemergence a t 4 to 5 lb/A. Use l ower rate on sandy soils . Ramrod is a se l ective) root - absorbed herbicide tha t will give f our to s i x weeks weed control. Ramrod i s especially effective on grassy weeds but weak on broadleaf weeds . Present FDA approved use limits the applicat ion of Ramrod to soy -beans intended for seed purposes only. (3) Vernam : Apply Vernam (vernola t e ) prepl ant at 3 lb/A. Vernam i s highly volatile and must be incorporated immedi a t e ly f or best weed control . It may be applied preplant (plant seed as soon a fter treatment as possible ) or preemergence. Vernam will l each readily but generally will give three to s ix weeks weed control of many annual broadleaf and grassy weeds . Soybeans should be planted at least 2 inches deep to avoid Vernam injury. (4) Lorox : Lorox (linuron ) should be applied preemergenc e at 2 lb/A. Lorox has s ome foliar as we ll as root activity. Lorox will control annual broadl eaf and grassy weeds for four to e i ght weeks. Lorox should be incorporated by rainfall or mechanically for maximum weed control effectiveness . Heavy rainfall immediately a fter seed-ing may cause excess ive leaching and s ubse quent soybean injury. -5-(5) Randox : Apply Randox (CDAA) preemergence at 5 l b/A . Randox is a selective, root - absorbed herbicide which affects youhg seedlings. Ra infall or mechanical incorporation two or three days after application improves weed control effectiveness. Randox will effectively control grassy weeds for three to six weeks but is weak on broadl eaf weeds. Randox is quite soluble and under condi-tions of high rainfall ~ay leach rapidly and not give weed control. (c) Postemergence Herbicides (l) There are only a f ew postemergence herbicides and these have been found relatively ineffective under Nebr aska conditions . 2,4-DB: soybean applied bloom. drought 2 ,4-DB is used postemergence at l/5 lb/A as an overall spray primarily for cocklebur control. It should be to soybeans seven to ten days before bloom up to mid-Later applicat ion, or application to soybeans under sever stress, may cause injury and reduced yields . Nebraska research indicates 2,4 -DB to be partially effective on cocklebur butirn.effective on other broadleaf weeds (e.g. pigweed). Do not confuse with the~ common 2,4 -D. (2 ) Tenoran: Tenoran is a postemergence soybean herbicide used at 3 lb/A or l to l/2 lb/A + 0.25 to 0 .5% surfactant WK. Tenoran may be applied postemergence up to l as t cultivation . Injury symptoms may appear following application but soybeans generally will outgrow them. Nebraska has only limited research data on Tenoran . Information from other states indicates control of broadl eaf weeds (not grasses) when these weeds are les s than l l/2 inches tall. General Considerations Weed control programs should be planned in advance with specific practices outlined for each field. The following points should be considered. (l) Plant good seed in moist, warm soil . This promotes rapid establishment and even stands. Uneven stands invite weed competition . (2) Soybeans should be planted on well drained fields which are conducive to cultivation and other weed control measures . Low spots --poorly drained--provide severe weed problems. (3) Avoid fields containing severe broadleaf weed problems. Use crop-herbicide rotations. If a field has a spec ific weed problem that cannot be controlled in soybeans, plant another crop and follow production prac tices which give control. (4) Plan weed control practices early. Try to anticipate the problem. Weeds are the number one problem in soybean production. Plant soybeans s o you can still take care of the weeds even if the herbicide fails . Herbicides for use in soybeans, like those for other crops, are most effective when incorporated into a \-Te ll-planned production program. -6-

CC201  Soybean Weed Control

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CC201 Soybean Weed Control

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