South Dakota State University Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange SDSU Extension Fact Sheets SDSU Extension 1974 Weed Control in Corn Cooperative Extension South Dakota State University Follow this and additional works at: https://openprairie.sdstate.edu/extension_fact Recommended Citation South Dakota State University, Cooperative Extension, "Weed Control in Corn" (1974). SDSU Extension Fact Sheets. 597. https://openprairie.sdstate.edu/extension_fact/597 This Fact Sheet is brought to you for free and open access by the SDSU Extension at Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange. It has been accepted for inclusion in SDSU Extension Fact Sheets by an authorized administrator of Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange. For more information, please contact [email protected]. Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. SDSU ® Extension For current policies and practices, contact SDSU Extension \,\Tebsite: extension.sdstate.edu Phone: 605-688-4 792 Email: [email protected] SDSU Extension is an equal opportunity provider and employer in accordance with the nondiscrimination policies of South Dakota State University, the South Dakota Board of Regents and the United States Department of Agriculture. The practice of applying and incorporating pre­ Fs 554 Weed plant herbicides with liquid fertilizer instead of water, is receiving increased interest. This saves one Control trip across the field, however, agronomists question how effectively plants utilize these shallow-incorpor­ in Corn ated applications of phosphorous and potash. Before using, mix a small amount of the fertilizer and herb­ icide together to determine if they are compatible. Do not mix fertilizer with herbicides unless they are labeled for use in this way. Mixing and applying preemergence herbicides with By Leon J. Wrage, Extension agronomi,t-weecls insecticides or granular fertilizer has generally not W. E. Arnold, associate professor W. B. O'Neal, a\sistant, Plant Science been satisfactory. This usually results in improper placement of one of the products. A good rotation, proper seedbed preparation, timely Granules vs Spray Formulations. Several herbicides cultivation and herbicides are useful to control weeds are available in spray or granular formulations. Gran­ in corn. Cultivation alone will not control most peren­ ules are preferred by some growers because they are nial weeds. Crop rotation and intensive cultivation are easier to handle when band treating. However, gran­ helpful, but herbicides are usually required. Controls ules usually cost slightly more per pound of active for specific perennials are given in other fact sheets. ingredient than spray formulations. Broadcast vs Band Application. Band applications Cuhivation for Weed Control Proper tillage immediately before planting will reduce the cost per acre for chemical. Band applica­ kill emerged weeds and keep weeds from getting tions provide early season weed control and reduce a head start on the crop. Several cultivation systems yield losses that occur during the first 3 to 4 weeks that is 12 to 14 inches can be used to control weeds after the crop is planted. after planting. Use a band wide for surface-planted corn. Herbicides are usually of inside shovels for furrow Use disks in place applied in a 7-inch band instead of broadcast on on first cultivation, "throw planted com, "throw out" furrow or lister-planted corn. Use special nozzles emerge. in" on second when weeds that apply the herbicide uniformly in the treated designed for minimum till Special row cultivators area for band spraying. Band applications should by plant planting systems reduce the problems caused be made behind the press wheel of the planter. the residue on the soil surface. Chopping or shredding Preplanted-incorporated herbicides usually are not reduces cultivation prob­ previous year's corn stalks banded because suitable equipment is generally not lems. A rotary hoe or flextine harrow is useful to con­ available to incorporate the herbicide properly in the trol emerging weeds when the crop is small. area ahead of the row. Rotary Hoe. The rotary hoe should be used at a With band application, at least 2 cultivations are speed of 8 to 10 miles per hour. It is most effective if required to control the weeds between the rows. One used before small weed seedlings develop green color. cultivation is usually required for broadcast treat­ Results are best if the soil is crusted. Hoeing during the ments. Do not throw untreated soil into the treated heat of the day reduces breakage if crop plants are band if no weeds are present during the first row large. Two hoeings can be done for about the same cost cultivation. Always operate a rotary hoe or flextine as the first row cultivation. harrow in the same direction as the rows if the crop Flextine Harrow. The flextine harrow is operated has been treated. at 2 miles per hour or less. It is most effective on weed For band application, determine the amount need­ seedlings less than ~i inch high. Three harrowings can ed for the area actually treated. For example, if the be done for about the same cost as the first row culti­ broadcast rate of 3 lb/ A of product is applied in 12- vation. inch bands to 36-inch rows, only a third of the area is actually treated as the field is crossed, and only one-third of the 3 lb/ A rate is needed. Therefore, Herbicides for Weed Control Herbicides can aid in controlling weeds in corn, 1 pound of product is all that is needed to band spray but are not intended as replacements for sound man­ each acre. (See fact sheet "Weed Sprayer Calibra­ agement. tion.") Mixtures of herbicides can capitalize on the good Preplant Applied Herbicides. These herbicides are points of several herbicides while minimizing weak applied before planting and are usually incorporated points. Herbicides used in mixtures may be purchased with a disk, PTO-driven tiller or other suitable equip­ separately and tank-mixed in the sprayer or some may ment. Some herbicides must be incorporated immedi­ be purchased in one container as a commercial pre­ ately after spraying to prevent loss of chemical due to mix. Tank mixtures allow more flexibility in selecting volatilization or breakdown from sunlight. The rain­ the rate of each herbicide to be used. Mix only those fall requirement is usually less critical and the sea­ herbicides that are labeled for use together. sonal variation in performance is usually less with preplant than with preemergence applied herbicides. Post-emergence Applied Herbicides. These herbi­ Herbicides usually are not applied preplant-incorpor­ cides are applied after the crop and weeds have emerg­ ated on furrow or lister-planted corn unless the fur­ ed. Spraying at the wrong time may result in crop row is very shallow. injury or poor weed control. Post-emergence treatments which must be directed so only the weeds are sprayed Preemergence Applied Herbicides. These herbi­ require special equipment and usually a height differ­ cides are applied after planting, but before the crop ential between the crop and the weed. and weeds emerge. Weed control is usually better if tillage operations for seedbed preparation are per­ Herbicide Recom menda,tions formed immediately before planting and if the herb­ The information presented in this publication is icide is applied immediately after planting. Emerged based on field tests and observations in South Dakota. weeds are usually not controlled. Some herbicides Herbicide uses must be approved by the Environmen­ will injure the crop if it is emerged at the time of tal Protection Agency (EPA) before they are recom­ application. Moisture is required within I to 2 weeks mended. The label directions often include additional after application to move the chemical into the soil. rates and uses that have not been tested or that do not Some herbicides are less soluble than others and re­ apply to general situations in South Dakota. The label­ quire more moisture, however, ¾to I inch of moisture er will assume responsibility only for those uses stated is usually adequate. fyiore moisture is required if the on the label. soil is dry than if it is moist. For best results, the soil should be free of large lumps and heavy amounts Safety First __________________ of plant residue. A shallow cultivation with a rotary hoe or flextine harrow is suggested if weeds emerge Read and follow all label directions and pre­ before adequate moisture is received. Preemergence cautions. Federal regulations and label direc­ herbicides are not effective if the area is disturbed tions are subject to change. by deep cultivation. Recommended l-lerbicides Table 1. Amount of 2,4-D Required to Control Numerous 2,4-D Weeds at Various Growth Stages Amount per acre broadcast ¼ lb/A ½ lb/ A ½ lb/A Chemical and formulation Acid equivalent Kochia, 2-4 in. Kochia, 4-8 in. Kochia, over 8 in. Ragweed, 2-4 in. Ragweed, over 4 in. 2-4-D ester ______ __ __ ____ __ __ __ _____ _______________ ¼ lb Pigweed, 2-4 in. Pigweed, over 4 in. 2,4-D amine _____ ___________ ______ _________________ ½ lb Mustard, 3-6 in. Mustard, over 6 in. Lambsquarters, Lambsquarters, over 6 in. 4-6 in. Cocklebur, 2-6 in. Cocklebur, over 6 in. Use 2,4-D to control many emerged broadleaved Sunflower, 2-6 in. Sunflower, over 6 in. annual and some perennial weeds. Spray over the Ladysthumb, 2-6 in. Ladysthumb, over 6 in. top of corn until it is 8 to 10 inches tall. Use drop Velvetleaf, 4-6 in. Velvetleaf, over 6 in. nozzles for taller corn. Use a high clearance sprayer Russian thistle, 2-4 in. Russian thistle, 4-6 in.