Explanation: Atrazine is listed in the table entitled "Weed Response to Herbicides in Corn" that can be found in Bulletin 789, Weed Control Guide for Ohio Field Crops. Thus, the answer is C, fall panicum.
The identification of fall panicum is important because postemergence herbicides need to be applied when plants are small. Responses "B, D, and E" contain "perennial" in the description, however, fall panicum is an annual. "A" indicates that the leaf is completely green, while "C" indicates the leaf has a prominent and white midrib. "C" is the best description.
Cultural control is important even when herbicides are used. All of the above is the correct answer.
Soil type, tillage practices, current and following crop, weed species currently and previously observed in the field and cost are all important characteristics that should be considered when designing an herbicide program.
Herbicide performance is affected by soil and weather conditions as well as by the application evenness, rate and procedures; but performance is not affected by cost.
Weather conditions and thorough coverage are very important for effective weed control with postemergence herbicides. "B & C" are true and the answer is "E."
Bicep II Magnum contains s-metolachlor and atrazine, which are the common names of the two active ingredients in this herbicide product. An herbicide that is given a trade name may contain one or more active ingredients.
4L means that there are 4 pounds active ingredient per gallon.
Gallons of commercial product/acre =
Pounds of active ingredient/acre 1.2 lb. /acre -------------------------------------- - ------------- = 0.3 Pounds of active ingredient in gallons 4 lb. /gal 0.3 gallons of commercial product/acre x 10 acres = 3 gallons
Therefore "C" is the correct answer
Soil-applied herbicide performance is affected by all of the items listed so the answer is "F."
Injury is more likely as less of the herbicide is "tied up" or absorbed in the soil by organic matter and clay.
The higher the soil pH, the more available soil-applied triazine herbicides become. As a result, better weed control is achieved in high pH soils but there is greater risk of crop injury.
Drift of Gramoxone to non-target plants, especially vegetables will injure them, but may not kill them. However, the residue may cause the sale of the crop to be illegal. For many herbicides no residue is allowed in food crops.
Herbicides with long (not short) soil residual are well suited for early preplant for two reasons. First, long residual assures season long weed control with an early preplant program. Second, the risk of carryover is reduced when long residual herbicides are applied earlier in the season.
The second part of the statement is true but the answer is false as the "and" between the statements indicates that both statements must be true for the answer to be true. Herbicides with low solubility require more moisture for them to be active but are less likely to leach beyond the zone of effectiveness, so they are well suited for early preplant.
Preemergence herbicides are applied to the soil surface after the crop is planted but before crop seedlings appear above the ground, so the correct answer is "C." Early preplant and preplant incorporated are applied before planting of the crop and postemergence applications are applied after the crop and weeds have emerged.
Smaller weed size increases the effectiveness of postemergence herbicides so "A" is not the answer. High temperature and relative humidity also generally increase the effectiveness of postemergence herbicides. Drought conditions do make postemergence herbicides less effective, but so does rainfall during or soon after application, as the herbicide can be diluted or washed off the target plant. Therefore, the correct answer is "F" which indicates both "B" and "D" are the answers.
High temperature, high relative humidity, and the use of an adjuvant generally increase the effectiveness of postemergence herbicides, which also increase the risk of crop injury. Small weed size generally increases the effectiveness of weed control but does not increase crop injury. So the answer is "A."
Glyphosate and other translocating herbicides can be applied with a carrier volume of 10 gallons/acre because these herbicides can move through the plant to where it kills the plant. However, paraquat needs a carrier volume of at least 15 gallons/acre and relatively high pressure because it is a contact herbicide. This allows for good spray coverage.
Increased pressure produces smaller droplets and improves penetration of dense canopies. Increased spray volume also increases foliar coverage, as does the addition of an adjuvant. However, temperature and humidity do not affect foliar coverage. Therefore, the correct answer is "H."
Increasing the spray droplet size by using an AI nozzle is an excellent way to decrease drift and maintain excellent weed control with translocating herbicides. Increasing the droplet size can decrease the weed control of contact herbicides. You can increase droplet size as you reduce spray pressure or use a larger output nozzle.
Floodjet and fullcone nozzles should not be used for any type of postemergence herbicide applications. Extended range flat fan nozzles allow too much drift of translocating herbicides. The best way to reduce the drift of postemergence herbicides is to use an air induction (AI) nozzle, however weed control may be decreased for contact herbicides. Therefore "C" is the correct answer.
Reduced or no-tillage does not always require more herbicides. Ways of maintaining herbicide rates with reduced or no-tillage are early preplant programs with long residual herbicides or a total postemergence program. Also, if no- or reduced tillage has been practiced for several years, the depth of tillage is reduced and fewer new seeds are brought up each year, which reduces weed pressure. The key word in this statement is "always." Absolutes in a true or false statement are very often best answered as false.
Roundup WeatherMax is the trade name and glyphosate the common name for the same material which is used extensively to kill existing vegetation for no-tillage. Gramoxone Max is the trade name and paraquat the common name for another burndown material used in no-tillage. Therefore, "E" is the correct answer as all of the responses are correct.
Certain herbicides can be as toxic to humans and the environment as insecticides or rodenticides. It is always necessary to handle any pesticide with extreme care and respect, regardless of whether it is an insecticide, rodenticide or herbicide.
It is against the law to apply any pesticide on a crop which is not labeled and to apply more than the recommended rate. However, it is not against the law to apply less than the labeled rate, which can provide good weed control if applied to small(<2" in height) weeds, but will cause poor weed control when applied to large weeds.
Hardened stainless steel nozzles are consistently the most wear resistant but also the most expensive. Ceramic nozzles are also wear resistant and expensive, but were not listed in the question.
Nozzles do wear, and wear results in a larger orifice and higher output. Nozzles should be changed when output increases 10% from that of new nozzles.
Many herbicides, especially those applied postemergence, require very small concentrations to control weeds. For these herbicides it is necessary to clean the sprayer with ammonia, sal soda, or trisodium phosphate. For more information about tank cleaning agents locate the University of Missouri publication (number G4852) titled "Cleaning Field Sprayers to Avoid Crop Injury." It can be found at the web site: http://muextension.missouri.edu/explore/agguides/crops/g04852.htm
Even with the correct order as indicated in "D," it is imperative that agitation is continued between and after the addition of each pesticide. Spray tanks should be at least half filled with the carrier before pesticides are added. If more than one pesticide is mixed without previous knowledge of their compatibility, it is recommended that the pesticides be tested by mixing appropriate proportions of all components in as small a batch as practical.
Numerous complaints reach ODA concerning drift to fields, gardens, lawns, trees, etc. Volatile herbicides can move long distances from the site of application and damage sensitive plants. Special care needs to be taken to assure the safety of sensitive non-target plants. Most problems arise from spraying when windy, with high pressure, with a volatile herbicide, and at high temperatures. A homeowner's tree is one of many to a producer, but a specimen to the homeowner.
All of the statements increase spray drift. Therefore, "E" or all of the above is correct.
All of the formulations listed are volatile except for the amine formulation of 2,4-D. For this reason the amine formulation should be used where volatility is likely to impact non-target species.
All of the statements increase the possibility of herbicide carryover problems. Therefore, "H" or all of the above is correct.
Atrazine and simazine are triazines that have been used as corn herbicides for a number of years with high carryover potential. Oats are the best species to use for a bioassay. Trifluralin, chlorimuron-ethyl, and imazaquin also have high carryover risk, and are best bio-assayed by corn. Glyphosate and paraquat have no or very little soil residual, so carryover is usually not a problem for these materials.
Bioassay is the best way to test for possible herbicide damage for the approaching crop year. It allows you to isolate herbicide damage from plant growth problems due to other factors. Bioassays are only as good as the soil samples taken.
Atrazine, Lasso and others have been found in water sources for municipal water systems. The level is very low but we need to take every precaution to keep herbicides out of groundwater or surface water.
The greatest risk to water contamination is erosion and water run-off from fields. Fertilizer and herbicides are materials carried from crop fields.
Groundwater contamination generally occurs from careless handling of pesticides and often could have been prevented. Contamination of soil by pesticides at loading sites and back-siphoning of pesticides into wells needs to be guarded against closely.
The potential for groundwater contamination is greater, not less, on sandy soils and with higher herbicide rates and with more persistent herbicides. However, the potential is less if a herbicide is used with a low leaching potential. An herbicide with low solubility is less likely to leach. So "B" is the correct answer.
All of the active ingredients listed have a groundwater advisory statement on any label containing these ingredients. These have warnings because they have been found in groundwater. Therefore, "F" is the correct answer.
The use of a triazine (atrazine or simazine) herbicide the previous year, coupled with the use of metribuzin on soybeans increases the chances of triazine injury to soybeans. The higher the triazine herbicide rate in corn, the greater the risk for soybean injury the following year.
On soils considered to be highly erodible and having less than 30% residue cover, the maximum preemergence rate for atrazine is 1.6 pounds active ingredient/acre, which is answer "A."
The total amount of atrazine that can be applied to a single field during one calendar year is 2.5 pounds active ingredient/acre. Therefore "D" is the correct answer. Two applications will need to be made to reach this maximum rate.
The maximum amount of atrazine applied in a single application 1) to soils considered highly erodible with greater than 30% residue cover, or 2) to soils not considered highly erodible or 3) in postemergence applications is 2.0 pounds active ingredient/acre. Therefore "C" is the correct answer.
Proper sprayer clean out and calibration is always important. However, it is critical for low use rate herbicides. Just a small amount of spray left in the sprayer of a highly active herbicide can cause significant damage. For highly active herbicides, proper calibration is important because too little herbicide applied will cause poor weed control and too much will cause excessive crop injury.
Nearly all postemergence herbicides need an adjuvant such as NIS, MSO, COC, 28%N, or AMS. An adjuvant is used to break down the surface tension of spray droplets. As a result the spray mixture can spread over the leaf surface more readily and break down the leaf surface to allow more herbicide to enter the leaf. Therefore "C" is the correct answer.
Proper crop rotation, tillage, and most importantly using herbicides with several different sites of action will delay the onset of herbicide resistant weeds for many years compared to planting the same crop every year, doing no tillage, and using a single herbicide site of action.
ALS inhibiting herbicides such as cloransulam (First Rate), Chlorimuron (Classic), imazamox (Raptor), and others, have the most number of herbicide resistant weed species. Therefore "D" is the correct answer.
The Corn, Soybean, Wheat and Alfalfa Field Guide has pictures of the weed species listed below and groups the weeds together by life cycle and type of plant. Most of the weeds below are discussed in the "Control of Problem Weeds" section of the Weed Control Guide for Ohio Field Crops. In that section, it is indicated whether a species is an annual (grows one year or less), a biennial (grows for two years), or a perennial (grows for more than two years). That section also indicates whether each species is a grass, broadleaf, or sedge. This information is very important in effectively controlling weeds.
bindweed, hedge _____P_____ _____B_____ carrot, wild _____B_____ _____B_____ chickweed, common WA (and SA) _____B_____ dandelion _____P_____ _____B______ deadnettle, purple ____WA____ _____B____ dogbane, hemp _____P_____ _____B_____ foxtail, giant ____SA____ _____G_____ foxtail, yellow ____SA____ _____G______ johnsongrass _____P_____ _____G_____ lambsquarters, common ____SA_____ _____B______ marestail/horseweed WA (and SA) _____B_____ milkweed, common _____P_____ _____B_____ morning glory, tall ____SA____ _____B_____ nutsedge, yellow _____P_____ _____S______ panicum, fall ____SA_____ _____G_____ quackgrass _____P_____ _____G_____ ragweed, common _____SA____ _____B____ ragweed, giant _____SA____ _____B____ shattercane _____SA____ _____G_____ thistle, canada _____P_____ _____B_____ velvetleaf _____SA____ _____B_____
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868