Unit 2: Preparation and Formulation of Bioherbicides - Practice Quiz

1 What is the main purpose of washing collected plant materials before extraction?

2 Why are plant materials commonly shade-dried before grinding?

3 What is the main purpose of grinding dried plant material?

4 Which step separates solid plant particles from a liquid extract?

5 Which liquid is commonly used to prepare a simple aqueous allelopathic extract?

6 What is the active plant-derived component of a plant-based herbicide intended to do?

7 What is the main role of a surfactant in a liquid plant-based herbicide?

8 Why should a formulated plant-based herbicide be mixed thoroughly before use?

9 Which formulation is designed to be mixed with water before spraying?

10 Why is a prepared plant-based herbicide commonly stored in a labeled container?

11 What is the main purpose of a seed germination bioassay for a plant-based herbicide?

12 Which treatment serves as a control in a simple aqueous extract germination bioassay?

13 If 16 of 20 seeds germinate, what is the germination percentage?

14 Which seedling measurement is commonly used to assess the inhibitory effect of a plant extract?

15 Why are replicates used in a seed germination bioassay?

16 What is the main purpose of testing several herbicide doses in the field?

17 Why is an untreated control plot included in a field experiment?

18 Which field observation directly indicates the number of weeds present in a plot?

19 A treatment plot has less weed dry weight than the untreated control. What does this generally indicate?

20 Why are field treatments commonly assigned randomly to plots?

21 A researcher processes 200 g of fresh leaves containing 70% moisture. After extraction, 12 g of dry crude extract is obtained. What is the extraction yield on a dry-plant-mass basis?

22 Grinding dried allelopathic plant material into an extremely fine powder increases extraction but causes repeated clogging during filtration. What is the most appropriate adjustment?

23 An allelochemical is known to degrade rapidly at elevated temperatures. Which processing method is most suitable before extraction?

24 A research team wants to separate nonpolar allelochemicals from polar allelochemicals in the same plant powder. Which extraction strategy is most appropriate?

25 Which storage condition best preserves dried plant powder intended for later preparation of an allelopathic extract?

26 How much dry plant extract is required to prepare 750 mL of a 10% herbicidal formulation?

27 A 20% plant-extract stock formulation must be diluted to prepare 2 L of a 5% spray solution. What volume of stock formulation is needed?

28 An oil-based plant extract separates into a distinct layer when added to water. Which formulation component should be added to produce a stable spray mixture?

29 Batch A contains 8 mg/mL of a marker allelochemical, while Batch B contains 10 mg/mL. To prepare 1 L formulations containing 2 mg/mL of the marker, how much of each batch is required?

30 A plant-based spray gives good weed control but runs off waxy leaves soon after application. Which modification is most likely to improve its performance?

31 In a germination bioassay, 80% of control seeds and 44% of treated seeds germinate. What is the relative inhibition of germination?

32 A plant extract is dissolved in 1% ethanol before being applied to seeds. Which control is essential for distinguishing extract activity from solvent effects?

33 Seeds exposed to an extract show 90% germination, similar to the control, but their average root length is reduced by 60%. What is the best interpretation?

34 An aqueous allelopathic extract has a pH of 3.5, and treated seeds germinate poorly. Which additional treatment would best test whether acidity is causing the response?

35 A plant extract causes 20%, 45%, and 65% germination inhibition at concentrations of 1, 2, and 4 mg/mL, respectively. Within which range is the approximate ?

36 The weed dry mass is 400 g per quadrat in the untreated control and 100 g per quadrat in a treated plot. What is the weed control efficiency?

37 A bioherbicide gives 65%, 86%, and 88% weed control at 2, 4, and 6 L/ha, respectively. Crop injury is 2%, 5%, and 14% at these doses. Which dose is the most appropriate candidate for standardization?

38 A field has a clear fertility gradient from one end to the other. Which experimental design is most suitable for comparing several bioherbicide doses?

39 A recommended application rate is 5 L/ha of formulated bioherbicide. How much formulation is required for a 40 experimental plot?

40 A treatment reduces weed density by 70% at 14 days but only by 30% at 42 days. What is the most likely field interpretation?

41 Fresh leaves contain 72% moisture. An extraction protocol requires dry-matter equivalent per liter, and of extract must be prepared. Assuming no material loss, what mass of fresh leaves is required?

42 A dry plant sample is extracted into , producing a marker concentration of . The extract is concentrated to , where the marker concentration is measured as . What is the marker recovery during concentration?

43 An aqueous extract prepared after hexane defatting shows lower phytotoxicity than an aqueous extract prepared directly from the same plant material. Which interpretation is most defensible?

44 During slow air-drying, an endogenous enzyme converts an allelochemical glycoside into a more active aglycone. Which pretreatment is most appropriate when the objective is to estimate the chemical profile present in freshly harvested tissue?

45 Extracts made from plant powder are more inhibitory than extracts made from particles after the same 2-hour extraction. Which experiment best tests whether the difference reflects extraction kinetics rather than a true difference in extractable allelochemical content?

46 A standardized crude extract contains of an allelochemical marker. What volume of this extract is needed to prepare of spray containing of the marker?

47 A formulation contains 25% crude plant extract by mass, and the extract contains 8% active marker by mass. How much formulation is required per hectare to deliver of marker?

48 An emulsifier blend with a required hydrophilic-lipophilic balance of 9 is prepared from emulsifier L with HLB 4 and emulsifier H with HLB 12. What mass percentage of emulsifier H should the blend contain, assuming linear blending?

49 A marker in a plant-based formulation follows first-order degradation and retains 80% of its initial concentration after 30 days. Under unchanged storage conditions, what percentage is expected to remain after 90 days?

50 A formulated extract containing a surfactant causes greater weed injury than the unformulated extract but also causes crop chlorosis. Which treatment set is essential for separating extract activity, surfactant activity, and their interaction?

51 A seedling-vigor index is defined as germination percentage multiplied by mean seedling length. A control has 90% germination and an mean length, whereas a treated group has 60% germination and a mean length. What is the percentage inhibition of the vigor index?

52 A plant extract produces 30% inhibition at and 70% inhibition at . Assuming inhibition is linear with the logarithm of concentration between these doses, what is the estimated ?

53 A concentrated aqueous plant extract has pH 4.1 and substantially lower water potential than the control. Which control design best distinguishes allelochemical inhibition from nonspecific pH and osmotic effects?

54 In a germination bioassay, 25 seeds are placed in each Petri plate, with four plates per concentration. All 100 seeds per concentration are analyzed as independent observations. What is the principal statistical problem?

55 After an extract treatment, many seeds fail to germinate but stain positively in a tetrazolium viability test. What conclusion is best supported?

56 Field doses of 1, 2, 4, and produce weed-control efficiencies of 45%, 70%, 88%, and 90%, respectively. Corresponding crop injuries are 0%, 3%, 8%, and 25%. If acceptable crop injury is at most 10%, which dose is the best candidate for standardization?

57 A treated plot has 600 weeds before application and 150 afterward. The untreated control has 400 weeds before application and 500 afterward. Using the Henderson–Tilton correction, what is the weed-control efficiency?

58 A field has a strong north-to-south soil-moisture gradient. Which randomized complete block arrangement most effectively controls this source of variation?

59 A formulation contains 15% active marker by mass. The target application rate is marker per hectare in a spray volume of . What formulation concentration is required in the spray tank?

60 Two bioherbicide doses provide similar weed control 14 days after treatment, but the field experiences several later weed-emergence flushes. Which response set gives the strongest basis for selecting the more durable standardized dose?