Weed Identification and Control Flashcards

Which weed is classified as a 'winter annual' and commonly infests winter wheat fields in the Great Plains?

Answer: Jointed goatgrass (Aegilops cylindrica)

Jointed goatgrass is a winter annual grass that germinates in fall alongside winter wheat and is extremely difficult to control due to its close botanical relationship to wheat.

The WSSA herbicide resistance classification system groups herbicides primarily by:

Answer: Mode of action (target site in the plant)

The WSSA/HRAC system assigns group numbers based on site of action (mode of action), which is the most relevant classification for resistance management.

Which diagnostic feature distinguishes morningglory species (Ipomoea spp.) from field bindweed (Convolvulus arvensis) in the field?

Answer: Morningglories are annual vines without basal bracts, while bindweed has two small bracts on the flower stalk

Field bindweed has two small leaf-like bracts (bracteoles) located on the flower peduncle well below the flower, while morningglory species lack these bracts near the flower.

A producer using minimum-till practices observes an increase in winter annual weed pressure. The most likely reason is:

Answer: Lack of soil disturbance allows more weed seeds to remain near the surface where they can germinate

Reduced tillage leaves weed seeds near the soil surface in the optimal germination zone, favoring small-seeded winter annuals that need light or shallow burial for germination.

Which statement best describes cross-resistance in weed management?

Answer: Resistance to multiple herbicides within the same mode-of-action group due to a single mechanism

Cross-resistance describes resistance to multiple herbicides within the same mode-of-action class caused by a single resistance mechanism, such as a target-site mutation or metabolic enzyme.

Common ragweed (Ambrosia artemisiifolia) and giant ragweed (Ambrosia trifida) are best distinguished by:

Answer: Leaf shape — common ragweed has deeply pinnately lobed leaves while giant ragweed typically has three to five palmate lobes

Common ragweed leaves are deeply pinnately dissected (fern-like), while giant ragweed leaves are large with three to five distinct palmate lobes, making leaf morphology the easiest identifier.

When tank-mixing herbicides to broaden the weed control spectrum, which of the following compatibility concerns should always be checked first?

Answer: Physical and chemical compatibility between products, plus label-mandated jar tests

Physical compatibility (e.g., precipitation, separation) and chemical antagonism or synergism should be evaluated via a jar test before field application; the label is the law for tank-mix guidance.