— Kochia Primer —
Wednesday, February 1, 2023
filed under: Weeds
Kochia Emergence —
Seed dormancy: none (usually)
GDD required: <50
Time to 95% emergence: 2 weeks
Temperature range: 40 to 100°F
Maximum emergence depth: 3.25 inches
Calendar time span: April through July
Soil conditions: Fertile, saline, drought
Seedling frost tolerance: Lower ’teens
Rooting depth: Up to 16 feet in drought
Wide genetic diversity in kochia is expressed in highly variable phenotypes: green, red and purple plants, tall and narrow plants, short and round plants, and plants with wide or narrow leaves. Wide genetic diversity caused ALS (Group 2) resistant kochia biotypes to develop in the late 1980s, not long after those ALS herbicides were developed.
Most kochia emerges in a two- or three-week time span very early in the spring. However, early spring tillage and herbicide burndown practices have selected for later-emerging kochia biotypes. As a result, multiple flushes of kochia now occur from April through July.
Kochia Biomass Production —
Ratio of seed mass per unit plant mass:
Foxtail = 75 Lambsquarters = 150 Kochia = 500
Kochia has one of the highest seed-to-plant mass ratios. This allows plants to disseminate numerous seeds that are weakly attaching to light, buoyant plants that roll (tumble weed) uninhibited across fields with the wind.
Carbon Assimilation Pathway (C3 or C4) —
Kochia is C4 — fixes four carbons vs. three during photosynthesis
C4 carbon assimilation physiology allows rapid kochia growth in hot temperatures and in low moisture conditions.
Kochia Pollen —
Type of pollination is ‘cross,’ but is able to ‘self’ pollinate. Length of pollen viability is up to 12 days.
Pollen from herbicide-resistant kochia can pollinate flowers on susceptible plants to make seed resistant to herbicides.
‘Chink in Armor’ Is Short Seed Viability —
Percent seeds viable after one year is 5%; after two years, 1%.
Seed from most weeds remain viable in the soil for a number of years; not so with kochia.