weed science
What is a weed? A plant out of place
Plants whose virtues have noy yet been discovered
How can we actually define weeds?
plants out of place that are competitive, persistent, and pernicious
weed characterisitcs:
-abundant seed production
-rapid production of establishment
-seed dormancy
-long term survival of buried seeds
-adaptation for spread
-presence of vegetative reproductive strucutres
-capacity to occupy sites distubed by human activity
dual purpose weeds:
annual morning glory
Johnson grass, canary grass, and bermuda grass
competitive ability:
-all green plants need: water, light, and minerals
-weeds establsih themselves earlier and have competitve advantage
-the effects of weed competition is greatest wjhen weeds are young
monterary loss by weeds:
-if left unchecked yields of corn, soybean, sugarbett by 50% to 65% are supressed
-$5 for every dollar invested by corn growers
-$23 for every dollar invested by sugarbeet
-between 50% to 70% of each crop would be lost if weeds were left alone
weed classification:
-weeds that are similar are grouped together
-the most common classification: aquatic and terrestrial
-botanical classification puts every weed in one specific place, no repitition
botanical classification:
-family
-genus
-species
-variety
-amaranthaceae (pigweeds)
-asteraceae (asters, ragweeds, canada thistle)
-chenopodiaceae (Lambsquarter, Kochiam and Russian thistle)
-poaceae (Johnson grass, barnyard grass, foxtails, sedges, crab grass, quack grass)
-polygonaceae (Jimson weed, nightshade)
annual weeds:
-take one year from vegetative to reproductive
-summer and winter annuals
-winter annual weeds: downy brome, tansy mustard, field pennycress
biannual weeds:
-complete life cycle in 2 years
-Queen Annes lace, burdock, sweet clover, and teasle
perennial weed:
-Johnson grass
-Either be simple of creeping
-simple perennial produces by seed only
-this includes: common milkweed, curly dock, and dandelion
-creeping perennial reproduce and multiply by both seeds and asexual means like underground roots, rhizomes, above ground runner, or above ground stolon
-this includes: Johnson grass, purple and yellow nut sedges, quack grass, silver leaf nightshade
-woody plants are perennial
paracitic and posionous weeds:
depends on the host for survival
form protopplasmic connections with their host plant
derive food, water, or both from the host tissue
3 economically important parasitic in USA:
-witchweed
-dodder
-mistletoe
-witchweed can reduce corn yields as much as 40-50%
dodder:
-non-photosynthetic
-it derives and depends on the host plant for food and water
-serious problem in small seeded legumes
mistletoe:
-parasitic of trees
-derive water andn nutrients from host and being able to carry out own photosynthesis
posionous weeds:
-cause livestock problems especially in western states
-this includes: wild black cherry, chokecherry, cocklebur, whorled milkweed
-poison hemlock and waterhemlock causes problems in huamns and livestock