Weed Biology and Management Curtis Rainbolt Extension Weed Scientist Everglades REC

Weed Biology and its Impact on Management What makes a plant a weed? Cost of weeds Why do weeds always win? Biology Get to know the enemy Anatomy of a weed Common south Florida weeds Strategies for weed management

Definition of a weed: A weed is an undesired plant out of place Water hyacinth in a aquatic garden: not a weed Water hyacinth clogging canals: a weed

Weed impacts Weeds are costly $24 billion in agricultural crop loss $3 billion in control costs Pimentel et al. 1999

Weeds are costly It is estimated that without control, sugarcane losses would be 50% from heavy infestations of fall panicum In 2000, over $51 million was spent for weed control in US sugarcane

Why do weeds always win? Dormancy: broken when conditions favor survival Rapid early growth and expansion Early and fast root growth Efficient uptake and processing of nutrients and water

Why do weeds always win? Ability to reproduce early in life cycle Prolific seed production Absorb resources in excess Tolerate low levels of resources Genetic and environmental adaptability Ability to develop resistance to control measures

Reproduction by seed First infestation is dependant on seed -First infestations in a field can also occur when vegetative structures are transported into new fields on tillage and harvesting equipment. -Seed production varies greatly within and among weed species. -Seed production also varies with environmental variation between locations and years, competition from neighboring plants, and genetic variability. Estimates of the total number of weed seeds in the soil range from 4 million to 133 million per acre furrow slice

Vegetative reproduction Less longevity in soil than seeds Very small structures can reproduce Canada thistle: ¼” piece of root results in new plant Torpedograss can reproduce from very small segments of rhizomes Can be as prolific as seed production Yellow nutsedge: 1,900 new plants and 18,000 tubers in one year from one plant -Another example of prolific vegetative reproduction: Whitetop has been observed to spread over an area greater than 10 feet in diameter and produce over 450 shoots in the first year of establishment.

Get to know the enemy: weed identification

Weed identification goals Impossible to learn the thousands of weeds found in Florida Learn the primary weeds Keep field notes The goal is to learn how to identify a weed Plant anatomy Plant keys

Weed classification: life cycles Annuals- reproduce by seed only Biennial: Life cycle completed in two years Flowering and fruiting in second year Examples: wild carrot, cudweed Perrenials: Simple- reproduce by seed only Creeping- reproduce by seed and vegetative propagules

Differences between grasses and sedges: Sedges have a solid, triangular in cross section, stem. Leaves are arranged in threes (extend in three directions). Grass stems may be round or flattened.

Purple vs Yellow Nutsedge

Purple vs Yellow Nutsedge

Common Sugarcane Weeds

Fall panicum (Panicum dichotomiflorum) Most common grass in the area Relatively easy to identify Stem can be hairy or smooth (hairy when young) Ligule fringe of hairs Round stem Widely dispersed seedhead

Wild oats (Sorghum almum) Not really an oat Closely related to johnsongrass No rhizomes Large, membranous ligule Robust plant Can look like sugarcane seedling when small

Broadleaf panicum Panicum adspersum (Urochloa adspersa) Relatively prostrate growth Wide leaves with wavy margins Round stems Usually dark green in color Very similar to alexandergrass

Alexandergrass (Brachiaria plantaginea) Relatively prostrate growth Somewhat wide leaves with straight margins Round stems Usually light green in color Very similar to broadleaf panicum leaves narrower (usually) margins straight rather than wavy (usually)

Alexandergrass vs Broadleaf panicum

Napiergrass (Pennisetum pupureum) Very robust plant Forms dense clumps in fields Long, wide leaves with finely toothed margin Up to 12 feet tall Seedhead has “bottle brush” appearance

Paragrass (Brachiaria mutica) Prostrate growing, medium size grass Long stems covered with hairs Short hairs on leaf surface Swollen nodes Grows in very wet areas Often moves out of ditches Pasture grass in Africa

Paragrass (Brachiaria mutica)

Goosegrass (Elusine indica) Found in many fields Low growing Very white, flattened stems Looks like it has been stepped on Probably not competitive

Crabgrass (Digitaria spp.) Very wide first leaf Initial clumping growth progressing to prostrate, tillering Visible membranous ligule Can be very hairy, or hairless, depending on species

Torpedograss (Panicum repens L.) Perennial with robust, creeping, sharply pointed rhizomes. Leaf blade stiff and erect. Hairs on upper and lower leaf surface. Seedheads with stiff, ascending branches. Occurs in wet areas.

Spiny pigweed (Amaranthus spinosus) Most common pigweed species Stickerweed Large, upright growth habit, entire leaves Very evident spines located at nodes

Alligatorweed (Alternanthera philoxeroides) Common in many areas of the EAA Prefers wet areas Often spread by cultivation Low growing Hollow stems when growing in wet spots Opposite leaves Small white blooms

Common lambsquarters (Chenopodium album) Common some years Usually during the cooler months (Dec, Jan) Can be difficult to control Waxy leaf surface Small “dots” of wax are useful for ID Gives leaves a white-gray color Alternate leaves Medium size lobes on leaves

Common purslane (Portulaca oleracea) Very common Probably not competitive Prostrate growing Succulent Leaves small, smooth, opposite or alternate Small, yellow flowers Red stems

Common ragweed (Ambrosia artemisiifolia) Often found on ditch banks and field edges Deeply dissected leaves Many hairs on upper and lower surfaces Long seedhead at top of plant Yellow flowers Similar in appearance to ragweed parthenium Different flower type

Ragweed parthenium (Parthenium hysterophorus) Primarily ditchbanks Less common than common ragweed Leaves less deeply dissected Divisions don’t go all the way to the stem White flowers Single, not multiples

American black nightshade (Solanum americanum) Occasional weed in EAA Problematic in vegetables (tomato, pepper) Same family (Solanaceae) Resistant to paraquat in some areas Alternate leaves Usually entire to somewhat lobed Purple fruit Seems quite competitive

American black nightshade (Solanum americanum)

Sources of Weed ID Information Picture books: Southern Weed Science Society ID Guide Excellent resource Very thorough (almost too many plants) Web Picture/Taxonomic Sites http://aquat1.ifas.ufl.edu/photos.html http://www.griffin.peachnet.edu/cssci/TURF/turf.h tm

Weed management strategies

Secrets to Successful Weed Control Prevention

Only you can prevent weed invasion! Be careful what you plant Consider all points of entry Keep an eye out for new invaders elsewhere Prevent reproduction of early invaders

Ecological weed management is based on how a plant is built Annual vs. biennial vs. perennial Growth stage – perennials act like annuals for a short period Timing relative to the seasons Control prior to seed production

Management timing relative to the seasons Perennial weed growth schedule: Spring: export carbohydrates from roots to new shoots Summer: capture and assimilate new energy Fall: “pack it in” for winter – carbohydrates transported to the roots Winter: usually, minimal growth or activity

Management timing relative to the seasons Perennial weed management – general terms: Spring: limit new growth – drain the roots Summer: prevent energy capture Fall: opportunity to attack the root storage system Winter: eliminate new seedlings

Manual removal Hoeing, Pulling, Cultivation Success determined by population and distribution – is it feasible? Annual weeds easily removed Perennial plants are often “subdivided” Vegetative root pieces often produce new plants

Biological control Biological control of weeds in cropping systems is a difficult proposition The control agent must be very host-specific and not injure non-target species The life cycle of the control agent must match that of the target species Surrounding habitat should support control agent survival and reproduction In the future, possibility of bioherbicides

Herbicides Several good options for most crops grown in EAA Applications should be timed to minimize competition with crop Should be made prior to weed seed head formation

Questions??