Weed Competition and Interference

Transcription

1 Weed Competition and Interference

2 Definition two organisms need essential materials for growth and the one best suited for the environment will succeed (humans usually manipulate so that crops succeed)

3 Competition vs. Interference competition is for essential elements of growth Light Water Nutrients Physical Space interference is the combination of competition plus other factors (harvest efficiency, parasitism, allelopathy)

4 Weed-Free Period the time that the crop needs to be weed-free to show no detrimental effect on yield (immediately after emergence) Weed Competition / Weed-Free Period lbs/a Weed-Free Cotton Yields Weed-Competition Weeks After Emergence

5 Weed-Competition Period the amount time that the crop can compete with weeds, with subsequent weed removal, and suffer no loss in yield Weed Competition / Weed-Free Period Cotton Yields lbs/a Weed-Free Weed-Competition Weeks After Emergence

6 Examples next 2 slides Corn Yield (bu/a) Grass Competition in Corn Wilson, Wild proso millet Weeks After Emergence

7 Cocklebur Competition in Soybean Barrentine, % yield reduction Weeks of Competition

8 Weed-free period for various crops and weeds to cause no effect on yield. Crop Weeks Weed-free Weed Species cotton 6-8 annuals peanut 6 pigweeds, crabgrass field corn 4 foxtail grasses onions 12 pigweed

9 Factors Affecting Weed/Crop Interference 1. Time of weed/crop emergence (most of time emerge with the crop, due to tillage) a) first plant to establish (water, nutrients, light) gains the advantage b) effect of competition greatest when crop is young c) late emerging/developing weeds have greater impact on quality, harvest efficiency

10 Factors Affecting Weed/Crop Interference 2. Growth Form a) root form - tap vs. fibrous, bunch vs. spreading b) height - prostrate vs. erect growing c) leaf area - horizontal vs. vertical d) free branching vs. single stalk, minimum branching * distinct advantage of rapid growth, with a tall, dense canopy (cocklebur, jimsonweed, sicklepod,, pigweeds) * lower competitive advantage of slow growth rate, with a prostrate, thin canopy (purslane( purslane,, prostrate pigweed, spurge, carpetweed, Virginia buttonweed) * however, this is highly dependent on the crop, the weed, and the outcome desired

11 Factors Affecting Weed/Crop Interference 3. Weed Density - as weed density increases, severity of crop damage increases - density at intraspecific competition is generally maximum crop competition * See examples in next 2 slides

12 Sicklepod Competition in Soybean Soybean Yield (lbs/a) Sicklepod Density (#/row)

13 Cocklebur Competition in Cotton 100 % yield reduction Cocklebur per foot

14 Weed competition in various crops (density of weeds) and effect on yield. Crop Weed Density (row ft) Yield Loss Cotton cocklebur 1 per 3 ft 50% Cotton morningglory 1 per 3 ft 50% Peanut Panicum 1 per 16 ft 25% Soybean Pigweed 1 per 1 ft 30%

15 Factors Affecting Weed/Crop Interference 4. Physiological Basis of Competition above ground a) light often the most critical pigweed can reduce light to vegetables by 85% giant ragweed competition in soybeans will result in death 1) leaf angle - horizontal leaves, alternative leaf arrangement intercept more light 2) rapid expansion of a tall canopy (sicklepod( sicklepod, cocklebur), rapid stem elongation 3) large leaves (cocklebur) 4) light compensation point - better survival under low light (forest canopies) 5) climbing habit (morningglories( morningglories) 6) high allocation of dry matter to stem b) C4 photosynthesis under conditions of limiting CO 2

16 Factors Affecting Weed/Crop Interference 5. Physiological Basis of Competition below ground a) root growth/morphology -- early and rapid root penetration -- high root density, high root/shoot ratio (cocklebur has 2X root volume of kochia) -- distribution - fibrous roots expand over wider area thus more effective competitor b) nutrients - nitrogen, phosphorus and potassium (others as well but not researched); the point is that weeds and crops need the same things and weeds are often better in obtaining nutrients

17 Pounds of nutrients required to produce an equal amount of dry matter. Crop/Weed Nitrogen Phosphorus Wheat Ragweed Pigweed Mustard

18 Factors Affecting Weed/Crop b) nutrients (cont d) Interference 1) nitrogen - main nutrient for competition, high mobility - pigweed, lambsquarters more competitive than corn - nitrogen is often early season, may overcome by fertilization 2) phosphorus and potassium - generally when crops begin to mature, roots overlap - more of a factor in perennial crops - hard to overcome with fertility 3) nutrient management - low N - legumes, P promotes annual bluegrass in bent c) water - root growth effects this factor more of an issue under irrigated conditions (desert environments) becomes a greater limiting factor during fruit/seed development

19 Pounds of water required to produce one pound of dry matter. Crop/Weed Pounds Water Required Corn 350 Wheat 500 Pigweed 306 Mustard 2400 Lambsquarters 660

20 Manipulating the crop to gain competitiveness a) row spacing - narrow row spacing allows for quicker canopy coverage, shading b) fertilizer placement - in the row near the crop, exclude from weeds c) drip irrigation - in the row near the crop, exclude from weeds d) breeding - some varieties are better adapted to weedier conditions

21 Mechanisms of Interference 1. crop quality - hard to measure quantitatively, critical in vegetables 2. harvest losses - hard to separate from direct competition 3. interference with other pest control methods, spray deposition 4. hand harvesting - fireweed in vegetables 5. staining of cotton, grass in cotton

22 Allelopathy - one plant chemically interferes with the growth of another plant 1. living or decaying tissues 2. first reported case 's, juglone of walnut 3. term defined by Molisch in in order to prove must go through a defined set of postulates (Koch s s postulates) a) observe, describe and quantify interference in the field, nature b) isolate, characterize and synthesize toxin c) reproduce symptoms, detailed monitoring of release, uptake, movement of toxin

23 Allelopathy 5. affect by the environment (temperature, moisture, light intensity, etc.) a) growth of the allelopathic plant b) growth of the affected plant c) breakdown rate of possible residue to cause allelopathic affect 6. where and how a) volatilization - creosote b) leaching of residues - rye and wheat c) exudation - juglone from walnut d) decomposition of plant residues - wheat, rye, celery

24 Allelopathic weeds and their affect on various weeds. Weed Lambsquarters Ragweed Nutsedge Italian ryegrass Wild garlic Celery? Crop Affected corn,cucumber several corn, cotton oats, lettuce, clover oats lettuce

25 Parasitism - one plant physically interferes with the growth and development of another plant

26 Parasitism 1. flowering plants 2. receive partial or all growth requirements from the host plant (nutrients, water, sugars) 3. fully photosynthetic (mistletoe) or non-photosynthetic 4. attaches to the host plant by means of a specialized structure termed a haustoria 5. special adaptations to ensure a parasitic partnership a) sticky seeds - mistletoe b) exploding seed pods - dwarf mistletoe c) host-excreted stimulant, root exudates - witchweed,, broomrape

27 Mistletoe is an example of a fully photosynthetic parasitic plant. It gains water and nutrients from the host plant, but makes it own carbohydrates.

28 Parasitic weeds and associated host plants. Parasitic Weed Host Plant Mistletoe pecan, oak, hickory Dwarf mistletoe ponderosa pine Dodder (Cuscuta( spp.) ivy, alfalfa, etc. Witchweed (Striga) corn, sorghum, millets Broomrape (Orobanche( Orobanche) vegetables, clover