Allelopathy in weeds and crops: myths and facts. Jed Colquhoun Department of Horticulture

Transcription

1 Allelopathy in weeds and crops: myths and facts Jed Colquhoun Department of Horticulture

2 Allelopathy in weeds and crops: outline What is allelopathy? Field observations of allelopathy Practical uses for weed management Can we put the sprayer away?

3 What is allelopathy? The effect of one plant on another plant through release of a chemical compound into the environment Plant-produced herbicides Greek derivation: allelo and pathos = mutual suffering

4 Allelopathy is not new Theophrastus, 300 B.C.: chickpea allelopathic to weeds Plinus Secudus, 1 A.D.: corn scorched by chickpea, barley, and bitter vetch Juglone and the walnut tree

5 Field observations attributed to allelopathy

6 Field observations attributed to allelopathy

7 Myth vs. Fact Allelopathy is very difficult to isolate: Weed suppression = allelopathy + physical interference Physical interference includes impedance of light, water, nutrients by cover crop residue or living mulch

8 Myth vs. Fact Allelopathy research is difficult: Greenhouse research: doesn t account for effect of microorganisms, plant stress, weather, soil type, growth stage Field research: difficult to separate physical interference from allelopathy Difficult to isolate complex allelopathic compounds

9 Crops can be allelopathic to weeds Three methods for using allelopathy in weed management: As a winter cover crop, with residue providing allelopathic compounds As a living mulch during the cropping season As an isolated compound from an allelopathic plant, applied as an herbicide

10 Crops can be allelopathic to weeds: examples Rye as an allelopathic cover crop in field studies Reduced common ragweed (43%), green foxtail (80%), redroot pigweed (95%), and common purslane (100%) Physical interference not separated from allelopathy

11 Crops can be allelopathic to weeds: examples Rye as an allelopathic cover crop Residue leached of allelopathic compounds compared to residue with allelopathic compounds Eastern black nightshade and yellow foxtail suppression did not differ between leached and non-leached residue The layer of rye residue on the soil surface accounts for majority of suppression Barley and crimson clover were allelopathic

12 Crops can be allelopathic to weeds: examples Oat cultivars differ in allelopathy 24 oat cultivars grown in greenhouse Oat residue soaked for 5 hours in water Common lambsquarters seed germinated with water from oat soaking Germination quantified

13 Crops can be allelopathic to weeds: examples Oat cultivars differ in allelopathy 20 of 24 cultivars reduced common lambsquarters germination Ruby cultivar reduced germination by 86% Minimal selectivity: pea germination also reduced by 71%

14 Crops can be allelopathic to weeds: examples Rape-turnip is allelopathic to several weeds Isolated compounds reduced spiny sowthistle, mayweed, smooth pigweed, and barnyardgrass germination At higher concentrations, germination was completely eliminated

15 Weeds can be allelopathic to the crop Over 240 allelopathic weed species documented Velvetleaf: radish, corn, soybean, tomato Common lambsquarters: corn, cucumber, oat, soybean, tomato, wheat Redroot pigweed: barley, cabbage, carrot, cauliflower, corn, cotton, eggplant, pepper, squash, soybean, tobacco, tomato, wheat

16 Allelopathic plants as natural herbicide sources Synthetic herbicides based on natural plant compounds Advantages:new target sites, water soluble, perceived as more environmentally friendly Disadvantages: chemically complex, difficult to isolate and produce, not stable Example: sorgoleone, from sorghum, inhibits photosynthesis better than atrazine, but is short-lived and not stable

17 Allelopathic plants as natural herbicide sources Callisto (mesotrione) Derived from a compound (leptospermone) isolated from the callistemon (bottle brush) plant Source:

18 Allelopathic plants as natural herbicide sources Rely, Liberty (glufosinate) Derived from microbes Synthetic version of phosphinothricin, a breakdown of a compound produced by Streptomyces spp.

19 Can we put the sprayer away? Allelopathic compounds: Short-lived in soil Complex and unpredictable Non-selective Expensive to synthesize Potential mammalian toxicity, carcinogenic, allergenic

20 Can we put the sprayer away? Over 2,900 papers published on allelopathy, dating back to 300 B.C. Despite allelopathic crops, weeds are still problematic Breed for allelopathy? Allelopathy is another tool in an integrated program, but is not a silver bullet

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