When weeds win the canopy, crops lose. Reid J. Smeda, Professor of Weed Science University of Missouri

Transcription

1 When weeds win the canopy, crops lose Reid J. Smeda, Professor of Weed Science University of Missouri

2 Do you ever feel trapped by the rat race? Life is competitive

3 Competition also occurs among plants Intraspecific competition (with each other) Interspecific competition WEEDS!

4 How long do plants compete? Season-long if life cycles match Winter annuals will compete early in the life of summer annual crops Summer annuals will compete late in the life of winter annual crops Henbit in leeks can be a big problem

5 Definition Competition occurs when the combined demand of 2 plants for a growth factor is below the immediate supply

6 Plants compete for 5 five factors Big three Water Light Nutrients Little two Oxygen (important for rice) CO 2 (C4 plants more competitive than C3)

7 Plants do not compete for space! They compete for the stuff in the space

8 How do we examine the competitive impact of a weed on a crop? Depends upon the particular weed species and density Depends upon the particular crop, planting design, and date of establishment Research at the University of Guelph: 1 pigweed per 2 square yards caused a 5% reduction in corn yield when emerging with corn; 40 plants for the same area were needed when pigweed came up after corn was established

9 Combined influence of weed and crop is reflected in what we call the critical weed-free period It is a time when the crop yield can be reduced from its optimum

10 Critical weed-free period Period during crop production when weeds are most likely to reduce yield or harvest

11 Shorter critical weed-free period means: Slow development of weed Rapid growth or high competitiveness of crop Common purslane

12 Longer critical weed-free period means: Rapid development of weed Slow growth or low competitiveness of crop Waterhemp Bell pepper

13 Are newly emerging weeds a threat in this situation?

14 Using bullets (tools) to control weeds at the wrong time is:..not going to accomplish your goal and will just cost you more money!

15 What does this boil down to? Data provided by Clarence Swanton

16 With competition, things on the surface may not be as simple as they appear Canada thistle 2 years after establishment

17 Competition for water >97% of water absorbed by plants is lost via evapotranspiration (cooling process)

18 Why do you feel cool coming out of pool?

19 Without sufficient water, plants wilt and internal temperature increases; plant growth stops

20 We do not seem to have a water shortage right now! Clarksville, MO; April 22, 2013

21 Weeds are inefficient water users 1 pound dry weight of barnyardgrass requires 80 gallons of water

22 Competition for water begins before light and nutrient competition Water is drawn some distance from roots and can be stored

23 Water is also needed for. Nutrient uptake

24 Macronutrients Nutrient uptake depends on availability and soil ph N, P, K, Ca, Mg, S Micronutrients B, Mn, Fe, Zn, Mo, Cu, Cl

25 Nutrients can be stored in plants? Phosphorous in Arabidopsis Continuously recycled at cellular level Low P Sufficient P

26 Can we add sufficient nutrients for both crop and weeds? Data generated by University of MN

27 Competition for nutrients and water depends upon relative root volume Grasses fibrous Broadleaves often modified taproot

28 Light is the most critical growth factor Only certain spectra are used (and removed by the tallest plants) There is a finite amount per acre (based upon area) Light cannot be stored in plants (use it or lose it) Far red (730 nm)

29 What happens when plants compete for light? Red light is removed by taller plants and far red light is passed through Change in ratio of R:FR light (reduced) This stimulates production of a PIN3 protein that regulates movement of auxin; more auxin stays in the upper shoot of plants Shaded plants elongate to compete for available light

30 Weeds have different methods to optimize light usage: Vining growth habit Movement toward available light Plant height

31 Vining growth habit - annuals Morningglory

32 Some plants adjust leaf angle to optimize sunlight usage

33 Most competitive weeds adjust internode length to grow taller Weed will want to optimize light utilization, but no need to waste resources on stems

34 Some plants are like people.. They want to be taller

35 Key to avoiding problems!

36 How does that translate to weed control? Pay most attention to weeds early in the growing season Do not let weeds get established or they will take available water and nutrients Use mulches to shade weeds Narrow crop rows restrict light and decrease weed emergence

37 QUESTIONS? Continued use of the same practice for weed control is like repetitive use of a bird deterrent; if birds can figure it out, so can weeds!