competition considerations

assumed to be a key factor determining distribution and abundance

competition

ecologists can investigate what about competition

ecological niches

strategies to acquire resources

succession

__________ are interested in distribution and abundance of plants.

ecologists

why do we study competition as weed scientists?

to understand how to reduce the effects of weed competition on crops

ways to test competition

interspecific - weed and crop growing together

check is completely divided above and below

inter-specific(below) - only belowground effects only

interspecific full - complete usually field

intraspecific, crops with crops or weeds with weeds

estimating crop yield loss graph

you can have 100% crop yield

but on weed density side you cant 0 out yield loss

(the second graph that doesn’t hit 0 is better!)

how to know when to control a weed

critical timing of weed removal

critical weed free period

those two give the critical weed free window (control in those times)

two studies you have to do

1. critical weed free period, no weeds, they emerge at multiple timing, let them invade then — find at what point you have arbitrary yield loss tells when you need to start controlling

2. critical time for weed removal, start with weeds and remove weeds each week and keep clean after

   1. creates a window between the two which is a critical period

critical period of weed control

measure when weeds begin to cause unacceptable crop yield loss anc calculating how long the field must stay clean afterward

has two components.

critical timing of weed removal

the time point early in season when weeds compete and yield loss begins, keep clean after

critical weed free timing

start of clean and then let the plot get hairy afterward, determine when yield loss begins to occur

weed free anything is driven by?????

YIELD YIELD YIELD

as weed scientists do we support only going by the model?

no no no

seedbank contributions can make problems worse for following years

if you dont begin controlling them till 35 days they are too large to control

if you wait that long you don’t have a pre option

the models assume 100"% control and we cant — resistance

these models would select for resistance much faster.

decision to control- agricultural settings

competition threshold (model of the critical period)

economic threshold (app, diesel, yield potential, herbicide cost)

cosmetic thresholds - farmers like to impress their neighbors

• renters like to keep if very clean so if the landowner sees

no seed threshold - eradicate before they mature

wh

what drives weed control in other systems?

turf - mainly cosmetic

forests - competition; safety affect yield and

woodlots - safety

roadside, right of way and forests - invasive species

how do we study competition

observation (correlation)

experimentation (causation)

• additive

  • target

• substitutive

  • replacement

we know there is competition how does it affect yield how do we mange it?

make judgement calls on how competitive a plant is

tests to predict how many quadrats should have different scenarios (amount of species per area etc)

chi squared test

not true competitiveness but whether one species is dominant

partial additive (target)

one soybean and two waterhemps, then four then eight waterhemps

replacement series

total plant density doesn’t change but proportions vary of the specie

0:12

2;10

4;8

6;6;

8;4

10;2

12;0 flip half way or whatever so it is opposite