Herbicide Resistance

What crop has he never seen weed free?

Weedy Onions

What are the 2 most impactful weed species in Ga?

1. Palmer Amaranth

2. Rye Grass

What are the 2 prerequisites for Resistance?

1. The gene for resistance must be present in the population

2. The population must receive pressure and from the herbicide the gene could form resistance to

How many acres to find a resistant plant in 1/billion?

918 acres

How many resistant species?

273

How many resistant cases (not species)

541 unique cases 

How many MoA’s are effected?

21/31

What happens when people rely on one herbicide?

It quickly develops herbicide resistance (EX. palmer)

What has occured with the Benghal Dayflower aka Tropical Spiderwort

It has a big weed shift towards it because it was tolerant to glyphosate.

What do you need to be carful of when cycling herbicides?

Make sure they have different MoA’s. If it has the same target, it can develop resistance all the same.

What are some of the main economic/decision factors behind resistance?

1. Single mechanism of action applied to large acreage

2. Few classes of chemistry used

3. Little to no tillage

4. Little to no rotation in crops

5. Often in stressful environments when herbicide activity is minimized

6. Reduced herbicide rates, poor coverage, etc.. that minimize activity

What are the 3 E’s of herbicide resistance?

Economics, Effectiveness, and Ease

Single Herbicide Resistance

Resistant to only one herbicide

Cross Herbicide Resistance

•Resistant to two or more herbicide families with same mechanism of action

•Single resistance mechanism

Multiple Herbicide Resistance

•Resistant to two or more herbicides with different mechanisms of action

•May be the result of two or more different resistance mechanisms

Why do weeds most often not get killed by herbicides?

Application Error or Environmental Challenges

What applicator errors can mimic resistance?

Poor spray coverage

Calibration issue

Wrong rate

Wrong adjuvant

Antagonism from mixes

Dust/soil on leaves

What enviornental factors can mimic resistance?

Drought stressed plants

Lack of herbicide activation

Soil pH (usually low)

Organic matter

Soil texture

Plant residues prevent coverage

What do we need to worry about in weeds that would be detrimental if resistant?

1. growth rate

2. seed production

3. overall competitive ability (yield loss)

4. rapid spread of resistance (dioecious outcrossing)

WHat are some strategies to curb resistance?

Starting the crop weed free

Diverse herbicide programs

Overlapping residual herbicides

Timely applications

Tank mixtures

How much biomass is needed for cover crop to not need herbicide?

7K lb/ac

What are some future control?

automated Weed pullers and laser weeders.