June 2010 Weed Counts
Weed population density data for June, prior to the first mint harvest, is presented below. The most prevalent weeds were mustards (tall hedge mustard and tumble mustard); this was also true of the September sampling date. In June, other weeds present were common lambsquarters, Russian thistle, kochia, prickly lettuce, and horseweed (marestail). Weed densities varied by herbicide treatment and/or irrigation treatment and there were only a few instances in which there was a significant herbicide by irrigation treatment interaction on weed density.
In each of the following tables, means within a column followed by the same letter are not significantly different at the P=0.05 level.
See results of the September 2010 weed counts at this link.
Total Weed Counts
There was a significant herbicide by irrigation level interaction on total weed counts in June. In the untreated check plots, weed numbers were greatest in the plots receiving the lowest irrigation level, probably a result of poor crop competition. Similar trends were evident in terbacil (Sinbar) and flumioxazin (Chateau) treated plots with the greatest number of escape weeds in the plots receiving low irrigation. A similar number of total weeds were present across all irrigation levels in plots treated with sulfentrazone (Spartan), but the species composition changed in response to irrigation levels.
| Herbicide Treatments | ||||
|---|---|---|---|---|
| Untreated | Sinbar | Chateau | Spartan | |
| No/m2 | ||||
| Deficit Irrig. | 22.78a | 5.35b | 2.90b | 4.04b |
| Med. Dry | 6.22b | 1.46b | 2.16b | 4.46b |
| Medium | 3.83b | 1.11b | 1.77b | 3.00b |
| Med. Wet | 3.60b | 0.84b | 1.27b | 2.11b |
| Full Irrig. | 3.94b | 0.67b | 1.11b | 3.06b |
Kochia
Kochia population density was not significantly affected by herbicide treatment although the lowest numbers of kochia were in the plots treated with flumioxazin and sulfentrazone regardless of irrigation level. Kochia density was greatest in the lowest irrigation treatment, probably a result of less crop competition, as the mint grew poorly in those plots and offered little competition with weeds.
| Irrigation Level | No/m2* |
|---|---|
| Deficit Irrigation | 3.78a |
| Medium Dry | 0.37b |
| Medium | 0.30b |
| Medium Wet | 0.27b |
| Full Irrigation | 0.18b |
| *Averaged over all herbicide treatments; herbicide interaction not significant. | |
Prickly Lettuce
Prickly lettuce population density was not affected by irrigation treatment and all three herbicides reduced prickly lettuce densities compared to the nontreated checks (paraquat without a residual herbicide).
| Herbicide | No/m2* |
|---|---|
| Untreated | 0.203a |
| Sinbar | 0.002b |
| Chateau | 0.041b |
| Spartan | 0.032b |
| *Averaged over all irrigation levels; irrigation amount not significant. | |
Tall Hedge Mustard
Tall hedge mustard population density was affected by both irrigation level and herbicide treatment. Lower densities of tall hedge mustard were recorded in plots receiving the least irrigation, possibly due to heavier densities of other weeds (tumble mustard, kochia, Russian thistle, common lambsquarters, and horseweed) in those plots. Terbacil and flumioxazin controlled tall hedge mustard well across all irrigation levels, whereas sulfentrazone did not control tall hedge mustard.
| Irrigaton Level | No/m2 | Herbicide | No/m2 | |
|---|---|---|---|---|
| Deficit Irrig. | 0.60b | Untreated | 2.21a | |
| Med. Dry | 1.65a | Sinbar | 0.04b | |
| Medium | 1.61a | Chateau | 0.07b | |
| Med. Wet | 1.16ab | Spartan | 2.39a | |
| Full Irrig. | 1.66a |
Tumble Mustard
Tumble mustard population density was impacted by both irrigation level and herbicide treatment and there was a significant herbicide by irrigation treatment interaction. Tumble mustard densities were greatest in the two lower irrigation treatments. Terbacil completely controlled tumble mustard across all irrigation levels, flumioxazin partly controlled tumble mustard, and sulfentrazone failed to control tumble mustard.
| Herbicide Treatments | ||||
|---|---|---|---|---|
| Untreated | Sinbar | Chateau | Spartan | |
| No/m2 | ||||
| Deficit Irrig. | 3.09a | 0.0c | 0.27c | 1.93b |
| Med. Dry | 2.38ab | 0.0c | 0.50c | 1.76b |
| Medium | 0.48c | 0.0c | 0.20c | 0.26c |
| Med. Wet | 0.48c | 0.0c | 0.15c | 0.13c |
| Full Irrig. | 0.31c | 0.0c | 0.12c | 0.25c |
Common Lambsquarters
Common lambsquarters density was more random and population density was not significantly affected by either herbicide or irrigation level in June, although lowest densities were recorded in sulfentrazone and terbacil treated plots. Nontreated plots receiving the least irrigation contained the most lambsquarters, probably due to lack of mint competition and sufficient early spring moisture to germinate some of the seed bank. There were no statistically significant differences among the treatments, and no tabular data are provided.
Russian Thistle
Russian thistle population density was greatest in the lowest irrigation treatment. Terbacil failed to control Russian thistle whereas sulfentrazone completely controlled Russian thistle and flumioxazin was intermediate.
| Irrigaton Level | No/m2 | Herbicide | No/m2 | |
|---|---|---|---|---|
| Deficit Irrig. | 0.27 a | Untreated | 0.08 b | |
| Med. Dry | 0.07 b | Sinbar | 0.21 a | |
| Medium | 0.04 b | Chateau | 0.08 b | |
| Med. Wet | 0.05 b | Spartan | 0.0 c | |
| Full Irrig. | 0.04 b |
Horseweed
Horseweed densities were also higher in the lowest irrigation treatment and terbacil and sulfentrazone controlled horseweed well across all irrigation levels. Flumioxazin did not control horseweed.
| Irrigaton Level | No/m2 | Herbicide | No/m2 | |
|---|---|---|---|---|
| Deficit Irrig. | 0.62 a | Untreated | 0.26 ab | |
| Med. Dry | 0.20 b | Sinbar | 0.0 b | |
| Medium | 0.06 b | Chateau | 0.49 a | |
| Med. Wet | 0.05 b | Spartan | 0.03 b | |
| Full Irrig. | 0.03 b |
Weed Science subpage
This page is designed to provide additional information pursuant to the Weed Science component of the overall project discussed on the Washington State University website http://hopmintstress.wsu.edu.
It is not designed to be viewed or utilized independently of that website.