Postplant tillage provides limited weed control in flax, lentil and hard red spring wheat (continued)

Keywords

Introduction

Materials and
Methods

Results and
Discussion

Conclusion/
Implications

Future Research
Needs

References

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Background

Crop Plant Stand and Seed Yield
Crop plant numbers varied with years (P < 0.05) (Table 1). Fewer flax and wheat plants occurred in 1995 than 1994, averaged over weed control treatments, for unknown reasons (data not presented). Lentil plant numbers were similar across plots in both years.

A crop by weed control treatment interaction occurred for crop plant numbers (Table 1). Controlling weeds with herbicides, tillage or a combination of herbicides and tillage reduced flax plant numbers by 8 to 25 plants/ft² (14 to 44%) compared to flax not treated for weed control (Figure 1 – color graph – 41KB gif). Plant numbers for lentil and wheat were not reduced by any postplant control treatment. These data suggest that lentil and wheat can be rotary hoed or harrowed twice without reducing crop plant numbers, whereas flax plant numbers will be reduced from postplant weed control, particularly from tillage.

Crop seed yield was similar (P = 0.14) even though hard red spring wheat produced almost twice the yield of flax and almost four times that of lentil (Table 1). Variability within plots without herbicides probably accounts for the large error and lack of statistical seed yield differences among crops. Yields were particularly variable for lentil when herbicides were not used (Figure 2 – color graph – 39KB gif). Weed control was inconsistent when herbicides were not used, and this was reflected in greater variability in crop yield.

Seed yield was greater when tillage was combined with herbicide treatment for weed control compared with tillage alone (Table 1). For example, crop yield was increased from 1290 to 1680 lb/acre (30%) when rotary hoed twice 5 and 28 DAP compared with rotary hoeing 5 DAP followed by herbicide treatment 28 DAP. Yield was similar when weeds were controlled by tillage combined with herbicides and only by herbicides (P = 0.11). These results suggest that the herbicide treatment contributed more to weed control than tillage in treatments using both methods. Yield was not increased when weeds were controlled with tillage alone compared to forgoing any attempt at controlling weeds.

Weed Biomass Production
Weed biomass was reduced by tillage, herbicides, or a combination weed control treatment compared to not treating for weed control (Table 2). However, weed biomass was greater where only postplant tillage was used compared to plots treated with herbicides. Tillage seemed more dependent on environmental factors favoring its success than were herbicides. It was observed that weed biomass was reduced when hot, dry conditions occurred during, and for several hours before and after tillage treatments were imposed. These conditions prevailed in conjunction with the first tillage operation in 1994. Conversely, weed control was inconsistent when soil remained moist following tillage when cool, cloudy conditions developed, as occurred after the first tillage operation of 1995. Weed biomass production was reduced when herbicides were applied regardless of the weather conditions before, during or after treatment.

A crop by weed control treatment interaction existed for weed biomass production (Table 2). Weed biomass was greater in lentil plots where herbicides alone were used to control weeds than in plots where weeds were controlled by both herbicides and tillage (Figure 3 – color graph – 40KB gif). Weed biomass produced in flax and wheat was similar where herbicides were applied, regardless of whether or not postplant tillage occurred.

Thinning of lentil plant populations occurred in plots receiving the herbicide treatment in 1994 (data not presented). That year, methylated seed oil (Scoil) at 1 pt/acre was applied along with the sethoxydim plus bromoxynil treatment. Extensive injury to lentil occurred and the weeds flourished with less competition from lentil for growth resources. Lentil plants were more competitive with weeds in 1995 when herbicides were applied without Scoil and no thinning of lentil plants was observed.

Grass weed biomass production was not reduced by tillage weed control treatments (Table 2). Grass weed biomass was similar in plots with no weed control to plots where tillage alone or in combination with broadleaf herbicides was used for weed control. Broadleaf weed biomass was reduced by tillage, but less than with herbicides applied for broadleaf weed control. These data indicate that tillage was not as effective as herbicides for reducing either grass or broadleaf weed growth.

Results of this research indicate that broadleaf weed biomass production can be reduced by postplant tillage in flax, lentil and hard red spring wheat. However, weed biomass reduction from postplant tillage is less than that provided by postplant herbicides. Similar findings have been reported by others for flax (Carr et al., 1996), lentil (Boerboom and Young, 1995) and hard red spring wheat (Smolik et al., 1991). We suggest that there is a lack of empirical evidence to support the use of postplant tillage for weed control in these three crops as an alternative or supplement to herbicides. Postplant tillage may provide minimal broadleaf weed control in crops in farming systems where herbicides are not used, but there is no evidence that tillage reduces grass weed growth. Smolik et al. (1991) even reported that postplant tillage enhanced grass weed production in wheat.

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Table of Contents – Fall 1997