Tolerance of Seven Native Forbs to Preemergence and Postemergence Herbicides

Clinton C. Shock and Joey Ishida

Malheur Experiment Station

Oregon State University

Ontario, OR

Corey V. Ransom

Utah State University

Logan, UT

Introduction

The trials reported here tested the tolerance of seven native forb species to conventional preemergence and postemergence herbicides in the field.  This work seeks to discover products that could eventually be registered for use for native forb seed production.  The information in this report is for the purpose of informing cooperators and colleagues in other agencies, universities, and industry of the research results.  Reference to products and companies in this publication is for the specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable. Nor should any information and interpretation thereof be considered as recommendations for the application of any of these herbicides.  Pesticide labels should always be consulted before any pesticide use.  Considerable efforts may be required to register these herbicides for use for native forb seed production.

Materials and Methods

Plant Establishment

Seed of seven Great Basin forb species (Table 1) received in October 2005 was planted November 1, 2005. The field had been disked, ground hogged, and marked out in rows 30 inches apart. The seven forb species were planted in individual rows 435 ft long and 30 inches apart. Planting depths were similar to those used in the irrigation trial and varied by species. The crop preceding forbs was wheat. Prior to planting, one drip tape was inserted 12 inches deep equidistant between pairs of rows to be planted. The drip tape was supplied with irrigation water using filtration and other common drip irrigation practices (Shock 2006).

Preemergence Treatments

The weather was wet and windy, delaying the application of preemergence herbicide treatments. The field was staked out to make 5-ft-wide plots perpendicular to the forb rows, crossing all seven species using the upper 200 ft of the field. Eight treatments (Table 2) including the untreated check were replicated four times in a randomized complete block design. Treatments were applied 5 January 2006 at 30 psi, 2.63 mph, in 20 gal/acre using 8002 nozzles with three nozzles spaced 20 inches apart.

By early January the planted area had volunteer wheat and blue mustard. Roundup^® UltraMax at 1.01 lb ai/acre was sprayed 6 January 2006 over the entire area to control the volunteer wheat and other weeds that had emerged. The Roundup was applied at 30 psi, 2.63 mph, in 20 gal/acre using 8002 nozzles with three nozzles spaced 20 inches apart.

On 16 March there was good emergence of the Lomatium species. The forbs were cultivated April 13. Cultivation of adjoining areas damaged part of the Eriogonum umbellatum that had emerged. Starting April 17 emerged plants were counted in 6 inches of row. Plants were evaluated subjectively for injury on a scale of 0 = no injury to 100 = plants dead.

Postemergence Treatments

Postemergence treatments (Table 3) were applied in the same fashion as the preemergence treatments. The field was staked out to make 5-ft-wide plots perpendicular to the forb rows, crossing all seven species using the lower 200 ft of the field. Eight treatments including the untreated check were replicated four times in a randomized complete block design. Treatments were applied May 24 at 30 psi, 2.63 mph, in 20 gal/acre using 8002 nozzles with three nozzles spaced 20 inches apart. Plant injury was rated on May 31, June 15, and June 30.

General Considerations

The focus of the evaluations was forb tolerance to the herbicides, not weed control. Therefore, weeds were removed as needed. In 2006 the trial was irrigated very little with the drip irrigation system because of ample rainfall.

The effects of herbicides for each species on plant stand and injury were evaluated independently from the effects on other species. Treatment differences were compared using ANOVA and protected least significant differences at the 95 percent confidence LSD (0.05) using NCSS Number Cruncher software (NCSS, Kaysville, UT).

Table 1. Forb species planted at the Malheur Experiment Station, Oregon State University, Ontario, OR and their origins.

Results and Discussion

All observations made on the herbicides tested are strictly preliminary observations. Herbicides that were observed to be damaging to the forbs as reported here might be helpful if used at a lower rate or in a different environment. Herbicides that were relatively safe for the forbs in these trials might be harmful if used at higher rates or in a different environment. Nothing in this report should be construed as a recommendation.

Eriogonum umbellatum (Sulfur buckwheat)

Sulfur buckwheat had no statistical differences between the preemergence treatments (Table 2) due to the considerable cultivation injury. Very few of the plants that survived cultivation injury survived the preemergence treatment with Outlook^® or Lorox^®. Plant stunting was observed in plants where the soil was treated with Kerb^® and Outlook. None of the sulfur buckwheat plants receiving Kerb preemergence survived.

Sulfur buckwheat was subject to foliar burn and chlorosis (yellowing) with several postemergence herbicides (Table 3). The buckwheat was sensitive to postemergence applications of Buctril^®, Goal^®, Caparol^®, and Lorox as evidenced by statistically significant foliar damage.

Table 2. Tolerance of Eriogonum umbellatum to preemergence herbicides screened at the Malheur Experiment Station, Oregon State University, Ontario, OR, 2006.

Table 3. Tolerance of Eriogonum umbellatum to postemergence herbicides screened at the Malheur Experiment Station, Oregon State University, Ontario, OR, 2006.

Plant stands of sand penstemon were reduced by preemergence treatments of Prefar^®, Kerb, Prowl^® and Balan^® (Table 4). Where Kerb or Prowl was applied preemergence, almost all sand penstemon plants died during the first growing season. Plant stands were best where Treflan^®, Outlook, and Lorox were applied. Scattered areas of stunted plants occurred in several treatments. Foliar damage was minimal by July 5 where Treflan or Lorox had been applied.

Few negative effects were noted on sand penstemon from most of the herbicides used as postemergence applications (Table 5). Symptoms of damage were yellowing and leaf burn. Leaf burn and plant stunting occurred with Caparol, a photosynthetic inhibitor. Less dramatic and temporary leaf damage was noted following the application of Buctril.

Penstemon deustus (Hotrock penstemon)

Hotrock penstemon plant stands were reduced by all the products tested except Treflan (Table 6). No hotrock penstemon plants were observed where the soil was treated with Kerb. The most common damage symptoms were yellowing and stunting.

Hotrock penstemon plant stands were reduced by postemergence applications of Caparol and Outlook (Table 7). Plants treated with Select^® and Prowl had no phytotoxic symptoms. Burnt and yellowing foliage were common with Caparol, Lorox, Buctril, and Goal. Burnt and stunted symptoms on plants persisted until June 30 following the application of Caparol and Lorox.

Table 4. Tolerance of Penstemon acuminatus to preemergence herbicides screened at the Malheur Experiment Station, Oregon State University, Ontario, OR, 2006.

Table 5. Tolerance of Penstemon acuminatus to postemergence herbicides screened at the Malheur Experiment Station, Oregon State University, Ontario, OR, 2006.

Table 6. Tolerance of Penstemon deustus to preemergence herbicides screened at the Malheur Experiment Station, Oregon State University, Ontario, OR, 2006.

Table 7. Tolerance of Penstemon deustus to postemergence herbicides screened at the Malheur Experiment Station, Oregon State University, Ontario, OR, 2006.

Penstemon speciosus (Royal or sagebrush penstemon)

Royal penstemon plant stands were not affected by Treflan, Balan, or Outlook, among others (Table 8). Phytotoxic effects of most herbicides were moderate and diminished with time. Prowl and Balan applied preemergence caused significant negative effects, and there was marked stunting with Prowl. No royal penstemon survived to 2007 where Kerb was applied preemergence.

None of the postemergence herbicides tested reduced the stands of royal penstemon (Table 9). Royal penstemon was sensitive to Lorox and extremely sensitive to Caparol. Symptoms of Caparol damage included yellowing, yellow-purple foliage, and plant death. Where other products damaged plants, symptoms were yellowing, stunting, and leaf burn.

Lomatium dissectum (Fernleaf biscuitroot)

Fernleaf biscuitroot had a very brief growing season, so observations on the effects of preemergence herbicides were ended on May 31. No significant decreases in plant counts were noted due to preemergence herbicides (Table 10); however, phytotoxic symptoms on the foliage were commonly noted. Prefar had significantly more foliar symptoms that the untreated check on April 17, while Kerb, Outlook, Prowl, and Lorox had significantly more symptoms that the untreated check on both April 17 and May 31. None of the herbicides applied preemergence appeared to be totally safe at the rates used in this trial.

Observations of the postemergence herbicides were begun in late May and continued until June 30. The postemergence herbicides had no significant effects on plant stands at the rates tested (Table 11). In contrast to the negative phytotoxic effects observed with the preemergence herbicide applications, none of the herbicides applied postemergence had significant phytotoxic effects on fernleaf biscuitroot at the rates tested.

Table 8. Tolerance of Penstemon speciosus to preemergence herbicides screened at the Malheur Experiment Station, Oregon State University, Ontario, OR, 2006.