In 2004 and 2005, potted white oak seedlings 0.6 m in height were treated with six herbicide treatments at three concentrations, 1/4, 1/10, and 1/100× of the standard field use rate. These herbicides and their standard field use rate of active ingredient (a.i.) included 2,4-D at 1.5 kg/ha, 2,4-D + glyphosate at 0.8 kg/ha + 1 kg/ha, acetochlor + atrazine at 3.5 kg/ha, dicamba at 0.7 kg/ha, glyphosate at 1.1 kg/ha and metolachlor at 2.0 kg/ha. The seedlings were treated at three growth stages: swollen buds, leaves unfolding, and expanded leaves. A compressed air spraying chamber delivering 187 L/ha was used to apply the herbicides. After treatment, the containers were placed in an open field plot in a completely randomized design. Oak seedlings were most susceptible to herbicide injury at all concentrations, at the leaves unfolding stage. Symptoms on seedlings treated with 2,4-D and dicamba at the leaves unfolding stage included leaf cupping and rolling, leaf curling, leaf rolling downward from leaf margin, and unusual elongation at leaf tip. Glyphosate + 2,4-D applications resulted in leaf cupping, yellowing, leaf rolling downward from leaf margin and abnormal leaf tips. Glyphosate symptoms ranged from leaf yellowing and browning, to slight browning of interveinal leaf tissues. Acetochlor + atrazine, or metolachlor alone caused the abnormality referred to as “leaf tatters” where in severe cases, only the main veins are present with limited amounts of interveinal tissues. Detailed description of the injury symptoms, supplemented with photographs are posted on a web site: http://www.nres.uiuc.edu/research/herbicide_research/index.htm
In some years, the emerging leaves of white oak and, to a lesser extent, of red oak in the Midwest have developed abnormally. This abnormality is referred to as leaf tatters. Reports to state foresters and Extension specialists associated tatters with herbicide applications. In 2005, white and red oak seedlings were treated in a spray chamber delivering 187 L/ha, with seven herbicides at three concentrations, 1/4×, 1/10×, and 1/100× of the standard field use rate. These herbicides and their standard field use rate of the active ingredients included atrazine at 2.3 kg/ha and chloroacetanilide herbicides: acetochlor at 2.0 kg/ha, metolachlor at 2.1 kg/ha, and dimethenamid at 0.8 kg/ha alone or mixed with atrazine at 2.3 kg/ha, at the leaves unfolding stage. After treatment, oaks were placed outdoors in a randomized complete-block design. Leaf symptoms in our study were similar to those seen in the landscape. In chloroacetanilide-treated white and red oak seedlings, browning of interveinal leaf tissues was noticed 5–6 days after treatment. The dried leaf tissues then dropped off, leaving only the main vein with little interveinal leaf area. In few seedlings treated with atrazine, the leaf tissues turned yellow to brown, while in few others, interveinal tissue damage was restricted, leaving small holes in the leaf. When chloroacetanilide herbicides were applied with atrazine, the dominant symptoms were those of leaf tatters. A few seedlings treated with dimethenamid and atrazine had predominately atrazine symptoms. Although new growth later in the season was not injured, the leaves with tatters remained on the plant until the end of the growing season. The study will be repeated in 2006.
Herbicide drift to landscape and woodland trees is a particular concern in midwestern United States where the topography is relatively flat, large-scale agriculture relies on herbicides, and housing developments and woodlands are intermingled with agricultural fields. Recently, leaf abnormalities (called leaf tatters) have been reported on white oak (Quercus alba L.). We evaluated the effects of field corn herbicides on white oak at the swollen bud, leaf unfolding, and expanded leaf stages. Container-grown white oak seedlings were treated with 1%, 10%, and 25% standard field use rates of 2,4-D isooctyl ester, glyphosate, 2,4-D isooctyl ester + glyphosate, dicamba, acetochlor + atrazine, and metolachlor. Loss of interveinal tissues (leaf tatters) occurred after treatment with the chloroacetanilide herbicides, acetochlor (+ atrazine) and metolachlor, only when oaks were in the leaf unfolding stage. No other herbicide caused tatter-like symptoms. Dicamba and 2,4-D ester applied at the leaf unfolding stage caused leaf cupping, downward rolling of leaf margins, elongation of leaf tips, leaf strapping with parallel veination, and initial leaf cupping followed by death of the growing point. Glyphosate applied at either the leaf unfolding or expanded leaf stage caused leaf chlorosis and necrosis, leaf tip browning, and curling of leaves. Herbicide applications near white oak should be timed before leaf unfolding or after the expanded leaf stages.
Previous research by the authors found simulated acetochlor (with atrazine) and s-metolachlor drift to white oak at the leaf unfolding stage caused loss of interveinal tissues (leaf tatters). Reports of leaf tatters in the landscape and nursery settings are more common on white oak (Quercus alba L.) than on northern red oak (Quercus rubra L.). Our objectives were to determine if white and northern red oak differed in susceptibility to chloroacetanilide herbicides, if injury varied between chloroacetanilide herbicides, and if adding atrazine increased leaf injury. Two-year-old seedlings at the leaf unfolding stage were treated with acetochlor, s-metolachlor, and dimethenamid-P alone or combined with atrazine at 1%, 10%, and 25% of the standard field use rate. Within 6 days, all chloroacetanilides at 10% and 25% field use rates, alone or combined with atrazine, caused leaf tatter injury in both species. Acetochlor, s-metolachlor, and dimethenamid-P caused a similar type of leaf injury. Atrazine did not cause loss of leaf tissues or increase injury from chloroacetanilides. At 1% field use rate, only acetochlor, acetochlor + atrazine, and dimethenamid-P caused leaf injury to northern red oaks. The white oaks were not injured by all of the chloroacetanilide treatments at 1% field use rate. The northern red oaks were slightly more susceptible to chloroacetanilides compared with the white oaks. A second study found acetochlor only injured northern red oak when applied at the leaf unfolding stage and only at 25% of field use rate. Acetochlor at 1% field use rate did not injure red oak. Research is needed to explain the greater frequency of leaf tatters on white oaks than on northern red oaks in the landscape and to develop strategies to avoid tree injury.
Herbicides can be an excellent supplemental treatment in cases where soil fumigant treatments alone fail to control weeds during the growing season or in situations where fumigants cannot be used as a result of regulatory restrictions. Previous studies have shown that oxyfluorfen and flumioxazin can provide satisfactory weed control in bedded strawberry (Fragaria ×ananassa Duch.) production. However, we need to know if tolerance to herbicides is uniform across strawberry cultivars under California conditions. The objective of this study was to determine if tolerance to oxyfluorfen and flumioxazin herbicides varied among strawberry cultivars. Trials were conducted in the 2007–2008 and 2009–2010 growing seasons at Salinas, CA. Treatments included an untreated control; pre-plant applications of flumioxazin at 0.07, 0.11, and 0.21 kg·ha−1 a.i.; and oxyfluorfen at 0.14 and 0.28 kg·ha−1 a.i. The entire trial was fumigated with an emulsified formulation of 60% 1,3-dichloropropene + 32% chloropicrin applied at 281 L·ha−1 by drip injection to all plots. Eight strawberry cultivars were included in the trial in the 2007–2008 growing season, and nine cultivars were included in the 2009–2010 growing season. In both growing seasons, slight to no crop phytotoxicity was observed. In the 2007–2008 growing season, several strawberry cultivars including ‘Albion’, ‘Festival’, ‘211G51’, ‘Palomar’, ‘Plant Sciences 5298’, and ‘Ventana’ had smaller crop plant canopy diameter as compared with the control when treated with 0.21 kg·ha−1 a.i. of flumioxazin. Compared with the control, flumioxazin at 0.21 kg·ha−1 a.i. reduced crop diameter for ‘Plant Sciences 4634’, ‘Plant Sciences 5298’, ‘San Andreas’, and ‘Ventana’ in the 2009–2010 growing season. In the 2007–2008 strawberry-growing season, none of the herbicide treatments reduced fruit yield compared with the control. In the 2009–2010 growing season, in seven of the nine cultivars, there were no significant differences in yield among treatments. For ‘Palomar’ strawberry, yields in plots treated with flumioxazin at 0.11 and 0.21 kg·ha−1 a.i. were significantly lower than the untreated control. With the exception of flumioxazin at 0.21 kg·ha−1 a.i., these herbicides are safe to use and can be incorporated in strawberry production practices for the cultivars tested to achieve satisfactory weed control over the growing season.
An integrated approach to weed control in nursery containers is crucial if herbicide applications during the growing season are to be reduced. This experiment, conducted in 2002 and 2003 in Urbana, Ill., evaluated rice hulls, leaf-waste pellets, and pine bark as herbicide carriers for the preemergence herbicides oryzalin at 2 lb/acre a.i. and diuron at 1 lb/acre a.i. The efficacy of the treatments in controlling annual weeds and the phytotoxic effects of the treatments on the woody plant species were evaluated in separate completely randomized designs. For the efficacy experiment, no ornamental plants were present and containers were each seeded with a mixture of 1:1:1 (by volume) of annual bluegrass (Poa annua), common groundsel (Senecio vulgaris), and shepherd's purse (Capsella bursa-pastoris) immediately after treatment applications. For the phytotoxicity experiment, ‘Goldflame’ spirea (Spiraea japonica), ‘Hetz Midget’ american arborvitae (Thuja occidentalis), and ‘Snowmound’ nippon spirea (Spiraea nipponica) were evaluated. No weed seeds were sown in the phytotoxicity containers. Treatments for both experiments included spray applications of herbicides with water or with one of the organic mulches as a carrier or one of the mulches alone. Evaluations were done 45 and 120 days after treatment (DAT) in both years. The organic carriers with herbicide sprays gave efficacy visual ratings equivalent to water as a carrier for both herbicides. Phytotoxicity was not observed in the spirea species in either year. For ‘Hetz Midget’ american arborvitae in 2002, diuron with water had the highest visual phytotoxicity rating. Diuron phytotoxicity on the ‘Hetz Midget’ american arborvitae was alleviated when diuron was applied with any of the three mulches as a carrier. Pine bark treatments increased plant biomass for ‘Goldflame’ spirea in 2003, 45 DAT. At 120 DAT in 2002, pine bark gave increased plant biomass as compared with no organic mulch treatments for ‘Goldflame’ spirea. The study was conducted to ascertain whether the use of organic mulches as carriers could reduce phytotoxic effects of a herbicide on container-grown woody ornamentals, improve crop plant biomass, and act as a herbicide carrier for container-grown woody ornamentals.
Fumigants are used to control soilborne pests before planting high-value crops such as strawberry. The use of specialized tarps during fumigation can reduce fumigant emissions and mitigate the need for large buffer zone requirements mandated by regulators. Increased fumigant retention by use of barrier films during fumigant application may increase fumigant retention and allow use of lower fumigant rates to control soil pests than would be needed with permeable film. The objective of this study was to determine the minimum effective rates of the alternative fumigants, 1,3-dichloropropene (1,3-D) + chloropicrin (Pic), and Pic required under virtually impermeable film (VIF) and a high-density polyethylene (HDPE) tarp to provide weed control equivalent to methyl bromide:chloropicrin (67/33% v/v MBPic) standard soil fumigation at 392 kg·ha−1 under HDPE. A second objective was to determine fumigant rates under VIF and HDPE tarps needed to provide weed control and the economic costs of using VIF and reduced rates of the alternative fumigants. In 2002–2003 and 2003–2004 growing seasons, the fumigants 1,3-D + Pic and Pic were tested at 0, 56, 112, 224, 336, and 448 kg·ha−1 under HDPE and VIF tarps at Oxnard and Watsonville, CA. An untreated control and a MBPic standard at 392 kg·ha−1 were also included in the study. Weed control was assessed using weed propagule viability bioassays for four common weeds, time required for hand weeding, and weed fresh biomass. The fumigant rate that would be needed for a 90% reduction in viability (GR90) for all weeds was 21% to 84% less for 1,3-D + Pic under VIF compared with the HDPE tarp. For Pic, the GR90 values were 5% to 64% less under VIF compared with the HDPE tarp. Hand weeding times and weed biomass decreased with increasing fumigant rates. With the exception of Pic in 2002–2003 at Oxnard, VIF reduced the rate required for weed control compared with the HDPE tarp for both fumigants and at both locations. Economic benefits of VIF relative to the HDPE tarp were not consistent and additional work is needed to quantify these relationships and the production conditions under which VIF will be beneficial.
The phase-out of methyl bromide as a soil fumigant for strawberry (Fragaria ×ananassa, Duch.) and increasingly strict regulations of all fumigants suggest that non-fumigant methods of soil disinfestation are needed. In warm climates, solarization controls soilborne pests, but fog and lower summer soil temperatures in coastal California render it unsuitable for pest control relative to chemical fumigation. The first objective of this study was to test the efficacy of steam in controlling soil pests in strawberry production. The second objective was to determine if combining solarization with steam in coastal California would achieve greater pest control and higher yields compared with steam or solarization used alone. The final objective was to determine the economic feasibility of steam and solarization treatments relative to MBPic fumigation. Field studies were conducted at Salinas, CA, in 2007–2008 and in 2008–2009 growing seasons. Treatments included MBPic 67/33% v/v at 392 kg·ha−1, untreated control, solarization, steam, and steam + solarization. For steam + solarization plots, beds were solarized for 2 weeks before and 2 weeks after steam application. Before application of a clear film for solarization, beds were irrigated so the soil moisture was optimal for solarization. Steam was injected into the beds to reach soil temperatures to 70°C or higher up to a depth of 25 cm for 20 min. Soil temperatures during steam and solarization treatments were monitored. Control of soil pests was measured using pathogen and weed propagule bioassays in all treatments. After the 4-week treatment period, ‘Albion’ strawberry was transplanted in all plots. After transplanting, weed density, weed fresh biomass, and hand weeding time were recorded periodically in each treatment over the cropping season. Weed seed viability in steam and steam + solarization-treated plots was the same or lower than MBPic standard fumigation. Compared with MBPic fumigation, solarization alone was less effective in controlling weeds or reducing the hand-weeding time. Steam and steam + solarization treatments resulted in weed control similar to MBPic fumigation. Only certain steam treatments reduced the number of Verticillium dahliae Kleb. microsclerotia similar to the MBPic fumigation at 15-cm depth with no reductions at greater depths. There were no significant differences among treatments in 2007–2008 with regard to yield, but in 2008–2009, yields from steam treatments were comparable to the MBPic-treated plots. Economic analysis performed for the 2008–2009 season showed that net returns from steam or solarization treatments were less than MBPic treatment.
Methyl bromide (MB) has been widely used in California cut-flower production for effective control of a broad range of soil pests, including plant pathogens and weeds. However, MB is an ozone-depleting substance, and its availability to growers is limited according to the Montreal Protocol guidelines. Steam has been suggested as a nonchemical option for preplant soil disinfestation. Five trials were conducted in protected greenhouse structure or open-field cut-flower nurseries in Monterey, San Luis Obispo, and Ventura counties to evaluate the effect of steam application, alone or in combination with solarization, on soilborne plant pathogen populations, weed densities, and crop growth. Several steam application methods were used including steam blanket, spike-hose, buried drip irrigation lines, or drain tile, and these varied among trials. Calla lily (Zantedeschia aethiopica) nursery trials initiated in 2007 and 2008 showed that steam alone or with solarization was similar to or more effective than MB:chloropicrin (MBPic), applied via drip lines, in controlling weeds and Verticillium dahliae at 6-inch depth. Trials conducted in Spring and Fall 2009 in an oriental hybrid lily (Lilium sp.) nursery showed that, 112 days after steam treatment (DAT) in the spring, the steam (spike-hose) treatment had fewer Fusarium oxysporum propagules than the MB treatment. Lily plant growth in the steam-treated plots was similar to MB-treated plots and taller than in control plots. In the fall trial, fewer lily plants emerged by 44 DAT in the untreated control than in steam- and MB-treated plots and steam was not as effective as MB in reducing Pythium populations. In the 2010 sunflower (Helianthus annuus) and bupleurum (Bupleurum griffithii) trial, all steam treatments reduced Pythium and Phytophthora cactorum survival compared with the untreated control plots, whereas weed densities were reduced only in the spike-hose steam-treated plots. These trial studies showed that steam appeared as effective as MB in suppressing pathogens and weeds and improving crop growth in cut-flower nurseries. However, additional information on fuel consumption, treatment time efficiency, and long-term effects of steam treatment on soil health are needed before steam can be recommended as a viable alternative to MB in California cut-flower nurseries.