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  • Author or Editor: Bradley D. Hanson x
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New plant-based products can be produced from seed harvested from Brassica species used for phytomanaging selenium (Se) in the west side of central California. Se-enriched seed meals produced from canola (Brassica napus) and mustard (Sinapis alba) plants were tested as potential bioherbicides and green fertilizers in strawberry production under controlled and field conditions for two seasons. Treatments consisted of adding each meal (containing 2.2 mg Se/kg dry mass) to the soil at rates equivalent to 0, 2, and 6 t/acre, respectively, 7 days before planting. In growth chamber studies, the highest rates of either meal lowered berry yields by a high of 30% compared with no application (control). Among the nutrient accumulation, berry Se, calcium (Ca), manganese (Mn), and zinc consistently increased with most Brassica meal treatments and most significantly with the mustard meal. In the field studies, mustard treatments lowered the emergence of summer-germinating and resident winter annual weeds more than canola and control treatments. Strawberry fruit yields increased with all Brassica treatments, except a 42% fruit yield reduction was observed at a 6 t/acre rate of mustard meal. Increases in fruit Se concentrations and increases in Ca, phosphorus, and Mn were often observed for all Brassica treatments. Amending soils with Brassica seed meals may have more practical viability in organic agriculture as a potential bioherbicide and green fertilizer.

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Producers of fruit and nut tree nursery stock need effective weed control for maximum production of vigorous, high-grade planting material. Current weed practices include methyl bromide fumigation, preemergence herbicides, hand labor, and multiple tillage operations. As methyl bromide use is phased out due to air quality concerns, and fuel and labor costs continue to increase, herbicides are likely to become even more important for weed management in the nursery industry. Before new herbicides can be registered and used in stonefruit (Prunus sp.) tree nurseries, weed control efficacy and crop safety data are needed under local conditions. Eleven experiments were conducted from 2007 to 2011 in California tree nurseries to evaluate the crop safety of preemergence (PRE) and postemergence (POST-directed) applications of various herbicides on commonly grown peach (Prunus persica), plum (Prunus domestica), and peach/plum hybrid rootstocks budded to almond (Prunus dulcis) scions. Rootstocks grown from cuttings generally were more tolerant to herbicides than those grown from seed. Crop safety was adequate in seeded and vegetatively propagated rootstocks with oryzalin, pendimethalin, and isoxaben, all of which are labeled for use in tree nurseries. The unregistered herbicides, dithiopyr, rimsulfuron, oxyfluorfen, and foramsulfuron; as well as lower rates of indaziflam and penoxsulam; applied PRE and POST-directed can provide good to excellent weed control in some stonefruit rootstocks. However, because slight crop injury was occasionally observed, additional work on application rates, timing, and method of application, especially on nonlabeled herbicides is needed before these materials can be considered for registration and broad scale use in tree nurseries.

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Nursery producers of perennial fruit and nut plants rely on preplant fumigation to meet regulatory requirements designed to ensure nematode-free planting stock. In the past, preplant treatments with methyl bromide or high rates of 1,3-dichloropropene were the preferred treatments. However, the phase out of methyl bromide due to environmental concerns and evolving regulations on the use of 1,3-dichloropropene has increased the need for effective and economical alternative fumigation treatments in open field nursery production. A field trial was conducted in a commercial nursery to test weed and nematode control with several tarped and untarped preplant applications of 1,3-dichloropropene, chloropicrin, and iodomethane in comparison with methyl bromide. Crop safety and nematode infestation were evaluated on a wide range of tree, vine, and berry nursery stock. No fall fumigation treatment in this study resulted in measurable injury to spring-planted nursery stock. There were few statistical differences between methyl bromide and the other fumigation treatments in crop establishment, crop quality, or nematode level at planting 5 months after treatment, although some untarped treatments had detectable levels of the root-knot nematode (Meloidogyne spp.). At grape (Vitus vinifera) and bramble (Rubus spp.) harvest after the first growing season, few statistical differences were noted in the number of nematodes isolated from roots; however, only methyl bromide had nondetectable levels in all varieties. The highest nematode levels were usually found in untarped iodomethane:chloropicrin and untarped chloropicrin plots. At tree harvest 26 months after fumigation, root-knot nematodes were isolated from the roots of highly susceptible tree varieties in several iodomethane:chloropicrin treatments and in chloropicrin alone plots. Untarped applications did not provide commercially acceptable control of weeds or root-knot nematode in this trial. Tarped applications of 30:70 and 50:50 iodomethane:chloropicrin provided nematode control similar to 1,3-dichloropropene, although not as good as methyl bromide. Iodomethane:chloropicrin combinations have been registered in other states and should be considered for use in California perennial fruit and nut crop nurseries as an alternative to methyl bromide.

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Walnut (Juglans regia) and rice (Oryza sativa) are among the most important crops grown in the Sacramento Valley of California. Because rice herbicides are often applied by air, there are occasional allegations of rice herbicide drift onto walnut trees. This study was established to investigate bispyribac-sodium residues on walnut leaves after simulated drift treatments. The objectives were to determine whether bispyribac-sodium can generate visual symptoms on walnut trees without leaving detectable residues in leaf tissues and to evaluate the subsequent impacts on walnut yield. Two experiments were conducted in a 3-year-old walnut orchard. In the first experiment bispyribac-sodium was applied to walnut trees at 0.125%, 0.25%, 0.5%, and 1% of the normal use rate in rice (45 g·ha−1). In the second experiment, rates were 1%, 3%, 10%, and 100% of the normal use rate in rice. Bispyribac-sodium caused general leaf chlorosis and discrete yellow spotting on walnut leaves even at very low concentrations; symptoms were recorded on trees exposed to rates as low as 0.125% of the normal use rate in rice. However, based on high-performance liquid chromatography analysis, the lowest simulated drift treatment from which bispyribac-sodium could be detected 10 d after treatment was 1% of the rice use rate. In general, visual injury symptoms remained constant over time, or even worsened, whereas bispyribac-sodium residues decreased or became not detectable. There was no measurable impact on walnut yield from any of the simulated drift treatments in these experiments.

Open Access

Threespike goosegrass (Eleusine tristachya) is a difficult-to-control perennial grass of increasing concern for orchard production systems in the Central Valley of California, USA. This grass has a bunch-type growth habit when tillered, which can interfere with orchard operations, particularly nut pickup from the ground at harvest. From 2016 to 2019, herbicide efficacy on threespike goosegrass was evaluated in a walnut (Juglans regia) orchard in Chico, CA, USA; an almond (Prunus dulcis) orchard in Livingston, CA, USA; and a prune (Prunus domestica) orchard in Orland, CA, USA. At each location, two independent experiments were conducted to evaluate 12 preemergent (PRE) herbicide treatments and eight postemergent (POST) treatments over several years, for a total of 16 trials. PRE herbicides were applied in January according to the region’s typical winter orchard management practices. One treatment included an additional sequential application in March to extend residual activity later into the warm season when threespike goosegrass germinates or resumes growth. In separate studies, POST control of established stands of threespike goosegrass was evaluated in May and June of each year. Each trial was conducted in a randomized complete block design with four replications. Threespike goosegrass control was visually estimated monthly for 5 months after the PRE treatments or at weekly intervals for 5 weeks following POST treatments. The most effective PRE treatment was a sequential application of indaziflam in January, followed by a March application of pendimethalin, providing 90% or greater control of threespike goosegrass 5 months after treatment across all sites and all years. Of the POST treatments, the three graminicides outperformed the other treatments with 73% to 91% control overall sites and years at 5 weeks after treatment. Fluazifop had the highest control ratings (85% to 91%) among the graminicide herbicides but was not always statistically better than clethodim or sethoxydim (74% to 83% control). Glyphosate alone resulted in unacceptable control (33% to 51%) regardless of rates tested, experimental sites, or years. Together, these results confirm grower reports of poor glyphosate performance on threespike goosegrass but suggest that effective herbicide programs can be developed to manage threespike goosegrass using PRE herbicides and POST graminicides registered in California orchard crops.

Open Access

Grape growers are concerned about the potential impact of drift from commonly used auxinic herbicides. In California, this is frequently related to herbicides used in cereals and noncrop areas, whereas in other parts of the United States concerns are often related to dicamba- and 2,4-D-resistant cropping systems. Our objective was to compare the relative sensitivity of winegrapes to simulated auxinic herbicide drift, including grapevine symptomology, grape yield, and grape quality. In a small-plot herbicide evaluation, we applied 1/900×, 1/300×, 1/100×, and 1/33× rates of 2,4-D, aminopyralid, dicamba, and triclopyr based on 1× field rates of 1454, 122.5, 280, and 2240 g⋅ha–1 ae, respectively. Aminopyralid resulted in similar symptomology to 2,4-D and dicamba—namely, leaf cupping, leaf crinkling, excessive tendril twisting, and tendril death, although these symptoms were generally subtle. Triclopyr resulted in much greater levels of necrosis compared with the other herbicides. In our study, triclopyr was the only herbicide associated with grape yield loss, and greater triclopyr rates were also associated with increased grape sugar levels. This study demonstrates that grapes are sensitive to low rates of simulated herbicide drift, but symptoms do not necessarily indicate yield loss or quality effects. This study indicates that auxin-type herbicide simulated drift symptoms are not reliable markers for winegrape yield or quality reduction.

Open Access

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.

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