Better Together? Combining Cover Crop Mulches, Organic Herbicides, and Weed Seed Biological Control in Reduced-Tillage Systems.

Organic vegetable farmers rely heavily on labor-intensive tillage for weed management, which adversely affects soil health and harms beneficial insects that consume crop pests and weed seeds. Using cover crop residues as a weed-suppressive mulch enables some reduction in tillage, and combining this tool with recently developed organic herbicides may further enhance weed suppression in vegetable production. However, organic herbicides may also adversely affect beneficial insects, and their nontarget effects are unknown. Here, we examine the combined impacts of cultural and chemical tools on weed cover while monitoring activity of beneficial epigeal insects and measuring rates of weed seed biological control to assess potential nontarget effects of organic herbicides. In a 2-yr experiment, we compared three cover crop mulch treatments and three organic herbicide treatments (capric/caprylic acid, corn gluten meal, and herbicide-free) in a reduced-tillage system. Organic herbicides led to no reductions in beneficial insect activity nor weed seed biocontrol. In both years, capric/caprylic acid herbicide and cover crop mulches reduced weed pressure relative to a fallow control treatment, whereas corn gluten meal had no effect. In year 2, a combination of cover crop mulch with organic herbicide had the greatest weed suppression relative to the fallow control. Integrated weed management is a perpetual challenge, but our results suggest that organic herbicides used in concert with cover crop mulch may enhance weed control and reduce the need for tillage, with limited collateral damage to natural enemies.

Non-target effects of herbicides on Tetranychus urticae and its predator, Phytoseiulus persimilis: implications for biological control.

BACKGROUND: A key element of conservation biocontrol is identifying and limiting the use of pesticides that have substantial non-target effects on natural enemies to prevent biocontrol disruption. The Phytoseiidae (predatory mites) are one of the most studied natural enemy groups in the field of pesticide non-target effects. Although there is substantial research on the non-target effects of insecticides on arthropod natural enemies, research on herbicide impacts is limited. Natural enemies, including phytoseiids, associate with weeds due to the presence of alternative prey, shelter, or floral resources. Therefore, a whole-systems approach to integrated pest management should integrate weed management with biocontrol. We conducted a study to examine the non-target effects of vegetable herbicides on Phytoseiulus persimilis Athias-Henriot, and the primary pest that it controls, Tetranychus urticae Koch. Two assays were used to assess the effects of direct application and walking on residues. RESULTS: In both assays, S-metolachlor was highly toxic to P. persimilis (80-90% mortality) and had minimal effect on T. urticae. Dicamba, oxyfluorfen, and napropamide also caused moderate levels of P. persimilis mortality (21-74%). Check mortality of P. persimilis was higher in the direct contact assay (19%) than the residue assay (3%). CONCLUSIONS: Halosulfuron-methyl, flumioxazin, and mesotrione were the most compatible herbicides with biocontrol by P. persimilis, whereas S-metolachlor and napropamide were the least compatible. We also determined that the residue assay may be more useful than direct contact slide-dips for future assessment of herbicide non-target effects. Future efforts should continue to examine the impacts of weed management on natural enemies to better integrate pest management practices. © 2019 Society of Chemical Industry.

Affinity of Hyperammonia-Producing Bacteria To Produce Bioammonium/Ammonia Utilizing Five Organic Nitrogen Substrates for Potential Use as an Organic Liquid Fertilizer.

This research was conducted to create a plant-available nitrogen nutrient solution utilizing ruminant bacteria for ultimate use as a liquid nitrogen fertilizer for precision fertigation of vegetable crops. Three hyperammonia-producing ruminant bacteria, Clostridium aminophilum, Peptostreptococcus anaerobius, and Clostridium sticklandii, were cultured anaerobically using five different organic nitrogen substrates to determine their efficiency in producing bioammonium/ammonia (BAA), a term defined here as a biologically produced solution containing both ammonium and ammonia. These bacteria were chosen because of their ability to produce ammonium at rates not experienced by any other bacteria. The five substrates were soy protein isolate (SPI), blood meal, feather meal, dried fish, and yeast extract (Y) used alone and in combination with Y. C. aminophilum and SPI were selected for further experimentation in an attempt to maximize BAA production. These substrates were chosen because they are commonly fed to cattle and they are also used as organic fertilizer amendments. C. aminophilum was cultured with SPI rates from 0.8 g·10 mL-1 salt solution reaching SPI's maximum solubility level at 1.6 g·10 mL-1 salt solution at 0.2 g intervals, and the BAA content was measured every 24 h for 168 h. It was concluded that there was no significant benefit in culturing C. aminophilum with more than 1.0 g·10 mL-1 for more than 96 h to achieve maximum BAA concentrations.

Several Pesticides Influence the Nutritional Content of Sweet Corn.

Herbicides are pesticides used to eradicate unwanted plants in both crop and non-crop environments. These chemistries are toxic to weeds due to inhibition of key enzymes or disruption of essential biochemical processes required for weedy plants to survive. Crops can survive systemic herbicidal applications through various forms of detoxification, including metabolism that can be enhanced by safeners. Field studies were conducted near Louisville, Tennessee and Painter, Virginia to determine how the herbicides mesotrione, topramezone, nicosulfuron, and atrazine applied with or without the safener isoxadifen-ethyl would impact the nutritional quality of "Incredible" sweet corn ( Zea mays L. var. rugosa). Several herbicide treatments increased the uptake of the mineral elements phosphorus, magnesium, and manganese by 8-75%. All herbicide treatments increased protein content by 4-12%. Applied alone, nicosulfuron produced similar levels of saturated, monounsaturated, and polyunsaturated fatty acids when compared to the nontreated check, but when applied with isoxadifen-ethyl, fatty acids increased 8 to 44% relative to the check or control. Nicosulfuron plus isoxadifen-ethyl or topramezone or the combination of all three actives increased the concentrations of fructose and glucose (40-68%), whereas reducing levels of maltose or sucrose when compared to the nontreated check (-15 to -21%). Disruptions in biochemical pathways in plants due to the application of herbicides, safeners, or other pesticides have the potential to alter the nutrient quality, taste, and overall plant health associated with edible crops.

Upscaled Bioammonium/Ammonia Production by Clostridium Aminophilum Cultured with Soy Protein Isolate.

The goal of this study was to scale up the production of bioammonium/ammonia (BAA) by Clostridium aminophilum from test tube size small batches of 1.0 g of soy protein isolate (SPI) with 10 mL of salt solution to the lab scale bioreactor level of 1.8 kg·18 L-1 salt solution in amounts required for precision fertigation in field trials. An 18 L bioreactor was designed and constructed similar to commercially available lab scale bioreactors. Novel methods were implemented to maintain sterility and anaerobic conditions throughout the preparation and operation of the bioreactor. C. aminophilum was cultured at rates of 1.8 kg·18 L-1 salt solution, ultimately producing a BAA mean concentration of 82.9 mM, which was 34% greater than the amount achieved in the test tubes of 61.7 mM.

Synthesis and evaluation of heterocyclic analogues of bromoxynil.

One attractive strategy to discover more active and/or crop-selective herbicides is to make structural changes to currently registered compounds. This strategy is especially appealing for those compounds with limited herbicide resistance and whose chemistry is accompanied with transgenic tools to enable herbicide tolerance in crop plants. Bromoxynil is a photosystem II (PSII) inhibitor registered for control of broadleaf weeds in several agronomic and specialty crops. Recently at the University of Tennessee-Knoxville several analogues of bromoxynil were synthesized including a previously synthesized pyridine (2,6-dibromo-5-hydroxypyridine-2-carbonitrile sodium salt), a novel pyrimidine (4,6-dibromo-5-hydroxypyrimidine-2-carbonitrile sodium salt), and a novel pyridine N-oxide (2,6-dibromo-1-oxidopyridin-1-ium-4-carbonitrile). These new analogues of bromoxynil were also evaluated for their herbicidal activity on soybean (Glycine max), cotton (Gossypium hirsutum), redroot pigweed (Amaranthus retroflexus), velvetleaf (Abutilon theophrasti), large crabgrass (Digitaria sanguinalis), and pitted morningglory ( Ipomoea lacunose ) when applied at 0.28 kg ha(-1). A second study was conducted on a glyphosate-resistant weed (Amaranthus palmeri) with the compounds being applied at 0.56 kg ha(-1). Although all compounds were believed to inhibit PSII by binding in the quinone binding pocket of D1, the pyridine and pyridine-N-oxide analogues were clearly more potent than bromoxynil on Amaranthus retroflexus. However, application of the pyrimidine herbicide resulted in the least injury to all species tested. These variations in efficacy were investigated using molecular docking simulations, which indicate that the pyridine analogue may form a stronger hydrogen bond in the pocket of the D1 protein than the original bromoxynil. A pyridine analogue was able to control the glyphosate-resistant Amaranthus palmeri with >80% efficacy. The pyridine analogues of bromoxynil showed potential to have a different weed control spectrum compared to bromoxynil. A pyridine analogue of bromoxynil synthesized in this research controlled several weed species greater than bromoxynil itself, potentially due to enhanced binding within the PSII binding pocket. Future research should compare this analogue to bromoxynil using optimized formulations at higher application rates.