Thomas Tworkoski

Herbicide effects of essential oils

Abstract Laboratory and greenhouse experiments were conducted to determine the herbicidal effect of plant-derived oils and to identify the active ingredient in an oil with herbicide activity. Twenty-five different oils were applied to detached leaves of dandelion in the laboratory. Essential oils (1%, v/v) from red thyme, summer savory, cinnamon, and clove were the most phytotoxic and caused electrolyte leakage resulting in cell death. Each of these essential oils in aqueous concentrations from 5 to 10% (v/v) plus two adjuvants (nonionic surfactant and paraffinic oil blend at 0.2% [v/v]) were applied to shoots of common lambsquarters, common ragweed, and johnsongrass in the greenhouse; shoot death occurred within 1 h to 1 d after application. Essential oil of cinnamon had high herbicidal activity, and eugenol (2-methoxy-4-[2-propenyl]phenol) was determined to be this oils major component (84%, v/v). Dandelion leaf disk and whole-plant assays verified that eugenol was the active ingredient in the essential oil of cinnamon. Essential oils are extracted from plants and thus may be useful as “natural product herbicides” for organic farming systems. Nomenclature: Cinnamon, Cinnamomum zeylanicum; clove, Syzgium aromaticum; red thyme, Thymus vulgaris; summer savory, Satureja hortensis; common lambsquarters, Chenopodium album L. CHEAL; common ragweed, Ambrosia artemisiifolia L. AMBEL; dandelion, Taraxacum officinale Weber in Wiggers TAROF; johnsongrass, Sorghum halepense (L.) Pers. SORHA.

Effect of heat shock treatment on stress tolerance and biocontrol efficacy of Metschnikowia fructicola

The effect of high temperature and oxidative stress on the cell viability of the yeast antagonist, Metschnikowia fructicola was determined. A mild heat shock (HS) pretreatment (30 min at 40 °C) improved the tolerance of M. fructicola to subsequent high temperature (45 °C, 20-30 min) and oxidative stress (0.4 mol L⁻¹ hydrogen peroxide, 20-60 min). HS-treated yeast cells showed less accumulation of reactive oxygen species (ROS) than nontreated cells in response to both stresses. Additionally, HS-treated yeast exhibited significantly greater (P<0.0001) biocontrol activity against Penicillium expansum and a significantly faster (P<0.0001) growth rate in wounds of apple fruits stored at 25 °C compared with the performance of untreated yeast cells. Transcription of a trehalose-6-phosphate synthase gene (TPS1) was upregulated in response to HS and trehalose content also increased. Results indicate that the higher levels of trehalose induced by the HS may contribute to an improvement in ROS scavenging, stress tolerance, population growth in apple wounds and biocontrol activity of M. fructicola.

The effect of nitrogen on stolon and ramet growth in four genotypes of Fragaria chiloensis L.

Plant foraging response is a process in which clonal plants proliferate in nutrient-rich sites by shortening stolon length and increasing ramet density. Conversely, stolon length increases and ramet density decreases in nutrient-poor sites. Four genotypes of strawberry (Fragaria chiloensis (L.) Duch.) were grown in a greenhouse for 10 weeks and treated with different concentrations of nitrogen. Genotypes differed in plant size, stolon and ramet production, and nitrogen distribution between parent and ramets. Genotype Q18 were the smallest plants with the greatest number of stolons and ramets, typical of the phalanx morphology. The other genotypes had fewer but longer stolons, typical of the guerrilla morphology. Number of stolons and ramet density increased with increased N more in Genotype Q18 than the other genotypes. Results indicate that vegetative growth changed in response to increasing N treatment of the parent plant by shortening the average stolon length, increasing the number of stolons, and increasing the number of ramets while maintaining total stolon length. Foraging response characteristics were observed in strawberry but varied among genotypes.

Response of bean to applications of hydrophobic mineral particles

Foliar applications of hydrophobic mineral particles can protect plants from some insects, but plant response to particle applications is not known. Bean (Phaseolus vulgaris L.) plants were grown for 8 wk in a greenhouse and the shoots were sprayed weekly with small-diameter hydrophobic mineral particles. Photosynthesis was similar in particle-treated and control bean plants over a photosynthetic photon flux (PPF) range from 0 to 1548 µmol m–2 s–1. The shoot-to-root dry weight ratio was 56% greater and pod weight was 20% lower in particle-treated plants than control plants, suggesting that particle films may alter dry weight partitioning of plants. In bean, particle residues of 2.71 mg cm–2 leaf area altered plant development without affecting photosynthesis. Key words: Phaseolus vulgaris, crop protection, photosynthesis, dry weight distribution, kaolin

Soil Residues Following Repeat Applications of Diuron, Simazine, and Terbacil1

Abstract: Diuron, simazine, and terbacil were applied in field plots annually from 1981 to 1995. Soil was sampled at selected times after herbicide application in 1993, 1994, and 1995 to determine herbicide residue changes with time and soil depth. Diuron residues were found mainly in the upper 20 cm of soil; residue concentration decreased exponentially with time. Less than 1% of the initial concentration after application in summer was present the following spring. Terbacil residues were found in soil below the upper 20 cm. Terbacil degraded more slowly than diuron, and residues in spring were less than 30% the level of the previous summer. Simazine plus hydroxysimazine soil residues were present in all depths to 100 cm and were higher than diuron or terbacil at these depths. Simazine plus hydroxysimazine residues in spring were nearly 40% the level of the previous summer. With all three herbicides, soil residues were greatest in the upper 20 cm of soil during 2 to 3 wk following application. Data confirmed that diuron did not leach, whereas simazine can migrate through the soil. Terbacil migrated intermediately in depth relative to diuron and simazine. After 15 annual applications, herbicide residues were present but were not accumulating. Nomenclature: Diuron, N′-(3,4-dichlorophenyl)-N,N-dimethylurea; simazine, 6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine; desethylsimazine, 2-chloro-4-(ethylamino)-6-amino-s-triazine; di-desethylsimazine, 2-chloro-4,6-diamino-s-triazine; hydroxysimazine, 2-hydroxy-4,6-bis(ethyl-amino)-s-triazine; terbacil, 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione. Additional index words: Herbicide movement. Abbreviations: DAT, days after herbicide treatment; GC-MS, gas chromatography–mass spectrometry; HPLC-PDA, high-performance liquid chromatography with photodiode array detector; MS, mass spectrometry; ODS, octadecyl silane; SFE, supercritical fluid extraction.

Weed Community Changes Following Diuron, Simazine, or Terbacil Application1

Abstract: Diuron, simazine, and terbacil were applied together or separately in the field each May from 1981 through 1996. Weed control was over 90% in 1981 and 1982, but by 1984 weeds increased in plots treated with diuron and simazine. Weed abundance was relatively low from 1981 through 1996 in plots treated with terbacil. Broadleaf and grass species abundance was similar in most herbicide-treated plots from 1992 through 1996. Perennial species, particularly fescue (Festuca arundinacea) and ailanthus (Ailanthus altissima), dominated sites treated with diuron and simazine. The weed community changed within 3 yr of the implementation of the weed management program that relied solely on herbicides. A relatively stable weed community persisted from 1992 through 1996. Repeated use of the combined high rate of diuron and low rate of terbacil provided excellent weed control for 15 yr. Nomenclature: Diuron, N′-(3,4-dichlorophenyl)-N,N-dimethylurea; simazine, 6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine; terbacil, 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione; ailanthus, Ailanthus altissima (Mill.) Swingle. #3 AILAL; tall fescue, Festuca arundinacea Schreb. # FESAR. Additional index words: Fruit orchards, selection, weed shifts, cheat, poison ivy, johnsongrass, yellow foxtail.

Weed Suppression by Grasses for Orchard Floor Management

Abstract Fruit trees in orchards of the mid-Atlantic region of the United States are often planted in vegetation-free rows alternating with grass alleys. Grass managed to suppress weeds but to compete minimally with fruit trees may be an alternative to herbicide and tillage. This research was conducted in the greenhouse and field to assess five different grasses that may suppress weeds without reducing yield of fruit trees. In the greenhouse with high seeding rates, red fescue competed more effectively than did chewings fescue, tall fescue, and perennial ryegrass with three weeds (damesrocket, cornflower, and chicory). However, with reduced seeding rates, similar to rates used in the field, grass competitiveness with weeds was similar between red fescue, tall fescue, and perennial ryegrass. Similar results were obtained during a 4-yr field experiment; roughstalk bluegrass competed least effectively with weeds but the other four grasses provided similar weed suppression—generally providing as much weed suppression as traditional herbicides. None of the candidate grasses significantly reduced yields of 10-yr-old apple and peach trees, although fruit size was affected by some grasses. The grass that was least suppressive of yield, roughstalk bluegrass, was the least effective in controlling weeds. Annual mowing in combination with four of the grasses tested is one option to manage the orchard floor with reduced herbicides, but fruit size may decrease. Nomenclature: Chicory, Cichorium intybus L.; cornflower, Centaurea cyanus L.; damesrocket, Hesperis matronalis L.; apple, Malus × domestica Borkh.; chewings red fescue, Festuca rubra var. commutata L. Gaudin; peach, Prunus persica (L.) Batch; perennial ryegrass, Lolium perenne L.; red fescue, Festuca rubra L.; roughstalk bluegrass, Poa trivialis L.; tall fescue, Lolium arundinaceum (Schreb.) S.J. Darbyshire.

Response of Young Apple Trees to Grass and Irrigation

ABSTRACT Ground covers and irrigation are important components of orchard floor management systems that affect fruit tree vigor and productivity. Three experiments were conducted in a greenhouse to determine the relative water use of candidate ground covers (roughstalk bluegrass, RB, Poa trivialis), Chewings fescue (CH, Festuca rubra subsp. commutata Gaudin), creeping red fescue (RF, Festuca rubra L. subsp. rubra), tall fescue (TF, Festuca arundinacea Schreber, Fawn), and perennial ryegrass (PR, Lolium perenne L., ‘Saint’) and the response of apple trees to those ground covers and to drip irrigation applied at two soilless substrate depths. Grass ground covers with large and deep root systems (TF and PR) used more water than a shallow- rooted grass (RB) and leaf water potential decreased more rapidly in apple trees grown with TF than RB when irrigation was withheld. Although apple tree shoot growth was greater with shallow- than deep-rooted grass, photosynthesis, transpiration, and root biomass distribution were not differentially affected by grass type. When grown with RB or TF, irrigation depth affected apple tree growth. During the first season in the greenhouse, deep irrigation at 37 cm depth increased apple root length density near emitters but shoot growth was less in apple grown with deep irrigation compared with apple grown with surface irrigation (0 cm) and with split irrigation at 0 and 37 cm. During the second season in the greenhouse, deep irrigation was beneficial to trees grown with grass that had large, deep root systems (TF) but it did not completely overcome interference effects of grass on apple trees, regardless of grass root system size or distribution. The results indicate that grasses with shallow root systems may be grown beneath apple trees and that split irrigation at two depths can provide flexibility that is necessary for water management of ground covers and apple trees.