Oleg Daugovish

Recent Developments on Strawberry Plant Collapse Problems in California Caused by Fusarium and Macrophomina

Beginning at least as early as 2005 and continuing through 2010, the California strawberry industry has suffered production losses caused by soilborne fungi not previously recognized as strawberry pathogens in California. The vast majority of these problems took place in fields that did not receive the traditional pre-plant fumigation treatment of methyl bromide + chloropicrin. These new disease developments have been consistently associated with two pathogens: Macrophomina phaseolina and Fusarium oxysporum f. sp. fragariae. Pathogenicity tests confirmed that these fungi caused symptoms similar to those observed in the field. Other experiments indicated that some strawberry cultivars are apparently less susceptible than others. Field trials using alternative fumigants provided some control of both diseases. In California, both Fusarium and Macrophomina are appearing in previously uninfested areas, indicating that these pathogens will be long-term concerns for this industry.

Survival of plant pathogens in static piles of ground green waste.

Ground green waste is used as mulch in ornamental landscapes and for tree crops such as avocados. Survival of Armillaria mellea, Phytophthora cinnamomi, Sclerotinia sclerotiorum, and Tylenchulus semipenetrans was assessed for 8 weeks within unturned piles of either recently ground or partially composted green waste. S. sclerotiorum survived at the pile surface and at 10, 30, and 100 cm within the pile for the entire 8 weeks in both fresh green waste (FGW) and aged green waste (AGW). A. mellea and T. semipenetrans did not survive more than 2 days in FGW, while P. cinnamomi persisted for over 21 days in FGW. AGW was less effective in reducing pathogen viability than FGW, most likely because temperatures in AGW peaked at 45 degrees C compared with 70 degrees C in FGW. Survival modeling curves based on pile temperatures indicate the time to inactivate 10 propagules of pathogens was 11, 30, 363, and 50 days for A. mellea, P. cinnamomi, S. sclerotiorum, and T. semipenetrans, respectively. Sclerotia-forming pathogens pose the greatest risk for escape; to ensure eradication of persistent fungi, green waste stockpiles should be turned intermittently to mix pile contents and move pathogen propagules to a location within the pile where they are more likely to be killed by heat, microbial attack, or chemical degradation.

Biological Control of Eotetranychus lewisi and Tetranychus urticae (Acari: Tetranychidae) on Strawberry by four Phytoseiids (Acari: Phytoseiidae)

ABSTRACT The spider mite, Eotetranychus lewisi (McGregor) (Acari: Tetranychidae), is a new emerging pest in California commercial strawberries. The predatory mite Phytoseiulus persimilis (Athias-Henriot) (Acari: Phytoseiidae), typically used for biocontrol of Tetranychus urticae (Koch) (Acari: Tetranychidae), provided growers little to no control of E. lewisi. Four commonly used phytoseiid predatory mites: P. persimilis, Neoseiulus californicus (McGregor), N. fallacis (Garman), and Amblyseius andersoni (Chant), were used in lab studies to investigate which is best at managing E. lewisi populations. We also investigated the interactions between T. urticae and E. lewisi and in relation to phytoseiid efficiency given the potential for indirect effects of biocontrol. When E. lewisi and T. urticae are present on the same leaf, T. urticae populations increase and begin displacing E. lewisi. P. persimilis did not feed on E. lewisi, but the other three predatory mites consumed the spider mites and lowered their populations. When both E. lewisi and T. urticae are present on the same leaf, N. fallacis and A. andersoni fed on both types of mites equally and were capable of decreasing both populations. N. californicus fed on E. lewisi first and decreased its population, but allowed T. urticae populations to increase. P. persimilis may be insufficient at controlling E. lewisi and its use may instead enhance E. lewisi populations.

Integration of Oxyfluorfen into Strawberry (Fragaria×ananassa) Weed Management Programs

Abstract Field trials were conducted at three California locations near Oxnard, Salinas, and Watsonville from 2002 to 2006 to evaluate broadleaf weed control and tolerance of strawberry to oxyfluorfen. Oxyfluorfen applied at 0.3 and 0.6 kg/ha before strawberry transplanting reduced densities of broadleaf weeds such as California burclover, hairy nightshade, little mallow, shepherds-purse, and yellow sweetclover 70 to 100% compared with nontreated plots but did not control horseweed. Oxyfluorfen application resulted in 9% and 19% greater visible injury to strawberry for the two rates, respectively, compared with nontreated plants in 1 yr but did not reduce strawberry yield. After oxyfluorfen application at 0.6 kg/ha, strawberry plants had 5 to 48% more injury than nontreated plants in subsequent years but early-season yields were similar. Hand-weeding time was reduced 30 to 50% compared with nontreated plots regardless of oxyfluorfen rate. Both water-based and solvent-carrier formulations of oxyfluorfen resulted in similar weed control, strawberry injury, and fruit yield. Plastic mulch installation after oxyfluorfen application but before planting reduced injury to strawberry more than 50% compared with nonmulched beds. Oxyfluorfen applied 30 d before strawberry transplanting had similar crop injury and yield to applications made 15 and 7 d before planting. These results suggest that oxyfluorfen can be used safely in California plasticulture strawberry production for control of common weed species and to reduce labor inputs associated with hand weeding. Nomenclature: Oxyfluorfen; California burclover, Medicago polymorpha L. MEDPO;hairy nightshade, Solanum physalifolium Rusby SOLSA; horseweed, Conyza canadensis L. ERICA; little mallow, Malva parviflora L. MALPA; shepherds-purse, Capsella bursa-pastoris L. CAPBP; yellow sweetclover, Melilotus officinalis L. MEUOF;strawberry, Fragaria×ananassa

The Population of Fusarium oxysporum f. sp. fragariae, Cause of Fusarium Wilt of Strawberry, in California

The objectives of this study were to investigate the structure of the population of Fusarium oxysporum f. sp. fragariae in California and to evaluate methods for its detection. Fifty-nine isolates of F. oxysporum f. sp. fragariae were obtained from diseased strawberry plants and their identity was confirmed by pathogenicity testing. The full nuclear ribosomal intergenic spacer (IGS) and elongation factor 1-α gene (EF-1α) were amplified by polymerase chain reaction (PCR) and sequenced to elucidate phylogenetic relationships among isolates. IGS and EF-1α sequences revealed three main lineages, which corresponded to three somatic compatibility groups. Primers designed to detect F. oxysporum f. sp. fragariae in Japan amplified a 239-bp product from 55 of 59 California isolates of F. oxysporum f. sp. fragariae and from no nonpathogenic isolates of F. oxysporum. The sequence of this PCR product was identical to the sequence obtained from F. oxysporum f. sp. fragariae isolates in Japan. Intensive sampling at two locations in California showed results of tests based on PCR and somatic compatibility to be in agreement for 97% (257 of 264) of isolates tested. Our findings revealed considerable diversity in the California population of F. oxysporum f. sp. fragariae, and indications that horizontal gene transfer may have occurred.

Herbicide Evaluation for Fresh Market Celery

Field studies were conducted near Oxnard, CA and in two locations near Salinas, CA in 2002 and 2003 to evaluate efficacy and safety of six herbicides in celery. s-metolachlor at 0.6 and 0.7 kg ai/ha and flufenacet at 0.5, 0.6, and 0.7 kg ai/ha PRE were safe to celery and controlled 81 to 94% of yellow nutsedge at densities < 20 plants/m2. At yellow nutsedge densities > 20 plants/m2, the most efficacious treatments were 1.1 kg/ha of s-metolachlor or 0.7 kg/ha of flufenacet, which reduced nutsedge densities by 71 or 53%, respectively; however, both resulted in slight injury to celery. All other herbicides generally did not injure celery and none reduced marketable crop yield. Flumioxazin pretransplant (PRE) at 0.1 and 0.2 kg ai/ha controlled broadleaf weeds near 100% at all locations, suggesting that it can be an effective alternative to standard linuron and prometryn, which are applied post-transplant (POST) in celery. Nomenclature: S-metolachlor, flufenacet, flumioxazin, prometryn, linuron, oxyfluorfen, yellow nutsedge, Cyperus esculentus L. CYPES, celery, Apium graveolens L

Barriers Prevent Emergence of Yellow Nutsedge (Cyperus esculentus) in Annual Plasticulture Strawberry (Fragaria × ananassa)

Abstract Yellow nutsedge is a problematic weed in plasticulture strawberry because herbicides and fumigants currently used in California provide little to no control and because nutsedge shoots easily penetrate standard low-density polyethylene (LDPE) mulch to rapidly establish and compete with the crop. Field studies were conducted at two California locations near Oxnard and Camarillo from 2007 to 2009 to evaluate yellow nutsedge control with physical barriers. Nutsedge germinated in both autumn and spring through LDPE mulch alone, but paper placed between two layers of standard 0.15-mm black LDPE mulch, weed barrier fabric commonly used in landscapes placed under LDPE mulch, and Tyvek Home Wrap placed under LDPE mulch suppressed nutsedge emergence. In 1 yr, the size of strawberry plants grown with weed barrier fabric was reduced 23% compared with the other treatments and the number of marketable fruit in the third month of harvest was reduced 20% compared with LDPE mulch alone, likely because inadequately cut planting holes in this barrier restricted plant growth. Estimated costs for barrier treatments ranged from

Anaerobic soil disinfestation is an alternative to soil fumigation for control of some soilborne pathogens in strawberry production

5,000 to

Fumigant Use for Strawberry Production in Europe: The Current Landscape and Solutions

12,000 ha−1 compared with estimated hand-weeding costs of up to

Stemphylium Leaf Spot of Parsley in California Caused by Stemphylium vesicarium

24,000 ha−1. In 2007 to 2008 barrier treatments reduced the number of wind-dispersed weeds that commonly land and germinate in strawberry planting holes 67% compared with LDPE mulch alone. Removing the barriers at the end of the two seasons revealed that nutsedge plants sprouted but failed to grow and produce new tubers under the barriers. This observation suggests that nutsedge-impermeable barriers may aid in depletion of the soil tuber bank and therefore can be an effective tool in managing nutsedge for the length of the growing season. Nomenclature: Yellow nutsedge, Cyperus esculentus L.; strawberry, Fragaria × ananassa Duch.