Methyl bromide is an effective pre-plant soil fumigant used to control nematodes in many high-input, high-value crops in the United States, including vegetables, nursery plants, ornamentals, tree fruits, strawberries, and grapes. Because methyl bromide has provided a reliable return on investment for nematode control, many of these commodities have standardized their production practices based on the use of this chemical and will be negatively impacted if effective and economical alternatives are not identified. Alternative control measures based on other chemicals, genetic resistance, and cultural practices require a greater knowledge of nematode biology to achieve satisfactory results. Here, we provide an overview of nematode management practices that we believe will be relied upon heavily in U.S. high-value crop production systems in a world without methyl bromide. Included are case studies of U.S. high-value crop production systems to demonstrate how nematode management practices other than methyl bromide may be incorporated.
Calonectria pseudonaviculata causes leaf and stem lesions resulting in defoliation and dieback of boxwood. Trials were conducted to evaluate fungicide management of boxwood blight under greenhouse and container nursery conditions in Connecticut using fungicides previously determined to have in vitro activity against conidial germination or mycelial growth. Plants of different boxwood cultivars were inoculated 48 h after fungicide application. Disease progression was monitored over 6 weeks and progressed from leaf and stem lesions to defoliation. The level of disease control achieved by fungicides was generally good, with the most efficacious treatments averaging from 95 to nearly 100% control. Products containing propiconazole, myclobutanil, thiophanate-methyl, fludioxonil, pyraclostrobin, kresoxim-methyl, and chlorothalonil had significant efficacy. The combination of systemic plus protectant fungicides in a single application resulted in superior disease control compared to the use of a systemic fungicide. There were no differences between the fungicide treatments that included thiophanate-methyl and those that included propiconazole as the systemic fungicide. Korean and ‘Winter Gem’ (Buxus sinica var. insularis) were the least susceptible of the cultivars evaluated, common boxwood (B. sempervirens) and True Dwarf (B. sempervirens ‘Suffruticosa’) were the most susceptible, and ‘Green Mountain’ (B. sinica var. insularis × B. sempervirens Suffruticosa) and ‘Green Velvet’ (B. sinica var. insularis × B. sempervirens Suffruticosa) were intermediate. These results suggest that B. sinica var. insularis may have some level of resistance to boxwood blight. Management of boxwood blight will rely on integrated best management practices that include inspection of incoming plant material, sanitation, cultural controls including use of cultivars tolerant to infection, and fungicide application.
The combined effects of rotation crops and nitrogen fertilizers were examined on the strawberry black root rot disease complex. In July 1995, microplots were filled with soil that had a history of strawberry black root rot and seeded with two types of oats (Avena strigosa ‘Saia oats’ or A. sativa ‘Garry oats’) or with sorgho-sudangrass (Sorghum bicolor × S. sudanense ‘Triple S’). Microplots planted with 1-year-old ‘Honeoye’ strawberry crowns served as the controls. In May 1996, the crops were chopped and incorporated into the soil. The soil was re-planted with 1-year-old strawberry ‘Honeoye’ crowns and then fertilized with (NH4)2SO4 or Ca(NO3)2 at equivalent rates of N. Two months later, (NH4)2SO4-treated plants had 36% more leaf area and 41% more runners than strawberries treated with Ca(NO3)2 Strawberries that had been pre- cropped with ‘Saia’ oats had 135% more runners and 38% more early fruit yield than strawberries grown in control microplots. Total fruit yield was not affected by the treatments. Compared to Ca(NO3)2, the (NH4)2SO4 treatment reduced the percentage of blackened roots. The influence of the cover crops on growth and disease was stronger with (NH4)2SO4 fertilization than with Ca(NO3)2 fertilization. Combining ‘Saia’ oats or sorgho-sudangrass rotation with (NH4)2SO4 fertilization reduced lesion nematode (Pratylenchus penetrans) numbers in subsequent strawberry roots when compared to controls. Also, the combination of ‘Saia’ or ‘Garry’ oats as a pre-crop with applications of (NH4)2SO4 reduced black root rot severity when compared to controls. Only the ‘Garry’ oat rotation reduced strawberry root colonization by Rhizoctonia fragariae when compared to controls. Other effects were associated with using (NH4)2SO4. The (NH4)2SO4 treatment lowered the rhizosphere soil pH by 0.2 units, reduced the numbers of fluorescent pseudomonads in the rhizosphere by 10- to 15-fold, and produced leaves that had more N, K, S, Mn, and Zn content than plants treated with Ca(NO3)2. Rotation with ‘Saia’ oats combined with (NH4)2SO4 fertilization may suppress strawberry black root rot and increase yields through multiple effects on the host, pathogens, and associated microflora.
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