Almond, [Prunus dulcis (synonym Prunus amygdalus)] planted on approximately 595,000 acres (240,797 ha), is California's largest acreage tree crop. California's Central Valley accounts for nearly 100% of the U.S. domestic production of almonds. Integrated pest management (IPM) programs that integrate cultural practices and pest and disease monitoring with selective controls have improved plant protection in almond. Methods of orchard floor management and their effects must also be taken into account. Minimizing dust reduces mites while harvesting earlier and the destruction of overwintering refugia are cultural practices that reduce worm damage. Improved methods for field sampling and monitoring have reduced the need for pesticide applications while improving timing and effectiveness of needed crop protection sprays. Selective controls have further reduced the impact on nontarget species. Augmentative parasite releases have also helped manage navel orangeworm (Ameylois transitella). Effective use of new selective fungicides will require precise application timing and greater knowledge of diseases and resistance management. A better understanding of disease life cycles leading to improved monitoring of the fungal diseases, shothole (Wilsonomyces carpophilus), almond scab (Cladosporium carpophilum), and anthracnose (Colletotrichum acutatum) have reduced fungicide applications. Future challenges include the potential loss of effective pest control products, the need to continually develop improved utilization strategies, and maintaining economic sustainability.
Fusarium basal rot (FBR), caused by Fusarium oxysporum f.sp. cepae, is a soilborne fungal disease that affects bulb onions (Allium cepa) worldwide. Winter-sown onion cultivars that are resistant to FBR are lacking. The goal of this project was to screen winter-sown onion germplasm for FBR resistance using a mature-bulb field screening at harvest and after 4 weeks in storage. The project was conducted for 2 years, and in each year, 22 winter-sown onion lines were grown in a field known to produce a high incidence of FBR-infected bulbs. At maturity, the basal plates of 20 randomly selected bulbs were cut transversely and each plate was scored for disease severity on a scale of 1 (no diseased tissue) to 9 (70% or more diseased tissue). Bulbs were stored and scored again at 4 weeks after harvest. Severity and incidence increased in storage for both years. NMSU 99-30, `NuMex Arthur', and `NuMex Jose Fernandez' showed the lowest disease severities and incidences in both years. For fields that produce a high incidence of FBR-infected bulbs, these cultivars could be grown with less loss to FBR at harvest and after storage than more FBR-susceptible cultivars. When developing FBR-resistant cultivars, breeding lines should be evaluated over multiple years and bulbs should be stored for 4 weeks before being screened.
The primary purpose of grafting vegetables worldwide has been to provide resistance to soilborne diseases. The potential loss of methyl bromide as a soil fumigant combined with pathogen resistance to commonly used pesticides will make resistance to soilborne pathogens even more important in the future. The major disease problems addressed by grafting include fusarium wilt, bacterial wilt, verticillium wilt, monosporascus root rot, and nematodes. Grafting has also been shown in some instances to increase tolerance to foliar fungal diseases, viruses, and insects. If the area devoted to grafting increases in the future, there will likely be a shift in the soil microbial environment that could lead to the development of new diseases or changes in the pathogen population of current diseases. This shift in pathogen populations could lead to the development of new diseases or the re-emergence of previously controlled diseases. Although grafting has been demonstrated to control many common diseases, the ultimate success will likely depend on how well we monitor for changes in pathogen populations and other unexpected consequences.
Powdery mildew is a fungal disease of crucifers, caused by Erysiphe polygoni D.C. and it can be problematic during seed increase in green-houses. Crosses were made between Brassica carinata (Ethiopian mustard) accession (PI 360883) and B. oleracea cultivars `Titleist' and `Cecile' to transfer resistance to powdery mildew to B. oleracea germplasm. It was not possible to obtain interspecific hybrids between Ethiopian mustard and B. oleracea through natural seed set. However, interspecific hybrids and backcross one (BC1) progenies were produced via embryo rescue following sexual crosses. Four interspecific hybrid plants were produced with the aid of embryo rescue from cultured pistils with B. carinata as the maternal parent, and their interspecific origin was confirmed through plant morphology and analysis of RAPD polymorphisms. No interspecific hybrids were obtained when `Titleist' was used as a maternal parent. Interspecific hybrid plants were male sterile and they were used as maternal parents to produce BC1 plants. Twenty one BC1 plants were obtained through natural seed set and embryo rescue, although embryo rescue was not necessary to produce first backcross generation plants. When tested in greenhouse with powdery mildew, all interspecific hybrids and eight of the BC1 plants were resistant to the disease. Crosses are being made to produce BC2 plants with 2n = 18 chromosomes for introgression of the resistance in B. oleracea.
Eastern filbert blight is an economically significant disease in European hazelnut (Corylus avellana L.) production in the United States. Since genetic resistance is the only viable disease control strategy to this fungal disease caused by Anisogramma anomala (Peck) E. Müller, greenhouse and field screening of germplasm was undertaken to study the inheritance from known resistant sources and to identify new sources for inclusion in the breeding program. We confirmed that `Gasaway' resistance to this disease is conferred by a single dominant gene. No major gen was identified in the field-resistant cultivar Gem. Representatives of six Corylus species were screened to identify new resistant germplasm. Corylus cornuta Marshall var. cornuta, C. cornuta var. californica (A.DC.) Sharp, C. heterophylla Fischer, and C. sieboldiana Blume were highly resistant, as were most C. americana Marshall genotypes and one C. colurna L. clone tested, but C. jacquenontii Decaisne was highly susceptible. In several cases, hybrids of these species with susceptible C. avellana were also resistant. These new sources of resisstance are being incorporated in the resistance breeding effort.
Downy mildew (DM) is a serious foliar fungal disease of cucurbits. DM can cause yield losses for New Jersey growers if not properly controlled. In 2004, five chemical control programs were evaluated in a research trial at the Rutgers Snyder Research and Extension Farm (Hunterdon Co.). Materials evaluated were: 1) Phostrol, 5 pt/A; 2) Phostrol, 5 pt/A plus Bravo WS, 3 pt/A; 3) Flint WDG, 2 oz/A alternated with Bravo WS, 3 pt/A plus Nova 40W, 5 oz/A; 4) Maneb 75DF, 2 lb/A plus Champ Formula 2 Flowable, 1 1/3 pt/A; and 5) untreated control. All fungicide programs were applied weekly. Phostrol (Nufarm Americas, Inc.) is a new product with systemic mode of action that is newly labeled for cucurbits for control of DM, but not powdery mildew (PM). The active ingredients are mono- and dibasic-sodium, potassium, and ammonium phosphates. Phostrol and Phostrol plus Bravo were evaluated against industry standard fungicide programs which include alternating chlorothalonil + myclobutanil with strobiluron chemistries on a weekly basis. Fungicide applications were made weekly beginning at first observance of DM in the field on 23 July. Plots were rated for DM and PM incidence and extent of defoliation on 6 Aug. and 24 Sept. Phostrol plus Bravo applied on a weekly basis (7 to 10 days) provided the best control of DM, which appeared much earlier in the season than usual in northern New Jersey. Treatments Phostrol, Flint alternated with Bravo + Nova, Maneb + Champ reduced DM compared to the UTC. Maneb plus Champ provided the best control for PM. At harvest, fruit was graded and weighed. Marketable yield from Phostrol, Phostrol plus Bravo and Maneb plus Champ treatments was significantly higher than the UTC and Flint/Bravo plus Nova treatment. Handle quality was not affected by treatment.
Longan (Dimocarpus longan) fruit production and global exports are rapidly expanding. Consumer acceptance of this high value crop requires that fruit arrive in excellent condition. Pericarp browning and fungal diseases are the main postharvest problems for longans. Research was conducted to establish optimum storage temperatures and packaging systems to retain fruit quality of ‘Biew Kiew’ longans. Average respiration rates for longans stored at 20 °C (61.6 mg CO2/kg/h) were about twice the rate as those stored at 10 °C (32.7 mg CO2/kg/h) and triple the rate for those stored at 5 °C (21.1 mg CO2/kg/h). Ethylene rates were below 0.4 μg·kg−1·h−1. Fruit quality and shelf life were greatest when stored at 10 °C. Longans held at 20 °C were unmarketable after 10 d, and fruit stored at 5 °C exhibited chilling injury (CI). After storage at 10 °C, longans packaged in microperforated (MP) bags, clamshell (CL) containers, or Peakfresh® film (PF) had the highest visual quality ratings, lowest disease incidences, and longest shelf life when compared with fruit in Lifespan® film (LS) or fiberboard boxes. The most promising packages (MP, CL, PF) were evaluated further under constant 10 °C or simulated shipping (SS) conditions with fluctuating temperatures (22 °C/10 °C/22 °C). Longans in CL containers had the highest visual quality and lowest disease incidence when stored at 10 °C, but there were no differences among package treatments under SS conditions. Also, sensory ratings were greatest for fruit packed in CL or PF when stored at 10 °C but all sensory scores decreased under SS temperatures. When longans were stored under fluctuating temperatures, aril texture and flavor ratings were highest for CL packages. CL, PF, and MP are suitable packages for longans stored under optimal temperatures. However, for longans stored under SS conditions, sensory quality was highest when packaged in CL containers.
Farmers' field trials conducted in western Kentucky counties in 1995 and 1996 showed that dramatic reductions in insecticide usage are possible using scouting and action thresholds. Five-acre plots were scouted and treated according to action thresholds while adjacent 5-acre plots were treated weekly with insecticides. Seven out of 10 insecticide sprays were eliminated, saving $65/acre for the 1995 season. There were no differences in yield, insect damage, or fruit quality between the scouted plots and the plots that were treated weekly. Assuming similar low pest populations in all 885 acres of the company's contracted fields, savings could have amounted to nearly $31,000 for 1995 after deducting scouting costs. There were no yield or quality differences from three test plots treated according to regularly scheduled applications and three plots treated according to action thresholds for insect pests and according to Tomcast predictions for fungal disease control in 1996. We have demonstrated the value of using Tomcast as an aid in making fungicide spray scheduling decisions for processing tomatoes in Kentucky. Although we were able to greatly simplify the Tomcast-CR10 datalogger interface program in 1996, there were still difficulties in getting information from the university-based computer to the company making spray applications. The company will be able to access the datalogger and obtain the information directly in 1997. The further analyses of “Skybit” satellite data collected in 1996 should also tell us whether this type of information might be used instead of a remote datalogger thus simplifying the process even further. We plan to build on the quick adoption of the Tomcast system and to make it sustainable by transferring “ownership” to the growers and processing company in 1997.
Several biological control agents for the control of fungal diseases have recently been commercialized. Do the claims of pest control meet the expectations of the growers? Do the biocontrol agents perform consistently? How do they compare to chemicals? These questions have yet to be answered but recent trials indicate mixed results. In Massachusetts, Mycostop worked well against fusarium stem rot but not against fusarium wilt. Deny (Burkholderia cepacia) did not perform well against Rhizoctonia or Pythium root rot of poinsettia. The following information was taken from the 1997 and 1998 Biological and Cultural Tests for Control of Plant Diseases. In Maryland, zinnia damping-off was controlled by both SoilGard (Gliocladium virens) and Bio-Trek (Trichoderma harzianum). The biocontrols performed as well as the conventional fungicide. In North Carolina, GlioGard (Gliocladium virens) and SoilGard gave only partial control against Pythium and Rhizoctonia damping-off of bedding plants. In Pennsylvania, Greygold (mixture of four microorganisms) did not provide adequate control of Botrytis on geranium. In Georgia, Pythium and Rhizoctonia diseases of a variety of plants were evaluated with SoilGard and RootShield (Trichoderma harzianum). Disease pressure was low and the results varied from inconclusive to both positive and negative. In addition, SoilGard apparently reduced fresh weight of several plant species. RootShield was reported to both increase root weight in one case and decrease root weight in another. In Connecticut, Rhizoctonia root rot of poinsettia was not significantly suppressed with SoilGard, RootShield, or Earthgro, a suppressive growing medium. However, the authors stated that the results indicated that the biocontrols had promise. Results of additional trials will be presented.
Stable genetic resistance to the fungal disease eastern filbert blight (EFB), caused by Anisogramma anomala, is vital for sustainable production of European hazelnut (Corylus avellana) in eastern North America. In this study, new hazelnut germplasm from the Russian Federation, Ukraine, and Poland (a total of 1844 trees from 66 seed lots) was subjected to A. anomala under field conditions over at least five years in New Jersey. Plants were then rated for the presence of EFB using an index of 0 (no disease) through 5 (all stems containing cankers). Nuts of the resistant trees were evaluated to identify plants with improved kernel characteristics. Genomic DNA of these trees was also screened with sequence-characterized amplified region (SCAR) markers generated by the primers BE-03, BE-33, and BE-68, which are closely linked to the single dominant R-gene of ‘Gasaway’, to assess the resistant seedlings for the presence of this well-known source of resistance. At final evaluation, 76 trees remained free of disease with nine expressing only minor symptoms (rating 1 or 2). The resistant trees spanned 24 different seed lots representing all three countries. The remaining trees ranged from moderately to severely infected with 81% of the total collection rating 5. Several of the resistant trees were found to produce commercial-sized (≈12 mm diameter), round kernels that blanched well. Although the results of the ‘Gasaway’ SCAR primers were inconclusive, the diverse collection origins and disease phenotypes provide evidence that novel sources of resistance were likely identified in this study. These new plants should broaden the genetic base of EFB-resistant C. avellana hazelnut germplasm available for breeding.