Screening root-knot nematode resistant carrot lines for resistance to carrot cyst nematode. T. A. BLAUEL, P. SIMON AND M. R. MCDONALD. Department of Plant Agriculture, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada; and (P.S.) USDA-ARS, 1575 Linden Drive, Madison, WI 53706, USA
Crop resistance is an effective method for managing plant-parasitic nematodes (PPN). Carrot lines that are resistant to some species of root-knot nematodes (Meloidogyne species) may also be resistant to other PPN, such as the carrot cyst nematode (CCN) (Heterodera carotae). Both root-knot and carrot cyst nematodes parasitize carrot roots, reducing marketability and overall yield, and are often found in soils where carrots are grown. The objective of this study was to determine the resistance of root-knot nematode resistant carrot lines to carrot cyst nematodes. Ten root-knot resistant carrot lines from the United States Department of Agriculture (USDA) carrot breeding programme were assessed, along with the commercial cultivar ‘Cellobunch’ in both high organic matter (muck) soil and sand. Tall narrow pots (conetainers) were seeded with 2 carrot seeds per pot and thinned to one. The conetainers were arranged in a randomized complete block design with 5 replications and 14 containers per replicate line. Carrots planted in sand were inoculated with 75 CCN eggs per carrot. The muck soil was naturally infested with ~550 CCN juveniles and 200 cysts per pot. Carrots were also seeded in non-infested soil as an untreated check. Carrots were grown outside during the summer months for 90 days before harvest. Disease incidence due to CCN parasitism was lower for the carrot line S278-1 Homs, compared with some other lines, in both muck and sand soil. These results will contribute to the carrot breeding programme of the USDA and also carrot breeding for Canadian production.
Potential for cultural control of bacterial spot (Xanthomonas gardneri) in field tomatoes (Solanum lycopersicum) of Southwestern Ontario. T. SIMONTON, D. ROBINSON, C. GILLARD, K. JORDAN AND C. TRUEMAN. Department of Plant Agriculture (DPA), University of Guelph (UOG), Ridgetown, 120 Main Street East, Ridgetown, ON N0P 2C0, Canada; and (K.J.) DPA, UOG, 50 Stone Road East, Guelph, ON N1G 2W1, Canada
Bacterial spot (Xanthomonas gardneri) of tomatoes (Solanum lycopersicum L.) is a major issue in Ontario field tomato production. There is widespread tolerance to copper-based chemical controls and few effective alternatives. The importance of transmission at or just prior to transplanting is unknown. To evaluate this, X. gardneri movement in irrigated trailers and planting equipment was studied in controlled environments. In the first study, symptomatic seedlings were placed at the top of a simulated plug trailer with healthy seedlings placed 30.5, 61.0, 91.5 and 122 cm below in four separate replicated experiments with different irrigation treatments. The Irrigation treatments (top to bottom, bottom to top, tray dip) were applied and trays were incubated overnight inside the trailer. Disease incidence (per cent seedlings with symptoms) in the top to bottom (3.9%) and bottom to top (5.4%) irrigation treatments were equivalent and greater than the dip treatment (0.4%) 14 days after irrigation. All irrigation treatments had higher disease incidence than the control. Symptoms were observed on seedlings located at all distances below the inoculation tray. In a separate study, wet or dry symptomatic seedlings were passed through a transplanter prior to healthy seedlings. Epiphytic X. gardneri (4627–1405 CFU g−1 of fresh tissue) was detected on healthy seedlings after 14 days on wet and dry treatments, demonstrating the potential for disease spread on transplanting equipment. Preliminary results indicate X. gardneri transmission is possible in plug trailers and during transplanting; this may play a role in field epidemics.
Fungicide application timing for the control of Stemphylium leaf blight of onion. S. STRICKER, B. D. GOSSEN AND M. R. MCDONALD. Department of Plant Agriculture, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada; and (B.D.G.) Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
Stemphylium leaf blight of onion, caused by Stemphylium vesicarium (Wallr.) Simmons, can cause severe defoliation and lead to small, unmarketable bulbs. Growers typically use a calendar-based schedule to apply fungicides, which does not depend on weather conditions or pathogen biology. This can result in more applications than necessary, which increases both input costs and the risk of fungicide insensitivity. A field trial of onion cv. LaSalle was established on a high organic soil at the Muck Crops Research Station, King, Ontario, to evaluate the efficacy of seven fungicide-timing treatments compared with a non-treated check. The treatments consisted of two pelleted fungicide seed treatments (Ergol Prime (penflufen) or Dynasty (azoxystrobin)) followed by sprays every 7–10 days, weekly sprays with two starting dates (2-leaf or 4-leaf growth stage), a mineral oil drench at emergence followed by weekly sprays, and two forecasting models (slightly modified versions of TOMcast or BSPcast). The foliar fungicide treatment was Quadris Top (difenoconazole + azoxystrobin) alternated with Luna Tranquility (fluopyram + pyrimethanil). The weekly schedules resulted in five or seven applications of fungicides. Disease pressure in 2018 was high and the forecasting models recommended five applications for TOMcast and six for BSPcast. The forecasting model treatments resulted in comparable disease as the weekly calendar sprays and used slightly less fungicide product. Weekly foliar applications did not suppress blight incidence or severity, but fungicide seed treatment in combination with weekly application reduced foliar symptoms by 20–39% relative to the control.