Reproduction of Pratylenchus penetrans on 24 Common Weeds in Potato Fields in Québec.

Twenty-four weeds commonly found in commercial potato fields in Quebec were evaluated for their host suitability to the root-lesion nematode, Pratylenchus penetrans, under greenhouse conditions. Brown mustard (Brassica juncea) and rye (Secale cereale) were included as susceptible controls and forage pearl millet hyb. CFPM 101 (Pennisetum glaucum) as a poor host. Pratylenchus penetrans multiplied well on 22 of the 24 weed species tested (Pf/Pi >/= rye or brown mustard). Cirsium arvense, Leucanthemum vulgare and Matricaria discoida were classified as very good hosts with a Pf/Pi ranging from 1.60 to 2.54, while Ambrosia artemisiifolia and Cyperus esculentus were classified as poor hosts with a Pf/Pi from 0.01 to 0.15. Amaranthus powellii, A. retrqflexus, Raphanus raphanistrum, Rorippa palustris, Cerastium fontanum, Spergula arvensis, Stellaria media, Chenopodium album, Vicia cracca, Elytrigia repens, Digitaria ischaemum, Echinochloa crusgalli, Panicum capillare, Setaria faberii, S. pumila, S. viridis, Polygonum convolvulus, P. scabrum and P. persicaria were intermediate hosts with Pf/Pi values ranging from 0.33 to 2.01. The plant species and the botanical family had a significant impact on nematode reproduction. The Brassicaceae family resulted in the greatest reproduction of P. penetrans, and the Cyperaceae resulted in the least. The plant life-cycle (annual vs. perennial) had no impact on nematode population.

Effect of Forage and Grain Pearl Millet on Pratylenchus penetrans and Potato Yields in Quebec.

Rotation crop experiments were conducted from 1998 to 2000 to assess the impact of forage and grain pearl millet (Pennisetum glaucum) on Pratylenchus penetrans populations in three potato (Solanum tuberosum cv. Superior) fields in Quebec. These crops were compared to oats and(or) barley. Forage millet had a suppressive effect on P. penetrans populations after a 1 year rotation. The following year, marketable potato yields were negatively correlated with initial P. penetrans densities on two experimental sites (r = -0.454, P = 0.044; r = -0.426, P = 0.017). Average marketable and total yields were increased by 10% in plots previously grown in forage millet hybrid CFPM 101 when compared to oats (P = 0.017). Damage functions between preplant nematode density (Pi) and marketable yield (y = 42.0 -4.091 log [Pi + 1]) and total yield (y = 43.9 -4.039 log [Pi + 1]) of potato were established on pooled yield data. Forage pearl millet is an efficient and economically viable alternative for managing root-lesion nematodes and improving potato yields in Quebec.

Efficacy of steinernematid nematodes against three insect pests of crucifers in quebec.

STEINERNEMATID NEMATODES WERE EVALUATED AGAINST THE THREE MAJOR CRUCIFEROUS INSECT PESTS: the imported cabbageworm Artogeia rapae, the diamondback moth Plutella xylostella, and the cabbage looper Trichoplusia ni. LC(50) values of S. carpocapsae All, S. feltiae UK, S. feltiae 27, and S. riobrave 335 were 18.2, 3.6, 5.7, and 8.3 on A. rapae L(2); 24.5, 2.3, 6.0, and 15.5 on P. xylostella L(3); and 10.1, 4.7, 9.5, and 7.8 on T. ni L(2), respectively. Insect mortality from the nematode species and isolates was modulated by temperature. Maximum mortality (100%) was recorded for A. rapae L(2) from S. riobrave at 30 degrees C, 95.8% from S. feltiae, and 91.7% from S. feltiae 27 at 25 degrees C and 75.7% from S. carpocapsae at 30 degrees C. Mortality of A. rapae L(2) increased with contact time to nematode. Mortality of 76% and 78% was achieved for S. carpocapsae and S. feltiae, respectively, after 12-hour exposure. Susceptibility of A. rapae, P. xylostella, and T. ni larvae to entomopathogenic nematodes increased with larval age development. The addition of adjuvants - Corn Oil (0.9%, 1.8%, 3.6%), Leafshield (3.0%, 6.0%, 12.0%), Seaweed (0.1%) and Agral (0.05%) - significantly increased the density and survival rate of S. carpocapsae on cabbage leaves compared to water only. At 20 degrees C and 70% relative humidity (RH), survival rates of S. carpocapsae All, S. feltiae UK, and S. riobrave 335 on cabbage leaves were 43%, 2%, and 0% after 4 hours following application. Under field conditions, foliar applications of S. carpocapsae provided 35.3% and 33.0% control of A. rapae (L(3)-L(5)) on Brussels sprouts and broccoli in 1996 and 24.9%, 19.4% and 14.9% on Brussels sprouts, broccoli, and cauliflower, respectively, in 1999. Based on our field results, foliar applications of S. carpocapsae do not provide an acceptable level of A. rapae control under Quebec's environmental conditions.