B. J. Landis

Effect of aphid control on the spread of leafroll in potatoes

SummaryFour applications of 10 insecticides were made with a power ground duster to Netted Gem potatoes planted for early and late crops at Yakima, Washington, to determine their relative values for controlling the green peach aphid (Myzus persicae (Sulz.)) and the potato aphid (Macrosiphum solanifolii (Ashm.)) and, indirectly, for preventing the spread of potato leafroll.In experiments 1 and 2, on potatoes planted for an early crop, dusts containing 4 per cent of DDT and 80 per cent of sulfur, 5 per cent of DDT and 75 per cent of sulfur, or 5 per cent of DDT all gave good control of aphids and the incidence of leafroll did not exceed 5.8 per cent. Aphid populations were highest where 33.3 per cent of sodium fluoaluminate dust was used, and on those plots the leafroll incidence was 23 per cent.In experiment 3, on potatoes planted for a late crop, the highest aphid population was again found in plots that had received 33.3 per cent of sodium fluoaluminate dust, and the leafroll incidence was 61.3 per cent. Five per cent of DDT, and 3 and 5 per cent of DDT with 2 per cent of oil were also relatively ineffective for aphid control, and the leafroll incidence was 49 to 57.4 per cent.A dust containing 5 per cent of DDT and 75 per cent of sulfur gave the best control of aphids throughout the entire season, and the incidence of leafroll was 43.1 per cent. Dusts containing parathion were relatively ineffective during the period of extensive winged-aphid migration; consequently leafroll transmission was high during this period. However, parathion gave good control after the migration had abated and leafroll incidence did not exceed 43 per cent. DDT-sulfur and parathion dusts were equally effective in preventing the spread of leafroll.

Populations of aphids on named varieties of Irish potatoes

Populations of the green peach aphid,Myzus persicae (Sulzer), and the potato aphid,Macrosiphum euphorbiae (Thomas), were observed on 27 named varieties of Irish potatoes in the Yakima Valley of Washington intermittently from 1947 through 1968. The Epicure, Great Scot, and B5141-6 varieties produced relatively fewer green peach aphids than other varieties tested; Bliss Triumph and Red Pontiac produced relatively fewer potato aphids. Except for Doebay Red, the red-skinned varieties, Bliss Triumph, Red McLure, Norland, and Earnly Rose, were extremely to moderately productive of the green peach aphid. No correlation was apparent between abundance of aphids and the specific gravity or yield of tubers.

Chemical control of the seed-corn maggot,Hylemya platura (Meigen), and seed-piece decay in potato seed pieces

When captan was applied to freshly-cut potato seed pieces to control seed-piece decay, it prevented infestation by the seed-corn maggot,Hylemya platura (Meigen), which may otherwise cause extensive damage during cool, wet springs. In 1969, diatomaceous dust mixtures and seed-piece soaks containing 5% captan, methiocarb, or phoxim applied at a rate of 1 1b/acre gave effective control of the seed-corn maggot and seed-piece decay. In 1970, in similar tests, captan, TD-1771 (dimethyl 4,4′-O-phenyl-enebis/3-thio=allophanate/), and TD-5056 (2-methyl sulfonyl 6-nitro benzo thiazole) gave significantly better control of the maggot and of seed-piece decay than methiocarb or phoxim and than five other treatments.

Control of the Colorado potato beetle by treatment of potato seed pieces

Dusting or soaking freshly cut potato seed pieces in systemic insecticides controlled the first generation larvae of the Colorado potato beetle at Yakima, Washington in 1970. The most promising materials were tested again in a larger experiment in 1971. Fifty days after treatment, Bay 37344 (4-(methylthio)-3,5,xylyl methylcarbamate), Dasanit® (O,O-diethyl-O-[p-(methylsulfinyl) phenyl] phosphorothioate), Shell SD 17250 (N-(methylcarbamoyl)oxy]thioacetimidic acid ester with 3-mercaptopropionitrile) and Plant Protection PP062 (dimethylamino)-4,5,6-dimethyl pyrimidinyl dimethylcarbamate) all gave significantly better control of the larvae than methomyl, azinphosmethyl and menazon.