Interaction of plastic, hay and grass mulches, and metam-sodium on control of Pratylenchus penetrans in tomatoes.

Black polyethylene film mulches affect the activity of some nematicides (1, 2, 3, 5, 6, 7, 8, 9). Other mulches also may influence the results of fumigat ion tests; for example, hay mulches, cause the soil to remain cooler (8). Salt-hay mulches are used by strawberry growers, many of whom fumigate. Mulches of grass clippings, wood chips, or leaf mold are used by homeowners. Clear plastic mulches cause the soil to retain heat, (8) and the activity of soil pesticides in warmer soil under clear plastic could change. Because black plastic mulch suppresses Pratylenchus penetrans populations (5), it should be useful to determine whether organic mulches act similarly. Therefore , three types of mulches were tested, on fine sandy loam soil fumigated with metam-sodium (sodium-Nmethyl-di thiocarbamate) , for control of Pratylenchus penetrans. In a field where tomatoes had grown the year before, a pre t rea tment sample for nematode counts was taken on 20 April and nematodes were extracted by sugar flotation (4). On 21 April, metam-sodium was applied, at the rate of 209 liters (a.i.)/ha, to 20 plots, each of which measured 3.0 x 2.8 m. T h e soil t empera ture at a depth of 15 cm was 12 C. A 10-10-10 fertilizer was plowed into the soil at the rate of 500 k g / h a before planting. Four tomato plants, Lycopersicum esculentum cv. 'Bonny Best', were planted 0.6 m apar t in each plot on 18 May. Each p lant received 300 ml of a solution containing 0.5 gm of a 23-10-8 ferti l izer/l i ter. Four fumigated and four nonfumigated plots were mulched with either a 7.5-cm layer of salt hay, a 2.5-cm layer of grass clippings, or a ].5-mil black polyethylene film. T h e film contained holes (4 cm diam) 30 cm apar t for moisture and