Eastern black nightshade (Solanum ptycanthum Dun.) management in plasticulture tomatoes (Lycopersicon esculentum)

by Buckelew, Juliana Kirsten.

BUCKELEW, JULIANA KIRSTEN. Eastern Black Nightshade (Solanum ptycanthum Dun.) Management in Plasticulture Tomato (Lycopersicon esculentum). (Under the direction of David W. Monks) Tomato production in North Carolina depends upon plastic mulch for increased total plant growth, earlier flowering, and earlier yield of tomato. Components of the plasticulture system include raised beds, plastic mulch, drip fertigation, and methyl bromide fumigation for pest control. With the phase-out of methyl bromide by the EPA, in-row weed growth will likely increase in this production system. Eastern black nightshade is a solanaceous annual weed that infests tomato. It is difficult to control without injuring tomato because of similar growth habit and physiology. Research was conducted in 2003 and 2004 to evaluate eastern black nightshade management and postemergence directed control of weeds that infest tomatoes in North Carolina. Field experiments were conducted to determine density-dependent effects of eastern black nightshade season-long interference on tomato yield loss when growing in-row with plasticulture tomato. Eastern black nightshade was transplanted at densities 0, 1, 2, 3, 4, and 5 per planting hole. Percent yield loss for jumbo grade fruit, the premium grade, as affected by eastern black nightshade density followed a rectangular hyperbola model. Number and weight of cull, medium, and large grades did not differ by any density. Mean number and weight comparisons of extra large, jumbo, marketable, and total fruit categories showed a reduction for densities 1 to 5 weeds per hole from the weed-free, but no difference among densities 1 to 5 weeds per hole. The economic threshold for jumbo grade was one weed per 11.25 m of row (with 45 cm crop spacing). In additional field experiments, the effect of eastern black nightshade on tomato yield loss growing in-row with plasticulture tomato, as well as eastern black nightshade berry production and seed viability were determined. Eastern black nightshade was transplanted at 1, 2, 3, 4, 5, 6, and 12 weeks after tomato planting (WAP) and remained until tomato harvest, or was established at tomato planting and removed at 2, 3, 4, 5, 6, and 8 and 12 WAP to determine the critical weed-free periods. The critical weed-free period to avoid viable seed production was 3 to 6 WAP. No treatment differences in tomato yield were found in year 1. In year 2 at the second location, differences in the sum weight of extra large and jumbo grades occurred. The critical weed-free period to avoid greater than 20% yield loss for the sum weight of extra large and jumbo grades was 28 to 50 days after tomato transplanting, and was economically justified based on 2004 tomato prices during weeks harvested. Field experiments were conducted in 2003 to identify those herbicides that were safe to tomato postemergence directed and in 2004 to determine the effect of these herbicides postdirected at various rates on tomato injury and control of apple of Peru (Nicandra physolodes), eastern black nightshade, fall panicum (Panicum dichotomiflorum Michx.), goosegrass (Eleusine indica (L.) Gaertn.), hairy galinsoga (Galinsoga ciliata (Raf.) Blake), ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.), jimsonweed (Datura stramonium L.), johnsongrass (Sorghum halapense (L.) Pers.), large crabgrass, (Digitaria sanguinalis (L.) Scop.) Mexican groundcherry (Physalis ixocarpa Brot. ex Hornem.), pitted morningglory (Ipomoea lacunosa L.), redroot pigweed (Amaranthus retroflexus L.), sicklepod (Senna obtusifolia L.), velvetleaf (Abutilon theophrasti). In 2003, cloransulam-methyl, flumioxazin, halosulfuron, imazamox, metribuzin, thifensulfuron, and trifloxysulfuron sodium were applied. With the exception of cloransulam-methyl at Clinton which caused 11% injury, cloransulam-methyl, flumioxazin and imazamox gave 24% or greater visual injury to tomato. Likewise, marketable fruit weight was 16 to 71% of the nontreated check for these herbicides. Tomato was injured 5% or less by all rates of halosulfuron, metribuzin, thifensulfuron, and trifloxysulfuron sodium and yielded similar to tomato in the nontreated control for these treatments. Thus cloransulam-methyl, flumioxazin, and imazamox were too injurious to tomato and excluded from 2004 studies. In 2004, trifloxysulfuron sodium, metribuzin, thifensulfuron, and halosulfuron again caused no differences in tomato yield from the non-treated control. Trifloxysulfuron sodium controlled apple of Peru, eastern black nightshade, jimsonweed, and Mexican groundcherry. Thifensulfuron controlled redroot pigweed, velvetleaf, Mexican groundcherry, hairy galinsoga, and jimsonweed. Metribuzin and halosulfuron consistently provided excellent control of Mexican groundcherry, velvetleaf, redroot pigweed, hairy galinsoga, and jimsonweed. Metribuzin consistently provided excellent control of sicklepod, apple of Peru, and eastern black nightshade.