Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant Pathology and Crop Physiology

First Advisor

Milton C. Rush

Second Advisor

Rodrigo A. Valverde

Abstract

In anticipation of the regional demand for tomatillo (Physalis ixocarpa Brot.) for the fresh market and sauce industry, four years of research trials (1990-1993) showed a significant adaptation of tomatillo to Louisiana planting conditions where, like tomato, it performed best in the cooler temperatures of spring and early fall. Field surveys indicated that virus diseases were major constraints on production. A foliar mosaic and yellow mottle found commonly affecting plants was caused by Physalis mosaic virus (PhyMV), identified by host reaction, electron microscopy, serology, and dsRNA analysis. Cucumber mosaic virus (CMV) and tomato spotted wilt virus (TSWV) were also found. Potato flea beetles, aphids, and thrips transmitted PhyMV, CMV, and TSWV, respectively. A high incidence of aphids and thrips occurred during the flowering periods of tomatillo (May and October) while flea beetle populations began to appear in May and peaked in late September to early October. Field evaluations of insecticides for the control of tomato fruitworm (Helicoverpa zea Boddie) indicated that pyrethroid treatments (permethrin, cypermethrin, esfenvalerate, cyfluthrin) were significantly more effective in controlling this pest than the organophosphates (azinphos-methyl, methomyl), a carbamate (carbaryl), or an organochlorine (endosulfan). Greenhouse and field weed control studies showed that tomatillo was tolerant to pendimethalin, napropamide, trifluralin, metolachlor, sethoxydim, quizalofop, and fluazifop-butyl. Tomatillo was more sensitive to alachlor and clomazone, and showed no tolerance to metribuzin, acifluorfen, imazethapyr, and fomesafen. Full season control of many grass and broadleaf weeds was obtained without reducing tomatillo yields with sequential treatments of metolachlor, trifluralin, napropamide, or pendimethalin preemergence followed by sethoxydim, fluazifop-butyl, or quizalofop postemergence. In the spring and fall tomatillo transplantings, the aluminum mulch + insecticide treatment provided a high level of fruitworm and insect vector control and gave higher yields. Beneficial effects of mulching, such as insect repellency, weed control, adjustment of soil temperature, reduction of water percolation, and prevention of fruit rot caused by Rhizoctonia solani and other soilborne pathogens accounted for increased yields. Pest management techniques for tomatillo in Louisiana were outlined in detail along with production practices.

Pages

143

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