The effect of soil disinfestation with methyl bromide (MB) or by soil solarization (solar heating) and the fungicides TMTD (tetramethylthiuram disulfide) and fentin acetate (triphenyltin acetate) on the degradation of terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-methylthio)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] were investigated. The degradation of terbutryn appeared to follow first-order kinetics with a half-life of about 2 weeks and was much slower in MB-treated or solarized soils, i.e. half-life of about 11 weeks. Suppression of terbutryn degradation in the MB-treated soil was still evident 8 months after soil fumigation, similar to that found in autoclaved soil. TMTD and fentin acetate at 20 μg/g soil strongly inhibited degradation of terbutryn in soil. Degradation of atrazine was affected to a lesser extent by soil disinfestation. Results from the present study suggest that biocidal soil treatments may slow herbicide degradation. Thus, herbicide dosages in disinfested soil should be adjusted in order to avoid phytotoxicity. Moreover, lower dosages might be sufficient to attain weed control, and combined disinfestation or fungicides with herbicide treatments might be intentionally used to extend herbicide activity.

Weed control by heat or flaming typically uses flames to burn small weeds, directed away from desired crops. This research studied an enclosed flaming system for weed control before turfgrass establishment. Field research trials were conducted to explore the efficacy of a PL-8750 flame sanitizer at two application timings. Treatments included various application methods of PL-8750 flame sanitizer and common thermal and chemical weed control methods. Data were weed control relative to the control treatment. Species evaluated included carpetweed, Virginia buttonweed, spotted spurge, large crabgrass, goosegrass, old world diamond-flower, cocks-comb kyllinga, and yellow nutsedge. Turfgrass establishment was not successful in summer but was successful in fall. Fall-application timing trials resulted in > 60% tall fescue establishment at 6 wk after seeding (WAS) for all treatments. Summer-application timing trials resulted in unacceptable turfgrass establishment (≤ 18%) for all evaluated turfgrass species at 6 WAS. Broadleaf and grassy weeds were better controlled compared with sedge weeds. Overall, solarization; covered, emerged-weed flaming; and double applications of covered, emerged-weed flaming were the most successful treatments. Solarization controlled carpetweed, Virginia buttonweed, spotted spurge, large crabgrass, and goosegrass > 80% at 6 WAS. Weed control across thermal treatments were equal to or greater than the comparison chemical treatment (dazomet at 389 kg ha−1). Results indicate thermal weed control has potential for reducing weed populations before turfgrass establishment.

Mortality of weed seeds at temperatures of 39, 42, 46, 50, 60, and 70 C was recorded through time under controlled laboratory conditions similar to those of soil solarization for six weed species: annual sowthistle, barnyardgrass, black nightshade, common purslane, London rocket, and tumble pigweed. Time and temperature requirements for thermal death varied considerably among the species studied. Barnyardgrass, London rocket, and annual sowthistle were more susceptible to heat treatment than black nightshade, common purslane, and tumble pigweed. Temperatures of 50 C and above were lethal for seeds of all species. Common purslane seeds were unaffected at 46 C and below, tumble pigweed and barnyardgrass seeds were unaffected at 42 C and below, and black nightshade seeds were unaffected at 39 C. Nonlinear models for mortality as a function of duration of heat treatment were developed for each species at each temperature at which mortality occurred. These models provide an empirical relationship for the construction of field-applicable decision models that could predict the accumulation of time and temperature combinations for effective solarization of weed seeds.

Downy brome (Bromus tectorum) is an invasive, annual grass that has spread through much of the Great Basin desert but remains patchy at high elevation. This study evaluates control options for outlier infestations in the eastern Sierra Nevada, CA, based on their ecological effectiveness and their economic and practical feasibility. I tested the efficacy of hand-pulling, sheet-mulching, and soil solarization followed by broadcast and seedball seeding of native forbs and grasses. Downy brome cover, density, and dominance in the seed bank decreased with all removal treatments. Soil solarization and sheet mulching were most successful at eliminating downy brome (decreasing density by 99% after just 1 yr of treatment in both cases), but they had negative nontarget impacts on other herbaceous species. Germination of native seeds was low with both broadcast and seedball seeding, probably because of dry conditions. Each of the methods tested has potential for decreasing or eliminating small-scale, outlier infestations of downy brome along roadsides and in disturbed sites and thereby helping to contain the invasion.

Tomato cultivation in the Mediterranean region is susceptible to infestation by the parasitic weed branched broomrape (Orobanche ramosa), and severe yield losses can result. The effectiveness of solarization, a soil disinfection technique that uses passive solar heating, to control the incidence of broomrape under greenhouse conditions was studied over two growing seasons. Solarization was accomplished by the application of clear polyethylene sheets to moist soil for 58 to 61 d during the hot season. The treatment increased maximum soil temperature by around 10 C, and at 5 cm below the soil surface, a temperature of more than 45 C was reached for 34 to 58 d, whereas this temperature was not reached at all in the first season and not for 20 d (second season) in unmulched soil. In solarized soil, no broomrape shoots emerged, and neither haustoria nor underground tubercles of the parasite were found on tomato roots. The treatment killed about 95% of buried viable seed, and induced secondary dormancy in the remaining 5%. In nonsolarized plots, broomrape shoots were present at a high density, decreasing plant growth and fruit production. Fruit yield was 133 to 258% higher in the solarized as compared with the nonsolarized treatment. Based on these results, we suggest that soil solarization, which precludes chemical contamination and is suitable for organic farming, is an appropriate technology where the risk of branched broomrape infestation is high.

Soil solarization is used to manage nematodes, pathogens and weeds, but relatively few studies have examined solarization effects on soil mineral nutrients, soil properties and plant tissue nutrients. This study was designed to optimize the duration of solarization treatment for the management of soil and plant nutrients and crop biomass in an agroecosystem utilizing an organic nutrient source. The experiment was a split-plot with treatment duration as the main effect and solarization as the sub-effect. Solarization treatments of 2-, 4- and 6-week durations began on sequential dates and concluded in mid-August. Immediately post-treatment, okra (Hibiscus esculentus L.) seedlings were transplanted into subplots for tissue nutrient analysis. Freshly chopped cowpea [Vigna unguiculata (L.) Walp.] hay was applied to the soil surface directly around the okra seedlings as an organic nutrient source. Immediately following solarization treatment, concentrations of soil K and Mn were higher, while Cu and Zn concentrations were lower in solarized soils than in non-solarized soils. Soil pH was slightly lower in solarized plots. Concentrations of K, N, Mg and Mn in okra leaf tissue were higher in solarized plots than in non-solarized plots, but concentrations of P and Zn were lower in plants grown in solarized soil. Okra biomass was three and four times higher in the 4- and 6-week solarization treatments than in non-solarized treatments. Based on data from this experiment, 4- and 6-week durations of solarization were optimal for increasing crop biomass. The data indicate that solarization has significant effects on soil and plant nutrients. Results of the nutrient analyses suggest that the availability of nutrients from an organic source was not limited by solarization.

This study was conducted in Florida in 1999 and 2000 to examine the impact of alternative crop production practices on soil quality and yields of fresh market pepper (Capsicum annuum). Replicated field plots were established on an organic vegetable farm that had been under certification for 5 years and on a conventional pepper farm that had been fumigated with methyl bromide for 25 consecutive years. Production practices evaluated included raised beds covered by white plastic mulch, soil solarization, no-till in a stubble crop of sunn hemp (Crotolaria juncea) or iron-clay pea (Vigna unguiculata) and the addition of 67 t ha−1 of urban plant debris (UPD). Soil fumigation with methyl bromide–chloropicrin was also evaluated at the conventional farm site. Soil organic carbon significantly increased following the addition of UPD in both years at the organic site but only in the second year at the conventional site. Cation exchange capacity increased significantly after addition of UPD in both years at both sites and a significant interaction with production practices was observed in the second year at the organic site. Soil phosphorus levels were high at both sites but were not impacted by production practices or UPD. In 1999, the addition of UPD significantly decreased soil nitrate levels at the organic site and the conventional site, except under the no-till treatments. In 2000, soil nitrate levels were not affected by UPD or production practice. Stand counts, determined by the number of surviving pepper plants 21–28 days after transplanting, were severely impacted in no-till treatments due to intense competition from weeds. Marketable yields equal to, or above, the 1999/2000 statewide average for conventional production systems were obtained with soil fumigation and soil solarization at the conventional site in 1999. In 2000, an epidemic of Phytophthora blight (Phytophthora capsici) eliminated production at the conventional site. Marketable yield at the organic site approached the statewide average for conventional systems under the solarization treatment. Yields under plastic mulch were increased at both sites with the addition of UPD. The results demonstrated that organic pepper yields from soil-solarized plots were similar to yields obtained by conventional farmers using high inputs of rapidly mobile nitrogen sources. However, no-till systems for fall production do not appear to be a viable alternative under Florida conditions due to the rapid proliferation of weeds under the cover crop stubble. The addition of urban plant debris was associated with an increase in soil organic carbon and cation exchange capacity in sandy soils typical of those found in Florida.