A. Grinstein

Combined soil treatments and sequence of application in improving the control of soilborne pathogens.

ABSTRACT The effects of reduced doses of methyl bromide (MB) or metham sodium, heating, short solarization, and soil microbial activity, alone or in combination, on survival of soilborne fungal pathogens were tested in a controlled-environment system and field plots. Sublethal doses of heating or MB delayed germination of Sclerotium rolfsii sclerotia. Combining MB and heating treatments was more effective than either treatment alone in controlling S. rolfsii and Fusarium oxysporum f. sp. basilici. The application heating followed by fumigation with MB, was significantly more effective in delaying and reducing germination of S. rolfsii sclerotia and in controlling F. oxysporum f. sp. basilici than the opposite sequence. Further, incubation in soil and exposure to microbial activity of previously heated or MB-treated sclerotia increased the mortality rate, indicating a weakening effect. Similarly, incubation of chlamydospores of F. oxysporum f. sp. melonis and F. oxysporum f. sp. radicis-lycopersici in soil in the field after fumigation further reduced their survival, confirming the laboratory results. In field tests, combining MB or metham sodium at reduced doses with short solarization was more effective in controlling fungal pathogens than either treatment alone. Treatment sequence significantly affected pathogen control in the field, similar to its effect under controlled conditions. This study demonstrates a frequent synergistic effect of combining soil treatments and its potential for improving pathogen control and reducing pesticide dose, especially when an appropriate sequence was followed.

Permeability of plastic films to methyl bromide: field study

Abstract The use of gas-impermeable films to minimize methyl bromide (MB) emission into the atmosphere from soil fumigation was studied in the field. Three experiments evaluated various plastic films during fumigation with a reduced dosage of MB. The concentration of MB decreased sharply in the soil during the first 24 h when polyethylene-based films were used. In contrast, films having a layer of barrier material, such as polyamide or ethylene vinyl alcohol, were significantly less permeable, shown by a gradual decrease in the MB concentration in the soil, a relatively higher concentration in deeper soil layers, and higher concentration ( C ) by exposure time ( T ) ( C × T ) values. A significant correlation was obtained between permeability values obtained in the laboratory and C × T values in the field. Fumigation under impermeable films at the reduced dosage of 20–25 g m −2 was effective in killing propagules of five pathogenic fungi to a depth of 40 cm. The significant correlation obtained between C × T values and the level of fungal killing suggests that using impermeable films reduces MB dosage and emission to the atmosphere while maintaining effective pest control.

Reduced Dosage of Methyl Bromide for Controlling Verticillium Wilt of Potato in Experimental and Commercial Plots

The use of gas-impermeable films to reduce the dosage of methyl bromide (MB) required to control Verticillium wilt in potatoes was examined in field experiments, conducted in soils naturally infested with Verticillium dahliae. The incidence and severity of Verticillium wilt were significantly reduced (by 74 to 94%) by fumigation with MB at 50 g/m2 under standard low density polyethylene (LDPE) or at 25 g/m2 under gas-impermeable films. Fumigation at 25 g/m2 under LDPE was less effective. Disease severity was inversely correlated (r2 = 0.89 to 0.91) with chlorophyll content in the leaves. Fumigation also reduced (by 89 to 100%) stem colonization by the pathogen. Potato yield in the fumigated plots was significantly higher (26 to 69%), than in their nonfumigated counterparts, and was inversely correlated with disease index (r2 = 0.69 to 0.9). The percentage of high-value tubers (above 45 g) was 52 to 56% of total yield in the fumigated plots as compared with 32 to 40% in the nonfumigated controls. Thus, fumigation also improved the commercial quality of tuber yield. Effective control of V. dahliae and yield increases following MB fumigation at the recommended dosage or at a reduced dosage with gas-impermeable films was also observed in a consecutive crop. These results were verified in a large-scale field experiment using commercial applications, further demonstrating the feasibility of reducing MB dosages under farm conditions, without reducing its effectiveness in terms of disease control and yield improvement.

The border effect of soil solarization

Abstract A gradient of reduced effectiveness of solarization toward the edge of the plastic mulch is known as a ‘border effect’, corresponding with decreasing soil temperatures from the middle toward the edge of the mulched area. The cyst nematode Heterodera avenae , of wheat was completely controlled by solarization at 90 cm or more inward from the edge of the mulched plots. A gradient of decreasing effectiveness of nematode control in the mulched plot, toward the edge of the mulch, was observed. There was a similar gradient with height of wheat planted after solarization, and in the incidence of pod wart disease of peanuts caused by Streptomyces spp., planted as a second crop after soil disinfestation. Disease reduction was correlated with a decrease in population of streptomycetes. A similar, but less pronounced, border effect was observed when solarization was combined with methyl bromide or formalin at reduced dosages.

Herbicide-induced resistance to plant wilt diseases

Abstract Pretreating tomato and eggplant seedlings with various dinitroaniline herbicides markedly increased their resistance to vascular wilts caused by Fusarium and Verticillium species. The present study compares the mechanisms of resistance to Fusarium oxysporum f. sp. lycopersici induced by trifluralin in susceptible tomato plants with those in monogenic resistant plants. It was found that fungitoxic compounds, extractable in ethanol, accumulated in herbicide-treated inoculated susceptible tomatoes and also in inoculated monogenic resistant plants. As these fungitoxic compounds only accumulate after inoculation and are not present in either uninoculated plants or in susceptible interactions they are unlikely to be metabolites of the herbicide and are probably phytoalexins. Trifluralin enables the susceptible plant to produce the compounds after inoculation and is therefore considered to be a sensitizer. The fungitoxic substances are different from the terpenoid phytoalexins known to be produced by solanaceous plants since they are insoluble both in chloroform and in water-saturated ethyl-acetate. Fungitoxic compounds, extractable with ethanol, also accumulated in cotton seedlings cv. Pima pretreated with trifluralin and inoculated with F. oxysporum f. sp. vasinfectum.

Permeability of Plastic Films to Methyl Bromide: A Comparative Laboratory Study

Abstract: The permeability of plastic Ðlms to the fumigant methyl bromide (MB)was measured by two di†erent methods, in order to facilitate the selection ofÐlms which are impermeable to the gas. Polyethylene-based Ðlms are highly per-meable to MB, as evidenced by both methods. In contrast, multilayer coextrudedÐlms which have a layer of barrier material such as polyamide (PA) or ethylene-vinyl alcohol copolymer (EVOH) were signiÐcantly less permeable to MB, asreNected by the parameters permeability rate, time to 90% concentration (TC90,by the di†usion method) and lag-time values (by the variable-volume method). AsigniÐcant correlation was found between the permeability rate assessed by thedi†usion method and that obtained with the variable-volume method. Per-meability of all Ðlms increased with temperature as evidenced by all testedparameters. This increase was more pronounced with polyethylene Ðlms, the per-meabilities of which increased Ðve- to six-fold when the temperature wasincreased from 20iC to 60iC. The e†ect of temperature on barrier-Ðlm per-meability was less signiÐcant. Permeability of Ðlms to MB was a†ected by addi-tional factors such as additives, the length of the monomer side-chain, and thethickness and density of polyethylene Ðlms. 1998 SCI(Pestic. Sci., 53, 141E148 (1998)Key words: ethylene-vinyl alcohol; polyamide; fumigation; barrier Ðlms; methylbromide

Improved uniformity of spray deposition in a dense plant canopy: methods and equipment

The global trend to shift from highly toxic pesticides to environmentally safe and less toxic chemicals requires, generally, very high spatial uniformity of the spray deposition. Effective penetration of the spray into a dense canopy can be achieved by utilizing fast air-streams. In contrast, slow and turbulent flow near the leaves and the stems is required for good deposition of the spray. A new sprayer was designed to achieve a sharp decline in air velocity to meet the two — seemingly contradictory — constraints, and thereby obtain effective penetration and coverage of dense canopy. In the present work, air ducts with several shapes of air outlets were developed and tested in an attmept to meet these requirements. Generally, a short and wide air slit created a moderate decline in air velocity; a longer and narrower air slit improved the uniformity of the air velocity along the slit outlet, and brought about a sharper decline in speed of the air-streams. Installing air deflectors at the air outlets added a slight upward motion to the air-streams and enhanced spray deposition on the underside of leaves. Preliminary field tests with the long and narrow air slit showed uniform spray deposition on all plant parts.

Improved technologies to reduce emission of methyl bromide from fumigated soil

Methyl bromide (MB) is the chemical most widely used for soil fumigation in intensive agriculture, and for commodity and postharvest quarantine treatments. MB was listed by the Montreal Protocol in 1992 as a controlled ozone-depleting substance, and a phase-out process has been initiated. Several technologies to reduce the fumigation dosage and subsequent emission of MB from the fumigated soil were tested and applied in field trials and commercial application. These include dosage reduction by using impermeable films, improving uniformity of distribution, and preventing possible escape sources such as the edges of the fumigated plot. Combining MB with other pesticides, solarization, or biocontrol agents is another approach to reducing MB emission and dosage. Adapting these technologies may result in a 60–90% reduction of MB emitted from fumigated soil.

Pod wart disease of peanuts

Peanut pod wart, a relatively new disease to peanut culture, was first reported in Israel in 1988 attacking peanut plants and causing dark warts on the pod. The causal agents are variousStreptomyces spp. Scanning electron microscopy showed a significant difference between healthy and diseased tissues of the exocarp and mesocarp layers of the pod; there were no effects on the endocarp layer. The mesocarp cells of infected tissue were smaller and more compressed than those of healthy tissue. In most cases two cells under the peak of the wart were extremely large and the cells growing from them toward the surface were uneven, forming the shape of a fan. The pathogen could be isolated from the soil and rhizosphere, but in the pod it was found only in the waited tissue. The microorganisms isolated from the warts belong to different groups ofStreptomyces spp.; subsequent pathogenicity tests proved their virulence to a limited host range. In potato, these isolates ofStreptomyces spp. caused deep pitted scab; in peanuts they caused warts. Peanut seeds which developed in infected pods were free of the pathogen if the shell was undamaged. However, the pathogen is surface seedborne, and contaminated seeds during the mechanical cracking process.

Abstracts of papers presented at the fourth israel congress of plant pathology

S OF PAPERS PRESENTED AT THE FOURTH ISRAEL CONGRESS OF PLANT PATHOLOGY F e b r u a r y 1 7 1 8 , 1975 R e h o v o t , Israel