FACTORS AFFECTING THE LOSS OF TRI-ALLATE FROM SOILS

Summary. Electron-capture gas chromatography was used to detect tri-allate residues in persistence studies with two soils. At rates equivalent to 0–75, 15 and 3 Ib/ac, 50% of the amount applied was degraded in 8–11 weeks at 25°C in moist Regina heavy clay and Weyburn loam. No loss occurred in sterile soils, indicating that microbial degradation may be a, major factor contributing to tri-allate breakdown.
When aqueous solutions buffered at pH 4–8 were held at 25° G, only 10–15% of the tri-allate was chemically degraded during 24 weeks.
At the normal field rate of 1·25 Ib/ac, tri-allate was not readily leached. From soil columns of Weyburn loam, 5–7% was eluted by 9 in. of water; with clay the corresponding value was 12–13% of the amount applied. When field plots were sprayed with 125 lb/ac in April, tri-allate could still be detected until the soil froze in November.
Facteurs agissant sur la perte de tri-allate dans les sots     

EFFECTS OF THE HERBICIDES TRIFLURALIN AND CARBETAMIDE ON NODULATION AND GROWTH OF LEGUME SEEDLINGS

Summary. The effects of pre-sowing incorporated applications of trifluralin and carbetamide on the growth and nodulation of Trifolium pratense L., T. repens L., T. dubium L. and Lotus pedunculatus Cav. were examined. At rates of 1·0 and 2·0 kg/ha a.i. of trifluralin and carbetamide respectively, nodulation and growth of all legumes was reduced. Root dry weight/plant and nodules/plant were positively correlated, suggesting that the herbicides affected plant growth but not the soil rhizobial population. There were several herbicide rate × legume species interactions.
Effets des herbicides trifluraline et carbétamide sur la formation de nodosités et la croissance des plantules de légumineuses     

DEGRADATION OF DICAMBA IN PRAIRIE SOILS

Summary. Electron-capture gas chromatography was used to detect dicamba residues in three prairie soils, and the breakdown under different moisture conditions was studied. At rates equivalent to 1·1 kg/ha degradation was rapid in all soils at 25°C and at moisture levels in excess of the wilting point, with over 50% of the applied dicamba being dissipated in 2 weeks. Negligible breakdown occurred in the sterile soils, over a 4–week period, indicating that microbial decomposition could be an important factor contributing to dicamba degradation.
The persistence of dicamba was investigated under field conditions at three locations using small plots. Applications equivalent to 1·1 kg/ha were made in October 1971 for analysis in May 1972, and in May 1972 for analysis in August 1972. At both sampling dates no dicamha residues were detected in any of the treatments at the 0–5, 5–10 or 10–15 cm soil levels.
Degradation du dicamba dans les sots de prairies     

Behaviour and persistence of trifluralin in soil

The growth response of sorghum to trifluralin, on various soils and soil mixtures, was significantly correlated with organic matter (ranging from <0–1% to 20–4%) but not with clay content (ranging from 3% to 63%). However, in soils with a similar, low organic matter content, the activity of trifluralin increased with increasing clay content. No correlation was found between phytotoxicity of trifluralin and lime content of soils. The persistence of trifluralin incorporated in soil was examined by repeated reseedings of sorghum. Phytotoxicity lasted longer in soil dried and mixed at each interval between seedings than in soil left undisturbed; after 2 months about 50% of the original 4 ppm trifluralin remained in undisturbed soil vs 60 % in repeatedly mixed soil. The rate of degradation, after 2 months of incubation at 50% field capacity, increased with temperatures from 10°to40° the concentration of trifluralin required for a given growth reduction was approximately eight times greater after incubation at 40° than at 10°C. Comportement et persistattce de la trifluraline dans le sol Les effets de Ia trifluraline sur la croissance du sorgho cultivé dans divers sols ou mélanges de sol se sont révlés être en corrélation significative avec la matiere organique (entre < 0,1 % et 20,4 %) mais pas avec la teneur en argile (de 3 % A 63 %). Toutefois dans les sols contenant un taux analogue et faible de matiére organique, l'activité de la trifluraline s'est accrue en même temps que Ia leneur en argile. Aucune corrélation n'a été constatée entre la phytotoxicité de la trifluraline et la teneur en calcaire des sols. La persistance de la trifluraline incorporée dans le sol a été examinée au moyen de ressemis répétés de sorgho. La phytotoxicité dura plus longtemps dans le sol séché et remuéà chaque intervalle entre les semis que dans le sol non travaillé; au bout de 2 mois, 50% environ des 4 ppm de trifluraline apportés à. I'origine restaient dans le sol non remué contre 60% dans le sol plusieurs fois remué. Le taux de degradation, aprés deux mois d'inciibation à 50% de la capacityé au champ, augmenta avec la température de 10°à 40°C; la concentration de trifturaline nécessaire pour obtenir une réduction de croissance donnée fut approximativement huit fois plus grande aprés incubation. à 40° qu'aprés incubation à 10°C. Verhalten und Perststenz von Trifluralin im Boden Die Wachstumsreaktion von Hirse gegenubcr Trifluralin in verschiedenen Böden und Bodenmischungen war signifikant mit dem Gehalt an organischer Substanz (<0–1 %–20–4%) korreliert, nicht aber mit dem Tongehalt (von 3%-63%). Jedoch nahm in Böden mit annähernd gleich niedrigen Gehalten an organischer Substanz die Wirksamkeit von Trifluralin mit steigendeni Tongehalt zu. Zwischen der Phytotoxizität von Trifluralin und dem Kalkgehalt der Böden wurde keine Korrelation gefunden. Die Persistenz von in den Boden eingearbeitetem Trifluralin wurde durch wiederholte Einsaat von Hirse untersucht. Die Phytotoxizität dauerte im Boden, der jeweils zwischen den Einsaaten getrocknet und gemischt worden war, langer an als im nicht derartig behandelten Boden. Nach 2 Monaten waren im letzteren Boden ungefähr 50% der ursprüinglichen 4 ppm Trifluralin verblicben gegenüber 60% im wiederholt durchmischten Boden. Nach 2 Monatlen Inkubation bei 50% Feldkapazität stieg die Abbaurate, wenn die Temperatur von 10° auf 40°C stieg; die für eine gegebene Wachstumsreduktion benötigte Trifluralinkonzentration war bei 40° annShernd achtfach grösser als bei 10°C.     

STUDIES ON THE DEGRADATION OF 4-AMINO-3,5,6-TRICHLOROPlCOLINIC ACID IN SOIL

Summary. Picloram was incubated at concentrations of 0, 0·25, 0·5 and 1 ppmw in Regina heavy clay topsoil maintained at moisture-holding capacity and a t 25° C The herbicide was quantitatively bioassayed at regular intervals. There was a lag period prior to degradation at all concentrations. The duration of the lag period increased as the concentration of picloram in the soil was increased. Al the end of each lag period, the degradation of picloram occurred as a first-order reaction, i.e. the rate of degradation was independent of the concentration of picloram in the soil. Due to the pronounced variations in the duration of the lag periods with concentration, the assignment of half-value or half-life periods to picloram degradation in soil is considered to be of doubtful significance.
Etude de la degradation de t'acide 4-amino-3,5,6-trichloropicolmique dans le sol     

UNTERSUCHUNGEN ZUR BIOLOGIE UND ÖKOLOGIE DER HÜHNER-HIRSE ECHWOCHLOA CRUS-GALLI L. BEAUV.

Summary. 1. Echinochloa crus-galli is a typical grass weed of root crops in warmer regions, germinating late and thus covering the soil at a late stage. It originates in central and east Asia and is now a weed of world-wide importance.
2. High temperatures are necessary for germination which begins in spring, but not before the soil temperature reaches 15° C. Minimum, optimum and maximum germination temperatures of 13° C, 20–30° C and 40° C were found in S.W. Germany.
3. Seeds of E. crus-galli are dormant during the first 3–4 months after harvest. Those developing relatively early in the growing season require rather longer for after-ripening than seeds which mature later.
4. For optimum germination, water saturation of the soil of 70–90% is required.
5. Soil acidity has some influence, and there is an apparent germination optimum around neutrality. Light also induces germination.
6. Seeds can emerge from a relatively wide range of depths. Greatest emergence and the strongest plants resulted from seeds at 2–6 cm, but even from 10 cm a high percentage of seedlings is likely to emerge.
7. Further development proceeds rapidly. The first panicles arc already formed 6–7 weeks after emergence in favourable conditions, but full maturity is possible only if there are high temperatures in late summer.
8. E. crus-galli is a hygrophilous species, with best development on medium heavy soil, sandy loam or loamy sand with sufficient water supply.
9. E. crus-galli is indifferent to the lime content of the soil.
10. Best development occurs with high fertility, and a rich supply of nitrogen is especially important.
Recherches sur la biologie et écologie du panic Echinochloa crus-galli (L.) Beauv.     

Solarization of soil in piles for the control of Meloidogyne incognita in olive nurseries in southern Spain

The potential of solarization to control Meloidogyne incognita in piles of soil used at olive nurseries in southern Spain was studied in 1999 and 2000. Kaolin and soil infested with free eggs and egg masses of the nematode in nylon bags were buried 20 and 40 cm deep inside conical piles of soil 80 cm high and with a base diameter of 1 m. Soil piles were solarized for 3 weeks in July and August. The effect of various periods of solarization was assessed by egg hatch bioassays in sterile water, and by infectivity to tomato plants. Maximum soil temperature at 20 cm depth in solarized piles was 47·4°C in 1999 and 48·2°C in 2000, compared with 32·9°C and 31·7°C in nonsolarized piles. Solarization reduced egg hatch by > 95% compared with nonsolarized samples, irrespective of type, burial depth and location of inocula in a soil pile. Egg hatch of egg mass-infested samples buried at 20 cm depth was higher than that of free eggs buried at the same depth. The differential effect associated with burial depth and type of inoculum was not found in solarized piles. In nonsolarized piles, hatch of free eggs from samples buried at 40 cm depth was higher than that from samples buried at 20 cm depth. Egg hatch in samples from solarized piles was lower than that from nonsolarized piles. A bioassay of tomato plants in 2000 confirmed the reduction in infectivity of free eggs buried in solarized soil piles. Under the conditions in southern Spain, solarization of 40 cm-high piles of soil for 3 weeks can therefore be used for the control of root-knot nematodes in potting soil for olive nursery production.     

The relative movement and persistence in soil of chlorsulfuron, metsulfuron-methyl and triasulfuron

Summary. Adsorption and degradation rates of triasulfuron in 8 different soils were negatively correlated with soil pH and were generally lower in subsoils than in soils from the plough layer. The half-life at 20°C varied from 33 days in a top soil at pH 5·8 to 120 days in a subsoil at pH 7·4. Adsorption distribution coefficients in these two soils were 0·55 and 0·19, respectively. Movement and persistence of residues of chlorsulfuron, triasulfuron and metsulfuron-methyl were compared in a field experiment prepared in spring 1987. Triasulfuron was less mobile in the soil than the other two compounds. Residues of all three herbicides were largely confined to the upper 40–50 cm soil 148 days after application. With an initial dose of 32 g ha⁻¹, residues in the surface soil layers were sufficient to affect growth of lettuce and sugar-beet sown approximately one year after application. Laboratory adsorption and degradation data were used with appropriate weather data in a computer model of herbicide transport in soil. The model gave good predictions of total soil residues during the first five months following application, and also predicted successfully the maximum depth of penetration of the herbicides into the soil during this period. However, more herbicide was retained close to the soil surface than was predicted by the model. The model predicted extensive movement of the herbicides in the soil during winter but did not predict that residues sufficient to affect crop growth could be present in the upper 15–20 cm soil after one year.     

Effect of soil solarization on the control of Phytophthora root rot in avocado

Phytophthora root rot is of paramount importance in avocado orchards of southern Spain. Soil solarization has been demonstrated to control the pathogen in infested areas from which infected trees had been removed. We aimed to determine whether soil solarization in established avocado orchards controls the disease. Soil solarization increased average maximum hourly soil temperatures by 6.5–6.9°C in unshaded areas of avocado orchards in coastal areas of southern Spain, depending on depth and year. The corresponding temperatures in shaded areas were c. 2–3°C lower. P. cinnamomi in soil, on infected avocado rootlets, and in a nutrient substrate buried at 30–60 cm depth was reduced to negligible amounts after 6–8 weeks of solarization in both unshaded and shaded locations of avocado orchards. P. cinnamomi could not be detected in avocado rootlets up to 14 months later, suggesting a long-term effect. Soil solarization did not affect growth of the trees, and fruit yields were increased as compared with control plots. Following soil solarization for 3 weeks from mid-July 1994, when maximum hourly temperatures reached 33–36°C, P. cinnamomi could not be recovered from a depth of up to 45 cm in unshaded areas or from a depth of up to 30 cm in shaded areas after the initial 10-day period. The viability of inoculum of the pathogen buried at depths between 15 and 60 cm in bare soil was determined by sequential sampling in two solarization experiments starting 12 June and 4 July 1995, respectively. In the first experiment, P. cinnamomi could not be detected at any depth after 4–8 weeks of solarization in unshaded areas but could be recovered at all depths except 15 cm in shaded areas. In the second experiment, where temperatures were higher and the soil surface not shaded, P. cinnamomi could not be recovered after 2 weeks at 15 and 30 cm.     

Root colonization by Phymatotrichum omnivorum and symptom expression of Phymatotrichum root rot in cotton in relation to planting date, soil temperature and soil water potential

Cotton was grown in containers of soil with sclerotia of Phymatotrichum omnivorum. Plants were grown for 3 weeks in the greenhouse and then transferred to field plots. Foliar and stem symptoms of Phymatotrichum root rot occurred 15–50 days after field placement. Mean incubation periods (defined as time from field placement to symptoms) were about 24 days for placements made in June and July and about 35 days for placements made in August and September 1984. Colonization of roots was more advanced in the top 24 cm of soil. The time taken for symptoms to appear was not related to the amount of root colonization at the time plants were transferred to the field. In the later two planting dates a drop in soil water potential to approximately −25 bars after 20–24 days was associated with the delay in symptom expression. There were significant linear relationships between the length of the incubation period (days), or its inverse (day⁻¹), and the independent variables: mean maximum daily temperature (°C) in the top 12 cm layer of soil, soil water potential in the 31–60 cm layer of soil and their product (representing the interaction of these two variables). In general, symptom expression was faster at higher temperatures and with wetter conditions. Newly-formed sclerotia were found most frequently in containers some 5–6 weeks after plant death when soil temperatures had decreased and soils were close to saturation (September and October).     

THE PERSISTENCE AND PENETRATION OF LARGE DOSES OF SIMAZINE IN UNCROPPED SOIL

Summary. The residues remaining in the soil from repeated annual application of simazine at 2–8, 5–6, and 22–4 kg/ha to uncropped plots on a loam soil were measured by chemical or bioassay methods at various intervals after treatment.
The total simazine residue present 12 months after the last of three treatments with 2–8 kg/ha and 8 months after the last of five treatments with 5–6 kg/ha was less than 10% of the annual dose. This rapid decomposition is considered consistent with the soil and climatic conditions. In contrast a much larger residue (a mean value of 1·7 kg/ha) was found on plots sampled 21/2 years after the last of two annual applications of simazine at 22·4 kg/ha and the reduction in the amount of residue during the next 12 months was only of the order of 25%.
In all treatments the highest concentration of simazine was found in the surface layers of the soil but measurable residues were detected to 60 cm depth, 31/2 years after the last 22·4 kg/ha application.
There was considerable variation in the total residues recovered between replicate plots and between different positions on the same plots in all treatments regardless of the depth of the sample. The possible causes of this variation are discussed.
Persistance et pénétration de fortes doses de simazine dans un sol non cultivé     

Solarization and natural heating of irrigated soil amended with cruciferous residues for improved control of Macrophomina phaseolina

The efficacy of summer irrigation and soil solarization combined with cruciferous residues was tested against the dry root rot pathogen Macrophomina phaseolina in an arid climate. In irrigated amended soil, polyethylene mulching during May increased the soil temperature to 57°C and 50°C at depths of 0–15 and 16–30 cm, respectively. As a result, within l5 days the population of M. phaseolina was almost eradicated (93–99%) at both soil depths. A considerable reduction (75–96%) was also achieved by natural heating of irrigated soil (46–53°C) for l5 days after amending with cruciferous residues. Mulching alone was only partially effective (69–89% reduction). These results suggest a new approach to controlling soil-borne pathogens in hot, arid regions by combining summer irrigation with soil amendment. Amendment with residues alone or in conjunction with soil solarization also increased the population of lytic bacteria against M. phaseolina .     

EFFECT OF TEMPERATURE ON THE ACTIVITY AND PERSISTENCE OF AMITROLE AND 2,4-D

Summary. One leaf of each of several tomato plants 5–6 weeks old maintained at 55, 70 or 85° F was dipped in 0.05 M amitrole or 0.005 M 2,4-D solution. The treated leaf was removed 1 week later. Scions taken from untreated plants were grafted to the treated plants at intervals up to 4 months after treatment.
Amitrole-treated plants maintained at 55° F were killed within 1 month but those at 70 and 85° F recovered.
Plants treated with 2,4-D showed typical symptoms when maintained at 70 and 85° F but no symptoms at 55° F. Scions grafted on plants maintained at 55, 70 and 85° F for 60 days after 2,4-D treatments exhibited typical symptoms. Grafts made more than 60 days following the 2,4-D application did not exhibit symptoms except a slight malformation on the plants held at 55° F.
New growth on the scions grafted up to 103 days after amitrole treatment on plants which had been maintained at 70 and 85° F exhibited typical amitrole symptoms (i.e. white foliage) but scions grafted after this lime did not. New shoots developing from buds on the treated plants also produced green growth 115 days after treatment but produced white foliage prior to that time.
Effet de la température sur l'activi'ité et la persistance de l'aminotriazole et du 2,4-D     

SOME PHYSICO-CHEMICAL INTERACTIONS OF PARAQUAT WITH SOIL ORGANIC MATERIALS AND MODEL COMPOUNDS I. EFFECTS OF TEMPERATURE, TIME AND ADSORBATE DEGRADATION ON ARAQUAT ADSORPTION

Summary. Some investigations were carried out on the adsorption of paraquat by a range of organic materials which included an organic soil, various humic fractions from that soil, model polymers prepared by the oxidative coupling of benzoquinone, the ion exchange resins Zeo-Karb 216 and 226, and Amberlite XAD-2. The time required for the adsorption process to reach equilibrium ranged from about 3 h (for the soil and humic preparations) to about 48 h (for the more highly cross-linked materials). Adsorption by Amberlite XAD-2, a cross-linked polystyrene resin, was very small, presumably because it lacked ion-exchange sites.
The results suggested that particle diffusion control was operating and the different equilibrium times reflected different degrees of molecular complexity within the adsorbents.
Temperature, within the 20°–70°C range, did not affect the adsorption equilibrium, and this is indirect evidence for ion exchange as the primary adsorption mechanism. No evidence was found for decomposition of paraquat in the adsorption systems studied.
Quelques interactions physico-chimiques du paraquat avec des inatéaux de sol organique et des composes modéles I. Effets de la température, du temps et de la dégradation sur I'adsorption du paraquat     

GRASS CONTROL IN NEWLY-SOWN LEGUMES WITH TRIFLURALIN AND CARBETAMIDE

Summary. Two trials comparing grass control by trifluralin and carbetamide in autumn-sown legumes ( Trifolium subterraneum L., T. pratense L., T. repens L., T. dubium L. and Lotus pedunculatus Cav.) were conducted. Trifluralin was used pre-sowing and carbetamide both pre-sowing and post-emergence.
Both herbicides gave good control of Lolium perenne L. and Poa annua L. at rates of 0·5 and 1·0 kg/ha a.i. for trifluralin and carbetamide respectively. Carbetamide showed no toxicity to any of the legumes up to 2·0 kg/ha except for Lotus pedunculatus at that rate, whereas trifluralin was toxic to all species at 2·0 kg/ha. Neither herbicide controlled broad-leaved weeds.
The results are discussed in terms of the effects of soil fertility, plant age and maturity on the activity of these herbicides.
La lutte contre les graminées adventices avec la trifluraline et le carbétamide dans les légumineuses récemment semées     

Factors affecting the incidence and severity of Spongospora subterranea infection and galling in potato roots

The incidence and severity of root infection and root galling caused by Spongospora subterranea were assessed in potato plants (cv. Estima) grown under controlled environmental conditions. The effects of temperature, soil type, soil moisture regime and soil inoculum level on infection and root gall development were determined by molecular and visual methods at two plant growth stages. Root gall severity was scored at harvest, after which DNA was extracted from the roots and quantified in a real-time polymerase chain reaction (PCR) assay specific for S. subterranea . Root galling was severe at 17°C, with a disease score of 3·1 on a 0–4 scale, low (0·6) at 12°C, and did not occur at 9°C. The level of inoculum in soil, in the form of artificially added sporosori, had no effect on the incidence and severity of visual symptoms, with 21%, 41% and 33% incidence observed at 5, 15 and 50 sporosori g⁻¹ soil, respectively. Incidence of infection, as detected by the real-time PCR assay, was greater with increasing soil inoculum concentrations, ranging from 48% at 5 sporosori g⁻¹ to 59% (15 sporosori g⁻¹) and 73% (50 sporosori g⁻¹) of plants infected at maturity, but this effect was not statistically significant. No correlation was found between the occurrence of galls on roots and powdery scab on tubers of the same plants.     

Effect of temperature on latent period of septoria leaf blotch on winter wheat under outdoor conditions

Batches of two winter wheat cultivars (Riband and Apollo) were inoculated with conidia of Mycosphaerella graminicola at weekly intervals over a 2 year period. Following 72 h incubation, plants were placed in ambient temperatures ranging between −7 and 32°C with mean batch temperatures of 2·9–20·2°C. Latent period until the first visible symptoms ranged between 11 and 42 days. The relationship between development of lesions and accumulated thermal time was described using a shifted cumulative gamma distribution model. The model provided good estimates of lesion development with r ² > 0·92 for both cultivars. Base temperatures, below which the pathogen did not develop, were estimated from the model as approximately −2·4°C for the two cultivars. Latent period was estimated as being 250 and 301 degree-days above the estimated base temperature, when defined as time from inoculation to first lesion and time to 50% of maximal lesions, respectively, for cv. Riband. The values for cv. Apollo were similar, but with estimates of thermal time periods c . 5% higher. The relationship between mean temperature and inverse latent period, expressed as days either to first lesion or to 50% of maximal lesions, was best described by a linear regression with r ² > 0·96 for both cultivars. The opportunity for plants to outgrow disease was reduced when prolonged periods of cold temperature occurred, because the base temperature for growth of the pathogen was less than that for the crop.     

Laboratory studies on the growth and reproduction of Cladosporium allii-cepae, the cause of leaf blotch of onion

Cladosporium allii-cepae is a slow-growing pathogen of onion which, on malt extract agar, had a mean colony diameter of 2.7 cm after 28 days at 16°C. Growth and reproduction were greatest on malt onion leaf agar and were poor on synthetic media. The optimum and maximum temperatures for growth were 20 and 28°C, respectively. Sporulation was most abundant at 10–15°C. The fungus grew poorly in buffered Czapek Dox medium at pH 2.2–7.8 and most growth was recorded at pH 6.5. Sporulation was enhanced by exposure of colonies to near ultraviolet light.
A large proportion of spores germinated in distilled water and at 100% r.h. In distilled water germination was greatest at 15–20° and in air at 100% r.h. at 20°C. Of 10 fungicides tested, fentin hydroxide, fentin acetate/maneb and iprodione were the most effective in inhibiting spore germination, growth and reproduction of the fungus.     

Effect of soil temperature on disease development in melon plants infected by Monosporascus cannonballus

The effect of soil temperature on melon collapse induced by Monosporascus cannonballus was studied in the laboratory and in the field. In the laboratory, ascospore germination and hyphal penetration into melon roots were enhanced by increasing the temperature from 20 to 32°C. The optimum temperature for mycelial growth of five isolates of M. cannonballus was 30°C. In the field, the effect of temperature was studied in experiments conducted during the winter and autumn cropping seasons from 1995 to 1998. Disease progress was much faster in the autumn than in the winter crop seasons. Disease incidence reached 100% in the three consecutive autumn seasons studied. In the winter seasons, however, planting date influenced disease incidence. Early planting, at the beginning of January, resulted in a low disease incidence (6–26%, 125 days after planting), whereas planting at the end of January resulted in higher disease incidence (72–88%, 95–119 days after planting). In plots in which the soil was artificially heated to 35°C during the winter season, disease incidence reached 85%, as in the autumn season. Plants grown during the winter in unheated soil, or in artificially heated soil disinfected with methyl bromide, did not collapse. Root colonization by the pathogen was higher in the autumn and in heated soil than in the winter season in nonheated soil. Fifty per cent of root segments were colonized 35, 42 and 67 days after planting in the winter-heated, autumn and winter-unheated plots, respectively. A high correlation was found between soil temperatures above 20°C during the first 30 days after planting and disease severity. It is suggested that soil temperature during the early stages of plant development is an important factor in disease development and the expression of melon collapse caused by M. cannonballus.     

Soil-incorporated trifluralin protects cotton (Gossypium hirsutum) from root-absorbed herbicides

Mechanical incorporation of a tank mixture of trifluralin in combination with fluometuron, diuron or prometryne in the soil to a depth of 10 cm protected emerging cotton from the damage caused by these herbicides in the absence of trifluralin. The incorporated tank mixtures, which were activated by sprinkler irrigation, controlled weeds which were tolerant to trifluralin alone. The different reaction of weeds and cotton to the soil-incorporated herbicide mixtures corresponded to the reaction of their root systems to trifluralin. Weeds whose root system was shortened significantly by trifluralin were sensitive to the tank-mixed, soil-incorporated herbicides. La trifluraline incorporée au sol protége le coton (Gossypium hirsutum) des herbicides à absorption racinaire L'incorporation mécanique de mélanges de trifluraline avec du fluométuron, du diuron ou de la prométryne, à des profondeurs de sol 10 cm, protégeait le coton au moment de la levée contre les dommages occasionnés par ces herbicides en l'absence de trifluraline. Les mélanges incorporés, quiétaient activés par irrigation par aspersion, détruisaient les mauvaises herbes qui étaient tolérantes à la trifluraline seule. La réaction différente des mauvaises herbes et du coton aux mélanges d'herbicides incorporés correspondait à la réaction de leur système racinaire à la trifluraline. Les mauvaises herbes dont le systéme racinaire était raccourci par la trifluraline étaient sensibles aux mélanges d'herbicides incorporés. Schutz der Baumwolle (Gossypium hirsutum) vor wurzelabsorbierten Herbiziden durch eingearbeitetes Trifluralin Nach Einarbeitung von Tankmischungen von Trifluralin mit Fluometuron, Diuron oder Prometryn bis in 10 cm Bodentiefe blieben Baumwoll-Keimpflanzen von den sonst von diesen 3 letzgenannten Herbiziden verursachten Schaden frei, Mittels der Tankmischungen ließen sich gegenuber Trifluralin allein unempfindliche Unkrauter bekampfen. Die unterschiedliche Reaktion der Unkrauter und der Baumwolle auf die eingearbeiteten Herbizidmischungen entsprachen der Reaktion ihrer Wurzeln auf Trifluralin. Soweit die Entwicklung von Unkrautwurzeln durch Trifluralin signifikant gehemmt wurde, waren diese Arten gegenuber den eingearbeitenen Tankmischungen empfindlich.