Experiments were conducted to examine the effects of low soil moisture on yellow nutsedge emergence in relation to thermal and chronological time and test the ability of thermal models generated previously to predict emergence under water stress. Unsprouted tubers from California and Arizona were planted in pots, buried at field sites in California and Arizona, and subjected to wet or dry treatments. Pots were monitored weekly to determine date of emergence and number of emerged shoots. The California genotype emerged 47 to 61 days after planting (DAP) in the dry treatment and 33 to 49 DAP in the wet treatment, depending on planting site. The range for the Arizona genotype was 51 to 76 DAP in the dry treatment and 43 to 61 DAP in the wet treatment. Days and degree-day intervals to first emergence differed between irrigation treatments and planting sites but interactions were not significant. All models were accurate in predicting emergence dates for genotypes in the wet treatment at the California site, while emergence in Arizona was underestimated by 9 d. Tubers subjected to the dry treatment needed a higher number of accumulated degree-day units before emergence occurred and had fewer emerged shoots as compared to the wet treatment. Degree-day models generated for yellow nutsedge under optimal conditions lack sufficient robustness to be predictive under water stress conditions.

Experiments were conducted to determine the influences of temperature, light, winter storage, and water stress on seed germination of fringed sage. Seeds collected in 3 yr in central Saskatchewan were placed in sealed vials and buried in the soil after harvest, and germination was tested in spring and early summer. Seeds germinated over a wide range of temperatures with alternating 25/15 C being optimal. The range of optimal temperatures was higher for older seeds than younger seeds. The stimulating effect of light on germination varied among collections and incubating temperatures. Total germination and germination rate was limited by water stress and no seeds germinated at osmotic potentials below −0.9 MPa. Seeds hydrated in the autumn and exposed to low winter temperatures had higher germination the following spring than dry seeds exposed to the same conditions. Results suggest that sufficient soil moisture combined with moderate seedbed temperatures are optimal for fringed sage germination. Periodicity of germination may be influenced by variable germination requirements in different aging seeds.

Field experiments were conducted in 2000 and 2001 near Painter, VA, to evaluate the potential of sulfentrazone for use in potato. Sulfentrazone was applied at 0.11, 0.14, 0.21, and 0.28 kg ai/ha preemergence (PRE) alone or in combination with metolachlor or metribuzin, or at emergence (AT EMERG) of potato to simulate a delayed PRE application where the herbicide would come into contact with potato foliage. Potato injury from sulfentrazone PRE at rates of up to 0.21 kg/ha was generally similar to injury from metribuzin, metolachlor, or metribuzin plus metolachlor PRE. However, AT EMERG applications resulted in excessive injury that ranged from 60 to 86%. AT EMERG applications also caused decreased potato height and alterations in potato-flowering patterns. Sulfentrazone at either application timing controlled common lambsquarters at least 98% even at the lowest rates and was more effective than metribuzin or metolachlor alone. Higher rates of sulfentrazone (0.28 kg/ha) also controlled goosegrass and large crabgrass. However, sulfentrazone at 0.28 kg/ha controlled common ragweed only 58%. Total potato yield and grade with sulfentrazone PRE applications were similar to those of potato treated with metribuzin, metolachlor, or metribuzin plus metolachlor in both years. Potato injury from AT EMERG applications of sulfentrazone plus metolachlor decreased total potato yield and caused changes in the grade distribution of B-size, small A–size, and extra-large potato in 2000.

Studies were conducted to calibrate and validate a mathematical model previously developed to predict common lambsquarters seedling emergence at different corn seedbed preparation times. The model was calibrated for different types of soil by adjusting the base temperature of common lambsquarters seedling emergence to the soil texture. A relationship was established with the sand mineral fraction of the soil and was integrated into the model. The calibrated model provided a good fit of the field data and was accurate in predicting cumulative weed emergence in different soil types. The validation was done using data collected independently at a site located 80 km from the original experimental area. There were no differences between observed and predicted values. The accuracy of the model is very satisfactory because the emergence of common lambsquarters populations was accurately predicted at the 95% probability level. This model is one of the first to take into consideration seedbed preparation time and soil texture. This common lambsquarters emergence model could be adapted to model other weed species whose emergence is limited by low spring temperature.

Velvetleaf has been a major concern of Southern cotton growers, yet information on its competitiveness and seed production in cotton is lacking. Experiments were conducted in 1997 and 1998 at the Central Crops Research Station in Clayton, NC, to evaluate density-dependent effects of velvetleaf interference and seed production dynamics in conventional tillage cotton. Velvetleaf at densities of up to 3.5 plants m−1 of row did not influence cotton height until at least 4 wk after planting. Velvetleaf height increased as plant density increased throughout the season in 1997, but it was not affected until 9 wk after planting in 1998. Because of differences in environmental conditions, velvetleaf and cotton achieved maximum height later in 1998 than in 1997; however, velvetleaf seed production and cotton yields were higher in 1998 than in 1997 regardless of velvetleaf density. Velvetleaf density had no effect on the fresh weight, dry weight, and stem diameter of velvetleaf plants in 1997. But in 1998, all these parameters decreased significantly with increasing velvetleaf density. Velvetleaf seed production in 1998 was nearly twice that in 1997. Averaged over velvetleaf densities, the greatest number of seed were produced between nodes 6 and 20 in 1997 and between nodes 1 and 10 in 1998. In both years, cotton yield loss increased with velvetleaf density. Maximum yield loss was 84% at 3.5 velvetleaf plants m−1 of row. Yield losses of 5 and 10% were caused by 0.2 and 0.4 velvetleaf plants m−1 of row (1,930 and 4,110 plants ha−1), respectively, in 1997 and by 0.03 and 0.08 velvetleaf plants m−1 of row (360 and 850 plants ha−1), respectively, in 1998. To understand better the applicability of these results, we hypothesized that environmental variation caused differences in measured responses between 1997 and 1998. Therefore, kriging methods were used to fit correlations between observed rainfall and growing degree days (GDD) each year at the experiment site. Results based on climate data from 4 yr at 110 sites indicated that inference space was higher for GDD than for rainfall. The conditions observed at the experiment site in 1997 were deemed most appropriate for the recommendations made in the surrounding area.

Weeds of the genus Orobanche parasitize many dicotyledonous species, causing severe damage to vegetable and field crops worldwide. In Oregon, the number of red clover fields contaminated with small broomrape has increased in recent years. Small broomrape parasitism in red clover is temperature related. In this study, the temperature-dependent relationship was developed into a predictive model based on growing degree-days (GDD) for small broomrape parasitism in red clover. The model was developed in greenhouse studies and validated in the field during three growing seasons. A strong relationship between GDD and parasite size allowed for the creation of a simple predictive model for tubercle number based on GDD. The proposed model is based on a temperature range realistic to western Oregon climatic conditions and predicts lag, log, and maximum phases for four parasitism sizes in relation to GDD. Small broomrape parasitism in red clover began at about 400 GDD, but red clover biomass accumulation was not affected by parasitism before 1,200 GDD. Small broomrape flower stalk emergence began at about 1,100 GDD. Field studies validated that GDD could be a predictive parameter for small broomrape parasitism and could be used to time detection surveys and herbicide applications.

Determination of critical threshold for induction and termination of diapause (hibernation) are important for better understanding the bio-ecology and population dynamics of Chilo partellus (Swinhoe) under varying climatic conditions. We studied initiation and termination of hibernation under five temperature and photoperiod regimes viz., 27°C + 12L:12D, 22°C + 11.5L:12.5D, 18°C + 11L:13D, 14°C + 10.5L:13.5D and 10°C + 10L:14D under fixed and ramping treatments, and the observations were recorded on various phenological and developmental characteristics at weekly intervals. Present studies revealed that the induction of hibernation in C. partellus larvae takes from 46 to 56 days depending upon temperature and photoperiod conditions. Induction of hibernation varied from 7.9 to 18.3% across treatment conditions, indicating that not all C. partellus larvae undergo diapause under prevailing environmental conditions. Weight, length and head capsule width of diapausing larvae were found significantly lower than the non-diapausing larvae. The non-diapausing C. partellus larvae required a thermal threshold of 1068 degree-days under ambient conditions, while in case of hibernating larvae it varied significantly across treatment conditions. Diapausing larvae underwent up to five supernumerary moults, wherein highest percentage of diapausing larvae (35.7%) exhibited two supernumerary moults. The developmental time of diapausing larvae varied from 94.9 to 160.4 days across treatments. A population loss of 17.2–28.3% was recorded in C. partellus due to hibernation, which has implications for population buildup of post-hibernation first brood and management strategies.

The effect of temperature on the reproduction and development of Busseola fusca was studied under laboratory conditions. Single male–female pairs were confined to oviposition chambers kept at 15, 20, 26 and 30 ± 1°C and a 14L:10D photoperiod. Data on reproduction parameters were captured daily. Oviposition occurred at all the mentioned temperatures but no fertility was recorded at 30°C. The total number of eggs laid per female moth was between 300 and 400 and the optimum temperature for oviposition and fertility was between 20 and 26°C. Larval development was studied at five different temperature regimes, i.e. 15, 18, 20, 26 and 30 ± 1°C and a 14L:10D photoperiod. The most favourable temperature as well as the upper threshold temperature for larval development was between 26 and 30°C. Total development period was 152.6–52.6 days, respectively, at 15°C, and 26–30°C. The thermal constants for B. fusca was 99.50, 536.48, 246.25 and 893.66°D and lower temperature thresholds were 10.36, 8.14, 8.99 and 8.84°C, for completion of the egg, larval, pupal and egg-to-adult stages, respectively. Results on the thermal constants and lower and upper threshold temperatures of B. fusca can be used to predict the impact of climate change on the distribution and population growth of this pest.

The biology of the immature stages and adult eclosion of Ufens principalis Owen, an important parasitoid of Homalodisca eggs in southern California, were studied. The duration of the egg, larval and pupal stages at 26.7°C were 0–1, 7 and 9 days, respectively. Sacciform larvae, which developed gregariously within host eggs, were motile until about five days of age, and then became sessile. Parasitized host eggs changed from whitish and soft when freshly-laid to yellow-orange and hard at five days and older. This change was accompanied by formation of septal walls separating the mature larvae and pupae. The rate of immature development had a strong positive linear relationship (R2=0.853, n=98) with temperatures in the range of 20.0–30.3°C. The theoretical minimum threshold for immature development was 13.5°C, and the required heat units were 241.0 degree-days. Adult eclosion from host eggs occurred mostly (85%) on the first two days of emergence. Although most females emerged during the morning hours (0600–1200 h), males tended to emerge earlier than females with equal emergence during the morning and late night hours (2400–0600 h). The rate of successful adult emergence was high (88%). The ratio of eclosed adults to the number of exit holes was 1.18, indicating that most adults tended to independently cut their exit holes. The number of exit holes had a strong negative relationship (R2=0.711, n=125) with exit hole size, suggesting that larger numbers of developing immatures per host egg result in an overall decrease in adult size.

Acanthoplus speiseri Brancsik, a pest of grain crops in Zambia, was reared in the laboratory at different temperatures. Mean development times of the eggs, nymphs and adults were determined at the different temperatures and used to develop a thermal unit model for use by farmers to predict the appearance dates of the different nymphal instars and the adults in the field in a given season. The predictions generated by the developed model for the 1990/1991 season, were compared to the actual dates on which the first specimen of each developmental stage was collected in the field during the season. The predicted dates of appearance all fell within 1 week of the observed dates of collection. Reasons for the slight deviations between the predicted and observed dates and the significance of the developed thermal unit model to the future control of A. speiseri in Zambia, are discussed.

Pheromone traps were used for monitoring flight activity of peach twig borer, Anarsia lineatella (Zeller), during a 3 year period between 1983–1985 in Iraq at Tarmiya and Madain regions, and cumulative emergence was related to physiological time (degree-days, DDs). Data of moth catches indicated the presence of two generations per year and perhaps a partial third generation. Flight in both regions peaked from April to mid-May and from early June to mid-June. First capture of peach twig male ranged from 16 to 29 March and corresponded to a mean DD accumulation from 1 March of 138 in Tarmiya and 127 in Madain. Such results are very important for managing this pest.