Graduation date: 1995

This study evaluated the effects of tillage system, rotational tillage sequences, and winter seed burial depth on weed seedling recruitment in irrigated cropping systems. Notill (NT) planting of vegetable crops reduced emergence of hairy nightshade by 77 to 99% and Powell amaranth emergence from 50 to 87% compared to conventional tillage (CT) and planting of crops. Cover crops suppressed weed emergence if soils were undisturbed but not if soils were tilled in the spring. Four years of NT vegetable crops reduced summer annual weed density by 48 to 79% at two sites. Rotational tillage sequences that alternated between NT and CT only reduced summer annual weed density if the shorter season crop of snap beans was paired with CT and sweet corn was paired with NT. Hairy nightshade density decreased by 83 to 90% if NT was paired with the longer season crop of sweet corn. Hairy nightshade seedling recruitment at 30.7 C was more than 15 times greater for seeds buried at 6, 13 and 25 cm than when buried at 1 cm in simulated NT. Recruitment potential was low in March and April but increased to a maximum in May and June. Germination rates for seeds buried at 1 cm were lower and mortality and dormancy greater than for seeds buried from 6 to 25 cm during the winter. Protecting the seeds buried at 1 cm from rainfall during the winter increased seedling recruitment from 0 to 2 of 10 buried seeds, but had a negligible effect on seed mortality and dormancy. Treatment of seeds buried at 25 cm with 1 cm soil temperature reduced recruitment from 4.8 to 2.3 of 10 buried seeds at 33.3 C, but did not significantly increase seed mortality or dormancy. Estimates of seed drift using electronic transponders found that 16% of the seeds at 5 cm moved to within the emergence zone for hairy nightshade. Seed drift coupled with the faster germination rate and lower mortality of seeds buried at 12 cm or below predicts that hairy nightshade recruitment will be optimized when soil is tilled in the spring. / Graduation date: 2005

No description available.

Three isolates of Curvularia belonging to Curvularia tuberculata (isolates 93-020 and 93-022) and Curvularia oryzae (isolate 93-061) were obtained from diseased Cyperus difformis, Cyperus iria, and Fimbristylis miliacea, respectively, in the Philippines in 1993. Under greenhouse conditions, these fungal isolates caused high mortality and significant plant dry weight reduction in C. difformis, C. iria, and F. miliacea when sprayed at the rate of 1 x 108 spores/m3. Cross-pathogenicity of the isolates was demonstrated in three other sedge weed species. C. difformis, C. iria, and F. miliacea were killed but C. rotundus was resistant. Most of the thirteen rice varieties tested were resistant to the fungal isolates. The order of decreasing pathogenicity to rice was C. oryzae (93-061), C. tuberculata (93-020), and C. tuberculata (93-022). The infection process of C. tuberculata and C. oryzae was similar. Spore germination was polar for C. tuberculata and bipolar for C. oryzae. Germ tube growth was random and branching. Appressoria were formed preferentially over epidermal cell wall junctions on sedge hosts and over stomatal apertures in rice. Complex infection cushions were observed only on sedge hosts. Infection hyphae developed inter- and intracellularly, causing epidermal cell walls to separate and mesophyll cells to shrink and collapse. The vascular bundles were not invaded. Colonization of susceptible weeds was rapid and conidiophores emerged from the stomatal aperture between 96 to 120 hours post inoculation (HPI). Resistance to C. tuberculata and C. oryzae in C. rotundus and rice was expressed as a delay in appressorial formation, inhibition of fungal growth after penetration, and lack of sporulation.

No description available.

The carrot weevil, Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae), is an insect pest in carrot production in Ontario. The aim of this study was to survey the egg parasitoids attacking the carrot weevil in carrot fields in Ontario, and elucidate the seasonal and chemical ecology of these natural enemies. / Field surveys were conducted during three years in commercial carrot fields in the Holland Marsh and district marshes to detect the presence of carrot weevil egg parasitoids, to determine their geographical distribution and to evaluate the effect of insecticides on the rate of emergence and the activity of parasitoid adults. Two egg parasitoids, Anaphes listronoti Huber and A. victus Huber were found. The dominant species Anaphes listronoti is gregarious, was recovered from most of the sampled fields and was distributed in all sampled marshes whereas the solitary parasitoid A. victus was only sporadically found in the Holland Marsh. These Anaphes species occurred in carrot fields from the end of April to the beginning of September and seasonal parasitism averaged 33% in commercial carrot fields and up to 79% in an untreated plot. The insecticides phosmet, diazinon and cypermethrin used in carrot production, did not affect emergence rate of parasitoid adults indicating that immature stages are protected against insecticide penetration in the host egg. However, insecticide applications decreased parasitism rates and suggest a lethal effect on parasitoid adults by direct contact and insecticide residues, although no difference was observed between treatments. / Laboratory studies were performed to determine the existence of a sexual pheromone produced by female A. listronoti using a four-arm olfactometer. An automated system of insect tracking was developed to quantify male behavior in the olfactometer. The response of males to odor emitted by virgin females less than two days of age was measured. Virgin females less than one-day-old released a long-range pheromone from 4 hours until 16 hours after the onset of the photophase. Females of one and two days of age started to emit the sexual pheromone earlier than younger females.

Amaranthus retroflexus L. (redroot pigweed) is a major weed of many crops in North America including corn, soybean, and potato. It can be readily controlled by chemical and cultural methods. However, some populations of A. retroflexus have developed resistance against the application of triazine herbicides. Biololical control could be an alternative method to control this weed species. In 1990, a Macrophoma sp. causing foliar lesions was isolated from redroot pigweed and the potential of this plant pathogenic fungus as a mycoherbicide was evaluated. Large numbers of infective propagules were produced in solid substrate fermentation with chickpeas. When inoculated with 10$ sp8$ or 10$ sp9$ conidia m$ sp{-2}$, plants at the cotyledon to 2-leaf stage showed the most severe damage. Disease developed over a wide range of dew period durations (6 hr to 24 hr) and temperature regimes (14 C to 26 C), and the most rapid and destructive disease development occurred following a 24-hr dew period at 18 C. In controlled environment studies, this Macrophoma sp. was pathogenic to the genus Amaranthus and the closely related genus Celosia.

In a survey conducted in Zimbabwe in 1993, waterhyacinth was present in seven out of the eight provinces. No control measures were imposed on 35% of the infested dams and 61% of the infested rivers, while in 47% of the infested dams and 11% of the infested rivers control of waterhyacinth was being attempted with a combination of 2,4-D and mechanical control methods. The population of Neochetina eichhorniae and N. bruchi declined during the period 1993 to 1995 in the Hunyani River system. Several fungi were isolated from diseased waterhyacinth, and Fusarium moniliforme (isolate 2ex 12), F. solani (isolates 5a ex25 and 2a3), and F. pallidoroseum (isolate 3ex1) were found to be the most pathogenic. Large numbers of viable conidia were produced in shake-flask liquid fermentation with modified Richard's medium and in solid fermentation with food grains. Conidia production in straw was poor with the exception of waterhyacinth straw. Host range studies conducted in pots and in the field indicated that Commelina benghalensis was moderately susceptible to both isolates of F. solani in the field, while Setaria verticilata grown in pots was moderately susceptible to isolate 2a3. Brassica rapa and Crotalaria juncea grown in pots were moderately susceptible to F. moniliforme but they showed no infection in the field. Fifty-nine additional plant species of ecological and agricultural importance were not susceptible to the Fusarium species. When F. solani, F. pallidoroseum and Neochetina spp. were used individually in ponds, they did not control waterhyacinth. When the fungi were combined with Neochetina spp., the area covered by waterhyacinth and the volume of waterhyacinth were significantly reduced.

Phomopsis convolvulus Ormeno, a foliar pathogen of field bindweed, is a good candidate to be developed as a bioherbicide. Large numbers of infective propagules were produced in shake-flask liquid fermentation with modified Richard's (V-8) medium and in solid-substrate fermentation with pearl barley grains. In complex liquid media, pycnidium-like structures were observed. Most conidia stored at $-$70$ sp circ$C remained viable and virulent for at least six months. / In controlled environment studies, a minimum of 18 hr of dew was required for severe disease development on inoculated plants. The addition of gelatin, Sorbo $ sp{ rm TM}$, or BOND$ sp{ rm TM}$ to the inoculum did not enhance the disease under various leaf wetness periods. A continuous dew period of 18 hr was superior to the cumulative effect of three interrupted 6 hr dew periods. Secondary inoculum was produced on diseased plants placed under moist conditions for 48 hr or more. / In greenhouse experiments, seedlings at the cotyledon and 3- to 5- leaf stage were severely diseased and killed when inoculated with 10$ sp9$ conidia/m$ sp2$. This inoculum density adversely affected the regenerative ability of 4 wk old seedlings and established plants, but few plants were killed. Inoculation of the healthy regrowth from plants previously inoculated with the fungus resulted in much less disease symptoms than expected.

The gregarious pupal endoparasitoid, Tetrastichus howardi Olliff (Hymenoptera: Eulophidae), was introduced into South Africa as a biocontrol agent against the maize and the sorghum stem borers, Busseola fusca Fuller and Chilo partellus Swinhoe. Preovipositional behaviour, ovipositional behaviour, development, fertility, sex-ratio, and longevity were studied in the laboratory. A complex courtship behaviour was observed, however 35.3% of females were mated before emergence from the host pupa. Preoviposition period ranged from 100 mins up to 5 days. Host searching time in Petri dishes was shorter for lepidopteran pupae than for their parasitoid pupae, and shortest when T. howardi had previously experienced the host. Duration of oviposition was significantly longer in the lepidopteran pupae than in the smaller tachinid puparia. T. howardi showed no difference in preference for hosts of different ages. The lepidopteran hosts were preferred to their parasitoids. If T. howardi had previously experienced a certain host its pereference for that host tended to increase, but not significantly. When reared on a certain host, the preference for that host did increase. The parasitoid was able to discriminate between parasitzed and unparasitzed pupae although this ability developed only 2 days after the pupa was parasitized. Cotesia sesamiae Cameron, the main indigenous parasitoid of B. fusca and C. partellus, was not attacked by T howardi. The total duration of development from egg deposition to the adult stage ranged from 18 to 26 days at 24°C and 60% RH. Emergence of adults began after first light, mean emergence time in winter being 09h00. Emergence rate of T. howardi from parasitized hosts, and mortality rate of parasitized hosts, was higher for C. partellus and H. armigera than for Eldana saccharina Walker and Palexorista laxa Curran. This decreased for C. partellus and H. armigera when superparasitized. A strong correlation existed between total parasitoids emerging from a host and percentage of females. When a lepidopteran pupa was parasitized by a single T. howardi female, 55 progeny emerged of which 94% were females. Larger females showed greater fertility and also produced a higher percentage of females. Younger hosts were more suitable for development of T. howardi. Females lived for 5.4 to 52.5 days, and males lived for 3.1 to 28.6 days, depending on presence or absence of food, water and hosts. Reasons for releasing T. howardi in the field are discussed. Only 2 recoveries of parasitized C. partellus pupae were made from the field.