The continuous use of synthetic anthelmintics against gastrointestinal nematodes (GINs) has resulted in the increased resistance, which is why alternative methods are being sought, such as the use of natural products. Plant essential oils (EOs) have been considered as potential products for the control of GINs. However, the chemical composition and, consequently, the biological activity of EOs vary in different plant cultivars. The aim of this study was to evaluate the anthelmintic activity of EOs from cultivars of Ocimum basilicum L. and that of their major constituents against Haemonchus contortus. The EOs from 16 cultivars as well the pure compound linalool, methyl chavicol, citral and eugenol were used in the assessment of the inhibition of H. contortus egg hatch. In addition, the composition of three cultivars was simulated using a combination of the two major compounds from each. The EOs from different cultivars showed mean Inhibition Concentration (IC50) varying from 0.56 to 2.22 mg/mL. The cultivar with the highest egg-hatch inhibition, Napoletano, is constituted mainly of linalool and methyl chavicol. Among the individual compounds tested, citral was the most effective (IC50 0.30 mg/mL). The best combination of compounds was obtained with 11% eugenol plus 64% linalool (IC50 0.44 mg/mL), simulating the Italian Large Leaf (Richters) cultivar. We conclude that different cultivars of O. basilicum show different anthelmintic potential, with cultivars containing linalool and methyl chavicol being the most promising; and that citral or methyl chavicol isolated should also be considered for the development of new anthelmintic formulations.

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a pest species complex that causes widespread damage to cassava, a staple food crop for millions of households in East Africa. Species in the complex cause direct feeding damage to cassava and are the vectors of multiple plant viruses. Whilst significant work has gone into developing virus-resistant cassava cultivars, there has been little research effort aimed at understanding the ecology of these insect vectors. Here we assess critically the knowledge base relating to factors that may lead to high population densities of sub-Saharan African (SSA) B. tabaci species in cassava production landscapes of East Africa. We focus first on empirical studies that have examined biotic or abiotic factors that may lead to high populations. We then identify knowledge gaps that need to be filled to deliver sustainable management solutions. We found that whilst many hypotheses have been put forward to explain the increases in abundance witnessed since the early 1990s, there are little published data and these tend to have been collected in a piecemeal manner. The most critical knowledge gaps identified were: (i) understanding how cassava cultivars and alternative host plants impact population dynamics and natural enemies; (ii) the impact of natural enemies in terms of reducing the frequency of outbreaks and (iii) the use and management of insecticides to delay the development of resistance. In addition, there are several fundamental methodologies that need to be developed and deployed in East Africa to address some of the more challenging knowledge gaps.

Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), 2,4-D [2,4-dichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), and 2,4-D plus dicamba were applied as postemergence herbicide treatments in two experiments to weed-free dormant bermudagrass [Cynodon dactylon (L.) ♯3 CYNDA] turf in the Piedmont region of Georgia. Herbicides were applied as a split application to separate plots on February 2 plus February 16 and February 16 plus March 3 (± 4 days) on four bermudagrass cultivars (‘Tifway’, ‘Tifgreen’, ‘Tifdwarf’, and ‘Ormond’) in one experiment and to Tifway with vertical mowing treatments for thatch removal in a second experiment. In 2 of 3 years, paraquat applied to dormant turf in February delayed growth of bermudagrass in April. The growth of Tifway and Tifdwarf was retarded more from paraquat at 1.2 kg ai/ha in one year than Tifgreen or Ormond. Dicamba applied alone or with 2,4-D delayed turf growth in early spring more than did 2,4-D alone. In thatch-free turf, selected treatments of paraquat, dicamba, and 2,4-D plus dicamba also delayed spring growth of bermudagrass more than did 2,4-D.

Sixteen sweet corn cultivars, representing a range of endosperm genotypes, were evaluated to determine cultivar tolerance to nicosulfuron plus rimsulfuron in greenhouse and field studies conducted over a two-year period. Response to nicosulfuron plus rimsulfuron varied widely, depending on cultivar and application rate. In the field, four cultivars were tolerant to applications of nicosulfuron plus rimsulfuron at rates of 50 g/ha. In the greenhouse, eight cultivars were tolerant to nicosulfuron plus rimsulfuron at 25 g/ha. ‘Merit’ and ‘Silver Extra Sweet’ were most sensitive, with applications of nicosulfuron plus rimsulfuron resulting in death of all plants. ‘Miracle,’ ‘Extra Early Super Sweet,’ ‘Bunker Hill,’ and ‘Sweet Belle’ were tolerant.

Experiments were conducted over 4 yr to investigate the effects of four postemergence herbicides on soybean [Glycine max (L.) Merr. ‘Williams 79’] yield under weed-free conditions. Bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, and naptalam/dinoseb {2-[(1-naphthalenylamino)carbonyl] benzoic acid}/[2-(1-methylpropyl)-4,6-dinitrophenol] alone and in combination with 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid] applied to soybeans at the V3 and V5 soybean growth stages caused early crop injury, but soybeans outgrew most of the injury by 21 days and there was no effect on yield. Bentazon plus 2,4-DB with or without adjuvant did not affect the yield of five soybean cultivars tested.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 6.7 kg/ha, twice the recommended rate, stunted early-season growth of ‘Jubilee,’ ‘Commander,’ and 'Stylepak’ sweetcorn (Zea mays L.) 9 to 15%, reduced plant populations of Commander and Stylepak 12 to 15%, reduced the kernel yield of Jubilee and Stylepak 14 to 16%, and delayed ripening of Jubilee and Stylepak by 2 or 3 days. Alachlor at 3.4 kg/ha slowed early-season growth of Jubilee and Stylepak, but reduced yield and delayed ripening of only Jubilee. EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloracetamide) and vernolate (S-propyl dipropylthiocarbamate) + R-25788 at 4.5 + 0.4 or 9.0 + 0.8 kg/ha did not reduce the growth, yield, or quality of the three sweetcorn cultivars. Planting date did not influence the response of sweetcorn to the herbicides. In these experiments, none of these herbicides injured sweetcorn severely, as has sometimes occurred in commercial fields.

Selected sweet potato clones were evaluated in greenhouse and field trials to identify clones with superior tolerance to bentazon. ‘Julian’ and NC 1519 were the most tolerant in the greenhouse. ‘Sweet Red’ exhibited foliar injury in the field, but yields were not reduced. The clone 79-BM-17 was equally tolerant in the field as Sweet Red, but in the greenhouse exhibited only intermediate tolerance. ‘Jewel,’ a widely grown commercial cultivar, was sensitive to bentazon in both the greenhouse and field. When averaged over all clones sweet potato injury increased as bentazon rate was increased from 1.1 to 2.2 kg ai ha-1, but it decreased as the season progressed. Bentazon did not reduce marketable yields at Clayton, NC. Bentazon as a split or late application at the 2.2 kg ha-1 rate, reduced yields at Clinton, NC. Percent culls among bentazon treatments did not differ at either location.

Eight sweet corn cultivars differed in response to 35 g ai ha–1 nicosulfuron or 42 g ai ha–1 primisulfuron. ‘Merit’ sweet corn was killed 4 wk after nicosulfuron or primisulfuron application. Nicosulfuron and primisulfuron reduced height of Merit, 'Silver Queen’, 'Silverado’ and ‘How Sweet It Is'. Ear number of How Sweet It Is, ‘Pinnacle’ and Silverado was reduced by primisulfuron. ‘Landmark’, Silver Queen, and 'Sweetie 76’ were the most tolerant cultivars to nicosulfuron and primisulfuron with yield similar to that of the control.

The tolerance of canola to soil applied flurtamone was investigated in greenhouse and field studies. In the greenhouse, the dosage of flurtamone required to reduce canola fresh weight by 50% was 7.1- to 8.4- and 4.4- to 6.1-fold higher for B. napus and B. campestris cultivars, respectively, than that required to reduced wild mustard fresh weight by 50%. B. campestris cultivars tended to be more sensitive to flurtamone than B. napus cultivars. In the field, flurtamone applied at 0.4 to 0.5 kg ai ha-1 controlled 80% of wild mustard in canola (B. napus cv. ‘Westar’). In 1991 canola plant densities were reduced by increasing rate of flurtamone, but seed yields were unaffected by rate of application in either year.

Imazethapyr at 0.07 and 0.10 kg ai ha-1 applied preplant incorporated (PPI), preemergence (PRE), and postemergence (POST) was evaluated at two locations in 1988 and 1989 for safety to dry edible beans. Bean stunting, leaf crinkling, and interveinal chlorosis were evident from imazethapyr and varied from 1 to 57%. Imazethapyr significantly reduced bean height and delayed maturity. PPI and POST applications of imazethapyr at 0.07 and 0.10 kg ha-1 did not reduce bean seed yields compared to yields of the untreated control. Bean cultivar by herbicide interactions were significant for bean injury but varied with year and location.

The inclusion of competitive crop cultivars in crop rotations is an important integrated weed management (IWM) tool. However, competitiveness is often not considered a priority for breeding or cultivar selection by growers. Field pea (Pisum sativum L.) is often considered a poor competitor with weeds, but it is not known whether competitiveness varies among semileafless cultivars. The objectives of this study were to determine if semileafless field pea cultivars vary in their ability to compete and/or withstand competition, as well as to identify aboveground trait(s) that may be associated with increased competitive ability. Field experiments were conducted in 2012 and 2013 at three locations in western Canada. Fourteen semileafless field pea cultivars were included in the study representing four different market classes. Cultivars were grown either in the presence or absence of model weeds (wheat and canola), and competitive ability of the cultivars was determined based on their ability to withstand competition (AWC) and their ability to compete (AC). Crop yield, weed biomass and weed fecundity varied among sites but not years. Cultivars exhibited inconsistent differences in competitive ability, although cv. Reward consistently exhibited the lowest AC and AWC. None of the traits measured in this study correlated highly with competitive ability. However, the highest-yielding cultivars generally were those that had the highest AC, whereas cultivars that ranked highest for AWC were associated with lower weed fecundity. Ranking the competitive ability of field pea cultivars could be an important IWM tool for growers and agronomists.

Wild parsnip is an invasive species with a global distribution in temperate climates. Parsnips are native to Eurasia and have been cultivated for more than five centuries. It is unclear whether the global invasion of this species is a consequence of escape from cultivation or the accidental introduction of a Eurasian wild subspecies. In this study, we used nuclear ribosomal DNA internal transcribed spacer (ITS) and chloroplast DNA (cpDNA) markers to evaluate the genetic structure of wild parsnip in its native range (Europe) and in three distinct geographic regions where it is considered invasive: eastern North America, western North America, and New Zealand. We also compared wild and cultivated parsnips to determine whether they are genetically distinct. From 112 individuals, we recovered 14 ITS and 27 cpDNA haplotypes. One ITS haplotype was widespread; few haplotypes were rare singletons. In contrast, at least two lineages of cpDNA haplotypes were recovered, with several novel haplotypes restricted to Europe. Cultivated parsnips were not genetically distinct from wild parsnips, and numerous wild parsnip populations shared haplotypes with cultivars. High genetic diversity was recovered in all three regions, suggesting multiple introductions.

Safflower is a traditional oilseed crop in the world. Its seed oil is a healthy edible oil containing high amount of unsaturated fatty acids. Genetically diverse exotic cultivars are valuable germplasm for introducing new diversity in safflower improvement programmes. In this study, we characterized safflower cultivars of India (30) and Mexico (23) comprising varieties, hybrids and advanced lines developed over 50 years for genetic distinctiveness using 38 simple sequence repeat (SSR) loci. Genetic diversity estimates across cultivar groups (total, India and Mexico) were as follows: mean number of alleles (3.2, 3.1, 2.6), expected heterozygosity (0.42, 0.37, 0.37) and polymorphism information content (0.36, 0.33, 0.32) respectively, which suggested narrow SSR allelic diversity within and between cultivar groups. However, distance-based cluster analysis (neighbour-joining tree) and model-based STRUCTURE analysis revealed that safflower cultivars of India and Mexico, with the exception of a few, form two genetically distinct groups. High level of genetic variation explained between the populations (40%) and Fst estimate (0.4) suggested that the cultivar groups were highly differentiated with limited gene flow supporting a strong genetic structuring. High oil (~38%) and high oleic (73–79%) contents of a subset of Mexican safflower varieties and advanced lines were confirmed in field trials in India. These exotic sources from Mexico are valuable for safflower breeding programmes in India to develop new cultivars with high oil yielding potential and high oleic acid content, which is the current market demand.

Rhubarb includes approximately 60 species in the genus Rheum. It has been utilized for thousands of years for medicinal purposes, but only recently identified for its culinary use. In the mid 1700s, edible petioles were discovered on seedlings from rhubarb species. Hundreds of cultivars have since been identified for a wide range of uses from tarts to wine. Unfortunately, propagation by seed and irregular naming has resulted in a plethora of similarly named cultivars and multitude of phenotypes. Fifteen morphological characters were evaluated to differentiate rhubarb cultivars in the USDA, ARS Rheum collection in Palmer, Alaska. Two years of morphological data, focusing on horticultural characteristics indicated variation between the years. To improve cultivar resolution, the results suggest using 1 year's data instead of combining data from different years. The mean °Brix observed was 3.8, with a range from 2.2 to 6.1. Flesh colour and basal skin colour were poorly correlated (R2 = 0.462); overall skin colour was more red at the base than in the middle of the petiole. Rhubarb character categories, in particular petiole number and petiole base thickness, need to be modified to better anticipate the range of expected values, and thereby contribute improved reproducibility and reliability to separate cultivars based on morphological characters.

The relative contributions of host plant, herbivore species and clone to variation in the interaction between cereal aphids and wheat were investigated using five clones each of three species, Rhopalosiphum padi (Linnaeus), Sitobion avenae (Fabricius) and Schizaphis graminum (Rondani), on seedlings of two cultivars of Triticum aestivum L. and one cultivar of Triticum durum Desf. More individuals and biomass of R. padi than of the other two species were produced on seedlings. The three wheat cultivars lost similar amounts of biomass as a result of infestation by aphids, with the amount lost depending on aphid species: S. avenae caused the lowest loss in biomass. Variation in aphid biomass production was due mostly to differences among aphid species (70%), less to the interaction between wheat type and aphid species (7%), and least to aphid clone (1%). The specific impact of the aphids on the plants ranged from 1.7 to 3.7 mg of plant biomass lost per mg of aphid biomass gained, being lowest for R. padi and highest for S. graminum. Variation in plant biomass lost to herbivory was due mostly to unknown sources of error (95%), probably phenotypic differences among individual seedlings, with 3% due to aphid species and none attributable to aphid clone. For these aphid–plant interactions, differences among aphid clones within species contributed little to variation in aphid and plant productivity; therefore, a small sample of clones was adequate for quantifying the interactions. Furthermore, one clone of each species maintained in the laboratory for about 200 parthenogenetic generations was indistinguishable from clones collected recently from the field.

The reproductive activity and the offspring development of the bruchid Callosobruchus maculatus (Coleoptera: Bruchidae) were monitored in the seeds of seven cultivars of Cicer arietinum and three cultivars of Vigna unguiculata. The number of eggs laid by the C. maculatus was higher on the V. unguiculata cultivars than on those of C. arietinum. The survival rate during the embryonic development was higher than 90% regardless of the plant species and cultivars while the post-embryonic development rates did not differ significantly between the cultivars. However, the duration of the embryonic and post-embryonic development and the weight of the emerging females varied with seed species. V. unguiculata seeds allow a higher reproduction and a better development than C. arietinum. In this study, no cultivar had been found to be resistant. In Algeria, C. maculatus can develop in stored grains of both chickpea and cowpea, and it is a major stored grain insect pest.

One hundred and five okra cultivars were evaluated in the field for resistance to the leafhopper Amrasca biguttula biguttula (Ishida) during the 1989–1990 season. On the basis of nymphal abundance and leafhopper injury index two resistant (Siswal Local and IC 7194) and nine moderately resistant [IC 6653, IC 8899, IC 13617, Sel. 1, HB 94, IC 6316,6 Dhari, Sel. 2–2 and Line 6(1)] genotypes were identified. Both of the resistant, two moderately resistant (Line 6(1) and IC 13617) and two highly susceptible (Pusa Sawani and Pusa Reshmi) genotypes were retested in 1990–1991. Resistant genotypes had significanlty (P < 0.05) fewer nymphs (18.5 to 22.0 nymphs/leaf) and lower values of injury index (2.2) compared with the other varieties. Nymphal duration was also longer (9.3 to 9.8 days) and nymphal survival lower (41.7 to 47.5%) in resistant cultivars. Higher trichome density, longer trichome length and higher concentration of sugars, silica, potassium, tannins and phenols in the leaves of resistant cultivars were associated with resistance to leafhopper.

The impact of larval defoliation by Aproaerema modicella (Deventer) on the growth, development and yield of two groundnut cultivars (Kadiri 3 and NC Ac 17090) was studied under a naturally occurring, high density infestation. Defoliation by leaf-mining larvae did not increase plant mortality in either cultivar. In both cultivars, leaf and stem production were significantly lower in untreated plots than in the treated plots. Unsprayed plants of both cultivars produced fewer flowers, pegs, and pods per plant compared to plants of the same cultivar protected with monocrotophos. Fruit growth rates, however, were marginally higher in control plots than in treated plots. Pod yields were 35 and 44% lower, and haulm yields 25 and 20% lower, in Kadiri 3 and NC Ac 17090, respectively in untreated control plots compared to plots treated with insecticide. A linear relationship between leafminer density and pod and haulm yields was observed, and differences between cultivars were not significant.