Agricultural production on the Mahafaly Plateau in SW-Madagascar has traditionally been based on subsistence rain-fed agriculture, with yields declining as a result of low soil fertility, recurrent droughts, and erratic rainfall. Market-oriented vegetable production in this area may help households improve their nutrition and diversify their income. In field trials between the 2013 and 2016 dry cropping seasons, the feasibility of carrot (Daucus carota L.) and onion (Allium cepa L.) production was assessed by testing effects of manure and charcoal amendments, shading, and seed quality on yields. Due to damage caused by cyclones and strong winds, only data from 2013 and 2016 are reported in this paper. Additionally to the field experiments, effects of salinity on seed germination were also examined under laboratory conditions and in the field. Carrot dry matter (DM) yields were 0.24 to 2.76 t·ha−1 while those of onion were 0.15 to 0.99 t·ha−1 DM. While the combination of manure and charcoal application had only minor effects on crop growth, manure alone increased carrot yield by 26% across years. After one cropping season, manure application reduced soil pH from 9.0 to 8.6 and increased soil Corg from 0.87 to 1.76%, N from 0.08 to 0.14%, and P from 10.6 to 15.1 mg·kg−1. Shading reduced carrot yields from 0.87 to 0.58 t·ha−1 DM in 2013 and from 1.87 to 0.85 t·ha−1 DM in 2016, but increased onion yield in 2013 from 0.24 to 0.62 t·ha−1 DM. Carrot seed procured locally performed better in the field than seed imported from the capital which translated into differences in seedling emergence. Saline irrigation water (electrical conductivity = 7.03 mS·cm−1) reduced seedling emergence rate of carrot from 73 to 20% and for onion from 44 to 28% and unprimed seeds performed better than primed ones. Using shading during the dry season is not advisable for carrot and onion production, but improving seed quality and targeted use of soil amendments (time of manure application, manure quality) may enhance vegetable yields.

Sulfentrazone was recently granted food-use tolerance approval for use on Brassica head and stem, as well as Brassica leafy vegetables. To date, one sulfentrazone registrant has listed those crops on its use label. In coastal California multiple crops per year including Brassica vegetables are grown in rapid succession; therefore, to avoid injury to rotational crops, herbicides used in those fields must be carefully selected. Given concerns about the relatively long soil persistence of sulfentrazone, studies were conducted to measure the response of direct-seeded carrot, lettuce, onion, spinach, and seeded tomato planted 3, 6, 9, and 12 mo after sulfentrazone application at 0, 112, 224, and 336 g ai ha−1. Eight plant-back studies were conducted during 2010–11 and 2012–13. Data collected were injury estimates, and stand and dry weights. Results indicate that it is safe to plant carrot and tomato 3 mo after sulfentrazone application at rates up to 336 g ai ha−1. Lettuce and green onion should not be planted within 9 mo of sulfentrazone application. Spinach should not be planted within 12 mo of sulfentrazone application.

Weed management in carrot is challenging, given slow and inconsistent crop emergence and early-season growth and the lack of practical season-long management tools such as herbicides. We investigated holistic carrot production systems with a focus on minimizing inputs while optimizing resource use. In an overall sense, results of this work were consistent between years, and stark. The choice of carrot variety had a moderate influence on carrot foliar canopy development and, subsequently, weed density. For example, ‘Cupar’ carrot formed a complete crop canopy sooner than the other dicer-type ‘Canada’ variety. Likely as a result, density of weed species such as spotted ladysthumb and common lambsquarters was less where ‘Cupar’ was grown compared with where ‘Canada’ was grown. Gibberellic acid as a foliar application was not successful in these studies and, in a few cases, may have even increased weed-seed germination and establishment. Adding two carrot rows to the current regional industry-standard three-row bed system not only enhanced competitiveness with weeds but also improved carrot yield without additional fertilizer, water, or pest management inputs. By far, though, the most successful strategy to reduce weed density while maintaining or improving carrot yield was to delay seeding by 17 to 19 d. We anticipate more holistic production system research that integrates low-input alternatives in other crops as herbicide-resistant weeds proliferate while few new herbicides are developed. As was demonstrated in this research, such novel approaches can be successful without adding significant economic burden to the farmer or increasing risk of crop failure.

Slow carrot emergence and canopy development render the crop a poor competitor with weeds. In this study, the ability to suppress weeds and maintain yield in the presence of weeds was compared among nine carrot varieties that included those selected by plant breeders for rapid vegetative canopy development compared to traditional varieties. Two weed management treatments were compared: handweeding for 21 d after carrot seeding versus handweeding for the entire carrot season. In years and locations with low to moderate weed pressure, such as in the 2014 study, differences among carrot varieties in weed competitiveness or tolerance were less apparent and therefore less relevant. Maximum carrot yield loss to weed competition among varieties was 28% in 2014. Yield loss in the presence of weeds was 15% or less with six of the nine carrot varieties. However, when weed pressure was intense in the 2015 study, both carrot plant density and carrot canopy development were inversely related to weed biomass. Carrot yield loss in the presence of weeds ranged from 38 to 87%. Despite correcting seeding populations for differences in germination among carrot varieties, carrot stand establishment varied greatly and would likely affect subsequent weed control measures such as timely cultivation or herbicide application. Future research efforts are warranted that consider carrot stand establishment factors and their relationship with integrated weed management programs.

We studied the effectiveness of glyphosate [N-(phosphono-methyl)glycine] for the control of Orobanche spp. in the field when applied to the crop foliage prior to the emergence of the parasite. The best Orobanche control in October-sown carrots (Daucus carota L.) parasitized by Orobanche crenata Forsk. and O. aegyptiaca Pers. and in December-sown broad bean (Vicia faba L.) and peas (Pisum sativum L.) parasitized by O. crenata was obtained by spraying twice, 2 weeks apart, in late January and in February, respectively. Carrot root yield remained unaffected by glyphosate at rates up to 200 g/ha. In heavily infested fields, carrots were irreversibly damaged by early Orobanche parasitism. The highest yields of pods of broad beans occurred after two or three applications of 150 g/ha glyphosate. Peas were seriously damaged by 150 g/ha. Two or three sprays of 50 g/ha glyphosate resulted in the highest green-kernel yield of pea where the soil was not heavily infested. Glyphosate effectively reduced O. cernua Loeffl. emergence in non-irrigated tomatoes (Lycopersicum esculentum Mill.), but was very phytotoxic to the crop. Glyphosate was highly effective in controlling Orobanche spp.; however, marginal selectivity may be sufficient in some crops and not in glyphosate-susceptible ones.

This study evaluated the effects of organic agriculture manuring systems on carrot (Daucus carota) root morphology and sugar and polyacetylene content. Carrots were harvested three times per season 2006–2007 in a long-term field experiment at Skilleby research farm, Sweden. The effects of pelleted chicken manure, fresh farmyard manure and composted farmyard manure (COM) were compared against control plots left unmanured since the field experiment started in 1991. The carrots were analyzed for root size, root shape, amount of soluble sugars and amount of falcarinol-type polyacetylenes. Differences between manuring systems were found to be smaller than the variation between harvest years and harvest occasions, probably due to the grass-clover ley included in the crop rotation system. On an average for the six harvests, manuring with COM increased root length by 6% compared with fertilizing with pelleted chicken manure. Carrots fertilized with pelleted chicken manure also had 6–7% lower total soluble sugar content than carrots manured with 50 t ha−1 of composted or fresh manure. The falcarinol to total falcarinol-type polyacetylenes ratio was 15.4% in carrots manured with 50 t ha−1 of composted or fresh manure and 14.7% in carrots fertilized with pelleted chicken manure. Seasonal fluctuations in falcarinol-type polyacetylenes were more pronounced in carrots manured with fresh or composted manure than in carrots fertilized with pelleted chicken manure. The results suggest that manuring organic carrots with compost may be the most beneficial strategy, at least in systems where fertilizer is applied only once per crop rotation, whether directly to the carrot crop or in the preceding crop.

Polyadenylic acid (poly(A)) content of carrot seeds reached a peak at 40 days after anthesis and then declined as desiccation occurred. A further decline occurred in the early stages of germination and was more extensive in seeds harvested whilst still immature. Accelerated ageing of seed led to significant losses of poly(A) and the content declined still further when aged seeds were set to germinate. In seeds harvested whilst immature and then subjected to ageing, the resumption of net accumulation of poly(A), a feature of normal germination, was barely detectable or did not occur.

Various sources of germination heterogeneity of carrot (Daucus carota L.) seeds were investigated: germination conditions (temperature, oxygen tension), size of seeds, position of the umbels on the mother plants, and pollination conditions of male-sterile plants in hybrid seed production. All seeds tested germinated over a large range of temperatures (5–35°C). However, low temperatures (5–10°C) and temperatures above 30°C reduced germination. Seeds were also sensitive to oxygen deprivation, but their sensitivity to hypoxia depended on the cultivar. The germination responses of seeds to temperature and oxygen depended on their size, particularly at sub- and supra-optimal temperatures. The largest seeds (1.8–2.1 mm) of commercial lots usually germinated better at 5°C and were more sensitive to oxygen deprivation than the smallest ones (1.2–1.8 mm). Experiments performed with open pollinated plants showed that seeds produced by umbels of first and second orders germinated faster and at higher percentages than those collected on third-order umbels. Evidence for the involvement of pollination conditions in the germination quality of carrot seeds was given by pollination by honey bees of male-sterile plants cultivated at various distances from the pollen donors. The longer the distance of the mother plants from the pollinating plants, the lower the seed yield, the heavier the mean seed weight, the more difficult the germination of seeds, and the higher their sensitivity to oxygen deprivation.

The prediction of the viability of stored seeds is important both for the management of germplasm collections and for the management of commercial seed production and storage. The Ellis and Roberts model for seed viability during storage is examined, and an inadequacy of the model highlighted. A modification is proposed, based on the ‘control mortality’ probit model developed for insecticide bioassays, to take proper account of variation in initial viability. This new ‘control viability’ model, relating seed viability to storage time, is fitted to data from a carrot seed storage experiment and found to fit well for a range of storage environments. A relationship, similar to that proposed by Ellis and Roberts for the effects of storage conditions on the rate of loss of viability, is fitted to the estimated rates from this new model. Data from a second carrot seed storage experiment are used to validate this relationship.

Phytoplasmas are insect-vectored pathogens that cause characteristic and destructive diseases in carrots and other vegetables. A phytoplasma disease was first observed in Israeli carrot fields in 1995. Analysis of infected carrots showed the presence of aster yellows and western-X phytoplasmas. In this study, commercial and experimental fields in the western Negev region of Israel were monitored for three years using yellow sticky traps and vacuum sampling. Potential vectors of leafhoppers and planthoppers were analysed by PCR for the presence of phytoplasma DNA. Infected plants were also assayed for phytoplasma DNA. Extracted phytoplasma DNA was subjected to RFLP analysis to determine groups to which the phytoplasmas belonged. It was determined that carrots and leafhoppers from the experimental station were infected with a phytoplasma belonging to the Elm Yellows (EY) group; this is the first report of EY infecting carrots. Based on our findings, the two most probable insect vectors are Circulifer haematoceps complex (Mulsant & Rey) and Neoaliturus fenestratus (Herrich-Schäffer).

Carrots, irrespective of their origin and whether they have been grown conventionally or organically, almost always harbour spores of Thielaviopsis basicola and T. thielavioides on their surface. Infections become visible as dark green mould patches upon prolonged incubation in polythene bags. These moulds produce beautiful asexual reproductive organs which are described here. We also present the first report of the previously unknown ocurrence of repetitious conidial germination in both species.