P. J. Wright

A soft rot of calla (Zantedeschia spp.) caused by Erwinia carotovora subspecies carotovora

Abstract A bacterium, isolated from infected tubers of calla (Zantedeschia spp.), was confirmed as a soft rot pathogen by completion of Kochs postulates and was identified as Erwinia carotovora subsp. carotovora (Jones 1901) Bergey et al. 1923. This paper confirms the identity of E. carotovora subsp. carotovora as the cause of bacterial soft rot of this important ornamental plant in New Zealand.

Effects of nitrogen fertiliser, plant maturity at lifting, and water during field‐curing on the incidence of bacterial soft rot of onions in store

Abstract Levels of bacterial soft rot in stored onion bulbs were affected by rates and application times of nitrogen (N) fertiliser, time of lifting, and water during the field‐curing period. Bulbs of onions given 240 kg N/ha (double the local recommended rate) had more rots during storage than onions that received no N or 120 kg N/ha. Onions that received N late in the growing season had more storage rots than onions that received N early in the season, or were not supplied with N. There were no noticeable differences in levels of rots in onions that were lifted at 50–70% top‐down or at >90% top‐down in each of the treatments. When N treatments were compared, the percentage of storage rots was higher in onions that were given supplementary water during field‐curing than in non‐irrigated onions. To reduce the incidence of storage rots it is recommended that onions are not over‐fertilised with N, and crops are lifted at >90% top‐down. Bulbs should be moved under cover and dried before storage if wet weathe...

Irrigation, sawdust mulch, and Enhance® biocide affects soft rot incidence, and flower and tuber production of calla

Abstract The incidence and severity of soft rot, flower grades, and tuber yields of calla (Zantedeschia spp.) plants were affected by the quantity of water received during the growing season, sawdust mulch, and Enhance® biocide applications to tubers before planting. Incidence of plants with soft rot symptoms increased at a relatively constant rate during the season reaching an average for all treatments of 61% at the end of flowering. Irrigated plus mulched callas had 15% less soft rot than the irrigation without mulch or the mulch without irrigation treatments. Yield of tubers was 90% greater from irrigated plants. Dipping tubers in Enhance® before planting slightly reduced the severity of rotting in harvested tubers from non‐irrigated plants. The total number of flowers was not affected by irrigation but was slightly reduced by sawdust mulch. However, the number of long stemmed flowers was increased 41% by irrigation, to over 1.5 per tuber.

Control of bacterial soft rot of calla (Zantedeschia spp.) by pathogen exclusion, elimination and removal

Abstract The incidence and severity of bacterial soft rot of calla (Zantedeschia spp.) tubers at harvest were substantially reduced by planting method, chemical control measures, and removal of infected plant material. Callas grown using a sawdust‐shadecloth method had fewer soft‐rotted plants and tubers than callas grown in soil. Dipping tubers before planting in an aqueous solution of 0.08% copper hydroxide, 0.12% thiram, plus 0.03% benomyl reduced plant and tuber losses from bacterial soft rot. Drenching plants during the growing season with an aqueous solution of 0.12% thiram, 0.08% copper hydroxide, plus 0.15% quintozene gave further control against rots. Weekly removal of rotting foliage and tubers during the growing season also reduced levels of plant and tuber soft rots. This study has demonstrated that effective control of calla soft rot can be achieved using disease management that combines appropriate pathogen exclusion, elimination, and removal methods.

Effects of cultural practices at harvest on onion bulb quality and incidence of rots in storage

Abstract A field study was carried out over two seasons to investigate the effects of maturity of onions (Allium cepa L.) at harvest and different curing conditions on bulb quality and the incidence of storage rots. Onion plants were lifted at one of three stages of maturity: 10, 70, or 90% leaf collapse (top‐down). Foliage was removed (topped) either before or after curing, and bulbs were subjected to one of three curing treatments: field curing with additional water, field curing without additional water, or heated forced air curing. Additional water applied during field curing increased the proportion of onions with stained skins and rots. Forced‐air curing of onions reduced the incidence of rots regardless of harvest method. Forced air drying also reduced skin staining in most harvest method treatments.

A field and storage rot of onion caused by Pseudomonas marginalis.

Abstract Pseudomonas marginalis (Brown 1918) Stevens 1925 isolated from infected leaves of onion (Allium cepa L.) in the field and from diseased bulbs in store, was confirmed as a soft rot pathogen of onion by Kochs postulates. The first official record of P. marginalis on onion in New Zealand is attributed to Hale in Pennycook 1989. This paper documents the evidence for that record.

Effects of onion (Allium cepa) plant maturity at harvest and method of topping on bulb quality and incidence of rots in storage

Abstract A field study was carried out over two growing seasons to investigate the effects of physiological maturity of onions (Allium cepa L.) at harvest and different topping methods on bulb colour, skin retention, and the incidence of storage rots. Onion plants were lifted at five different stages of maturity from 0 to 4 weeks after 50% leaf collapse (top‐down). Foliage was removed from the bulbs (topped) either before or after field‐curing. The effects of time of lifting of onion plants and method of topping on the incidence of bulb storage rots were the same in both seasons. Onions that were lifted 3 weeks after 50% top‐down and topped before curing had the greatest incidence of rots in store. Increasing harvest maturity increased the mean skin colour score of onions, and decreased markedly the mean number of intact outer skins. The timing of foliage removal had no effect on mean skin colour score, but onions that were topped before curing had slightly more bulb skins than onions topped after curing. Timing of onion lifting to optimise bulb quality appears to be a trade‐off between skin retention and colour. These results confirm that traditional method of harvesting onions in New Zealand, where onions are lifted at 60–80% top‐down, the bulbs are field‐cured, and the foliage is removed after curing, is the simplest method and best compromise to ensure postharvest onion quality and successful storage.

Effects of cessation of irrigation and time of lifting of tubers on bacterial soft rot of calla (Zantedeschia spp.) tubers

Abstract The incidence and severity of bacterial soft rot of calla (Zantedeschia spp.) tubers at harvest were affected by the time that irrigation ceased and the time when tubers were lifted from the ground. The longer that tubers were left in the ground after the onset of foliage senescence, the greater the levels of soft rot. When irrigation was terminated early, foliage senescence occurred more rapidly than when irrigation was terminated later. Early cessation of irrigation reduced the incidence and severity of tuber rots at lifting without greatly affecting tuber size. Early lifting of tubers reduced the incidence of rots but also reduced tuber yield because tubers were still actively growing.

A storage soft rot of New Zealand onions caused by Pseudomonas gladioli pv. alliicola

Abstract A bacterium, isolated from infected bulbs of onion (Allium cepa L.) in store, was identified as Pseudomonas gladioli pv. alliicola (Burkholder 1942) Young et al. 1978, and was confirmed as a soft rot pathogen of onion by completion of Kochs postulates. P. gladioli pv. alliicola was first reported as an onion pathogen in New Zealand by Hale in Pennycook (1989). This paper documents the evidence for that record.

Fungicide control of head smut (Sporisorium reilianum) of sweetcorn (Zea mays)

Abstract A field trial was carried out to compare the efficacy of the fungicides carboxin + thiram (Vitafio®), carbendazim (Prolific®), tebuconazole (Raxil®), propiconazole (Tilt®), fiutriafol + imazalil sulphate (Vincit™), and azoxystrobin (Amistar®) as seed applications for the control of head smut of sweetcorn (Zea mays), caused by the fungus Sporisporium reilianum (Sphacelotheca reiliana). The trial was carried out in the Poverty Bay region of New Zealand in a field that had a previous history of head smut. Carbendazim, fiutriafol + imazalil sulphate, propiconazole, and azoxystrobin seed treatments resulted in significantly greater plant numbers and increased early plant growth compared with the untreated experimental control, carboxin + thiram, and tebuconazole treatments. Plots in the control and carboxin + thiram treatments had a relatively high number of stunted plants (<10 cm) 1 month after sowing (7.6% and 14.9% respectively). Carbendazim, tebuconazole, propiconazole, fiutriafol + imazalil sulphate, and azoxystrobin seed treatments all produced low numbers of stunted plants (0.4–3.1%). Of the plants in the untreated control plots, an average of 8.7% were infected with head smut at harvest maturity. Seed treatment with carboxin + thiram didnotreduce numbers of smutted plants compared with the untreated control. All other fungicides reduced the proportion of diseased plants. The most effective were propiconazole and fiutriafol + imazalil sulphate, which respectively gave 2.3% and 2.4% plants infected with head smut. Carbendazim, tebuconazole, and azoxystrobin were slightly less effective reducing infection to 5–6%. Fiutriafol + imazalil sulphate and propiconazole both offer alternatives to carboxin + thiram for control of head smut of sweetcorn.