Saturday, December 24, 2011

Short Description of Onion seed production in USA

Description of crop:
Onion seed is a biennial crop produced either as a seed-to-seed crop or as a bulb-to-seed crop. If direct-seeded, the crop is planted in July and harvested in August the next year. If the crop is grown from vernalized bulbs, the bulbs (produced elsewhere) are transplanted in March and harvested in August the same year. Fields are left fallow following harvest. After planning, the fields are cultivated mechanically and hoed. Onion seed is harvested by hand or mechanically means. If cut mechanically, the crop is swathed onto paper and tied down to protect the umbels and seed from being blown away by wind. The crop is dried in the field for two to four weeks and then threshed. When harvested by hand, the crop is cut, placed in burlap sacks and dried via forced air. The dried crop is then fed by hand into a combine. After harvest, the seed is sent to a conditioning plant and cleaned to 99% purity. A majority of onion seed crops are grown in central Washington, with a few crops in western Washington.
Key pests:
Western flower thrips, onion thrips and seed corn maggot are the primary insect pests. These feed on flowers/pollen in the seed crop causing reduced seed set and smaller seeds. Weed pests include barnyardgrass, smartweed, wild buckwheat and nightshade. Umbel blight, scape blight, and neck rot (Botrytis aclada and Botrytis allii) can be severe in onion seed crops, as the pathogens are ubiquitous in the Columbia Basin of central Washington and inoculum of these fungi moves readily between annual bulb crops and biennial seed crops. Stemphylium vesicarium, Alternaria porri and downy mildew can occasionally be problematic. Iris yellow spot virus (IYSV) has emerged as a major threat to the onion seed industry in Washington, caused some complete crop failures annually. IYSV is vectored by the onion thrips, Thrips tabaci. Fusarium basal rot and pink root are very occasionally a problem for highly susceptible parent lines.
Key pesticides
A wide array of insecticides is applied five to six times during the biennial production cycle to control thrips. Many products cannot be applied during bloom, however, because they are toxic to bees. Lorsban is used for onion maggot and seed corn maggot control. Bensulide, Dacthal, Prowl, Goal, Fluazifop-butyl, Buctril, MCPA and Banvel will control weeds. Chlorothalonil and mancozeb are used for general disease control. Iprodione, boscalid, and cyprodinil + fludioxonil are sometimes used for control of Botrytis spp. Strobilurin fungicides (e.g., azoxystrobin and pyraclostrobin) are occasionally used for Stemphylium vesicarium and Alternaria porri, and mefenoxam or metalaxyl is occasionally applied for control of downy mildew (more problematic in the cooler, wetter conditions of western Washington). Insecticides are used routinely to try and control the thrips and, hence, the virus vectored by onion thrips, IYSV. Overhead irrigation reduces the impact of thrips and, therefore, IYSV in onion seed crops, but promotes fungal pathogens such as Botrytis spp.

Critical pest  control issues:
IYSV is a very serious disease facing onion seed growers in central Washington. Some complete crop failures within a month of harvest (after an entire biennial season of expenses have been incurred) have resulted in some growers no longer raising onion seed crops, and some seed companies seeking alternative locations with lower thrips and IYSV pressure, e.g., western Washington. IYSV is very difficult to manage because of the tremendous difficulty in controlling the thrips vector under the hot, dry summer conditions of central Washington when onion seed crops are in full bloom. Efficacious herbicides are critical for onion seed production. Weeds not only compete with the seed crop but act as host for insect pests and diseases. Weed control includes crop rotation and cultivation. Weed seeds that cannot easily be sorted from the harvested onion seed cause the value of the seed crop to drop or be unmarketable.

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