Onion Crop Guide

Onion
Frank J. Dainello,
Extension Horticulturist
Department of
Horticultural Sciences,
Texas A&M University

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VARIETIES
Onion varieties are day length sensitive regarding bulbing. As such, they are classified as short, intermediate and/or long day types according to length of day light hours required for bulbing to initiate.

Short day(11-12 hrs.)

Yellow- Tx 1015, Chula Vista, Cougar, Colossals, Mercedes. Riojas, Sweet Sunrise, Jaguar, Diamante, Marquesa, Linda Vista, Ebano

White- TX Early White, Diamante, Contessa, Cirrus, Monsoon

Red- Rio, Rio Santiago, Sulsula Red

Intermediate day (11-12 hrs.)

Yellow- Cimarron, Caballero, Dessex, Yula, Riviera, Utopia

White- Alabaster, Mid Star, Spano

Red- Fuego

Long (14-16hrs.)

Yellow- Armada, Vaquero, El Charo, Sweet Perfection, Ole, Durango

White- Sterling, Blanco Duro

Red- Tango

SOIL PREFERENCE:
Fertile, well-drained sandy loam, soils with good moisture holding capacity and a pH range of 6.0 - 8.4. Will tolerate a wide range of soil types. Avoid acid soils or heavy, tight soils with poor internal drainage or those that crust or bake. Will require liming if pH below 6.

OPTIMUM GROWING CONDITIONS:
Cool, moist to dry conditions following planting and early growth(mean temperature of 60^oF), and hot, dry conditions during maturity (bulbing favored by 70 - 80^oF in combination with correct day length, no bulbing occurs below 50 - 60^oF regardless of day length).

ESTABLISHMENT METHODS:
Predominantly direct seeded, can be transplanted.

Optimum time=

Fall- temperature < 95^oF in seed zone.

Spring- temperature > 50 ^o F in seed zone

Seed/oz= 8,500

Seeding rate(lbs/A)= Raw, 2 - 4; coated, 10 - 20

Seeding depth= 0.25 - 0.75"

Seedling spacing= 2- 4 " in-row with 2 - 4 rows on 38 - 40 "wide raised beds; 5-7 rows on 80" wide raised beds

FERTILITY/FERTILIZATION:
Rates presented as actual lbs/Acre N, K 205 and K2O(base actual rates on soil analysis).

Generalized rate lbs/A: 120 - 80 - 80

N- 70 - 150, 20 lbs pre-plant + 25 - 40 lbs side-dressed (banded, knifed or injected into irrigation water) of on 3 wk intervals until 40 days prior to maturity

P- 60 - 80 lbs/A banded 2 " below seed at planting

K- 60 - 80 lbs/A(not normally required in most areas of Texas)

WATER/IRRIGATION:
High demand (25 - 30 "/season or 1 - 3 "/wk), critical periods during stand establishment and bulb development through maturity, discontinue irrigation at first evidence of top falling. Moisture stress induces splits and doubles.

PEST MANAGEMENT:

Major Diseases Control

Purple blotch and Stemphyllium blight Bravo, Cabrio, Endura, mancozeb, Pristine, Quadris, Rovral, Switch

Pink root Resistant varieties, Telone C-17

Downy mildew Acrobat, Aliette, Ridomil Gold Bravo, Ridomil Gold MZ

Botrytis blast and neck rot Botran, Bravo, Endura, Rovral

Basal rot (various species) Bravo, mancozeb, Quadris

Nematode K-Pam, Telone II, Telone C-17, Vydate

Major Insects Control

Onion maggot Ambush, diazinon, Lorsban, malathion, Warrior

Thrip Ambush, Ammo, diazinon, Fury/Mustang, Guthion, Lannate, Penncap-M, Vydate,Warrior

Army worm and cutworm Ammo, B.t.'s, Fury/Mustang, Lannate, Warrior

White grub and wireworm diazinon, Lorsban

Weeds Control

Preplant incorporated Prefar

Preemergence Dacthal, Dual Magnum (24c)

Postemergence Buctril, Fusilade, Goal, Poast, Select, Treflan (layby application), sulfuric acid (with proper equipment)

*Note*--The above is a partial listing of controls intended as examples. some labels may have been revoked since the publication of this guide. Refer to product labels for specifics and use accordingly. Failure to do so may result in crop injury, death and/or citation for law vilation. Humans, animals and the enviroment may also be adversely affected by misuse.

HARVEST:

Days after planting-

Direct seeded- 120 - 210

Transplanted- 85 - 95. Initiate harvest when 50 to 80 % of the tops have fallen over.

Normal method- Hand(Can be machine harvested), soil loosened with wing sweeps or rod weeder run several inches below bulbs, hand pulled, tops and roots clipped, and bagged. Normally allowed to field dry in bags prior to grading and packaging (can be forced air dried at 90 - 93^oF for 8 - 16hrs)

Containers- 50 lb sacks or fiberboard cartons.

Grades- based on bulb diameters ranging from 1 " boilers/prepacks to over 4"(colossal)

Packaging/handling- graded, sorted and sacked(50 lbs)

STORAGE/TRANSIT CONDITIONS:
32^oF at 65 - 70 % RH for 1 - 8 months; Chill injury at 310^o F

COMMENTS/PRODUCTION KEYS

Unlike many other vegetables, bolting (flower production) in onion is dependent upon temperature and not day-lenght.
If pencil size plants are exposed to temperatures in the low to mid 40's for a prolonged period, the incidence of bolting increases. This ie especially true when rapid growth of early seeded onions is followed by a period of cool weather. The chilling effect appears to be accumulative over time.
Successful production is dependent upon proper day-length class and variety selection for growing area. Bulbing is dependent upon day-length and temperature, not size or age of plants.
Onions bulb earlier at warm temperatures than at colder temperatures.
Excessive moisture and fertility, particularly N, can delay maturity, reduce bulb quality and enhance transit or storage decay.
Bulb pungency genetically controlled but influenced by growing conditions and soil nutrient content. High sulfur can increase bulb pungency.

Texas Cooperative Extension, Horticulture Crop Guides Series
Revised November, 2003
http://aggie-horticulture.tamu.edu/extension/vegetable/cropguides/onion.html
Prepared for Web delivery by Brooke Bludau, Amanda Zan, and Dan Lineberger